The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Athanasios Nenes - One of the best experts on this subject based on the ideXlab platform.
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aerosol acidity and Liquid Water Content regulate the dry deposition of inorganic reactive nitrogen
Atmospheric Chemistry and Physics, 2020Co-Authors: Athanasios Nenes, Spyros N Pandis, Armistead G Russell, M Kanakidou, Shaojie Song, Petros Vasilakos, Rodney J WeberAbstract:Abstract. Ecosystem productivity is strongly modulated by the atmospheric deposition of inorganic reactive nitrogen (the sum of ammonium and nitrate). The individual contributions of ammonium and nitrate vary considerably over space and time, giving rise to complex patterns of nitrogen deposition. In the absence of rain, much of this complexity is driven by the large difference between the dry deposition velocity of nitrogen-containing molecules in the gas or condensed phase. Here we quantify how aerosol Liquid Water and acidity, through their impact on gas-to-particle partitioning, modulate the deposition velocity of NH3 and HNO3 individually, while simultaneously affecting the dry deposition of inorganic reactive nitrogen. Four regimes of deposition velocity emerge: i) HNO3-fast, NH3-slow, ii) HNO3-slow, NH3-fast, iii) HNO3-fast, NH3-fast, and, iv) HNO3-slow, NH3-slow. Conditions that favor partitioning of species to the aerosol phase strongly reduce the deposition of reactive nitrogen species and promote their accumulation in the boundary layer and potential for long-range transport. Application of this framework to select locations around the world reveals fundamentally important insights: The dry deposition of total ammonia displays little sensitivity to pH and Liquid Water variations, except under conditions of extreme acidity and/or low aerosol Liquid Water Content. The dry deposition of total nitric acid, on the other hand, is quite variable, with maximum deposition velocities (close to gas-deposition rates) found in the Eastern US and minimum velocities in Northern Europe and China. In the latter case, the low deposition velocity leads to up to 10-fold increases in PM2.5 nitrate aerosol, thus contributing to the high PM2.5 levels observed during haze episodes. In this light, aerosol pH and associated Liquid Water Content can be considered as control parameters that drive dry deposition flux and can accelerate the accumulation of aerosol contributing to intense haze events throughout the globe.
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aerosol ph and Liquid Water Content determine when particulate matter is sensitive to ammonia and nitrate availability
Atmospheric Chemistry and Physics, 2020Co-Authors: Athanasios Nenes, Spyros N Pandis, Rodney J Weber, Armistead G RussellAbstract:Abstract. Nitrogen oxides ( NOx ) and ammonia ( NH3 ) from anthropogenic and biogenic emissions are central contributors to particulate matter (PM) concentrations worldwide. The response of PM to changes in the emissions of both compounds is typically studied on a case-by-case basis, owing in part to the complex thermodynamic interactions of these aerosol precursors with other PM constituents. Here we present a simple but thermodynamically consistent approach that expresses the chemical domains of sensitivity of aerosol particulate matter to NH3 and HNO3 availability in terms of aerosol pH and Liquid Water Content. From our analysis, four policy-relevant regimes emerge in terms of sensitivity: (i) NH3 sensitive, (ii) HNO3 sensitive, (iii) NH3 and HNO3 sensitive, and (iv) insensitive to NH3 or HNO3 . For all regimes, the PM remains sensitive to nonvolatile precursors, such as nonvolatile cations and sulfate. When this framework is applied to ambient measurements or predictions of PM and gaseous precursors, the “chemical regime” of PM sensitivity to NH3 and HNO3 availability is directly determined. The use of these regimes allows for novel insights, and this framework is an important tool to evaluate chemical transport models. With this extended understanding, aerosol pH and associated Liquid Water Content naturally emerge as previously ignored state parameters that drive PM formation.
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characteristic updrafts for computing distribution averaged cloud droplet number and stratocumulus cloud properties
Journal of Geophysical Research, 2010Co-Authors: Ricardo Morales, Athanasios NenesAbstract:[1] A computationally effective framework is presented that addresses the contribution of subgrid-scale vertical velocity variations in predictions of cloud droplet number concentration (CDNC) in large-scale models. Central to the framework is the concept of a “characteristic updraft velocity” , which yields CDNC value representative of integration over a probability density function (PDF) of updraft (i.e., positive vertical) velocity. Analytical formulations for are developed for computation of average CDNC over a Gaussian PDF using the Twomey droplet parameterization. The analytical relationship also agrees with numerical integrations using a state-of-the-art droplet activation parameterization. For situations where the variabilities of vertical velocity and Liquid Water Content can be decoupled, the concept of is extended to the calculation of cloud properties and process rates that complements existing treatments for subgrid variability of Liquid Water Content. It is shown that using the average updraft velocity (instead of ) for calculations of Nd, re, and A (a common practice in atmospheric models) can overestimate PDF-averaged Nd by 10%, underestimate re by 10%–15%, and significantly underpredict autoconversion rate between a factor of 2–10. The simple expressions of presented here can account for an important source of parameterization “tuning” in a physically based manner.
Marta Nelson - One of the best experts on this subject based on the ideXlab platform.
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supercooled Liquid Water Content profiling case studies with a new vibrating wire sonde compared to a ground based microwave radiometer
Atmospheric Research, 2014Co-Authors: David Serke, E Hall, John Bognar, A F Jordan, Spencer Abdo, Kirstin Baker, Tom Seitel, Marta NelsonAbstract:Abstract An improved version of the vibrating wire sensor, used to measure supercooled cloud Liquid Water Content, was developed by Anasphere Inc. and tested during early 2012. The sensor works on the principle that supercooled Liquid will freeze to the vibrating wire and reduce the frequency at a known rate proportional to the Liquid Water Content as the sensor rises through the cloud attached to a weather balloon and radiosonde. The disposable Anasphere sensor interfaces with an InterMet Systems iMet radiosonde. This updated sensor reduces the weight of the instrument while updating the technology when compared to the preceding balloon-borne sensor that was developed in the 1980's by Hill and Woffinden. Balloon-borne test flights were performed from Boulder, Colorado during February and March of 2012. These flights provided comparisons to integrated Liquid Water and profiles of Liquid Water Content derived from a collocated multichannel microwave radiometer, built and operated by Radiometrics Corporation. Inter-comparison data such as these are invaluable for calibration, verification and validation of remote-sensing instruments. The data gathered from this sensor are potentially important to detection of icing hazards to aircraft, validation of microphysical output from numerical models, and calibrating remote sensors measuring supercooled Liquid Water.
A F Jordan - One of the best experts on this subject based on the ideXlab platform.
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supercooled Liquid Water Content profiling case studies with a new vibrating wire sonde compared to a ground based microwave radiometer
Atmospheric Research, 2014Co-Authors: David Serke, E Hall, John Bognar, A F Jordan, Spencer Abdo, Kirstin Baker, Tom Seitel, Marta NelsonAbstract:Abstract An improved version of the vibrating wire sensor, used to measure supercooled cloud Liquid Water Content, was developed by Anasphere Inc. and tested during early 2012. The sensor works on the principle that supercooled Liquid will freeze to the vibrating wire and reduce the frequency at a known rate proportional to the Liquid Water Content as the sensor rises through the cloud attached to a weather balloon and radiosonde. The disposable Anasphere sensor interfaces with an InterMet Systems iMet radiosonde. This updated sensor reduces the weight of the instrument while updating the technology when compared to the preceding balloon-borne sensor that was developed in the 1980's by Hill and Woffinden. Balloon-borne test flights were performed from Boulder, Colorado during February and March of 2012. These flights provided comparisons to integrated Liquid Water and profiles of Liquid Water Content derived from a collocated multichannel microwave radiometer, built and operated by Radiometrics Corporation. Inter-comparison data such as these are invaluable for calibration, verification and validation of remote-sensing instruments. The data gathered from this sensor are potentially important to detection of icing hazards to aircraft, validation of microphysical output from numerical models, and calibrating remote sensors measuring supercooled Liquid Water.
E Hall - One of the best experts on this subject based on the ideXlab platform.
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supercooled Liquid Water Content profiling case studies with a new vibrating wire sonde compared to a ground based microwave radiometer
Atmospheric Research, 2014Co-Authors: David Serke, E Hall, John Bognar, A F Jordan, Spencer Abdo, Kirstin Baker, Tom Seitel, Marta NelsonAbstract:Abstract An improved version of the vibrating wire sensor, used to measure supercooled cloud Liquid Water Content, was developed by Anasphere Inc. and tested during early 2012. The sensor works on the principle that supercooled Liquid will freeze to the vibrating wire and reduce the frequency at a known rate proportional to the Liquid Water Content as the sensor rises through the cloud attached to a weather balloon and radiosonde. The disposable Anasphere sensor interfaces with an InterMet Systems iMet radiosonde. This updated sensor reduces the weight of the instrument while updating the technology when compared to the preceding balloon-borne sensor that was developed in the 1980's by Hill and Woffinden. Balloon-borne test flights were performed from Boulder, Colorado during February and March of 2012. These flights provided comparisons to integrated Liquid Water and profiles of Liquid Water Content derived from a collocated multichannel microwave radiometer, built and operated by Radiometrics Corporation. Inter-comparison data such as these are invaluable for calibration, verification and validation of remote-sensing instruments. The data gathered from this sensor are potentially important to detection of icing hazards to aircraft, validation of microphysical output from numerical models, and calibrating remote sensors measuring supercooled Liquid Water.
William A Coope - One of the best experts on this subject based on the ideXlab platform.
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a study of thermals in cumulus clouds
Quarterly Journal of the Royal Meteorological Society, 2005Co-Authors: Ala M Lyth, Sonia Lashertrapp, William A CoopeAbstract:Air motions in the thermals contained within shallow Florida cumulus clouds were observed to be similar to the circulation observed in laboratory thermals. There was outward flow in the updraughts of individual thermals at most levels and there were usually downdraughts observed at the edges of the updraught or of the cloud. Widespread inward flow towards the centre of the cloud and a narrow, but strong, updraught was occasionally observed, reminiscent of the tail found at the rear of the laboratory thermals. A region of reduced Liquid Water Content was frequently observed in the centre of several thermals where the updraught and horizontal 1D divergence were strongest, and complete holes were observed on two occasions. Although horizontal wind shear was generally weak, it was significant in a few cases, causing the flow pattern in the cloud to be asymmetric. Ascending regions of cloud with high values of Liquid Water Content (cloud cores) were commonly observed at all altitudes, but generally the percentage of clouds measured with high Liquid Water Content decreased with altitude. The observations of airflow and Liquid Water Content structure in warm cumulus clouds described in this paper are consistent with the schematic model of a thermal where a core of high Liquid Water Content survives for several kilometres above cloud base, but erodes as it ascends. Copyright © 2005 Royal Meteorological Society
