Hosted by: Art Sedlacek

Atmospheric ice crystal formation is recognized as one of the grand challenges in the atmospheric sciences. Aerosol particles that can serve as ice nucleating particles (INPs) initiate the freezing process by various ice nucleation pathways. Those depend on the particle types and ambient conditions such as temperature and humidity which define the supersaturation with respect to ice. For temperatures above -38 °C, ice nucleation commences, in most cases, on the particle surface. Measurements of INPs are challenging and typically do not provide the size, morphological, and compositional information of the particles that acted as INPs. Studying ice nucleation by a particles-on-substrate approach allows for the application of single-particle micro-spectroscopic analytical tools that resolve particle morphology and composition in the order of 10s of nanometers. In recent years computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis and scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure spectroscopy have been employed to study ice nucleation. These techniques allow us to determine the aerosol population and associated INPs in terms of size, composition, and mixing state. This capability enables us to characterize the physicochemical nature of INPs and their relationship with the aerosol population. This in turn, has implications for the interpretation and description of ice nucleation in experiments and cloud-resolving models. Application of a simplified large eddy simulation informed 1D aerosol-cloud model of a long-lived stratus mixed-phase cloud demonstrates how different interpretations of freezing by aerosol particles impact the ice crystal number concentrations

Hosted by: Mike Jensen

We develop a time-gated time-correlated single-photon counting lidar to observe cloud base structures up to 10 cm range resolution, two orders of magnitude higher than most atmospheric lidars. Results show that the air-cloud interface is not a perfect boundary but rather is a transition zone where transformation of aerosol particles into cloud droplets occurs. The lidar observation within the transition zone reflects the formation of cloud droplets through activation and condensational growth. Further, the highly resolved vertical profile of backscattered photons above cloud base enables remote estimation of droplet concentration, an elusive but critical property to understand aerosol-cloud interactions.

Hosted by: Ogo Enekwizu

Dr. Ladeinde will talk on the synergy between aerospace engineering and atmospheric science research, with the goal of establishing an SBU-BNL team where the expertise in the two fields could be leveraged. Dr. Ladeinde's expertise is in flow turbulence, at all speeds, with and without chemical reactions. He has devoted three decades to research, mostly theoretical and computational, within this scope, and has carried out truly pioneering work in several areas, including the direct numerical simulation (DNS) of compressible turbulence, modeling rarefied and non-equilibrium (non-continuum) flow fields, dynamics of supersonic combustion in hypersonic air vehicles, the physics of rotating detonation engines, and modern approaches to air-vehicle thermal management. More recently, Dr. Ladeinde has been contributing to the particle-resolved DNS efforts at BNL, with a focus on fundamental investigation of the interactions between turbulence, clouds, and aerosol particles and the implications for climate change. Dr. Ladeinde also envisions collaborations in other atmospheric science topics, including modeling of turbulent flows around unmanned aerial vehicles (UAVS) or drones for remote sensing, with the goal of assessing data and drone interference on measurements. There is also a great deal of interest in modeling of cloud chambers, the collision and coalescence of cloud particles, radiative heat transfer in the atmosphere, air vehicle-atmosphere interactions, including contrails modeling, and the modeling of microscale turbulent droplet clustering on radar cloud observations. A few details will be presented on some of these interests during the talk.

Hosted by: Arthur Sedlacek

Based on more than 20 years of experience with operating the AIDAc (Aerosol Interaction and Dynamics in the Atmosphere – "classic" version) facility at the Karlsruhe Institute of Technology as an expansion-type cloud simulation chamber, we have developed and built the dynamic cloud simulation chamber AIDAd, which has active wall cooling for cloud simulation experiments at well controlled cooling rates up to 10 K/min, and the small Portable Ice Nucleation Experiment (PINE) for automated long-term measurements of atmospheric ice-nucleating particles. This seminar will introduce the basic working principles and operational aspects of the three chambers and will give examples of recent results on the ice-nucleating properties of mineral dust aerosols in the immersion freezing mode.

Hosted by: Tamanna Subba

A new multi-year research campaign in northern Alabama will gather data on how clouds, the land surface, and aerosol particles in the atmosphere interact at local weather scales up to and including those important to Earth's climate. This effort will take place in and around the Bankhead National Forest (BNF) at a new observatory deployed by the Atmospheric Radiation Measurement (ARM) program, a U.S. Department of Energy (DOE) Office of Science user facility. Starting in Spring 2024, the BNF climate observatory will operate for at least five years and will provide unique opportunities for scientists to unravel complex surface-atmosphere interactions and feedbacks, and investigate those interactions from the top of the canopy to the clouds through a suite of ground-based sensing, tower and aerial facilities. These data will help scientists improve how two-way land-atmosphere processes are represented in weather and climate models. In turn, these activities will also help researchers understand the effects of weather and a changing climate on the Southeastern United States – a region of interest because of its abundant convective clouds, some of which are potentially strongly influenced by the surface and large amounts of natural emissions. A multi-institutional site science team supported by ARM and DOE's Atmospheric System Research program identified northern Alabama as a preferred region for ARM's newest U.S. site, and developed the AMF3 science and deployment plan for this longer-term BNF study.

Hosted by: Fan Yang

Deep convective clouds play a critical role in precipitation, radiation, and the general circulation. Significant progress in our understanding of aerosol impacts on convective cloud microphysics, dynamics and radiative properties has been made over the past ~20 years, however, the role of aerosols in invigorating or enervating convective updrafts remains an area of significant debate in the scientific literature. Towards resolving this debate, the Department of Energy's Atmospheric Radiation Measurement facility undertook the TRacking Aerosol Cloud interactions ExpeRiment (TRACER) in the southeastern Texas region during the period from October 2021 through September 2022. The major objective of the campaign was to collect state-of-the-art detailed observations of isolated convective cells throughout their lifecycle in varying aerosol and thermodynamic conditions to facilitate high-resolution modeling studies of aerosol-convection interactions. The seminar will highlight the scientific design, experimental set-up, data highlights, planned modeling studies and early science results from the TRACER campaign.

Hosted by: Fan Yang

Aerosol-cloud interaction and cloud processes are reasons for some of the large uncertainties in future climate projections. A multifaceted approach of theory, observation, and idealized simulation is essential to understanding and representing a cloud process in climate models. Measurements of steady-state clouds produced in the Pi convection cloud chamber at the Michigan Technological University have helped us understand the role of turbulence in droplet activation and cloud microphysical properties. Idealized numerical modeling studies complement laboratory observations by providing high spatial and temporal resolution results. Despite advances in computing, Direct Numerical Simulation (DNS) of the convection and cloud microphysics in the Pi chamber is barely feasible. Therefore, we are using the computationally economical One-Dimensional Turbulence (ODT) model that resolves all relevant scales in one dimension as well as individual droplets to study the effects of aerosol and turbulence on droplet size distribution in the chamber. The ODT is a stochastic model that has been successfully used to simulate dry and moist (no cloud) Rayleigh-Bernard convection (RBC). We modified the ODT model to include particle-by-particle Lagrangian microphysics. We compare the cloudy ODT model results against Pi chamber observations to evaluate the ODT model's ability to simulate the observed droplet size distribution for various aerosol injection rates that correspond to different supersaturation regimes (mean-dominated, fluctuation-influenced, and fluctuation-dominated). The ODT model has the potential to simulate a much larger cloud chamber at a high resolution to understand the drizzle formation process, which is a critical knowledge gap in the warm rain formation.

Hosted by: Fan Yang

Cloud microphysical processes, such as droplet activation, condensational, and collisional growth, play a crucial role in the evolution of clouds and precipitation. Accurate representations of these processes in numerical models, which are essential to weather and climate models predictions, are challenging partially due to incomplete understanding of those processes at the process level arising from limited observations. Specifically, typical cloud radars have a resolution on the order of tens of meters. This resolution is insufficient to resolve critical microphysical processes that manifest at finer scales (meter and sub-meter). To mitigate this observational gap, we introduce two novel radar systems with high range resolution capability: 1) The first system is a W-band (94GHz) radar with a range resolution down to 3 m, which is a factor of 10 finer than the typical cloud radar. The first-light cloud observations reveal detailed cloud structures that conventional sensors could only perceive in a bulk sense, providing new avenues to investigate cloud microphysical processes and their impact on climate system. 2) The second instrument is a THz (680 GHz) radar system operating with a centimeter scale resolution. An experiment is conducted by applying the THz radar to measure the hydrometeors generated in a spray chamber and observations show fine-scale particle distribution patterns. Finally, the potential application of the THz radar for drizzle detection in a cloud chamber facility is discussed. The high-resolution capability allows the THz radar to detect a single particle with a diameter around 50 micrometers. The theoretical foundation of this particle detection concept is discussed followed by a validation from the Pi Cloud Chamber observation.

Hosted by: Ogo Enekwizu

Climate change can influence air pollution, one of the leading environmental and health risk factors, through complex pathways. Better understanding of how a changing climate will influence the levels and distributions of air quality will improve climate impact assessment and inform decisions to address the negative effects of climate change on human health. In this talk, I will present two projects focusing on climate impacts on energy systems and wildfires. In the first study, we study how droughts influence the emissions from electricity systems, air quality, and human health in the Western US. We find significant increases in fossil fuel usage under droughts and quantify the effects on emissions and air quality. Under future climate, these drought-induced impacts likely remain large, and even rapid expansion of renewable energy has limited ability to curb these impacts. In the second study, we combine remote sensing, statistical models, and global climate models to project wildfire PM2.5 and its health effects in the US under future climate. We quantify the changes in wildfire PM2.5 in each census tract under future climate change, and find that wildfire will likely become the most important source of PM2.5 in many parts of the US.

Hosted by: Alistair Rogers

Terrestrial vegetation plays an important role in regulating global carbon, water, and energy fluxes and moderates anthropogenic warming. In the remote Arctic, the climate has warmed two to four times faster than the rest of the planet, driving pronounced changes in vegetation distribution, function, and seasonal dynamics (known as "Arctic greening"). These changes in Arctic vegetation, on par with permafrost thaw, essentially determine the fate of the carbon and energy budget of the Arctic. However, complex interactions among climate, permafrost, landforms, and vegetation create highly-complex Arctic ecosystems that are hard to characterize across spatial and temporal scales. This is further complicated by the region's remoteness and harsh environmental conditions. Incomplete understanding and simplified representation of Arctic vegetation in Earth System Models has led to large uncertainties in our prediction of Arctic processes. In this seminar, I will present how novel multi-scale remote sensing technologies - from ground to unoccupied aerial systems (UASs), airborne, and satellites - can address these observational challenges to improve our understanding of Arctic ecosystems across spatial and temporal scales.

Hosted by: Fan Yang

Phased array configuration is currently being considered a leading contender for next generation weather radars in USA. Polarization diversity is an important part of the design. To that end, we pose a problem of detecting and monitoring imbalances (unwanted lack of orthogonality or cross-talk) of two orthogonally polarized radar receivers by using noise. Towards solving this problem, we then describe some recently obtained (preliminary) results in statistical ellipsometry. In particular, we relate polarimetric mismatches or imbalances in radars in terms of intuitive polarization ellipse variables to suitably chosen cross-correlation measures.

Hosted by: Janek Uin

Ship tracks are well known natural experiments of aerosol-cloud interactions. More recently, we have analysed polluted cloud tracks induced by aerosols emitted from volcanoes and wildfires and various industrial sources - such as oil refineries, smelters, coal-fired power plants, and cities (Toll et al. 2019; Nature, https://doi.org/10.1038/s41586-019-1423-9). We have been able to shed light on cloud water adjustment to aerosol-induced cloud droplet number perturbations, diurnal evolution of polluted cloud tracks and meteorological dependence of aerosol impacts on clouds. Work-in-progress shows that anthropogenic aerosols can lead both to increases and decreases in cloud fraction. While increases in cloud fraction are caused by relatively well understood aerosol-induced suppression of precipitation, decreases are induced by anthropogenic ice nuclei leading to glaciation of supercooled liquid- phase clouds. So far, we have relied mostly on passive remote sensing. For further advances in physical understanding of aerosol-cloud interactions, we suggest a field campaign sampling aerosol and polluted cloud plumes downwind of industrial aerosol sources.

Hosted by: Maria Zawadowicz

Multiphase chemistry of isoprene photooxidation products has been shown to be one of the major sources of secondary organic aerosol (SOA) in the atmosphere. A number of recent studies, including those conducted in our lab, indicate that aqueous aerosol phase provides a medium for reactive uptake of isoprene photooxidation products, and in particular, isomeric isoprene epoxydiols (IEPOX), with reaction rates, yields, and particle properties being dependent on aerosol acidity, water content, sulfate concentration, and organic coatings. However, very few studies focused on chemistry occurring within actual cloud droplets. I will present the aircraft-based single-particle measurements of the size and mixing state of individual below-cloud particles, interstitial aerosol particles, and cloud droplet residuals characterized during two contrasting seasons. Our measurements reveal enhanced contribution from larger and sulfate-rich particles in cloud droplet residuals and provide direct evidence for sulfate and IEPOX-derived SOA formation in cloud droplets. We observe a strong dependence of the size and mixing state of below-cloud aerosol on their cloud droplet activation fraction especially during the spring campaign, when the observed dynamic range in aerosol properties was large. Ultimately, the combined cloud, aerosol, and gas-phase measurements are used to develop and evaluate model treatments of aqueous-phase isoprene SOA formation and aerosol-cloud-climate interactions.

Hosted by: Die Wang

The devastating socioeconomic impacts of extreme weather events, fueled by climate change, stress the pressing need for effective mitigation strategies. One of the proposed climate intervention (geoengineering) approaches involves enhancing the reflectivity of marine warm clouds through deliberate aerosol injections, known as Marine Cloud Brightening (MCB). The viability of such a geoengineering approach depends crucially on our understanding of aerosol-cloud interactions (ACI) in a changing climate. The long-standing impression that aerosols brighten the clouds stems from the fact that more, smaller cloud droplets are more reflective than fewer, bigger drops, known as the Twomey effect. On the other hand, there is a growing body of literature that suggests cloud water decreases as aerosol loading increases, owing to enhanced evaporation and entrainment. This negative cloud water adjustment partially or even entirely offsets the Twomey brightening effect, depending on environmental conditions. Moreover, scale interactions, both spatially and temporally, involved in these micro- and macro-physical responses make it challenging to constrain the overall cloud brightness responses to aerosol perturbations. In this presentation, I will first introduce a cloud albedo susceptibility assessment framework based on satellite observations. This will be followed by the finding that the potential for cloud darkening, attributed to negative cloud water adjustments, is quite often observed in non-precipitating clouds, especially under deep boundary layers. Next, I will present results from an ensemble of large-eddy simulations that supports the view of a buffered evolution of cloud water adjustments driven by solar heating. Lastly, I will address the detectability cloud brightening in a hypothetical MCB scenario where targeted aerosol injection is implemented, relying on predictions from neural networks trained on climatological fields of meteorology, aerosol, and cloud properties. These findings underscore the benefits of a bespoke MCB strategy compared to perturbing the targeted region uniformly.

Hosted by: Alistair Rogers

Vegetation acts as a substantial link between the geosphere and atmosphere, mediating transpiration (E), and carbon assimilation (A). At the center of this process lie stomata, small pores which actively regulate the rate of CO2 and H2O diffusion between vegetation and the environment. This process, known as stomatal conductance (gs) helps set the upper limit on E, and through stomatal limitation on A, is a strong determinant of net primary productivity. A series of mathematical models have been developed to predict the sensitivity of gs to environmental factors, which have been incorporated into land surface models (LSMs). Despite the clear importance of accurately representing gs in LSMs, major uncertainty remains in the factors influencing the model parameters related to gs (the stomatal slope and stomatal intercept), particularly in how they are estimated from data, their temporal consistency, and their degree of variation within plant functional types (PFTs). In my talk, I will detail research which has been done to assess these three main sources of stomatal parameter uncertainty. Topics include the impact of branch excision on estimating stomatal parameters, the temporal consistency (diurnal, seasonal, and annual) of stomatal traits, and the model implications of failure to account for Arctic specific stomatal parameters. Overall, I demonstrate the effects of several biotic and abiotic drivers of variation in stomatal parameters, which contribute to significant uncertainty in LSM representation of instantaneous gs and evapotranspiration.

Hosted by: Ogo Enekwizu

Characterizing the aerosol number budget plays a crucial role in addressing the critical challenge of understanding current and projecting future climate scenarios by improving the understanding of aerosol-climate interactions. Various microphysical, dynamical, and environmental controls exert influence over atmospheric aerosols and its climate impacts. Microphysical controls, such as new particle formation (NPF), which includes the formation of new particles and their subsequent growth, impact the aerosol number size distribution, cloud condensation nuclei, air quality, and climate. Sea breeze circulations (SBC), as part of meteorological dynamical controls, transport aerosols inland, enhance vertical mixing and dispersion, and influence the spatio-temporal aerosol distribution. Additionally, different atmospheric environments exhibit diverse aerosol characteristics driven by their unique natural and anthropogenic sources, and atmospheric processes. The DOE ARM measurement campaign Tracking aerosol convection interactions experiment (TRACER), conducted from October 1, 2021, to September 30, 2022, offered a unique opportunity to study aerosol processes in Houston's distinctive urban and coastal environment. The region is characterized by isolated convection systems, frequent SBC, and emission impacts from industrial, urban, and rural areas. Additional aerosol measurements from June 1 to September 30, 2022, at a rural site exhibit a strong contrast with urban aerosol measurements at the main and other urban sites. Comprehensive observational data were analyzed, including the aerosol number size distribution, bulk aerosol chemical composition, gas-phase precursors such as SO2 and SO2-based proxies (e.g., H2SO4), and meteorology. The analysis reveals strong day-to-day variability in aerosol size distribution at all sites across the TRACER domain. The coastal regions of Houston exhibit unique characteristics in NPF frequency, seasonality, formation, and growth rates, showing a clear 'regional behavior' with an urban-rural contrast. WRF-Chem model simulations, informed by meteorological observations, were performed to gain valuable insights into the spatio-temporal factors influencing the aerosol-climate interactions in the urban-coastal region of Houston.

Hosted by: Wuyin Lin

The representation of convection in global climate models is one of the most challenging scientific issues in climate modeling. Many deficiencies in precipitation and climate variability simulations and uncertainties in climate change projections can be traced to the poor representation of convection. Two major recent enhancements of Zhang and McFarlane (ZM, 1995) convection parameterization scheme for the version 3 of E3SM:convective mass flux adjustment and convective microphysics parameterization, will be discussed in this presentation. Recent observational studies suggest that the large-scale dynamical forcing (vertical motion) plays important roles in deep convection development. We developed a convective mass flux adjustment approach to represent the dynamical effects of large-scale vertical motion on convection. The coupling of convection with large-scale circulation significantly improves the simulation of climate variability in E3SM across multiple scales from the diurnal cycle, convectively coupled equatorial waves, to the Madden-Julian Oscillation (MJO). Microphysical processes in convective clouds play important roles in aerosol, cloud, circulation, and climate interaction, which can greatly affect cloud precipitation efficiency, latent heating, cloud radiative properties, and thus climate. We developed a two-moment (mass and number concentration), five-class (liquid, ice, rain, snow, and graupel) convective microphysics parameterization and implemented it in the ZM convection scheme in E3SM. This scheme is linked to aerosols through cloud droplet activation and ice nucleation processes, and to stratiform cloud parameterization through convective detrainment of cloud liquid/ice water content and droplet/crystal number concentration, which improves the representation of interactions between aerosols, convective, and stratiform clouds in E3SM. The convective microphysics parameterization also improves the simulation of tropical variability in E3SM.

Hosted by: Aryeh Drager

Convective clouds, such as thunderstorm clouds, significantly affect weather and climate. They are responsible for most of the world's severe storms and play essential roles in Earth's water cycle and radiative budget. Environmental thermodynamics, dynamics, and other conditions, such as aerosol particle number and type, influence the properties of convective storms. Some of the basics of how these environmental properties influence the development of convective storms are known. However, it is unknown precisely how environmental conditions control the evolution of convective clouds and how clouds modify the environment. Understanding the relationship between environmental conditions and cloud properties is particularly important as climate change alters the underlying environment. Quantifying the relationship between environmental conditions and convective clouds requires comprehensive information about clouds and their environments. Although some cloud properties can be sampled through observations, numerical model simulations can provide information about environmental and cloud characteristics and the processes occurring inside clouds. In this presentation, we will discuss the development of a database of clouds occurring in simulations generated using the Regional Atmospheric Modeling System (RAMS) model. These high-resolution simulations are conducted over six weeks with a large domain encompassing much of the western Pacific basin. To identify clouds and storms across their lifecycle, we use the Tracking and Object-Based Analysis of Clouds (tobac) package, which tracks each convective cloud and can identify its initial formation environment and properties over its lifetime. Using this tobac-tracked database of clouds, we obtain statistics on how cloud properties vary as a function of their initial environment. Using these statistics, we will examine how convective clouds' updrafts, precipitation, and morphology vary as a function of environmental characteristics.

Hosted by: Shawn Serbin

The Arctic-boreal zone covers ~ 20% of Earth's land surface and is characterized by cold temperatures, long winters, and permafrost. This region is extremely important because it holds over 50% of the global soil organic carbon pool, and is now warming four times faster than elsewhere on the planet. Historically cold protected soil carbon is becoming more vulnerable to loss as CO2 and CH4, threatening to shift the northern carbon budget into a net source if these emissions begin to outpace annual carbon uptake by plants, especially forests. Here I present recent insights gained from satellite-informed models, and field research, which provide new understandings of regional vulnerability (and perhaps resilience), and ecosystem-climate feedbacks.

Hosted by: Fan Yang

Clouds are collections of droplets and ice crystals, formed on aerosol particles, all interacting within a turbulent environment. Understanding these interactions is challenging, especially because the atmosphere is ever changing and the initial and boundary conditions are poorly constrained. Turning to the laboratory is one way to make progress. In the "Pi convection-cloud chamber", a pi-cubic-meter turbulent cloud is generated by feeding aerosols into a water-supersaturated environment created by moist Rayleigh-Benard convection. All microphysical processes that are usually considered "sub-grid-scale" even in detailed models, are fully represented. The resulting cloud microphysical and optical properties are similar to those observed in stratocumulus, and the Pi chamber has provided insight into the role of turbulence on cloud droplet activation and growth, the formation of persistent mixed-phase clouds, and the cloud dispersion indirect effect. A consortium of 12 universities, national laboratories, and industry/international partners, with support from DOE and NSF, has been developing a design for a much larger convection-cloud chamber that will allow droplet growth by collision-coalescence in addition to growth by condensation. That capability will allow interactions within a fully-coupled aerosol-cloud-precipitation system to be explored and directly compared to detailed models. We envision that this would exist as a national user facility available to the atmospheric research community for advancing our understanding of cloud processes relevant key uncertainties in weather and climate models.

Hosted by: Maria Zawadowicz

The sources and nature of emissions of ice nucleating particles (INPs) to the atmosphere affect aerosol-cloud interactions, precipitation, and climate (via cloud phase and lifetime influences). There is a need to characterize INP emissions, categorized in some manner to define the most important classes over different regions and at different times. While past research has emphasized the global relevance of mineral dusts and other inorganic particles as atmospheric INPs, we highlight unique measurements identifying the most abundant and important classes of INPs in many regions as emanating from organic and biological sources. INPs whose actions are dominated by unresolved biological and organic materials are features not only of emissions from non-desert continental soils, but also marine emissions (via sea spray), from biomass burning, and from yet to be identified sources in the Arctic over large portions of the year. We will show, mostly using data from DOE ARM campaigns that INPs of organic and inorganic types may be amenable to relatively simple parameterizations for use in numerical modeling studies. However, strong needs remain for quantifying biological INPs that dominate ice nucleation in many regions in the cloud activation regime from 0 to 20°C (or lower). This will likely require targeted and novel measurements of both bioaerosols and INPs in field studies, a few examples of which will be introduced.

Hosted by: Minnie Park

Cold pools, cool gusty outflows at the surface that are formed by latent cooling associated with convective storms, have long been recognized as important atmospheric features. They influence the development and organization of convective storms; they impact surface fluxes of energy, moisture, and momentum; they loft and transport dust and other particulates; and they have been linked to a phenomenon called "Thunderstorm Asthma," whereby pollen grains can osmotically rupture into sub-pollen particles that easily penetrate the lungs. This latter phenomenon has been the subject of recent research and formed the base motivation for an NSF-sponsored project called BioAerosols and Convective Storms (BACS). The overall goal of BACS is to characterize the fluxes of biological particles between the surface and atmosphere, assess the vertical distribution of bioaerosols and how this distribution is influenced by convective cold pools, and investigate feedbacks between cold pools, bioaerosols, and convective storms. In this talk, I will present an overview of the first field phase of BACS (BACS-I), which took place in May-June 2022 in the plains of northern Colorado. I will highlight some of the measurement systems employed, including drone-based methodologies for measuring the vertical structure of cold pool thermodynamics and aerosol concentrations. I will then show some preliminary results from BACS-I. These include variability in the observed properties and vertical structure of cold pools, which is particularly strongly modulated by the class of parent convection producing the cold pool; variation in the observed responses of bioaerosols to cold pool passages, even on the same day; and modeling work on the impact of successive cold pools (two or more cold pools passing over the same area on the same day) on aerosol transport and vertical redistribution. Finally, I will highlight implications for cold pool impacts on bioaerosols and avenues for future work, including bioaerosol feedbacks to convection.

Hosted by: Daryl Yang

Human activities such as the combustion of fossil fuels release greenhouse gases to the atmosphere, contributing to global warming. A portion of emissions are sequestered in natural and managed ecosystems on land in the ocean, the balance of which determines the carbon budget. Major efforts are undertaken to account for net GHG emissions at regional, national, and global scales for the purposes of developing policy for, and fulfilling the requirements of, emissions reductions and climate change mitigation agreements. This seminar will provide an overview of the different methods scientists use to measure and model the various sources and sinks of GHGs such as carbon dioxide and methane at multiple scales, present examples of efforts to balance these source and sink estimates across the major components that make up the carbon budget, and discuss the uncertainties and research priorities that emerge from attempts to reconcile carbon budget estimates from different scientific approaches and policy perspectives.

Hosted by: Janek Uin

Remote marine environments, dominated by pristine atmospheric conditions of low aerosol concentrations, are the most impacted by perturbations in aerosol properties and represent one of the major constraints to accurate future climate predictions. With the objective of expanding the knowledge of aerosol properties and key processes in the marine environment, between 2015 and 2018, NASA deployed the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) field campaign in the Western North Atlantic region. In situ ship- and aircraft-based measurements, and airborne-based remote sensing retrievals were coupled during three field campaigns: NAAMES-1 (November 2015), NAAMES-2 (May 2016), and NAAMES-3 (September 2017). In this study, I integrate aerosol microphysical, optical, and chemical datasets collected during the NAAMES field campaigns to provide summary statistics of marine aerosol characteristics and aerosol budget over the Western North Atlantic Ocean region. In this presentation, I will discuss the spatiotemporal variability of aerosol and aerosol key processes in function of different aerosol loadings and meteorological regimes. Preliminary analysis of the consistency between in situ and remote sensing aerosol observations will also be assessed.

Hosted by: Sid Gupta

Ice particle terminal fall velocity (Vt) is fundamental for determining microphysical processes, yet remains extremely challenging to measure. Current theoretical best estimates of Vt are functions of Reynolds number. The Reynolds number is related to the Best number, which is a function of ice particle mass, area ratio (Ar), and maximum dimension (Dmax). These estimates are not conducive for use in most models since model parameterizations often take the form Vt=αDβmax, where (α, β) depend on habit and Dmax. A previously developed framework is used to determine surfaces of equally plausible (α, β) coefficients whereby ice particle size/shape distributions are combined with Vt best estimates to determine mass- (VM) or reflectivity-weighted (VZ) velocities that closely match parameterized VM,SD or VZ,SD calculated using the (α, β) coefficients using two approaches. The first uses surfaces of equally plausible (a, b) coefficients describing mass (M)–dimension relationships (i.e., M=αDbmax) to calculate mass- or reflectivity-weighted velocity from size/shape distributions that are then used to determine (α, β) coefficients. The second investigates how uncertainties in Ar, Dmax, and size distribution N(D) affect VM or VZ. For seven of nine flight legs flown on 20 and 23 May 2011 during the Mesoscale Continental Convective Clouds Experiment (MC3E), uncertainty from natural parameter variability—namely, the variability in ice particle parameters in similar meteorological conditions—exceeds uncertainties arising from different Ar assumptions or Dmax estimates. Natural variability relative to measurement uncertainty, however, has some dependence on the measurement averaging time, where measurement uncertainties become more important with increasing averaging time but the exact reasoning for this remains under investigation. Regardless, the combined uncertainty between Ar, Dmax, and N(D) produced smaller variability in (α, β) compared to varying M(D), demonstrating M(D) must be accurately quantified for model fall velocities. Finally, the roles of gravity waves and turbulence in producing increased natural variability within the ice particle parameters is investigated.

Hosted by: Ken Davidson

The tropics are the hottest biome with closed-canopy forests, and these lush, biodiverse forests help regulate the global climate by fixing large amounts of CO2 from the atmosphere in photosynthesis and storing carbon in trees and soils. But temperatures are rising, with unknown consequences for the forests as we know them. I will discuss how warming affects carbon fluxes in tropical forests, at timescales ranging from minutes to centuries, using results from warming experiments and field observations in Panama. Bio: Dr. Slot earned his undergraduate degree in forestry at Wageningen University in his native Netherlands, he got his master's at the University of York, UK, and his doctorate from the University of Florida, in 2013. He joined the Smithsonian Tropical Research Institute in Panama as staff scientist in 2020.

Hosted by: Maria Zawadowicz

Climate change is increasing abiotic and biotic disturbance events that lead to plant stress. This affects the composition and spatiotemporal distribution of biogenic volatile organic compounds (BVOCs) across Earth's surface. Perturbations to the types of compounds emitted could have significant impacts on secondary organic aerosol (SOA) production, but predictive understanding of the chemistry of many of these compounds (including complex mixtures of these compounds) has not been achieved. This presentation will summarize laboratory studies investigating SOA formation from complex mixtures of real plant emissions representing different plant emission types. Unexpected effects on aerosol chemistry, composition, and properties attributed to the presence of plant stress emissions were observed. Acyclic terpenes (i.e. myrcene and farnesene) that are often associated with plant stress, reduce SOA yields and promote fragmentation reactions while increasing the viscosity of the resulting SOA. Aerosol chemistry of these compounds could become increasingly important with elevated frequency and severity of plant stressors such as insect outbreaks, heatwaves, and drought.

Hosted by: Olga Mayol-Bracero

Aircraft measurements have revealed that super coarse dust (diameter > 10 mm) is surprisingly abundant in Earth's atmosphere. However, most current models either neglect or greatly underestimate the abundance of super coarse dust. In this seminar, I explore the causes of this model underestimation of super coarse dust. I derive a new parameterization for the size distribution of emitted dust aerosols that matches measurements of super coarse dust close to source regions. Despite this improvement in the accuracy of coarse dust emissions, models still greatly underestimate super coarse dust in dust outflow regions. Thus, the model underestimation of super coarse atmospheric dust is in part due to the underestimation of super coarse dust emission and likely in part due to errors in deposition processes.

Hosted by: Olga Mayol-Bracero

The oceans contribute to aerosol particles in the atmosphere through two different physical mechanisms: first by the production of sea spray aerosol, and second by emitting gases that condense to produce secondary marine aerosol. These aerosol emissions include three types of chemical compounds: salt particles account for >90% of the mass, most of which is >1 µm dry diameter; sulfate particles are

Hosted by: Fan Yang

The discovery of cloud microphysical responses to artificial ice nucleating particles by Schaefer and Vonnegut in the late 1940s set the stage for glaciogenic cloud seeding as a technology to increase water supplies especially in mountainous regions during wintertime. This talk provides a short review of the research related to wintertime glaciogenic cloud seeding under the background of aerosol-cloud-precipitation interactions at the beginning. Then, recent experiments and modeling progress that help to quantitatively assess glaciogenic seeding impacts on clouds and precipitation falling across a mountain watershed are introduced in detail. The recent development and advancement of laboratory facilities and experiments for aerosol-cloud research will be discussed at the end of the talk.

Hosted by: Maria Zawadowicz

Aqueous-phase reactions can produce and transform atmospheric organic aerosols in important ways, but the processes remain poorly understood. As an effort to close this knowledge gap, we have performed laboratory and field studies to investigate the photochemical formation and aging of organic compounds in atmospheric aqueous phases. I will present ambient observations from areas of high humidity, where aqueous reactions are shown to be an important source of oxygenated and nitrogen-containing SOA and can significantly influence the light-absorption properties of BrC. I will also present results from lab-based experiments on the aqueous-phase oxidation of phenols (an important class of VOCs/SVOCs from biomass burning) and the formation and aging of SOA and BrC over the course of simulated sunlight illumination. Finally, I will present some results from integrated analysis of ambient aerosol mass spectrometry data to eludicate the role that aqueous-phase chemistry plays on aerosol chemistry.

Hosted by: Andy Vogelmann

Changes in the composition of the atmosphere cause changes to the planetary radiation budget to which the Earth responds by changing its temperature; changes in temperature may also change the atmosphere's opacity in ways that damp or amplify the temperature change. This framework — radiative forcing, adjustments, and feedbacks — provides a useful lens though which to think about future atmospheric conditions and allows us to use the Earth's past and present-day behavior as a guide to the future. A focus on adjustments, including aerosol-mediated changes to clouds, also highlights challenges and opportunities for process-based modeling, data assimilation and state estimation, and satellite observations. In this talk I'll focus on understanding the radiative forcing to which the earth has been subject over the course of industrialization. I'll describe an effort to provide highly-accurate estimates of instantaneous radiative forcing by greenhouse gases across a wide range of scenarios, and highlight how efforts to compute adjustments inevitably dominate the uncertainty in effective radiative forcing. Developing an understanding of real-world forcing also lets us understand the surprisingly wide range of forcings reported by climate models for the same change in atmospheric composition, highlighting the difference between model diversity and true uncertainty.

Hosted by: Allison McComiskey

Dust aerosols are soil particles that are mobilized through wind erosion. They alter the energy and water cycles of the atmosphere through a combination of radiative and microphysical effects, while providing clues to the circulation of past climates. These effects depend upon composition in addition to particle size and shape. Here, we describe modeling of dust aerosol composition based on the content of the soil within dust source regions. These calculations are computationally expensive; it remains unknown whether regional variations in composition need to be considered to calculate the climate effect of dust, or alternatively, whether models can approximate dust aerosol composition as globally uniform. Resolution of this question may depend upon the radiative effect of coarse and super-coarse dust particles whose concentration is systematically underestimated by models. We will discuss sources of uncertainty in our calculations of aerosol size and composition, and the implications for whether regional variations in aerosol composition are crucial for calculating the dust effect upon climate.

Hosted by: Fan Yang

Prediction of ice nucleating particle (INP) number concentrations from ambient aerosol particles represents an urgent and challenging issue when simulating cloud processes in climate models. Immersion freezing, where an INP is engulfed in supercooled water or aqueous solution, is considered the dominant primary ice formation pathway in the atmosphere. How to parameterize immersion freezing for interpretation of ice nucleation experiments and implementation in cloud models is currently debated. I present two schools of thought where one is based on classical nucleation theory involving a stochastic nucleation process, and the other one is based on a deterministic process which assumes that nucleation proceeds at special ice nucleation active sites. Historically, the latter was suggested to approximate the former model. However, the application of these two approaches yields very different outcomes and conceptual insights in immersion freezing and cloud modeling. I will outline these differences using examples taken from the laboratory, field, and cloud modeling. These include: i) immersion freezing experiments of illite mineral dust; ii) results of the first-of-its-kind aerosol-ice formation closure study at the ARM SGP site; and iii) preliminary results from a minimalistic 1D aerosol-cloud model to understand INP reservoir dynamics in mixed-phase clouds. The presentation concludes with a summary and outlook of the next research steps.

Hosted by: Chongai Kuang

Many New Particle Formation (NPF) events occur in a residual layer, near the top of the boundary layer. Therefore, measurements of the meteorological parameters, precursor gases, and aerosol loadings conducted at the ground are often not representative of the conditions where the NPFs take place. I will present new measurements obtained at the Southern Great Plains research site that suggests that 1) turbulent fluxes of 3-10 nm particles provide a good indication for the vertical location of NPFs; 2) organic compounds dominate the chemical composition of sub-50 nm particles 3) current methodologies may be inadequate for estimating dry deposition velocity of sub-10 nm particles.

Hosted by: Die Wang

We have performed some new theoretical calculations based on parcel theory to quantify possible invigoration by aerosols in deep convection due to warm phase and cold phase processes. In the warm phase we find that reduced supersaturation causes enhanced buoyancy, but that enhancement diminishes as the parcel ascends to higher levels. In the cold-phase, which is traditionally where invigoration is thought to occur, we find instead that under most scenarios polluted parcels are actually weaker than clean parcels. Furthermore, the magnitude of change due to the cold-phase processes is generally small. These results differ from previous work due to our assumption of gradual freezing and gradual unloading rather than instantaneous freezing and unloading. Overall, we find that the warm phase and cold phase processes typically counteract one another and act to minimize the total invigoration of updrafts in polluted storms.

Hosted by: Olga Mayol-Bracero

Atmospheric aerosols, microscopic particles suspended in air, play an important role in the Earth System as key factors in radiative transfer, cloud formation and water cycle. Several climactically important properties of aerosols, such as index of refraction, hygroscopicity and ability to seed ice clouds, are functions of their chemical composition. Atmospheric aerosols are complex mixtures of organic and inorganic components—their composition reflects their emission source, photochemical age, and interactions with other components of the atmosphere: reactive trace gases, cloud and rain droplets and gas-phase oxidants. Comprehensive characterization of these chemically complex and dynamic mixtures is generally achieved by mass spectrometry, both in situ and off-line, following collection of aerosols on filter. Aerosol and trace gas mass spectrometers produce multivariate datasets rich in information. The topic of this seminar is an overview of data collected by the ACSM deployed at the on-going TRacking Aerosol-Convection interactions ExpeRiment (TRACER) campaign in Houston, TX. I will discuss on-going efforts in data quality assessment and source apportionment of the TRACER ACSM data.

Hosted by: Shawn Serbin

Hosted by: Qianyu (Cherry) Li

The increasing complexity of Earth System Models makes it difficult to understand and interpret the model predictions. Recent progresses show that the eco-evolutionary optimality principles, rooted in natural selection, can lead to parameter-sparse and transparent representations in models and improve our understanding from first-principles. In this talk, I will show how we apply eco-evolutionary optimality principle to develop a universal primary productivity model (Pmodel), how we further apply Pmodel to understand the environmental responses of diverse plant processes, to develop parsimonious models of crop yield and ecosystem evapotranspiration, and to improve the representation of photosynthesis and respiration in Earth System Models.

Hosted by: Julien Lamour

Leaf stomatal pores represent a key bottleneck in the exchange of CO2 and water vapor between land plants and the atmosphere. The diffusive conductivity of the leaf surface, conventionally called 'stomatal conductance', varies dynamically as stomata respond to changes in light, VPD and soil moisture. In this talk, I will briefly describe stomatal conductance and its importance for ecology, hydrology and climate. I will then describe a range of approaches to predicting stomatal conductance in models. Finally, I will conclude with a brief discussion of some topical issues involving the prediction and interpretation of stomatal conductance.

Hosted by: Fan Yang

Marine Boundary Layer (MBL) cloud is an important component of the climate system. However, the representation of cloud-scale processes that determine microphysical and dynamical interactions in climate models remains poor, thus, leading to large uncertainties in climate prediction. Improving the representation of MBL clouds in climate models calls for comprehensive, long-term, process-oriented observations. In this presentation, I will discuss the work of using remote sensing-based measurements to investigate the microphysics and dynamics of MBL clouds. First, I will discuss the limitations of retrieving two basic MBL cloud properties, i.e., liquid water content and vertical air motion, and explore how we can improve the retrieval algorithms using remote sensing observations. Then I will focus on the investigation of the warm precipitation formation process. Novel technique is developed to detect the drizzle particles and is applied to three observational campaigns to investigate the drizzle occurrence. Here I will present a new drizzle distribution climatology of the MBL clouds, which is significantly different from the traditional perspective. Next the dynamical factors controlling the precipitation process is investigated. Based on the utilization of a comprehensive retrieval products, I will provide direct observational evidence to show how the development of drizzle droplet is affected by the dynamical process, especially the turbulence in MBL clouds.

Hosted by: Katia Lamer

While urban heat islands have mostly been studied as climatological phenomena, the temporal variability of their signal hints at significant meso to synoptic time-scale dynamics. In this talk, we will overview the physical processes responsible for the urban heat island, how we represent these physics in numerical weather prediction models, and what the model results then tell us about the meteorological variability of urban weather. We combine observations and simulations from the Weather Research and Forecasting model to focus on the evolution of urban heat islands during both heat waves and cold waves to understand their dynamics under meteorological extremes and how classic mitigation measures, such as green or cool roofs, can be applied to improve urban environmental conditions across all seasons and weather patterns. We conclude with an overview of some novel mitigation measures we are evaluating such as thermochromic roofs covers and phase change material.

Hosted by: Yangang Liu

The talk will summarize Dr. Ladeinde's contributions to three research areas of his interest and expertise. One of these areas is theoretical and DNS studies of scalar and chemical species transport, mixing, and combustion in turbulent flows, for which his recent work on compressible turbulence in detonation will be presented. Dr. Ladeinde has also contributed significantly to the knowledge of supersonic combustion, which pertains to the propulsion of hypersonic vehicles, for which combustion takes place in an environment where the velocities of the reactants are in the high subsonic or supersonic regimes. A snapshot of Dr. Ladeinde's recent LES studies on the rotating detonation engines (RDE) will be summarized during the talk. The third research area of current interest to Dr. Ladeinde is two-phase flows in its various occurrences: condensation, boiling, and evaporation in heat transfer, as well as fuel primary and secondary breakup and eventual evaporation, mixing, and reaction with an oxidizer, in combustion. Both empirical and CFD-based techniques for two-phase flow studies have been undertaken by Dr. Ladeinde and these will be discussed briefly. The relevance of these backgrounds to climate studies, which can be found in theoretical, LES, and DNS analysis of atmospheric turbulence - with and without transported species or chemical reactions and phase-change – will be discussed.

Hosted by: Yangang Liu

This seminar introduces our efforts to develop an integrative renewable energy forecasting system by combining physics-based Weather Research and Forecast (WRF) model and data-driven machine learning models, with a focus on wind forecast. Long-term surface wind simulations with WRF are first evaluated against observations at 22 sites over the New York State divided into six terrain types (i.e., continent, lakeside, river-valley, Long-Island, offshore-island and offshore-ocean). The results show that WRF model overestimates typical inland (i.e., continent) winds by 1 m/s throughout the whole day. WRF model underestimates diurnal variability of local circulation impacting surface wind and misses the physical nature that local circulation increases typical inland surface wind speeds. Simulated offshore-island winds cannot reproduce the observed diurnal variation but exhibit constant average and standard deviation; but offshore-ocean winds are successfully reproduced. Among the six terrain types, the WRF produces the best estimation of offshore-ocean winds, the secondly best estimation of Long-Island winds, and almost same performance in wind estimation at the other sites. The simulation of coastal region wind profiles shows remarkably overestimated Planetary Boundary Layer (PBL) wind speeds and underestimated free troposphere winds, whereas the WRF simulation at a mountain region site shows underestimated PBL wind speeds. Model deficiencies and potential reasons underlying the wind biases and the discrepancies among different terrains are explored. Comparative analysis reveals that the best data-driven machine learning model outperforms the physics-based WRF forecast in short lead time; but the WRF model achieves higher accuracy once the lead time is beyond a few hours.

Hosted by: Ernie Lewis

The Amazon and equatorial North Atlantic Ocean are nutrient-depleted ecosystems that rely on long-range transported aerosols to maintain primary productivity. African dust is believed to provide iron (Fe) and phosphorus (P) to these ecosystems, which leads to the sequestration of carbon dioxide. However, there are few measurements of African dust in South America that can robustly quantify the amount and solubility of nutrients associated with long-range transported aerosols. Additionally, the transport of supermicron and super-coarse mode aerosols, which can deposit more nutrient mass than smaller particles, is routinely underestimated due to poorly constrained physical properties. In this presentation, I will present both single-particle measurements that were used to identify a possible mechanism for the efficient long-range transport of super-coarse mode particles as well as bulk phosphorus measurements used to quantify P deposition to the Amazon and global oceans. Our results show that particle asphericity and low density increase the residence time of particles in the atmosphere, which increases the likelihood of atmospheric reactions between dust and trace species that can elevate nutrient solubility, and in the upper water column. Our measurements of bulk phosphorus confirm that North African dust transport supplies the majority of the P to the Amazon. Contrary to prior thought, we show that African biomass burning aerosol is responsible for up to half of the soluble P deposition to the Amazon. Using a chemical transport model that African biomass burning aerosols supply up to 70% of the soluble P deposited to the Southern Ocean during boreal Fall. Together, our results further elucidate the impacts of African aerosols on marine and terrestrial biogeochemical cycles. ZoomGov Meeting Link: https://bnl.zoomgov.com/j/1619345364?pwd=UEFKTmltQjJWTXpVelppTnlIUFNSdz09

Hosted by: Shawn Serbin

Avoiding the worst impacts of climate change will likely require removal of CO2 from the atmosphere, for example with managed alterations to land cover including reforestation and crop diversification. These so-called "natural climate solutions" (NCS) have growing private and public sector support, despite being characterized by substantial biophysical uncertainty. This talk addresses the potential for NCS to directly alter local temperature regimes, using new approaches to disentangle interactions between land cover, surface temperature, and air temperature dynamics. I will show that, in the Eastern US, biophysical impacts of reforestation confer a substantial climate adaptation benefit and play a role in explaining historic patterns of air temperature change. Opportunities to extend these approaches to other NCS, including cover crops, will be presented. I will end by discussing strategies to overcome key knowledge gaps hindering our ability to forecast NCS mitigation and adaptation potentials into the future. Zoom Link: https://bnl.zoomgov.com/j/1619679821?pwd=cFZmSWpQa2Erc2t1ZlpBU2tLZlgxQT09&from=addon

Hosted by: Alistair Rogers

Climate change, driven by rising atmospheric CO2 concentrations, is well under way. Rising temperatures, increased heat extremes, and hotter (and therefore more severe) droughts are already having major impacts on native vegetation. Predicting the likely impacts of these changes in the near-term has become a pressing need, but requires a quantitative, model-oriented understanding of the effects of these environmental factors on the ecology and ecophysiology of plant species. In this seminar I will summarise recent results from our experimental research on the effects of CO2 enrichment, warming, heatwaves, drought and fire on tree species, and explain how this research is both being directed by, and informing, predictive models of forest function under global change.

Hosted by: Die Wang

Shallow precipitating clouds are often a precursor to subsequent deep convection. This study investigates the land-atmosphere interactions and boundary layer processes that lead to the formation of such clouds observed over the Southern Great Plain during the Holistic Interactions of Shallow Clouds, Aerosols and Land-Ecosystems (HI-SCALE) field campaign in 2016. We conducted Large Eddy Simulations (LES) version of the Weather Research and Forecasting Model for a selected day with transition from clear-sky to shallow precipitating clouds and then to the deep convection transition. The results shed new lights on the understanding of the mechanisms of land-atmospheric interactions and convection initiations. Video Conf Link: https://bluejeans.com/105659461

Hosted by: Fan Yang

Clouds are one of the wildcards in weather and climate studies. Their macroscopic properties and processes intimately depend on small-scale cloud properties, such as the cloud droplet size distribution (DSD), which in turn are directly coupled to the turbulent flow field. The first part of this talk will focus on the experimental evaluation of theoretical DSD shapes using the Pi cloud chamber measurements. In the second part, a modeling study of the influence of turbulent entrainment and secondary activation on cumulus cloud properties will be discussed. The "super-droplet method'' is implemented in the CM1 LES framework for this investigation.

Hosted by: Ernie Lewis

An emerging trend of increasing organic carbon (OC) has been observed in cloud water over the past decade at Whiteface Mountain (WFM) in Upstate New York, correlated with a growing inorganic ion imbalance and a growing abundance of ammonium. The driving factors behind these changes and potential impacts on secondary organic aerosol mass are not clear, underlining the need to better characterize the chemical makeup of the organic constituents in cloud water. Low molecular weight organic acids were added to the routine suite of cloud water chemical measurements at WFM beginning in 2018. The organic component of cloud water residuals (the particles left behind after droplets evaporate) was further characterized using a high resolution time-of-flight aerosol mass spectrometer. Comparisons between all of these measurements and historical observations at WFM are discussed, and a plan for future measurements of aerosol and cloud droplet residual composition is described. Blue Jeans Meeting ID: 565168891 - https://bluejeans.com/565168891

Hosted by: Alistair Rogers

Climate change will increase global temperatures 3-4 degrees C by 2100. This warming will affect photosynthesis, a temperature-sensitive process that helps dictate plant growth. Warming-induced shifts in photosynthesis also affect the global carbon cycle, mitigating or accelerating further climate change. Understanding how photosynthesis acclimates to future temperatures is therefore critical for accurately predicting the trajectory of future climate change, as well as for estimating plant productivity in a warmer world. I'll discuss how elevated growth temperatures impact photosynthesis, using meta-analyses, modeling and results from my lab, highlighting both what we know and the key questions that remain to be answered.

Hosted by: Allison McComiskey

Sea breeze circulations are one of the ubiquitous mesoscale flow regimes in coastal areas, where nearly half of the world's population resides. The leading edge of these thermally driven circulations presents as a boundary layer forcing mechanism for convective initiation. Despite the far-reaching impacts of sea breezes, numerical forecasting of sea breeze convection is still challenging due to uncertainties in the initial conditions, as well as the covariance and interaction of multiple meteorological and surface parameters. Due to the computational expense of cloud-resolving models, the sensitivity of sea breeze convection to a variety of environmental parameters has primarily been studied by perturbing one or two parameters at a time. Therefore, the overarching goal of this study is to extend these previous studies by quantifying the relative importance of a suite of environmental parameters, including meteorological properties, land surface characteristics, and aerosol loading, on the continental convection within tropical sea breeze regimes. The key parameters impacting the intensity of the convection within the tropical sea breeze regime have been identified through the application of Gaussian process emulation and variance based sensitivity analysis techniques. An ensemble of 130 initial conditions for tropical sea breeze simulations has been designed by simultaneously perturbing six atmospheric and four surface properties to address this goal. Using the Regional Atmospheric Modeling System (RAMS) coupled to a two-way interactive land surface parameterization, 130 pairs for a total of 260 tropical sea breeze simulations have been performed in low- and high-aerosol loading conditions. We find that sea breeze convective intensity is dominated by inversion strength for shallower clouds and boundary layer potential temperature for deeper clouds. In high aerosol loading conditions, the relative contribution of parameters to

Hosted by: Mike Jensen

Ice clouds currently reflect ~17 W m-2 of shortwave radiation and trap ~22 W m-2 of longwave radiation on global average. However, if the distribution of cloud heights and microphysical properties changes in response to increases in greenhouse gases and aerosols, associated changes in the radiative impact of clouds could feed back on Earth's climate. Representations of ice particle density, scattering and sedimentation are needed for global and regional climate models that predict these effects. Parameterizations of other processes, such as riming, aggregation, sedimentation and evaporation, are also needed for numerical weather models that predict the destructive impact and quantitative precipitation forecasts for winter storms, hurricanes, mesoscale convective systems and other events. Further, algorithms retrieving cloud properties from ground- and satellite-based sensors require assumptions about ice crystal properties. To develop such parameterizations, accurate observations of ice particle sizes, shapes, phases and concentrations are needed. Techniques measuring these ice crystal properties are reviewed. Sources of uncertainty, related to statistical counting, variability in cloud properties for similar environmental conditions, and errors induced by the processing of data and the instruments themselves are discussed using data collected over Alaska, Australia, and the continental United States. It is shown that although there are still uncertainties in in-situ observations of small ice crystals due to potential shattering of large particles on probe tips and the limited resolution of state-of-the-art cloud particle imagers, progress on characterizing small crystals has been made. The use of instrumental and statistical uncertainties in the development of stochastic cloud parameterizations is then introduced. A specific application to the representation of mass-dimensional (m-D) relationships m=aDb is shown, where (a,b) are given as surf

Hosted by: Mike Jensen

Weather can cause significant damage to the electrical power system, leading to prolonged power interruptions to a large number of customers. The estimated annual cost to the U.S. economy from storm-related power outages is >$20 billion. The number of weather-related outages has increased significantly in recent years. One approach to deal with this problem is to develop predictive techniques for forecasting how storms will impact the power grid hours to days in advance. This information can help utilities, first responders, and emergency managers to better prepare for the outages and more quickly restore power. This presentation summarizes the data-driven power outage models that we have developed for the U.S. Department of Energy and a number of investor-owned electrical utilities in the United States. These models are used to support decision making for near-term events (e.g., pre-storm preparation) and longer-term planning. The development and validation of our models will be presented and our approach for quantifying uncertainty will also be discussed. The talk will also highlight the challenges and successes from recent applications for American Electric Power, FirstEnergy, Southern Company and Southern California Edison.

Hosted by: Mike Jensen

Global Climate Models (GCMs) are depicted as the holy grail of climate science. However, they are far from reliably simulating the current and future climate. One of the components that represents a source of errors and biases in these models is the convective parametrization scheme and the ad-hoc treatment of deep convection and entrainment. In this talk, I will focus on two tropical atmospheric events that GCMs struggle to simulate: Amazonian deep precipitating convection, and the Madden Julian Oscillations. I will present how idealized cloud-resolving models (CRMs) coupled with simulated and forced large-scale circulation can capture the essential dynamics of these events. In particular, when diagnosed from the CRMs, I will show that entrainment is merely a response to the convective regime and cannot have a constant rate as GCMs suggest. If time allows, I will also point out to another potential source of biases in the simulated mean climate stemming from the representation of numerical noise damping in the model dynamical core.

Hosted by: Ernie Lewis

Atmospheric aerosols directly affect the earth's energy balance through the scattering and absorption of solar radiation. While aerosols are expected to have a net negative forcing (i.e. cooling), the actual magnitude of this effect remains highly uncertain due to physical, chemical, spatial and temporal variability. To complicate matters, strongly absorbing carbonaceous aerosols (i.e. black carbon, BC) exhibit a positive radiative forcing rivaling methane. A better understanding of the magnitude of these aerosol-radiation interactions requires a multi-pronged approach with fundamental metrology (e.g. instrumentation, methods, standards and calibrations) utilizing well-characterized systems under controlled conditions representing just one piece of the puzzle. Highlights of recent projects at the National Institute of Standards and Technology (NIST) will be presented including: 1) the characterization and use of a water-stabilized carbon black (CB) nanomaterial that mimics aged BC that can be used to calibrate aerosol instrumentation, 2) results from the first-ever photoacoustic spectrometer intercomparison study, 3) variability in the aerosol absorption spectra of highly-absorbing carbonaceous aerosols from a variety of sources and 4) aerosol absorption spectra of terrestrial mineral dusts and Martian soil simulants.

Hosted by: Shawn Serbin

The terrestrial biosphere is the largest source of uncertainty in the global carbon budget. We know that Earth system models (ESMs) over simplify patterns and processes, yet often we lack global scale information that could constrain these models. This situation is, however, rapidly changing with the development of new remote sensing tools (from space, air, or ground), new ESMs, and new approaches to data analysis. To help constrain and inform ESMs, my group is working to understand ecological diversity at multiple spatial and temporal scales. We are quantifying plant functional traits in four-dimensions (x-y-z and through time) using data collected with the NEON Airborne Observation Platform and NASA's G-LiHT. We are using Landsat to map phenological diversity ('phenoregions') and woody cover in savanna vegetation across eastern Africa. And we are developing new tools to understand the drivers of ecological diversity (bio- and geo- ) across different resolutions and extents. These projects all target the same fundamental question: How can we better quantify ecological diversity to improve forecasts of the Earth system?

Hosted by: Shawn Serbin

Terrestrial photosynthesis (gross primary productivity) is the largest carbon flux on the planet and the gatekeeper process for the subsidy of fossil fuel use provided by the terrestrial carbon sink. Increasing confidence in model representation of photosynthesis is an essential part of reducing uncertainty in projections of global change. Focusing on leaf level physiology, I will discuss the how parametric and structural representation of photosynthesis impacts model responses to key environmental drivers and show how data from field work in the Arctic and tropics is aiming to inform model parameterization and representation of photosynthesis in next generation models.

Hosted by: Art Sedlacek

Smoke aerosol properties and ozone evolve within plumes through physical and chemical processes, impacting smoke climate and health impacts. Many of these physical and chemical processes, in theory, depend strongly on smoke concentrations. Hence, the initial concentrations and dilution rates should affect smoke aging. In general, plumes from small fires should dilute more rapidly than those from large fires, all else equal; and in recent publications, we have used theory to demonstrate the smoke properties from small fires should evolve differently than those from large fires. However, until recently, we have been unable to test these findings with measurements due to a lack of Langrangian-style smoke aging field studies of small fires (due to the challenge of following small, fast-diluting plumes with time). In this talk, I will discuss how we have used observations of concentration gradients in large plumes from the Pacific Northwest portion of BBOP campaign to test these hypotheses. Using the high time resolution BBOP measurements, we have separated the dilute edges of the large plumes from the concentrated cores. We expect that the dilute edges of large plumes have similar chemical and physical process rates as small, fast-diluting plumes. The BBOP data show that the dilute portions of plumes (1) have faster number losses and diameter growth from coagulation, (2) transition more quickly POA-like to SOA-like aerosol composition potentially through faster OA evaporation and faster photochemistry, and (3) have higher enhancements of ozone. We recommend that future smoke studies compare concentrate plume cores to dilute edges to help elucidate physical/chemical processes and understand inter-plume differences.

Hosted by: Yangang Liu

East Asia is a major source of global dust aerosols originating from the Taklamakan desert and the Gobi desert. Over this region, the estimated several hundred Tg per year of dusts are emitted directly into the air and partly transported to downstream land and ocean regions through westerly winds, e.g., eastern China and northern Pacific, which significantly affect the global and regional energy balance, climate and hydrological cycle by dust direct radiative forcing (DRF) and dust-in-snow radiative forcing (SRF) based on previous studies. This study shows the DRF and SRF and their feedbacks on the regional climate and the dust cycle over East Asia through the use of the Community Atmosphere Model version 4 with a Bulk Aerosol Model parameterizations of the dust size distribution (CAM4-BAM). Our results show that SRF increases the eastern Asian dust emissions significantly by 13.7% in the spring, countering a 7.6% decrease in the regional emissions by DRF. We proposed a significant feature of SRF on the Tibetan Plateau (TP) is the creation of a positive feedback loop that affects the dust cycle over eastern Asia through enhancing the TP heat source. Additionally, we also examine the relationship in the interannual variability between the TP heat source and East Asian dust cycle from observations and models to check this new feedback.

Hosted by: Fan Yang

Although Lagrangian methods for the representation of cloud microphysics date back more than half a century, they have regained considerable attention in the last decade due to the advent of so-called Lagrangian cloud models (LCMs). Today, LCMs are not only considered a valuable alternative to commonly applied Eulerian cloud models (ECMs), but also the future of cloud microphysical modeling. The main difference between LCMs and ECMs is the representation of cloud microphysics, e.g., the cloud droplet size distribution (DSD): ECMs discretize the DSD by several bins or only predict a few statistical moments of it. LCMs, on the other hand, model the DSD by Lagrangian particles, each representing an ensemble of identical droplets. This talk will cover the fundamentals of LCMs, covering the implementation of warm-phase microphysical processes, the differences and advantages to ECMs, as well as novel analysis techniques only possible in LCMs. Subsequently, I will focus on a recent approach for the modeling of unresolved supersaturation fluctuations to be applied in LCMs. Since LCMs are typically coupled to a large-eddy simulation (LES) model for predicting dynamics and thermodynamics, supersaturation fluctuations are constrained by the LES resolution. Using the new approach, supersaturation fluctuations down to the Kolmogorov length scale may be considered, including their specific effects on cloud microphysics, most importantly typically unresolved inhomogeneous mixing. Results from warm-phase boundary layer cloud simulations will be presented, focusing on the entrainment process in stratocumulus clouds. Finally, an initial view toward the modeling of entrainment and mixing in mixed-phase clouds will be given, assessing the importance of inhomogeneous microphysical processes in these clouds.

Hosted by: Allison McComiskey

The turbulence and interactions between the land surface and the atmosphere needs to be represented in all numerical weather prediction and climate models. The Land-Atmosphere Feedback Experiment (LAFE) was conducted at the ARM SGP to collect a comprehensive dataset to evaluate the similarity relationships used to represent these processes in most numerical models. This seminar will present an overview of the LAFE campaign, present some observational results, and demonstrate how observations like this can be used to improve similarity relationships.

Hosted by: Andy Vogelmann

Reanalysis and observations collected at ENA are analyzed to document the properties of rain and boundary layer clouds during general subsidence conditions and following cold front passages. Clouds in the wake of cold fronts exhibit on average a 10% higher propensity to precipitate and higher rain-to-cloud fraction than clouds found in general subsidence conditions. The identification of monotonic relationships between rain-to-cloud fraction with surface forcing and boundary layer stability parameters as well as between virga base height with stability and humidity measures further supports that large-scale conditions impact precipitation variability. That being said, these relationships are less clear than those established between cloud and rain properties suggesting that cloud macrophysics have a more direct impact on the properties of rain than the large-scale environment.

Hosted by: Mike Jensen

The initial formation of precipitation in warm clouds remains shrouded in mystery. Precipitation initiation in bulk microphysical parameterizations is typically cast as a nonlinear function dependent on liquid water content and droplet concentration, which suggests two possible paths to precipitation initiation in actual clouds—high liquid water content or low droplet concentration. A bin-microphysics large-eddy simulation (LES) model is employed investigate the dominant microphysical precursor conditions influencing precipitation initiation for a case of marine stratocumulus over the eastern North Atlantic. Results suggest that new regions of precipitation are associated with fluid parcels that previously participated in the precipitation process.

Hosted by: Steve Schwartz

The effective radiative forcing due to aerosol-cloud interaction, ERFaci, is composed of the radiative forcing due to aerosol-cloud interactions, RFaci (Twomey effect) that is the immediate response of cloud albedo to an increase in droplet number concentration, Nd. Previous satellite-based quantification of this effect was hampered by deficiencies in the retrieval of aerosol and also, of Nd. The talk will firstly discuss progress in this regard, which leads to a stronger estimated RFaci than previous satellite-based approaches. The other component of ERFaci is in the cloud adjustments. These can be split into adjustments of cloud fraction, f, and liquid water path, L. In terms of the latter, statistical relationships between L and Nd show on average negative adjustments of L (a positive forcing component). In turn, the analysis of ship-, volcano- and industry tracks leads to an estimated small overall effect on L; these results are trustworthy since a cause-effect relation is assured. In terms of the f adjustment, the current results point to an increase in cloud fraction at larger Nd. It is unclear which processes lead to this result. The talk will also briefly discuss how cloud-resolving simulations may help to better understand the remaining uncertainties. In the last part, a brief discussion will be presented on initial steps towards an estimate of the response of cirrus to anthropogenic aerosols.

Hosted by: Fan Yang

Selective detection of signal over noise is essential to measurement and signal processing. Time-frequency filtering has been the standard approach for the optimal detection of non-stationary signals. However, there is a fundamental tradeoff between the signal detection efficiency and the amount of undesirable noise detected simultaneously. By tailoring the nonlinear process in a lithium-niobate waveguide, we demonstrate highly selective detection of picosecond single photons against broadband noise overlapping temporally and spectrally but in orthogonal time-frequency modes, with performance well exceeding the theoretical limit of the optimized time-frequency filtering. To this end, our technique can achieve signal to noise exceeding by far what's possible with linear optics filters even in the presence of strong background noise, which are highly desirable for many atmospheric remote sensing and imaging applications. Here, we present some feasibility studies in connecting our mode selective detection technique for applications in atmospherics science. Our results and visions may lead to enhanced resolution, sensitivity and detection limit for atmospheric instruments such as lidar and disdrometer.

Hosted by: Mike Jensen

Outgoing radiative fluxes at top-of-atmosphere (TOA) are driven by the interaction of clouds, aerosols, and radiation. The upcoming EarthCARE mission aims to improve our understanding of this interaction and compares shortwave (SW) and longwave TOA fluxes from (1) radiative transfer simulations – acting on cloud and aerosol properties retrieved from onboard active and passive instruments – with (2) flux estimates based on broadband radiometer (BBR) measured radiances over horizontal domains of 10x10 km. To improve BBR-based TOA SW flux estimates, this talk explores a new approach that incorporates additional parameters (cloud-top effective radius and cloud-topped water vapor) and produces significantly different flux estimates when compared against state-of-the-art methodology.

Hosted by: Art Sedlacek and Ernie Lewis

Primary biological atmospheric particles (PBAP), also called bioaerosols, are ubiquitous in the atmosphere with potentially important impacts on human health1,2, cloud formation3, the hydrological cycle4,5, and biogeochemical cycles6. Measuring PBAP poses a challenge for established biological tools due to generally low atmospheric concentration. Bioaerosols are currently measured by light-induced fluorescence (LIF) instrumentation using the autofluorescence of cell macromolecules, but the frequency of misidentification of abiotic particles by LIF is unclear. As a result, a robust protocol using a state-of-the-art cyclone to collect liquid samples and subsequent flow cytometry analysis, a more specific single-cell detection technique, was effectively designed and applied to quantify the speciated abundance of PBAP7. Tests conducted in Atlanta, GA showed clearly defined low nucleic acid (LNA), high nucleic acid (HNA), and pollen PBAP populations. LNA dominated during dry days and HNA dominated warm and humid days. Our instrumentation pipeline has been deployed during the Biological and Oceanic Atmospheric Study (BOAS) and the Finokalia Aerosol Measurement Experiment (FAME) campaigns. BOAS results show bacteria enrichment at cloud formation altitudes in the marine free troposphere. FAME studied PBAP loadings reaching Crete from continental Europe and Africa air transport; concentrations reached 105 cells m-3 during dust events. Overall, the optimization of detection and quantification techniques has provided tools to study closely speciated bioaerosol populations over different environments and meteorology to better understand bioaerosols lifecycle. References: (1) Fröhlich-Nowoisky et al., Atmos. Res. 2016; (2) Pöschl, Angew. Chem., 2005; (3) Hoose et al., Environ. Res. Lett., 2010; (4) Morris et al., Glob Chang Biol, 2014; (5) DeLeon-Rodriguez et al., PNAS, 2013; (6) Myriokefalitakis et al., Biogeosciences, 2016; (7) Negron-Marty et al., ACP, in

Hosted by: Art Sedlacek and Ernie Lewis

Sugars (primary saccharides, saccharide polyols and anhydro-saccharides) are a major class of water-soluble organic carbon (WSOC) that significantly contribute to atmospheric organic aerosol particular matter (PM). [1] The heterogeneous oxidation of organic materials plays a significant role during the chemical aging of organic aerosols in the atmosphere. The kinetic of such heterogeneous reactions has been shown to be very dependent on the chemical component of the particle phase. [2] The experiments were performed using an atmospheric pressure aerosol flow tube coupled with Scanning Mobility Particle Sizer (SMPS), Gas Chromatography – Flame Ionization Detector (GC-FID) and Aerosol Mass Spectrometer or Teflon filter collection. The kinetics are determined from the loss of particle species as a function of OH exposure. We reported results on the OH-initiated heterogeneous oxidation of pure monosaccharide semi solid nanoparticles over a wide range of relative humidity (RH) conditions. The decay rate of the monosaccharide is found to strongly depend on the gas phase water concentration. [3] We recently report results on heterogeneous oxidation of OH radicals with ternary component of monosaccharide-disaccharide-water semi solid nanoparticles over a range of mole ratio of mixtures of monosaccharide and disaccharide. The presence of disaccharide slows down the decay rate of monosaccharide in semi solid phase. [4] Then we moved on to aqueous phase oxidation of saccharides by OH radicals study. Contrast to what we observed in semi solid phase study, the presence of monosaccharide slows down the kinetic of disaccharide in aqueous phase. [5] A reaction-diffusion kinetic model solved in Matlab software is developed in order to investigate the effect composition-dependent diffusion on heterogeneous reaction behaviors in solid phase study. [3,4] Molecular dynamics simulations and kinetic mechanism of the heterogeneous oxidation of aqueous droplets based

Hosted by: Bob McGraw

Two simple and efficient models for the description of multicomponent Fick diffusion in mixtures with high numbers of components have been recently developed [1]. Both models are based on the Kinetic Theory of Gases and make use of perturbation schemes in terms convenient dimensionless variables, leading to efficient algorithms for the calculation of mass diffusion fluxes in mixtures of interest in combustion science. The first model, termed Model 1, which is extremely simple, assumes that all components in the mixture are dilute in a single species, and provides an accurate description of the multicomponent fluxes by means of a perturbation scheme. In the second model, termed Model 1+M, the number of main species (those species which are not in the dilute limit) is increased from 1 to 1+M, with 1+M being at most an order O(10) number, and the perturbation strategy is only applied to the remaining dilute species, often in trace amounts. The performance of these two descriptions of multicomponent diffusion fluxes is compared to the formulation of Dixon-Lewis [2], used for instance in the Chemkin package [3], and also to the widely used mixture-average simplification. The results are illustrated with steady flamelets of hydrogen or dodecane, in order to compare computational costs when different number of species are involved. An unsteady auto-igniting counterflow diffusion flamelet of methane in a coflow of hot products is also considered. The different comparisons in terms of precision and cost show that Model 1+M can be more effective than the mixture-average approach in terms of computation time, while reproducing the results of Dixon-Lewis multicomponent diffusion [4]. REFERENCES [1] Arias-Zugasti, M., Garcia-Ybarra, P.L., Castillo, J.L., "Efficient calculation of multicomponent diffusion fluxes based on kinetic theory", Combust. Flame 163:540–556 (2016)

Hosted by: Ernie Lewis

Aerosols and clouds effect Earth's radiative balance, and aerosol-cloud interactions are major sources of uncertainties in predicting future climate. The climate effects of water and ice cloud particles formed from atmospheric particulate matter are not well understood due to the complex physical and chemical properties of these aerosols. Measurements from fixed sites and field campaigns have shown that organic aerosols (OA) dominate the non-refractory aerosols in the free troposphere where clouds typically form, and cloud water and ice cloud residue both show the presence of organic materials. Despite the abundance of OA, their effects on both cloud condensation nuclei (CCN) and ice nucleation (IN) are not fully understood and even controversial. To probe into these issues, the CCN and IN properties of complex inorganic-organic aerosol mixtures that simulate ambient conditions were measured with a cloud condensation nuclei counter (CCNC, DMT, Inc.) and a spectrometer for ice nucleation (SPIN, DMT, Inc.) at a variety of laboratory conditions. Our studies suggest that the composition of the organic-containing aerosols, as well as their morphology and phase state, jointly impact their cloud forming potential. The results highlight the importance of combining aerosol physical and chemical properties to accurately understand cloud particle formation processes and their implications on the climate.

Hosted by: Mike Jensen

Parcel theory is the basis for many of convective indices (e.g., CAPE, LNB) that are used extensively throughout the community. While it is widely known that parcel theory is only an approximation, and therefore the indices that derive from parcel theory are also just approximations, much more research is needed so that we can better link our theory to observations. One example is the relationship between the level of neutral buoyancy (LNB) and the level of maximum detrainment (LMD). Both models and observations show departures from LNB depend on storm morphology, season and geographical region.

Hosted by: Angie Burnett

Improved photosynthetic rates have been shown to increase crop biomass, making improved photosynthesis a focus for driving future grain yield increases. Improving the photosynthetic pathway offers opportunity to meet food demand, but requires high throughput measurement techniques to detect photosynthetic variation in natural accessions and transgenically improved plants. Gas exchange measurements are the most widely used method of measuring photosynthesis in field trials but this process is laborious and slow, and requires further modeling to estimate meaningful parameters and to upscale to the plot or canopy level. In field trials of tobacco with modifications made to the photosynthetic pathway, we infer key photosynthetic parameters from imaging spectroscopy using a partial least squares regression technique. We used two hyperspectral cameras with resolution 2.1nm in the visible range and 4.9nm in the NIR. Ground-truth measurements from leaf-level photosynthetic gas exchange, full-range (400-2500nm) hyperspectral reflectance and extracted pigments support the model. The results from a range of wild-type cultivars and from genetically modified germplasm offer a high-throughput screening tool for crop trials aimed at identifying increased photosynthetic capacity.

Hosted by: Mike Jensen

This talk will begin with an overview of recent development in the representation of deep convection in the NASA Goddard Institute for Space Studies (GISS) General Circulation Model (GCM). Global satellite remote sensing products are important references for continual GCM development and evaluation, but such products often provide data at coarse temporal and/or spatial resolutions, thus making it difficult to conceptualize and evaluate "process representations" in a GCM. I will discuss the various approaches I am taking to average global satellite retrievals in new ways, coincident with efforts to use new DOE/ARM observations, to derive composite high-resolution evolutions of deep convection and the nearby environment. These depictions will not only inform future development, but they are also crucial for ensuring that recent improved mean-state representations are not the result of errors cancelling at the process level.

Hosted by: Damao Zhang

Mixed-phase clouds are frequently observed in the Arctic and Antarctic and over the Southern Ocean, and have important impacts on the surface energy budget and regional climate. Global climate models (GCMs), an important tool for studying the climate change still have large biases in simulating the mixed-phase cloud properties, including supercooled liquid amount and liquid and ice phase partitioning. In this talk, I will present our recent works on mixed-phase clouds: (1) improving the representations of subgrid mixing and partitioning between cloud liquid and ice in mixed-phase clouds in the DOE's Energy Exascale Earth System Model (E3SM). Model simulations are evaluated against observation data obtained in the DOE Atmospheric Radiation Measurement (ARM) Program's field campaigns and long-term ground-based multi-sensor measurements; and (2) investigating the effects of aerosols, including dust and sea spray aerosol, on mixed-phase clouds. We found that dust, as ice nucleating particles (INPs), induces a global net warming via its indirect effect on mixed-phase clouds with a predominant warming in the NH midlatitudes and a cooling in the Arctic. INP sources of sea spray aerosol vary with time and geographic location with the maximum contribution in the marine boundary layer over the Southern Ocean, where dust has a limited influence. Modeled INP concentrations are compared with observations from different campaigns (e.g., MARCUS, SOCRATES, CAPRICORN).

Hosted by: Mike Jensen

Knowledge of the adjustment time of anthropogenic CO2, the e-folding time by which excess CO2 (above preindustrial) would decrease in the absence of anthropogenic emissions, is central to understanding the influence of anthropogenic CO2 on climate change and to prospective control of CO2 emissions to reach desired targets. Estimates of this adjustment time from current carbon-cycle models range from about 100 years to over 700 years. This talk examines the CO2 budget by a top-down, observationally based approach. Major stocks and fluxes are quantified. The net flux from the atmosphere and the ocean mixed layer, which are in near equilibrium, to the deep ocean and terrestrial biosphere is found to be proportional to the excess CO2 in these compartments throughout the Anthropocene. These observations, together with knowledge of the underlying physical and chemical processes, are used to develop a simple, transparent model that describes the transport of CO2 between major compartments — the atmosphere, the mixed-layer ocean, the deep ocean, and the terrestrial biosphere. This model compares well with observed atmospheric CO2 from 1750 to the present. The adjustment time of excess CO2, evaluated by multiple measures including the 1/e decay time and the negative inverse of the fractional annual transfer rate of excess CO2 into the terrestrial biosphere and the deep ocean, is found to be 54 ± 10 years. Such a short adjustment time, if correct, would mean that the atmospheric amount of CO2 would respond quickly and strongly to emission changes. For example, atmospheric CO2 could be immediately stabilized at its present value by decreasing anthropogenic emissions by about 50%.

Hosted by: Mike Jensen

Using observations collected at the ARM Eastern North Atlantic (ENA) site, we examine the relationship between the large-scale environment and the properties of low-level clouds that occur in conditions of subsidence. The cloud boundary cloud properties correlate well with the difference in potential temperature between the 800 hPa level and the surface, a measure of the degree of boundary layer instability. Moreover, consistent relationships are found between near-surface stability, surface energy fluxes, and cloud fraction, optical thickness, and top temperature in various regions of strong post-cold frontal activity. To help understand these mechanisms, we use the Weather Research Forecast (WRF) model to explore post-cold frontal clouds with a case study. The modeled cloud properties are sensitive to the interactions between the shallow convection and the boundary layer parameterizations. We will report how this sensitivity is related to boundary layer decoupling, vertical shear in the horizontal winds at cloud top, and drizzle. We also test the robustness of these conclusions by analyzing a perturbed initial conditions ensemble using WRF. A comparison of the perturbed physics and the perturbed initial condition ensembles explores the relative impact of circulation changes and physical processes on low-level cloud in the model.

Hosted by: Mike Jensen

Despite progress in understanding of aerosol-cloud interactions (ACI) and their representation in climate models, climate models still suffer from large uncertainty in estimated aerosol indirect effects and large discrepancy compared to observations. This tenacious problem poses vital challenges to accurately represent aerosol-cloud interactions even in warm clouds, the apparently simplest of all clouds. In this talk, I will discuss several potentially important yet poorly understood factors that likely compensate/buffer aerosol-cloud interactions as conventionally represented in climate models (e.g., dispersion effect associated with the aerosol-induced changes of the spectral shape of the cloud droplet size distribution; regime dependence of cloud properties on aerosol concentration and updraft velocity; effect of turbulent entrainment-mixing processes; microphysics-turbulence interactions; scale-dependence; process coupling). I will explore the challenges and the main knowledge gaps that are needed to fill to address these challenges, and discuss the approaches that hold potentials to fill the knowledge gaps and address the ACI challenges.

Hosted by: Allison McComiskey

Large Eddy Simulations (LES) are the tool of choice to study the dynamics, microphysics, and aerosol-cloud interactions of boundary layer clouds. LES traditionally operate with idealized large scale meteorological conditions, derived from a snapshot of the atmospheric state, and leave aside the role of mesoscale organization. The need for better scientific understanding, supported by technical progress, has prompted the development of LES approaches geared towards greater realism. This seminar will introduce realistic Lagrangian LES, which capture boundary layer and cloud state development and mesoscale organization along reanalysis trajectories. The approach is applied, together with satellite observations and in-situ data, to study the impact of continental outflow on the transition from the closed- to the open-cell stratocumulus state, and the impact of long-range transport of biomass burning aerosol on a pocket of open cells in the South-east Atlantic. Furthermore, some fundamental questions on the dynamics of stratocumulus clouds with relevance for large scale modeling and satellite remote sensing are answered.

Hosted by: Scott Giangrande

Deep convective clouds (DCCs) regulate the global energy and water cycles through their extensive cloud coverage and the exchange of latent heat. Through the influence of DCCs on the large-scale atmospheric Hadley and Walker circulations, DCCs affect the cloud and precipitation properties in remote tropical and subtropical environments. Unfortunately, current general circulation models (GCMs) do not properly simulate DCC role in our climate system, since relevant DCC processes operate across GCM resolved and parameterized scales. In addition, inadequate observational constraints inhibit high-resolution convective model process improvement. This talk will focus on the kinematic characteristics of DCCs using ARM ground-based observations (e.g., radar wind profiler), and the challenges faced in model evaluation (e.g., WRF). The convective up- and downdrafts of DCCs will be discussed in particular, which are the most fundamental property and are among the most difficult aspects of convection to measure.

Hosted by: Mike Jensen

During the first phase of the Biomass Burn Operational Period (BBOP) field campaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was used to follow the time evolution of wildfire smoke from near the point of emission to locations several hours downwind. In nine flights we made repeated transects of wildfire plumes at varying downwind distances and could thereby follow the plume's time evolution. We observed an active photochemistry: rapid depletion of NOx and O3 concentrations up to 170 ppb. The peak concentration of biomass burning aerosols was 16,000 μg/m3. On average there was little change in dilution-normalized aerosol concentration during 2-4 hours of pseudo-Lagrangian sampling. This consistency seemingly hides a dynamic system in which primary aerosols are evaporating and secondary condensing. Particle size increases with downwind distance causing the particles to be more efficient scatters. Aerosol light scattering increases by up to a factor of two even though aerosol mass is nearly constant. Near-fire aerosol had a single scatter albedo (SSA) of 0.8-0.85. After 1-3 hours of aging, SSAs were typically 0.9 and above. For average surface and atmospheric conditions, the observed increases in SSA change plumes from having a small warming effect due to light absorption, to a cooling effect due to the scattering of sunlight upwards, back to space.

Stratiform mixed-phase clouds are prevalent at high latitudes and greatly impact regional radiative fluxes. Satellite and ground-based remote sensing measurements enable statistical analyses of mixed-phase cloud properties and their underlying processes. A comprehensive database is constructed of retrieved mixed-phase cloud microphysical properties using ground-based remote sensing measurements from the Atmospheric Radiation Measurement Program (ARM) West Antarctic Radiation Experiment (AWARE) campaign at the McMurdo station, and multiple years of measurements at the ARM North Slope of Alaska (NSA) Utqiagvik Facility. The database includes ice and liquid components of water content, average particle size and concentration, and dynamics including vertical air velocity and turbulence. With the database, polar stratiform mixed-phase cloud macro- and microphysical properties are analyzed and compared for the dramatically different environments. In addition, lidar backscattering and polarization measurements are used to study polar aerosol profiles that may impact stratiform mixed-phase cloud microphysical properties through aerosol-cloud interactions. Such long-term remote sensing observations of polar stratiform mixed-phase cloud properties may be used to evaluate and improve model simulations.

Despite their climatic importance, multi-scale models continue to have persistent biases produced by insufficient representation of convective clouds. To increase our understanding of convective cloud lifecycles and aerosol-convection interactions, the TRacking Aerosol Convection interactions ExpeRiment (TRACER) will take place in the Houson, TX region from April 2021 through April 2022 with an intensive observation period from June to September 2022. TRACER (currently) includes the deployment of the ARM Mobile Facility, a C-band scanning polarimetric radar, and additional aerosol and atmospheric state measurements within existing surface meteorology, air quality and lightning dection neworks. A unique component of TRACER is that a large number of individual, isolated convective cells will be tracked and measured in high spatial and temporal resolution for the purposes of: (i) Characterizing and linking convective cloud kinematic and microphysical lifecycles, (ii) Quantifying environmental thermodynamic and kinematic controls on convective lifecycle properties, and (iii) Isolating and quantifying the impacts of aerosol properties on convective cloud kinematic and microphysical evolution. The seminar will present the scientific motivation for the TRACER campaign, details on the deployment strategies, and evolving opportunities for participation. The unique combination of cloud, precipitation, lightning, aerosol, and atmospheric state measurements associated with tracked convective cells will ultimately improve our understanding of the convective cloud lifecycle and its interaction with individual environmental factors such that improved, next generation cumulus, microphysics, turbulence, and aerosol parameterizations can be designed.

Hosted by: Fan Yang

Inspired by early convection-tank experiments (e.g., Deardorff and Willis) and diffusion-chamber experiments, we have developed a cloud chamber that operates on the principle of isobaric mixing within turbulent Rayleigh-Bénard convection. The "Pi cloud chamber" has a height of 1 m and diameter of 2 m. An attractive aspect of this approach is the ability to make direct comparison to large eddy simulation with detailed cloud microphysics, with well characterized boundary conditions, and statistical stationarity of both turbulence and cloud properties. Highlights of what we have learned are: cloud microphysical and optical properties are representative of those observed in stratocumulus; aerosol number concentration plays a critical role in cloud droplet size dispersion, i.e., dispersion indirect effect; aerosol-cloud interactions can lead to a condition conducive to accelerated cloud collapse; realistic and persistent mixed-phase cloud conditions can be sustained; LES is able to capture the essential features of the turbulent convection and warm-phase cloud microphysical conditions. It is worth considering what more could be learned with a larger-scale cloudy-convection chamber. Turbulence Reynolds numbers and Lagrangian-correlation times would be scaled up, therefore allowing more enhanced role of fluctuations in the condensation-growth process. Larger vertical extent (of order 10 m) would approach typical collision mean free paths, thereby allowing for direct observation of the transition from condensation- to coalescence-growth. In combination with cloudy LES, this would be an opportunity for microphysical model validation, and for synergistic learning from model-measurement comparison under controlled experimental conditions.

Hosted by: Mike Jensen

Cloud feedbacks and an appropriate representation of clouds in climate models have long been one of the largest sources of uncertainty in predicting any potential future climate change. Although it is already a great challenge to derive true cloud fractions (CFs) from both active and passive remote sensing observations, it is even more difficult to infer their vertical distributions. Here we use the NASA CERES) Edition 4 cloud products in conjunction with the availability of ARM ground-based and NASA CloudSat-CALIPSO (CC) spaceborne radar-lidar observations over four ARM sites (SGP, ENA, TWP, and NSA) to answer two questions: Can spaceborne and ground-based radar-lidar combinations observe the same types and amounts of clouds? Are clouds detected and analyzed using passive satellite remote sensing comparable to these actively sensed clouds? From the long-term satellite-surface comparisons over these four sites, we found that ARM missed some optically thin high-level clouds at ARM SGP and ENA and even more at TWP, while CC missed some low-level clouds at NSA but identified more low-level clouds at SGP and ENA, even more at TWP. Passive sensors could not detect optically thin clouds, which is beyond their limitation. Based on the results, we conclude that true CFs can only be estimated from multiple instruments on various platforms. At the end of talk, we will present some comparisons between satellite observed and model simulated cloud properties.

Hosted by: Yangang Liu

The WRF-Solar model is an augmentation of the Weather Research and Forecasting (WRF) model specifically designed for solar energy applications. The developments have focused on improving the representation of the aerosol-cloud-radiation physics. In this direction, WRF-Solar includes a fast radiative transfer parameterization to provide surface irradiance forecast only limited by the model time step; an improved representation of the aerosol-radiation feedback (aerosol direct effect); incorporation of the cloud-aerosol feedbacks (aerosol indirect effects); and improved cloud-radiation feedbacks. During this seminar I will provide an overview of the WRF-Solar model and present evaluations that illustrate the benefits of the augmentations. Ongoing developments including a better cloud initialization and extending the model to provide probabilistic forecasts will be also discussed.

Hosted by: Laura Fierce

The links of atmospheric vertical motions and the ice content within clouds are numerous. Vertical motions generate the supersaturation that allows ice nucleation; they determine whether mass transfer will occur from droplets to crystals by the Bergeron process; and they control the sedimentation rate from the cloudy layer to lower altitudes. I will present the ways in which we have tried to better understand this dynamic-microphysical relationship over the past few years. First, with an automatic differentiation-based attribution analysis, we see the importance of accurately representing updrafts for the number concentration of nucleated ice crystals on a global scale. Then we zoom in, using a parcel model to identify joint temperature-updraft regimes in which secondary ice production processes like rime splintering or frozen droplet shattering can significantly enhance ice content. Along with these direct connections via hydrometeor formation, the relationship of vertical velocity and cloud ice content affects surface precipitation. We illustrate this indirect hydrological impact with mesoscale simulation of a mid-latitude cold frontal rain band and satellite data analyses of cloud top phase and precipitation from mesoscale convective systems throughout the tropics.

Hosted by: Laura Fierce

The Kathmandu Valley in Nepal is home to over 4 Million people, and is one of the fastest growing metropolitan areas in South Asia. It is subject to extreme pollution events due to numerous unregulated localized pollution sources and regional transport from the Indo-Gangetic Plain (IGP). Previous field work has studied gas species, wintertime VOCs and PM in the valley. The Nepal Ambient Measurement and Site Testing Experiment [NAMaSTE] is the first deployment of an Aerosol Mass Spectrometer (HR-ToF-AMS and mini-AMS) in Nepal and allows for a more comprehensive analysis of aerosol species and their source contributions. Source and ambient measurements were made in April 2015, but were interrupted by the Ghorka earthquake. Source measurements were nearly complete, but ambient measurements required additional data. We returned in December and January of 2017-2018 for a multi-site measurement campaign, and again in April 2018 to make additional real-time mobile measurements of aerosol composition throughout the Kathmandu Valley. Clear meteorological influences are observed with regular diurnal wind patterns in the valley. These patterns are key in establishing the influence of regional brick kiln operation with urban air pollution burden in Kathmandu. While organic species dominate the submicron aerosol composition measured throughout Nepal, the inorganic component of the aerosol (e.g. sulfate and chloride) are key species to identify brick kiln emissions and biomass/trash emissions.

Hosted by: Laura Fierce

In this seminar I will introduce the CERN CLOUD chamber experiment studying atmospheric new particle formation. I will then focus on work we have done to parameterize new particle formation and growth rates for atmospheric models. I will discuss the implementation of the parameterizations into the models, and the implications of the results from these models for estimated cloud condensation nuclei concentrations and indirect aerosol radiative forcing. The uncertainties in modelling new particle formation remain large, and I will outline how we are moving forward to try to reduce them.

Hosted by: Mike Jensen

Over the past ~20 years, there has been a significant advancement in knowledge regarding severe thunderstorms and tornadoes through the use of high-resolution data from high-frequency, truck-mounted, mobile Doppler radar systems. Recently, two advanced radar technologies, phased-array radar (PAR) and dual-polarization radar, have offered promise as a way to learn even more about severe weather systems. PAR allows for the collection of increased temporal resolution data of the phenomenon being studied. In turn, the processes that a quickly-evolving feature undergoes can be analyzed more accurately. Dual-polarization radars scan with the same update times as conventional mobile Doppler radars, but provide information about several characteristics of the hydrometeors being sampled. This information also can provide insight into processes occurring within the phenomenon of interest. Recent past observational work that has used these radar technologies to better understand supercell thunderstorms and tornadoes will be summarized. In addition, new efforts to generalize results from past case studies to large numbers of storms will be motivated and some preliminary results discussed.

Hosted by: Yangang Liu

The cloud droplet 'growth gap' problem in warm rain formation has troubled the cloud physics community for a few decades now. Turbulence has been considered as one of the mechanisms to overcome this bottleneck between cloud droplet growth by diffusion and growth by collision-coalescence. Being able to better understand and predict droplet growth rates would mean better estimates of cloud properties such as lifetime, precipitation, albedo etc. In this study, we use digital in-line holography to obtain volume measurements of cloud droplets with sizes near this growth gap in a turbulent laboratory chamber. We find that turbulent fluctuations in droplet number concentrations may lead to fluctuations in local supersaturation. Droplet growth through this stochastic condensation process results in broader droplet size distributions with some droplets growing large enough to jump the growth gap. We find similar results for airborne measurements of warm clouds suggesting this process should occur in the atmosphere as well. This approach is then extended to mixed phase clouds, and our first results show the importance of aerosol properties in controlling cloud glaciation.

Hosted by: Scott Giangrande

Stationary mesoscale convective systems (MCSs) are responsible for most of the warm season major flood events. Recent examples in North America are the West Virginia and Louisiana flooding of 2016, or the Houston flooding after the landfall of hurricane Harvey in 2017. Observations showed that MCSs became more frequent, intense, and long-lived in the Central US during the past 30 years. State-of-the-art climate models are not able to simulate MCSs realistically due to their coarse grid spacing leading to significant errors in simulating convective precipitation and uncertainties in extreme precipitation projections. Convection-permitting climate simulations (CPCS), which are able to simulate deep convection explicitly due to their high resolution, are promising tools that improve the representation of convective extremes. Here we use the weather research and forecasting model (WRF) to perform a current and end-of-century business as usual CPCS with 4 km horizontal grid spacing over a North American domain. Tracking MCS precipitation with a Lagrangian storm tracking algorithm shows that the current climate simulation can realistically simulate MCSs including the size, intensity, movement speed, and dynamical evolution of MCS precipitation. The future intensification of peak MCS precipitation rates is with about 7 % per degree warming in line with expectations from the Clausius-Capayron relation. However, these intensity increases combined with the spread of heavy rainfall areas of up to 70 % and additional changes in MCS movement speed lead to an almost doubling of MCS rainfall volume. The aim of this study is to understand the processes that lead to the rapid response of MCS precipitation volume to global warming. We show that interactions in future storm dynamics, thermodynamics, and microphysics are responsible for the large response. We will discuss the importance of model grid spacings to capture these changes. Further, i

Hosted by: Pavlos Kollias

Mixed phase clouds contain both ice particles and super-cooled cloud water droplets in the same volume of air. Currently, one of the main challenges is to observe and understand how ice particles grow by interacting with liquid water within the mixed-phase clouds. In the mid latitudes this process is one of the most efficient processes for precipitation formation. It is particularly important to understand under which conditions growth processes are most efficient within such clouds. The observation of microphysical cloud properties from the ground is one possible approach to study the liquid-ice interaction that play a role on the ice crystal growth processes. In the seminar I will give an overview on spectral polarimetric radar measurements and what the observations can tell us about ice particle growth within mid-latitude precipitation mid-latitude cloud systems.

Hosted by: Mike Jensen

Ice nucleation is the crucial step for ice formation in atmospheric clouds, and therefore underlies climatologically-relevant precipitation and radiative properties. Progress has been made in understanding the roles of temperature, supersaturation and material properties, but an explanation for the efficient ice nucleation occurring when a particle contacts a supercooled water drop (contact nucleation) has been elusive for over half a century. This work considers what other factors can affect ice nucleation, e.g., can electric fields or the dynamics of multi-phase contact lines affect ice nucleation? I have investigated these questions using conceptually-simple laboratory experiments in which the nucleation and freezing of supercooled water droplets resting on a substrate are observed with high-speed video. Two serendipitous and surprising results suggest that ice nucleation is strongly related to the contact line motion and distortion and a possible mechanism is proposed. It might interpret long-mysterious observations related to contact nucleation and its efficiency relative to immersion nucleation.

Hosted by: Bob McGraw

A Fast Integrated Mobility Spectrometer (FIMS) based on image processing was developed for rapid measurements of aerosol size distributions from 10 to 500 nm. The FIMS consists of a parallel plate classifier, a condenser, and a CCD detector array. Inside the classifier an electric field separates charged aerosols based on electrical mobilities. Upon exiting the classifier, the aerosols pass through a three-stage growth channel, where aerosols as small as 7 nm are enlarged to above 1 μm through water or heptanol condensation. Finally, the grown aerosols are illuminated by a laser sheet and imaged onto a CCD array. The images provide both aerosol concentration and position, which directly relate to the aerosol size distribution after data inversion, considering the FIMS transfer function, particle penetration efficiency, and multiple charging of aerosols. The parallel Comparisons between the FIMS and a scanning mobility particle sizer (SMPS) demonstrated excellent agreement when measuring aerosols with various size spectra, showing differences within 5% in average particle size and total number concentration. But by simultaneously measuring aerosols with different sizes, the FIMS provides aerosol size spectra nearly 100 times faster than the SMPS. Recent deployment onboard research aircraft demonstrated that the FIMS is capable of measuring aerosol size distributions in 1s, thereby offering a great advantage in applications requiring high time resolution. The deployment of the FIMS during the recent Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign helped identify new particle formation in the decoupled layer of the marine boundary layer during cold air outbreak periods. The vertical profiles of the aerosol size distributions during these events further explained the fate and transport of the newly formed aerosols.

Hosted by: Yangang Liu

Clouds are inherently multiscale phenomena: the particles that make up clouds are typically microns to millimeters, while the large-scale circulations that drive cloud systems can be hundreds of kilometers across. Limited computational power and the need to accurately represent the large-scale circulations in numerical simulations of the atmosphere make explicit inclusion of cloud microphysics a practical impossibility. In the last 20 years there has been a shift toward representing microphysics as scale-aware processes. Despite this shift, many unanswered questions remain regarding the scaling characteristics of microphysical fields and how best to incorporate that information into parameterizations. In this talk, I will present results from analysis of high frequency in situ aircraft measurements of marine stratocumulus taken over the southeastern Pacific Ocean aboard the NCAR/NSF C-130 during VOCALS-REx. First, I will show that cloud and rain water have distinct scaling properties, indicating that there is a statistically and potentially physically significant difference in the spatial structure of the two fields. Covariance of cloud and rain is a strong function of length/grid scale and this information can easily be incorporated in large-scale model parameterizations. Next I will show results from multifractal analysis of cloud and rain water to understand the spatial structure of these fields, the results of which provide a framework for development of a scale-insensitive microphysics parameterization. Finally, I compare observed microphysical scaling properties with those inferred from large eddy simulations of drizzling stratocumulus, applying the same analyses as applied to the aircraft observations. We find that simulated cloud water agrees well with the observations but the drizzle field is substantially smoother than observed, which has implications for the ability of limited-area models to adequately reproduce the spatial structure o

Hosted by: Yangang Liu

Realistic representation of cloud microphysical processes is of vital importance to the simulation of climate and weather in atmospheric model. In this talk, I am going to talk about my model development work in climate and regional models, especially with emphasis on the microphysical processes which consists of: 1) Developing a novel cloud microphysical scheme in the CESM-CAM5 aiming at improving the representation of ice-phase cloud process. Different from conventional microphysics schemes separating cloud ice from snow, a single prognostic category is used to represent the whole spectrum of solid hydrometeors in this scheme. Instead of using fixed physical properties for separate ice classes, e.g., the mass, area, and fall velocity, we consider the particle shape and riming impacts on ice properties. This scheme is notable for its improved representation of cloud and cloud radiative forcing with reduced the computational time in global simulation; 2) Optimizing physical process of the single-moment SBU_YLIN scheme aiming at improving convection simulation, and further developing it into a double-moment scheme and coupling it with WRF-Chem model in WRF model. The double-moment scheme is notable for its significant improvement in squall line simulation.

Hosted by: Mike Jensen

Level of neutral buoyancy (LNB) is an important parameter for understanding convection because it sets the potential vertical extent for convective development. It can be estimated from the parcel theory using the ambient sounding without having to observe any actual convective cloud development. In reality, however, convection interacts with the environment in complicated ways; it will eventually find its own effective LNB and manifests it through detraining masses and developing cirrus anvils. In a series of recent papers, we investigated the relationship between the LNB and actual deep convective outflow using 5 years of CloudSat observations. Due to entrainment dilution, the actual outflow level is almost always lower than the LNB. The difference between the two can be interpreted as a proxy for entrainment rate. It was found that the entrainment rate as determined this way is larger over tropical ocean (e.g., TWP warm pool) than tropical land (e.g., Africa and Amazon). Analysis of radar reflectivity profiles further shows that land convection has wider and more intense cores than the oceanic counterpart. These findings lend observational support to a long-standing assumption in convection models concerning the negative relationship between entrainment rate and convective core size. Finally, we examined the environment conditions for the observed convection cases and found that convective outflow tends to occur at a higher level when the mid-troposphere is more humid and when convective system size is smaller. Application of similar analysis to ground-based radar observations (such as those from the DOE ARM program) will be discussed. ?

Hosted by: Mike Jensen

There are about 45 flashes per second worldwide. About 90% of the flashes occur in cloud. A lightning flash is triggered when the ambient electric field exceeds a threshold. The ambient electric field is due to zones of electrical charges spreading within the thundercloud. Electrical charges are exchanged during hydrometeor collisions and are carried by the hydrometeors which are transported within the cloud. Consequently the lightning properties (e.g. flash rate; lightning type, i.e. intra-cloud and cloud-to-ground; flash extension; triggering altitude...) are strongly related to the microphysical, dynamical and electrification processes occurring in the parent storms. At the flash scale, a lightning flash is not a continuous phenomenon but is in fact composed of successive events, also called flash components, with different physical properties in terms of discharge propagation, radiation type, current properties, space and time scales. First a brief description of lightning detection techniques will be given. Then examples of flashes observed simultaneously by different instruments and replaced in their cloud context will be presented. Properties of the lightning activity will be discussed according to the dynamical and microphysical characteristics of the parent thunderclouds based on observational and modeling-based studies. Finally the EXAEDRE (EXploiting new Atmospheric Electricity Data for Research and the Environment) project will be introduced with an emphasis on the airborne field campaign scheduled between mid-September and mid-October 2018 in Western Mediterranean Sea.

Hosted by: Janek Uin

A parallel electrical aerosol spectrometer is essentially a differential mobility analyzer with many output sections and measurement channels. Instead of varying the analyzer voltage to scan over a range of particle mobilities, the whole distribution is captured at once. The principle is used by the Neutral cluster and Air Ion spectrometer (NAIS) to measure ions in the size range from 0.8 nm to 40 nm and neutral particles from 2 nm to 40 nm. The instrument is used in many places around the world, from polluted downtowns to jungles and mountain tops, to study new particle formation and other aerosol phenomena. The talk will give an overview of the principles and designs of the NAIS and other aerosol instrumentation developed at the University of Tartu and the spin-off company Airel Ltd.

Hosted by: Mike Jensen

Level of neutral buoyancy (LNB) is an important parameter for understanding convection because it sets the potential vertical extent for convective development. It can be estimated from the parcel theory using the ambient sounding without having to observe any actual convective cloud development. In reality, however, convection interacts with the environment in complicated ways; it will eventually find its own effective LNB and manifests it through detraining masses and developing cirrus anvils. In a series of recent papers, we investigated the relationship between the LNB and actual deep convective outflow using 5 years of CloudSat observations. Due to entrainment dilution, the actual outflow level is almost always lower than the LNB. The difference between the two can be interpreted as a proxy for entrainment rate. It was found that the entrainment rate as determined this way is larger over tropical ocean (e.g., TWP warm pool) than tropical land (e.g., Africa and Amazon). Analysis of radar reflectivity profiles further shows that land convection has wider and more intense cores than the oceanic counterpart. These findings lend observational support to a long-standing assumption in convection models concerning the negative relationship between entrainment rate and convective core size. Finally, we examined the environment conditions for the observed convection cases and found that convective outflow tends to occur at a higher level when the mid-troposphere is more humid and when convective system size is smaller. Application of similar analysis to ground-based radar observations (such as those from the DOE ARM program) will be discussed. ?

Hosted by: Laura Fierce

We examined the impact of condensing organic aerosols on activated cloud number concentration in a new aerosol microphysics model, MATRIX-VBS. The model, which can be used as a box model or a module in a global model, includes the volatilitybasis set (VBS) framework in an aerosol microphysical scheme MATRIX (Multiconfiguration Aerosol TRacker of mIXing state) that resolves aerosol mass and number concentrations and aerosol mixing state. Parameters such as aerosol chemical composition, mass and number concentrations, and particle sizes which affect activated cloud number concentration were thoroughly evaluated via a suite of Monte-Carlo simulations. Results from the box model show that by including the condensation of organic aerosols, under most conditions, the new model (MATRIX-VBS) has less activated particles compared to the original model (MATRIX), which treats organic aerosols as non-volatile. When implemented in the global model GISS ModelE as a module, we expect that the improved box model in the global scale would more accurately represent aerosol-cloud interactions. Thus it would offer us valuable insights on how the addition of organic partitioning would change cloud activation in the global atmosphere and its implications for climate.

Hosted by: Bob McGraw

Long duration floods cause substantial damage and prolonged interruptions to water resource facilities, critical infrastructure, and regional economic development. We present a novel physics-based model for inference of such floods with a deeper understanding of dynamically integrated nexus of land surface wetness, effective atmospheric blocking/circulation, and moisture transport/release mechanism. Diagnostic results indicate that the flood duration is varying in proportion to the antecedent flow condition which itself is a function of the available moisture in the air, the persistency in atmospheric pressure blocking, convergence of water vapor, and the effectiveness of divergent wind to condense the aforesaid atmospheric water vapor into liquid precipitation. A physics-based Bayesian inference model is developed that considers the complex interactions between moisture transport, synoptic-to-large-scale atmospheric blocking/circulation pattern, and the antecedent wetness condition in the basin. We explain more than 80% variations in flood duration with a high success rate on the occurrence of long duration floods. Our findings underline that the synergy between a large persistent low-pressure blocking system and a higher rate of divergent wind often triggers a long duration flood, even in the presence of moderate moisture supply in the atmosphere. This condition in turn causes an extremely long duration flood if the basin-wide surface wetness prior to the flood event was already high.

Hosted by: Mike Jensen

pending

Hosted by: Bob McGraw

Convection contributes significantly to the uncertainty of the climate feedbacks to the forcing due to increasing presence of anthropogenic green-house gases as simulated by the contemporary global climate models (GCMs). In nature, convection tends to self-organize on larger scales, from squall-lines to tropical cyclones (TCs), or even planetary-scale systems associated with the Madden-Julian Oscillation. Cloud-resolving models (CRMs) have been used to gain some insight into these important issues. In this talk, the results of application of a particular CRM, the System for Atmospheric Modeling, or SAM, to several problems involving self-organized tropical convection among others will be presented. In particular, preliminary results of global cloud-resolving simulations with a 4 km horizontal grid spacing will be shown. Also, a high-resolution building-resolving LES of pollutant transport over Manhattan and simulation of tsunami in New York Harbor will be introduced as examples of urban modeling.

Hosted by: Steve Schwartz

Earth system models rely on accurate representations of processes and emissions that are evaluated using observations. Iterative refinements are crucial for reliable and robust climate assessments, as I will illustrate with following recent case studies: Carbonaceous aerosol (CA) forcing in current models is prescribed as a balance between the warming by black carbon and the cooling by organic aerosol. However, data show that some organic aerosols called brown carbon absorb sunlight. Furthermore, transparent coatings on black carbon amplify their light absorbing potency by lensing. Such coatings could make black carbon more hydrophilic thereby reducing their lifetime and burden. I will use field and laboratory studies to uncover the fundamental chemistry controlling the optical properties and water affinity of CAs as they age to enable prognostic treatments. Atmospheric carbon dioxide (CO2) accumulation is moderated by its uptake by forests and oceans that soak up 25% each of the human emissions. How carbon sinks will respond to future climate change is uncertain. I will present observations of daily and seasonal variations of column CO2 and CO over the Amazon rainforest. I will show that both biomass burning and net ecosystem exchange that are out of phase control the seasonal CO2 cycle and are captured well by models. However, the daily CO2 drop driven by photosynthesis is biased low in models, a problem that needs to be fixed. Atmospheric Methane (CH4) that accounts for 25% of climate forcing is rising after a long hiatus. Potential causes include leaks from shale gas revolution, intensive agriculture, permafrost thaw, expand wetlands or shorter lifetime by higher Hydroxyl. I will review recent findings and focus on our discovery of the methane hot spot over Four Corners, NM attributed to fossil fuel that demonstrated reported emissions were low by a factor of 3. I will close with our development of an automated neural network methane leak detection

Hosted by: Mike Jensen

Passive microwave observations from satellites are increasingly used for the quantification of cloud and precipitation parameters. The frequencies above 80 GHz are sensitive to the cloud and precipitation frozen phase, and can provide unique information on the ice water path as well as on the size and shape of the hydrometeors. On board the Global Precipitation Measurement (GPM) mission for instance, the Microwave Imager (GMI) includes channels up to 190 GHz for a better estimation of the snowfall, to complement the lower frequency channels that were already present on TRMM (Tropical Rainfall Measuring Mission). The meteorological observations from satellites in the microwave domain are currently limited to below 190 GHz. However, the next generation of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) Polar System-Second Generation-EPS-SG will carry an instrument, the Ice Cloud Imager (ICI), with frequencies up to 664 GHz, to improve the characterization of the cloud frozen phase. This presentation will propose an overview of the application of the millimeter wave observations for cloud and precipitation estimation, insisting on the challenges that have to be faced and the methodology developed to exploit this wavelength range.

Hosted by: Ernie Lewis

Marine dissolved organic matter (DOM) is a complex mixture of molecules comprising the largest reservoir of organic matter in seawater, yet its sources and sinks remain largely unconstrained. While radiocarbon (14C) is a powerful tracer of time and mass, the lack of specificity in bulk 14C measurements and the analytical costs of compound specific 14C analyses have limited our observations. As an alternative, monitoring the 14C content of CO2 evolved during quantitative oxidation in concert with chemical kinetics analyses provides rapid insights into the compositions, reactivities, and coarse 14C "age" spectra of complex natural mixtures. In this talk, I will first demonstrate how monitoring photochemical and thermal oxidation reinforces a long-standing, but confusing, two-component age model of marine DOM. That is, the 14C age of DOM throughout the water column can be described as a mixture of molecules that fall into just two distinct age groups: recently produced vs. refractory DOM (RDOM). Second, I will discuss a test of one recently hypothesized sink of RDOC: namely, that RDOC could be removed from the oceans through adsorption onto the surfaces of rising bubble plumes produced by breaking waves, ejection into the atmosphere via bubble bursting as a component of primary marine aerosol (PMA), and subsequent oxidation in the atmosphere. In this test, measured the 14C signatures of PMA produced in a high capacity generator at two biologically-productive and two oligotrophic hydrographic stations in the Northwest Atlantic Ocean during a research cruise aboard the R/V Endeavor (Sep – Oct 2016). The 14C signatures of PMA generated were compared with corresponding 14C signatures in seawater of near-surface dissolved inorganic carbon (DIC, a proxy for recently produced organic matter), bulk deep DOC (a proxy for RDOC), and near-surface bulk DOC. Preliminary results and their constraints on the selectivity of PMA formation from RDOC will be discusse

Hosted by: Steve Schwartz

Airborne particles are ubiquitous components of our atmosphere, originating from a variety of natural and anthropogenic sources, exhibiting a wide range of physical properties, and contributing in multiple ways to regional air quality as well as regional-to-global-scale climate. Most remain in the atmosphere for a week or less, but can traverse oceans or continents in that time, carrying nutrients or disease vectors in some cases. Bright aerosols reflect sunlight, and can cool the surface; light-absorbing particles can heat the atmosphere, suppressing cloud formation or mediating larger-scale circulations. In most cases, particles are required to collect water vapor as the initial step in cloud formation, so their presence (or absence) and their hygroscopic or hydrophilic properties can affect cloud occurrence, structure, and ability to precipitate. Grasping the scope and nature of aerosol environmental impacts requires understanding microphysical-to-global scale processes, operating on timescales from minutes to days or longer. Satellites are the primary source of observations on kilometer-to-global scales. Spacecraft observations are complemented by suborbital platforms: aircraft in situ measurements and surface-based instrument networks that operate on smaller spatial scales, some on shorter timescales. Numerical models play a third key role in this work — providing a synthesis of current physical understanding with the aggregate of measurements, and allowing for some predictive capability. This presentation will focus on what we can say about aerosol amount and type from space. Constraining particle "type" is at present the leading challenge for satellite aerosol remote sensing. We will review recent advances and future prospects, including the strengths and limitations of available approaches, and current work toward better integrating measurements with models to create a clearer picture of aerosol environmental impacts, globally.

Hosted by: Mike Jensen

Deep moist convection plays a pivotal role ranging from daily weather impacts to long-term climatic feedbacks. The height and depth of deep convection are particularly important parameters for studies focusing on convective mass transport. Deep convection has the potential to rapidly transport mass and chemical constituents from the boundary layer into the upper tropospheric and lower stratospheric layer. Depending on whether convection is able to reach and penetrate the tropopause has significant implications on whether mass is rapidly transported into the troposphere or the stratosphere, where long residence times can alter the chemical budget and have important effects on climate. Nevertheless, accurately identifying the dynamic convective detrainment height is not easily achieved and commonly used methods contain considerable limitations or assumptions. Observations, such as taken by satellite or aircraft, are typical limited temporally and/or spatially. To account for limited observations, focus is either directed on the use of parcel theory or chemical modeling; however, assumptions in parcel theory are often invalid in observed convection and limited knowledge is available on the accuracy of simulated storm depths and heights. To enhance our understanding and enable more common retrievals of convective detrainment heights, a methodology utilizing the reflectivity field from ground-based radars is used to locate the detrainment envelope and level of maximum detrainment (LMD). A new radar classification algorithm that uses three-dimensional radar observations to stratify radar echo is used to identify suitable regions of convectively-generated anvil, which are used as a proxy for dynamic detrainment. The methodology is validated against dual-Doppler observations and preliminary results of applying the methodology to several months of volumetric radar composites are presented. Additionally, four months of convective forecasts are evaluated to determine the ac

Hosted by: Bob McGraw

Biomass burning (BB) is one of the most important contributors to atmospheric aerosols on a global scale and the environmental impacts of BB aerosols are strongly correlated with their chemical, optical, and microphysical properties. In this study, we investigated the properties and atmospheric aging of BB aerosols from wildfires in the Western US from the Mt. Bachelor Observatory (MBO; ~ 2700 m a.s.l.) in Central Oregon, as part of the DOE Biomass Burning Observation Project (BBOP) campaign in summer 2013. Plumes transported from forest fires in N California and SW Oregon were frequently observed. Organic aerosol (OA) dominated aerosol composition in BB plumes and three types of BBOA was identified: a less oxidized (O/C = 0.35), semivolatile BBOA-1 (~ 20% of OA mass) and two more oxidized BBOAs (BBOA-2 and BBOA-3). BBOA-1 was enriched of levoglucosan and was chemically similar to POA in fresh BB emissions. BBOA-3 was highly oxidized (O/C = 1.06; 31% of OA mass), contained no levoglucosan, showed very low volatility with only ~ 40% mass loss at 200°C, and had a similar mass spectrum as low-volatility oxygenated OA (LV-OOA) commonly observed in regional airmass. This finding highlights the possibility that the influence of BB emission could be significantly underestimated in regional air masses where highly oxidized BBOA (e.g., BBOA-3) might be a significant aerosol component. Increasing oxidation of BBOA was observed in more aged BB plumes but the enhancement ratios of BBOA relative to CO were nearly constant independent of plume aging. The chemical evolution of BBOA was examined for a BB plume event where fire plumes originated from a single fire source were sampled continuously for 36 hours. The average oxidation state of BBOA and the mass fraction of aged BBOA (= BBOA-2 + BBOA-3) in fire smoke increased with the increase of cumulative solar irradiance during transport, but the OA/CO ratios remained constant in the plumes. A possible explanation is that SOA f

Hosted by: Mike Jensen

The polar amplification of warming and the ability of the inter-tropical convergence zone (ITCZ) to shift to the north or south are two very important problems in climate science. Examining these behaviors in global climate models (GCMs) running solar geoengineering experiments is helpful not only for predicting the effects of solar geoengineering, but also for understanding how these processes work under increased CO2. Both polar amplification and ITCZ shifts are closely related to the meridional transport of moist static energy (MSE) by the atmosphere. This study examines changes in MSE transport in 10 fully coupled GCMs in Experiment G1 of the Geoengineering Model Intercomparison Project, in which the solar constant is reduced to compensate for abruptly quadrupled CO2 concentrations. In this experiment, poleward MSE transport decreases relative to preindustrial conditions in all models, in contrast to the CMIP5 abrupt4xCO2 experiment, in which poleward MSE transport increases. Since poleward energy transport decreases rather than increasing, and local feedbacks cannot reverse the sign of an initial temperature change, the residual polar amplification in the G1 experiment must be due to the different spatial patterns of the simultaneously imposed solar and CO2 forcings. However, the reduction in poleward energy transport likely plays a role in limiting the polar warming in G1. The seasonal migration of the ITCZ is dampened in G1 relative to abrupt4xCO2 due to preferential cooling of the summer hemisphere by the solar reduction. The ITCZ shifts northward in G1 by 0.14 degrees in the annual, multi-model mean, with an inter-model range of -0.33 to 0.89 degrees. These shifts are anticorrelated with changes in cross-equatorial MSE transport. An attribution study with a moist energy balance model shows that cloud feedbacks are the largest source of uncertainty regarding changes in cross-equatorial energy transport under solar geoengineering. Analysis of cloud changes in

Hosted by: Ernie Lewis

Although wood stoves are a carbon-neutral renewable energy source, they are the largest source of particulate matter (PM) emissions in New York State. A Differential Mobility Analyzer (DMA), which classifies particles by their mobility diameter, has traditionally been employed to characterize such particulate emissions. However, because the black carbon (BC) particles produced by combustion that contribute to PM are fractal, their mobility diameters are not equal to their mass-equivalent diameters. In contrast to the DMA, the Centrifugal Particle Mass Analyzer (CPMA) classifies aerosol particles by their mass, using two rotating cylinders and an electric potential; when the centrifugal and electrostatic forces on a particle are equal, it passes through. The CPMA can select particles with masses ranging from 2×10 4 to 1.05×103 fg (corresponding to diameters, for particles with density 1 g cm 3, ranging from 7 to 1300 nm). It can be operated in two different ways: the "Run" classification method can be used to select for a single particle mass, and the "Step Scan" method can be used to select particles over a set range of masses. A neutralizer must be used upstream of the CPMA to create a charge distribution on particles before they enter the instrument. A DMA can optionally be used to pre-select particles of a specific mobility diameter before entering the CPMA. Downstream of the instrument, a Condensation Particle Counter (CPC) must be used in order to determine the number concentration of particles that pass through the CPMA. The basic operating principles of the CPMA are discussed, and results are presented for its characterization of polystyrene latex (PSL) particles, ammonium sulfate particles, and emissions from a wood burning stove.

Clouds greatly affect short- and longwave radiation transfer in the atmosphere and consequently climate. Hence it is essential that the amount and radiative influences of clouds be accurately represented in climate models. The conventional measure of the amount of cloud in a grid cell is cloud fraction, CF, the fraction of the surface area covered by cloud. CF is a commonly reported meteorological quantity, with a long record of surface observations, greatly augmented in the past several decades by satellite observations. Global cloud fraction determined from satellite measurements has systematically increased with time, a consequence not of secular increase in cloud fraction but of an increase with time in the sensitivity of active and passive satellite instruments. Such a situation raises the question of whether CF can be defined and how well it can be measured. Commercially available digital cameras provide an unprecedented opportunity for detailed study of cloud structure from the surface, looking upward. Key attributes of such cameras include large number of pixels, (e.g., 3456 x 4608; 16 M pixel) yielding rich detail of spatial structure, high spatial resolution, and high dynamic range (16 bit in each of three color channels at visible wavelengths). In the work reported here two cameras were pointed vertically, typically with field of view FOV 21 × 29 mrad and 120 × 160 mrad, respectively, denoted here narrow field of view, NFOV, and wide field of view WFOV, corresponding, for cloud base at 1 km, to 21 × 29 m (NFOV) and 120 × 160 m (WFOV). For perspective, the FOV for the NFOV camera is 2 × 3 sun diameters and for the WFOV camera 11 × 15 sun diameters. Nominal angular dimension of a single pixel is 6 μrad for the NFOV camera and 34 μrad for the WFOV camera, corresponding, again for cloud height 1 km, to 6 mm and 34 mm, respectively. Such single-pixel resolution is some 3 to 5 orders of magnitude finer than that avai

Hosted by: Janek Uin

Aerosols and their climate forcing represent one of the largest uncertainties in global climate models (GCMs) today. Despite being tiny in size (~1nm - ~10 µm in diameter), ambient aerosols have large impacts through their microphysical interactions and climate feedbacks. For these reasons, direct in situ measurement of aerosol chemical, physical and morphological properties is a high priority to reduce these uncertainties. Absorbing aerosols that absorb light and contribute to atmospheric warming are of particular interest due to their anthropogenic sources, potential to increase in the future due to climate change, and impacts on human health. Large uncertainties exist on the extent of the warming that absorbing aerosols cause, specifically due to morphology and mixing state as black carbon physical and optical properties change as particles are transported in the atmosphere due to oxidation, coagulation, and condensation. For this reason, black carbon and organic carbon aerosol species that are emitted from combustion sources such as biomass burning and diesel sources will be presented. Emission ratios, physical and optical properties will be compared to those from controlled laboratory studies to understand carbonaceous aerosols and their transformations in the atmosphere. Laboratory measurements are used as a framework to understand the ambient observations and to improve model treatment of aerosols and aging in global climate models.

Hosted by: Jian Wang

Aerosol science and technology enable continual advances in material synthesis and atmospheric pollutant control. Among these advances, one important frontier is characterizing the initial stages of particle formation by real time measurement of particles below 2 nm in size. Sub 2 nm particles play important roles by acting as seeds for particle growth, ultimately determining the final properties of the generated particles. Tailoring nanoparticle properties requires a thorough understanding and precise control of the particle formation processes, which in turn requires characterizing nanoparticle formation from the initial stages. This work pursued two approaches in investigating incipient particle characterization in systems with aerosol formation and growth: (1) using a high-resolution differential mobility analyzer (DMA) to measure the size distributions of sub 2 nm particles generated from high-temperature aerosol reactors, and (2) analyzing the physical and chemical pathways of aerosol formation during combustion. Part. 1. Particle size distributions reveal important information about particle formation dynamics. DMAs are widely utilized to measure particle size distributions. However, our knowledge of the initial stages of particle formation is incomplete, due to the Brownian broadening effects in conventional DMAs. The first part of this presentation discusses the applicability of high-resolution DMAs in characterizing sub 2 nm particles generated from high-temperature aerosol reactors, including a flame aerosol reactor (FLAR) and a furnace aerosol reactor (FUAR). Comparison against a conventional DMA (Nano DMA, Model 3085, TSI Inc.) demonstrated that the increased sheath flow rates and shortened residence time indeed greatly suppressed the diffusion broadening effect in a high-resolution DMA (half mini type). The incipient particle size distributions were discrete, suggesting the formation of stable clusters that may be intermediate phases betw

Hosted by: Robert McGraw

A newly developed box model, MATRIX-VBS [Gao et al., 2017], includes the volatility-basis set (VBS) framework in an aerosol microphysical scheme MATRIX (Multiconfiguration Aerosol TRacker of mIXing state) [Bauer et al., 2008], which is a module within GISS ModelE that resolves aerosol mass and number concentrations and aerosol mixing state. By including the gas-particle partitioning and chemical aging of semi-volatile organic aerosol in MATRIX, we were able to examine its effects on the growth, composition and mixing state of particles. MATRIX-VBS is unique and advances the representation of organic aerosols in Earth system models by greatly improving the traditional and very simplistic treatment of organic aerosols as non-volatile and with a fixed size distribution. Idealized cases representing Beijing, Mexico City, a Finnish and a Southeast U.S. forest were simulated, and we investigated the evolution of mass concentrations and volatility distributions for organic species across the gas and particle phases, as well as their mixing state among aerosol populations. To test and simplify the model, a Monte-Carlo analysis is performed to pin point which processes affect organics the most under varied chemical and meteorological conditions. Since the model's parameterizations have the ability to capture a very wide range of conditions, all possible scenarios on Earth across the whole parameter space, including temperature, humidity, location, emissions and oxidant levels, are examined. These simulations provide information on which parameters play a critical role in the aerosol distribution and evolution in the atmosphere and which do not, and that will facilitate the simplification of the box model, an important step in its implementation in the global model GISS ModelE as a module.

Hosted by: Jorge Gonzalez/Alice Cialella

Half the global population will be in cities by 2025, many having more than 10 million people. Urbanization modifies atmospheric energy and moisture balances, forming local climates, e.g. urban heat islands (UHIs) and enhanced precipitation. These produce significant challenges to science and society, e.g. flooding, heat waves strengthened by UHIs, and air pollutant hazes. The Beijing megacity experiences such severe events, e.g., 2012 flooding killed 79 and caused losses of $2B. Despite significant research into urban effects on weather and air quality, important science issues remain, e.g., urban-thermodynamic and aerosol impacts on summer convective precipitation and interactions between urban and regional climate changes. Observations are fundamental for understanding these interactions, improving forecasts, and providing useful information to end-users. Previous large urban field campaigns have not been coordinated by a group such as the Beijing Institute of Urban Meteorology (IUM), with its responsibilities for both boundary layer research and real time urban weather forecasting. The overall science objective of the 2014-8 SURF Project is thus a better understanding of urban, terrain, convection, and aerosol interactions for improved forecast accuracy. Beijing is a test case, but the improved understandings are transferable to many large cities globally. Specific objectives include: Promote cooperative international-research to improve understanding of urban weather-systems via summer thunderstorm-rainfall and winter aerosol field studies; Improve high-resolution (∼1 km grid) urban weather and air quality forecast-models; and, Enhance urban weather forecasts for societal applications, e.g., health, energy, hydrologic, climate change, air quality, urban planning, emergency-response management.

Hosted by: Jian Wang

Motor vehicles emit gas- and particle-phase air pollutants, including organic and inorganic gasses, black carbon (BC), organic aerosols (OA) and other species, which are linked with adverse human health effects, visibility reductions, and climate effects. There are steep gradients in concentrations of these species within 10s to 100s of meters from the roadway. The mechanistic evolution of vehicle emissions downwind of a roadway involves complex physicochemical processes and varies spatially and temporally. Exposure concentrations of different pollutants in a near-road environments are influenced by the complex dispersion process, built environments and meteorological factors which lead to physicochemical transformations of primary reactive species. For a better understanding of exposure and evolution of near-road air pollutants, we conducted a comprehensive field study at a site near Interstate 40, near Durham, North Carolina. The specific aims of this study were: 1) characterizing the spatio-temporal and seasonal trends of multiple air pollutant concentrations in a near highway setting, 2) characterizing near-road submicron aerosol volatility and mixing state, and 3) determining the extent to which motor vehicles contribute to ambient secondary OA production. Results from this study show strong seasonal and diurnal differences in downwind concentration gradients with a less-sharp near-road gradients in winter in many species, decreasing of the semi-volatile fraction in ultrafine particle with downwind distance, and a substantial seasonal differences in secondary OA (SOA) formation due to oxidation of near-highway air in an oxidation flow reactor. Details observations from this field study will be discussed. This talk may also briefly address two other projects those are part of my Ph.D. work, (i) improve quantification of gas-particle partitioning parameter values of organic aerosol using a dual-thermodenuder system, and (ii) laboratory aging of wood smoke from d

Hosted by: Mike Jensen

Mixed-phase stratiform clouds can persist with steady ice precipitation for hours and even days. The origin and microphysical properties of the ice crystals are of interest. Vapor deposition growth and sedimentation of ice particles along with a uniform volume source of ice nucleation lead to a power law relation between ice water content (wi) and ice number concentration (ni) with exponent 2.5. The relation is confirmed by both a large-eddy simulation cloud model and Lagrangian ice particle tracking with cloud volume source of ice particles through a time-dependent cloud field. Initial indications of the scaling law are observed in data from the Indirect and Semi-Direct Aerosol Campaign (ISDAC). Based on the observed wi and ni from ISDAC, a lower bound of 0.006 m-3s-1 is obtained for the volume ice crystal formation rate. Results from Lagrangian ice particle tracking method also show that more than 10% of ice particles have lifetimes longer than 1.5 h, much longer than the large eddy turnover time or the time for a crystal to fall through the depth of a nonturbulent cloud. An analysis of trajectories in a 2-D idealized field shows that there are two types of long-lifetime ice particles: quasi-steady and recycled growth. For quasi-steady growth, ice particles are suspended in the updraft velocity region for a long time. For recycled growth, ice particles are trapped in the large eddy structures, and whether ice particles grow or sublimate depends on the ice relative humidity profile within the boundary layer. Some ice particles can grow after each cycle in the trapping region, until they are too large to be trapped, and thus have long lifetimes. The relative contribution of the recycled ice particles to the cloud mean ice water content depends on both the dynamic and thermodynamic properties of the mixing layer. In particular, the total ice water content of a mixed-phase cloud in a decoupled boundary layer can be much larger than that in a fully coupled boundary la

Hosted by: Robert McGraw

Mixed-phase clouds are comprised of both liquid droplets and ice crystals. For a given total water content, mixed-phase clouds with higher liquid water contents are optically thicker and therefore more reflective to sunlight compared to those with higher ice water contents. This is due to the fact that liquid droplets tend to be smaller in size and more abundant than ice crystals in Earth's atmosphere. Given the ubiquity of mixed-phase clouds, the ratio of liquid to ice in these clouds is expected to be important for Earth's radiation budget. We determine the climatic impact of thermodynamic phase partitioning in mixed-phase clouds by using five pairs of simulations run with CAM5/CESM. Of the five pairs of simulations, the thermodynamic phase partitioning of two of the simulations were constrained to better agree with observations from CALIPSO. The other three pairs of simulations include a control simulation, as well as an upper and lower bound simulation with maximally high and low amounts of mixed-phase cloud liquid fractions. An analysis of the simulations shows that a negative "cloud phase feedback" that occurs due to the repartitioning of cloud droplets and ice crystals under global warming is weakened when mixed-phase clouds initially contain a higher amount of liquid. Simulations that exhibited weaker cloud phase feedbacks also had higher climate sensitivities. The results suggest that an unrealistically strong cloud phase feedback leading to lower climate sensitivities may be lurking in the many climate models that underestimate mixed-phase cloud liquid fractions compared to observations.

Hosted by: Tom Watson

Discussion of the harsh truths of rising seas, and the ethical and policy challenges, with a focus on Florida.

Hosted by: Mike Jensen

The ubiquitous presence of clouds within the troposphere (global total cloud frequency about 70%) strongly characterizes the radiative balance of the earth-atmosphere system. Knowledge of the distribution of clouds and their response to a warmer climate are crucial to anticipate the evolution of our future climate. Yet, this challenge remains subject to large uncertainties in climate modeling, wherein the vertical structure of clouds plays a crucial role. Due to the potential for significant variations in the height, temperature and microphysical properties of a cloud, there is a significant range of radiative impacts from clouds. In this presentation, I will take advantage of active sensor observations from the CALIPSO satellite and recent climate simulations from multi-model experiments to characterize systematic biases in the representation of clouds and cloud microphysics in contemporary climate models. To this end, I will introduce the satellite simulator approach, which reduces uncertainties related to instrument biases and ensures a consistent comparison between models and observations. Then, I will show a couple of examples of model biases focused on the vertical structure of clouds and the transition between supercooled liquid clouds and ice clouds. Finally, I will determine whether these biases are systematic or not, and explore their origin.

Hosted by: Laura Fierce

Air quality exceedances in California are frequently attributed to Asian pollution, but global Eulerian models consistently fail to reproduce the intercontinental chemical plumes which are responsible. This has been attributed to excessive numerical diffusion. We apply a global model over a wide range of horizontal resolutions in both 2-D and 3-D to isolate the specific causes and effects of this diffusion on the representation of intercontinental pollution. Our results show that the vast increases in computation power required to increase model horizontal grid resolutions are wasted if the aim is to better represent intercontinental transport of pollution. We instead provide motivation for modelers and researchers to experiment with higher vertical grid resolution if they wish to reproduce the ubiquitous quasi-horizontal plumes observed in atmospheric measurements.

Hosted by: Robert McGraw

Field measurements in the recent past have shown that secondary organic aerosol (SOA) particles are often amorphous glasses or highly viscous liquids under dry and/or cold conditions. Chemical and physical processes occurring in the interior of the aerosol particle and at the gas/particle interface are influenced by the viscous state in which condensed-phase diffusion is slows down considerably. I will discuss measurements of water diffusion in single, levitated aerosol particles for a number of model systems of SOA. In particular, I will show how Mie-resonance spectroscopy allows to "image" diffusion fronts within these particles and discuss atmospheric implications of kinetic limitations of water uptake.

Hosted by: Michael Jensen

Mid-level stratiform clouds (MSCs) are not well studied and their macrophysical, microphysical, and radiative properties are poorly documented. A comprehensive view of MSCs is presented with four years of collocated CALIPSO/CloudSat measurements and with long-term ground-based remote sensing measurements. Algorithms are developed for identifying MSCs and for detecting ice particle occurrence by combining lidar and radar measurements. A global view of MSCs in terms of their occurrence frequencies, day-night and seasonal variations, and vertical distributions is provided. Multi-sensor remote sensing measurements are also used to quantify the impacts of dust on heterogeneous ice generation in supercooled MSCs over the 'dust belt'. Furthermore, algorithms are developed to retrieve ice number concentration (Ni) in stratiform mixed-phase clouds by combining cloud radar reflectivity (Ze) measurements and 1-D ice growth model simulations at given cloud top temperature (CTT) and liquid water path (LWP). Evaluations of the retrieved Ni in stratiform mixed-phase clouds with in situ measurements and with the simulations from a 3-D cloud-resolving model with bin microphysical physics scheme show that the retrieved Ni are within an uncertainty of a factor of 2, statistically.

Hosted by: Mike Jensen

Large areas over subtropical and tropical oceans experience neither strong subsidence nor strong ascent. In these regions shallow trade-wind clouds prevail, whose vertical distribution has emerged as a key factor determining the sensitivity of our climate in global climate models. But how susceptible are trade-wind clouds in our current climate? Do we understand the role of the large-scale flow in observed variations in these clouds? And do global models represent those patterns of variability? Using long time series of ground-based and space-borne remote sensing in the trades (the Barbados Cloud Observatory), combined with Large-Eddy Simulation, I will analyze how shallow cumuli and their associated cloudiness respond to changes in the large-scale atmospheric state, providing constraints on modeled cloud feedbacks. Unlike climate models, the major component of trade-wind cloudiness, which is cloudiness near the saturation level, appears remarkably robust to variability in the thermal structure of the lower atmosphere, and I will explain how convection itself plays an important role in that robustness. Variability in cloudiness is far more pronounced at levels further aloft, related to the deepening of shallow convection on mesoscale and synoptic time scales. This mesoscale variability explains, in part, why cloudiness is poorly predicted by large-scale factors on longer time scales. However, variations in vertical motion and wind speed are shown to play an important role, suggesting that we should be mindful of how the large-scale flow conditions the lower atmosphere. Global models underestimate the strength of a relationship with wind speed and diverge in particular in their response to large-scale vertical motion. I will explain why models overestimate the low cloud feedback in these regions, and discuss possible pathways through which these seemingly persistent clouds are critical to climate, even if their feedback on global mean temperature is small

Hosted by: Alice Cialella

Large-eddy simulation (LES) has emerged as a powerful simulation-based engineering science tool in a broad range of engineering applications involving complex turbulent flows. In my talk I will review computational advances that have enabled the LES of multi-physics flows in arbitrarily complex domains and with flow-structure interaction. I will highlight the predictive power of these algorithms by presenting simulations of: 1) atmospheric turbulence past land-based and offshore wind farms; 2) complex floating structures in the ocean under the action of broadband waves; 3) marine and hydrokinetic energy harvesting devices in real-life waterways, and 4) flow, sediment transport and scour in large rivers during extreme flooding events. I will also discuss the potential of coupling such computational power with field-scale experiments with DNA-based flow tracers to study pathogen and pollutant transport in indoor and outdoor environments.

Initial results are presented of a analysis of high resolution photographs of clouds at the ARM SGP site in July, 2015. A commercially available camera having 35-mm equivalent focal length up to 1200 mm (nominal resolution as fine as 6 µrad, which corresponds to 12 mm for cloud height 2 km) is used to obtain a measure of zenith radiance of a 40 m x 40 m domain as a two-dimensional image consisting of 3456 x 3456 pixels (12 million pixels). Downwelling zenith radiance varies substantially within single images and between successive images obtained at 4-s intervals. Variation in zenith radiance found on scales down to about 10 cm is attributed to variation in cloud optical depth (COD). Attention here is directed primarily to optically thin clouds, COD less than roughly 3. A radiation transfer model used to relate downwelling zenith radiance to COD and to relate the counts in the camera image to zenith radiance, permits determination of COD and cloud albedo on a pixel-by-pixel basis. COD for thin clouds determined in this way exhibits considerable variation, for example, an order of magnitude within the 40 m domain examined here and 50% over a distance of 1 m. An alternative to the widely used areal or temporal cloud fraction, denoted radiative cloud fraction, also evaluated on a pixel-by-pixel basis, is introduced. This highly data-intensive approach, which examines cloud structure on scales 3 to 5 orders of magnitude finer than satellite products, opens new avenues for examination of cloud structure and evolution.

Hosted by: Jian Wang

pending

Hosted by: Jian Wang

Mountains around the globe control precipitation patterns and water resources. Here the focus is on understanding orographic precipitation in the tropics over a small island. An aircraft dataset from the Dominica Experiment (DOMEX) which took place in the eastern Caribbean is utilized. The aircraft measured upstream and downstream airflow properties as well as the properties of the convective clouds over the island. These flight data along with an idealized numerical model are used to understand the role of wind speed in controlling the transition from thermally to mechanically forced orographic convection. When the convection is thermally driven, DOMEX observations show clear evidence of aerosol-cloud-precipitation interactions; the aerosol-aware Thompson microphysics scheme in WRF is used to investigate. Using this framework of understanding from an orographic case, a broader view of marine cloud microphysics can be gained.

Hosted by: Jian Wang

Non-spherical, chemically inhomogeneous nanoparticles are encountered in a number of natural and engineered environments, including combustion systems, reactors used in gas-phase materials synthesis, and in ambient air. To better characterize these complex nanoparticles, tandem measurement techniques are well suited, in which analytes are characterized by two orthogonal properties (e.g. size and mass). Tandem measurement techniques have been applied in a number of situations; however, there are still a considerable number of fundamental developments needed to advance these approaches. Specifically, new instrument combinations (with existing instruments) and appropriate data inversion routines need to be developed to determine combined two-dimensional mass-size distribution functions, pure mass distribution and for mobility-mass analysis for sub 2-nm clusters (ions). With this motivation, we first develop and apply a data inversion routine to determine the number based size-mass distribution function (two dimensional distribution) from tandem differential mobility analyzer-aerosol particle mass analyzer (DMA-APM) measurements, while correcting for multiple charging, instrument transfer functions and other system efficiencies. This two dimensional distribution can be used to calculate the number based size distribution or the mass based size distribution. We employ this technique to analyze various spherical and non-spherical nanoparticles and examine the validity of this approach by comparing the calculated size distribution functions and mass concentrations with direct measurements of these quantities. In a second study, we utilize a transversal modulation ion mobility spectrometer (TMIMS) coupled with a mass spectrometer (MS) to study vapor dopant induced mobility shifts of sub 2 nm ion clusters. Isopropanol vapor is introduced into the TMIMS, shifting the mobilities of ions to varying extents depending on ion surface chemistry, which provides an improved separa

Hosted by: Laura Fierce

Over recent decades temperatures in the Arctic have increased at twice the global rate, largely as a result of ice–albedo and temperature feedbacks. Although deep cuts in global CO2 emissions are required to slow this warming, there is also growing interest in the potential for reducing short-lived climate forcers (SLCFs). Politically, action on SLCFs may be particularly promising because the benefits of mitigation are seen more quickly than for mitigation of CO2 and there are large co-benefits in terms of improved air quality. This study systematically quantifies the Arctic climate impact of regional SLCFs emissions, taking into account black carbon, sulphur dioxide, nitrogen oxides, volatile organic compounds, organic carbon and tropospheric ozone, and their transport processes and transformations in the atmosphere. Using several chemical transport models we perform detailed radiative forcing calculations from emissions of these species. We look at six main sectors known to account for nearly all of these emissions: households (domestic), energy/industry/waste, transport, agricultural fires, grass/forest fires, and gas flaring. To estimate the Arctic surface temperature we apply regional climate sensitivities, the temperature response per unit of radiative forcing for each SLCF. We find that the largest Arctic warming source is from emissions within the Asian nations owing to the large absolute amount of emissions. However, the Arctic is most sensitive, per unit mass emitted, to SLCFs emissions from a small number of activities within the Arctic nations themselves. A stringent, but technically feasible mitigation scenario for SLCFs, phased in from 2015 to 2030, could cut warming by 0.2 (±0.17) K in 2050.

Hosted by: Bob McGraw

This talk will highlight modeling efforts focused on probing the dynamics of the air and sea in the complex coastal zone utilizing high-resolution (~1 km) coupled models. Results will cover the ocean response to atmospheric flows around island topography (Philippines and Madeira), as well as sea breeze interactions with city morphology (New York and Tokyo) - and associated transport & dispersion applications. Dr. Julie Pullen is an Associate Professor in Ocean Engineering at Stevens Institute of Technology. She uses high-resolution coupled ocean-atmosphere modeling in order to understand and forecast the dynamics of coastal urban regions throughout the world. Applications include predicting chemical, biological, radiological and nuclear (CBRN) dispersion in coastal cities in the event of a terrorist or accidental release. She has served on the steering team for field studies in urban air dispersion (DHS/DTRA NYC Urban Dispersion Program) and archipelago oceanography (ONR Philippines Straits Dynamics Experiment). She is a member of the international GODAE Coastal Ocean and Shelf Seas Task Team and is the physical oceanography councilor for The Oceanography Society. Dr. Pullen earned her Ph.D. in Physical Oceanography at Oregon State University and did postdoctoral work at the Naval Research Laboratory's Marine Meteorology Division. She is an Adjunct Research Scientist at Columbia's Lamont Doherty Earth Observatory.