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  1. Environmental & Climate Sciences Department Seminar

    "Emission and Aging of Organic Aerosols from Wildfires in the Western US: Insights from the BBOP campaign"

    Presented by Qi Zhang, University of California, Davis

    Thursday, August 17, 2017, 11 am
    Conference Room Bldg 815E

    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

  2. Environmental & Climate Sciences Department Seminar

    "Effects of Solar Geoengineering on Clouds, Energy Transport and the ITCZ"

    Presented by Rick Russotto, University of Washington

    Monday, July 31, 2017, 11 am
    Conference Room Bldg 815E

    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

  3. Environmental & Climate Sciences Department Seminar

    "Classifying Aerosol Particles with a Centrifugal Particle Mass Analyzer (CPMA)"

    Presented by Kristen Okorn, Stevens Institute of Technology (SULI Student Summer 2017)

    Thursday, July 27, 2017, 11 am
    Conference Room Bldg 815E

    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.

  4. Environmental & Climate Sciences Department Seminar

    "Cloud radiative fraction: Determination by high resolution photography from the surface looking upward"

    Presented by Stephen E. Schwartz, Environmental & Climate Sciences Department

    Thursday, June 1, 2017, 11 am
    Conference Room Bldg 815E

    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

  5. Environmental & Climate Sciences Department Seminar

    "Direct Measurements of Absorbing Aerosols to Reduce Uncertainties in Climate Models"

    Presented by Allison C. Aiken, Los Alamos National Laboratory

    Wednesday, May 10, 2017, 11 pm
    Conference Room Bldg 815E

    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.

  6. Environmental & Climate Sciences Department Seminar

    "Sub 2 nm Particle Characterization in Systems with Aerosol Formation and Growth"

    Presented by Yang Wang, Washington University

    Wednesday, March 8, 2017, 10 am
    Conference Room Bldg 815E

    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

  7. Environmental & Climate Sciences Department Seminar

    "The Impact of Organic Aerosol Volatility on Aerosol Microphysics for Global Climate Modeling Applications"

    Presented by Yuchao 'Chloe' Gao, NASA Goddard Institute for Space Studies, China

    Thursday, February 9, 2017, 11 am
    Conference Room Bldg 815E

    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.

  8. Environmental & Climate Sciences Department Seminar

    "SURF Project: Understanding Urban Convection and Haze"

    Presented by Shiguang Miao, Beijing Institute for Urban Meteorology, China

    Thursday, February 2, 2017, 11 am
    Conference Room Bldg 815E

    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.

  9. Environmental & Climate Sciences Department Seminar

    "What's happening in near-road air quality? Insights from a recent field study near a North Carolina Interstate freeway"

    Presented by Provat Saha, North Carolina State University

    Thursday, January 12, 2017, 11:45 am
    Conference Room Bldg 815E

    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

  10. Environmental & Climate Sciences Department Seminar

    "Stochastic ice nucleation and its effect on the microphysical properties of mixed-phase stratiform cloud"

    Presented by Fan Yang, Michigan Technological University

    Monday, November 21, 2016, 11 am
    Conference Room Bldg 815E

    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

  11. Environmental & Climate Sciences Department Seminar

    "Observational constraints on mixed-phase clouds imply higher climate sensitivity"

    Presented by Ivy Tan, Yale Univ.

    Thursday, November 10, 2016, 11 am
    Conference Room Bldg 815E

    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.

  12. Environmental & Climate Sciences Department Seminar

    "Sea Level Lies: Ethics and Policy Realities for Coastal Communities"

    Presented by Keith Rizzardi, St. Thomas University School of Law, Miami Gardens, FL

    Thursday, November 3, 2016, 11 am
    Conference Room Bldg 815E

    Hosted by: ''Tom Watson''

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

  13. Environmental & Climate Sciences Department Seminar

    "Using satellite observations to evaluate the representation of clouds in climate models"

    Presented by Gregory Cesana, Jet Propulsion Laboratory

    Friday, October 28, 2016, 11 am
    Conference Room Bldg 815E

    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.

  14. Environmental & Climate Sciences Department Seminar

    "Intercontinental smog: how and why global models fail to resolve intercontinental chemical plumes"

    Presented by Sebastian Eastham, Harvard University Center for the Environment

    Thursday, October 27, 2016, 11 am
    Conference Room Bldg 815E

    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.

  15. Environmental & Climate Sciences Department Seminar

    "Viscous organic aerosol particles and water uptake: From observations of internal diffusion fronts in single, levitated particles to estimating kinetic limitations under atmospheric conditions"

    Presented by Dr. Ulrich Krieger, Institut für Atmosphäre und Klima, Zürich, Switzerland

    Friday, September 30, 2016, 11 am
    Conference Room Bldg 815E

    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.

  16. Environmental & Climate Sciences Department Seminar

    "Multi-sensor Remote Sensing of Midlevel Stratiform Cloud Macro- and Microphysical Properties"

    Presented by Damao Zhang, University of Wyoming

    Thursday, September 8, 2016, 11 am
    Building 815 Conference Room

    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.

  17. Environmental & Climate Sciences Department Seminar

    "Observed and modeled sensitivity of trade-wind clouds to changes in the large-scale flow"

    Presented by Louise Nuijens, MIT

    Tuesday, June 28, 2016, 11 am
    Conference Room, Bldg 815E

    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

  18. Environmental & Climate Sciences Department Seminar

    "Large-eddy simulation of complex turbulent flows in energy and environmental applications"

    Presented by Dr. Fotis Sotiropoulos, Dean, College of Engineering and Applied Sciences, Stony Brook University

    Wednesday, June 22, 2016, 11 am
    Conference Room, Bldg 815E

    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.

  19. Environmental & Climate Sciences Department Seminar

    "High-Resolution Photography of Clouds from the Surface: Retrieval of Cloud Optical Depth down to Centimeter Scales"

    Presented by Stephen Schwartz, Environmental and Climate Sciences Department

    Thursday, June 16, 2016, 11 am
    Conference Room, Bldg 815E

    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.

  20. Environmental & Climate Sciences Department Seminar

    "title pending"

    Presented by Kimmo Neitola, Finnish Meteorological Institute

    Monday, May 16, 2016, 11 pm
    Conference Room, Bldg 815E

    Hosted by: 'Jian Wang'

    pending

  21. Environmental & Climate Sciences Department Seminar

    "Orographic Convection and Precipitation in the Tropics: Wind Speed Control and Aerosol Interactions"

    Presented by Alison Nugent, UCAR

    Tuesday, April 26, 2016, 11 am
    Conference Room, Bldg 815E

    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.

  22. Environmental & Climate Sciences Department Seminar

    "Improved Tandem Measurement Techniques for Gas Phase Nanoparticle Analysis"

    Presented by Vivek Rawat, University of Minnesota

    Wednesday, April 20, 2016, 11 am
    Conference Room, Bldg 815E

    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

  23. Environmental & Climate Sciences Department Seminar

    "Response of Arctic Temperature to Changes in Emissions of Short-Lived Climate Forcers"

    Presented by Maria Sand, NASA-GISS

    Thursday, April 7, 2016, 11 am
    Conference Room, Bldg 815E

    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.

  24. Environmental & Climate Sciences Department Seminar

    "Coupled Air-Sea Modeling in Coastal Regions"

    Presented by Julie Pullen, Stevens Institute of Technology

    Thursday, March 17, 2016, 11 am
    Conference Room, Bldg 815E

    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.