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  1. 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

  2. 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.

  3. 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.

  4. 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'


  5. 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.

  6. 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

  7. 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.

  8. 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.