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Robert T. Ryan
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Robert T. Ryan

Abstract

A vertical wind tunnel was constructed to study the behavior of large, low-surface-tension drops in free fall. The tunnel is simple, but provides a low turbulence (0.7%) flow which stably supports large water drops falling at terminal velocity. The influence of reduced surface tension on maximum drop size, drop terminal velocity, and drop shape was investigated. It was found that drops of low surface tension break up at a smaller size than drops with normal surface tension, are more deformed than drops of equal mass having normal surface tension, and have a lower terminal velocity than drops of equal mass and normal surface tension. Drops only partially coated with surfactant cannot be stably supported and undergo violent oscillations. Before any field testing of possible cloud modification by reducing rainwater surface tension is warranted, further investigation of the behavior of low-surface-tension drops should be undertaken and, in particular, the behavior of drops only partially coated with surfactant should be studied.

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Robert T. Ryan
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Daniel T. McCoy, Ryan Eastman, Dennis L. Hartmann, and Robert Wood

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Decreases in subtropical low cloud cover (LCC) occur in climate model simulations of global warming. In this study 8-day-averaged observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Atmospheric Infrared Sounder (AIRS) spanning 2002–14 are combined with European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis to compute the dependence of the observed variability of LCC on various predictor variables. Large-scale thermodynamic and dynamic predictors of LCC are selected based on insight from large-eddy simulations (LESs) and observational analysis. It is found that increased estimated inversion strength (EIS) is associated with increased LCC. Drying of the free troposphere is associated with decreased LCC. Decreased LCC accompanies subsidence in regions of relatively low EIS; the opposite is found in regions of high EIS. Finally, it is found that increasing sea surface temperature (SST) leads to a decrease in LCC. These results are in keeping with previous studies of monthly and annual data. Based upon the observed response of LCC to natural variability of the control parameters, the change in LCC is estimated for an idealized warming scenario where SST increases by 1 K and EIS increases by 0.2 K. For this change in EIS and SST the LCC is inferred to decrease by 0.5%–2.7% when the regression models are trained on data observed between 40°S and 40°N and by 1.1%–1.4% when trained on data from trade cumulus–dominated regions. When the data used to train the regression model are restricted to stratocumulus-dominated regions the change in LCC is highly uncertain and varies between −1.6% and +1.4%, depending on the stratocumulus-dominated region used to train the regression model.

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R. T. Ryan, H. H. Blau Jr., P. C. von Thüna, M. L. Cohen, and G. D. Roberts

Abstract

An improved single-particle light scattering instrument for measurement of cloud microstructure has been built and used in field studies. Cloud particle size and number information is measured over 12 sizing intervals, in the range 4 to 85 μ diameter. The microstructure can be observed in real time and with a spatial resolution not previously reported. The general features of water cloud droplet size and number distributions are consistent with previous direct capture and replication studies. The transition from water to ice phase regions in cumuliform clouds can be inferred from dramatic changes observed in the distribution features. Results are also presented for stratus and cirrus cloud penetrations.

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EXECUTIVE COMMITTEE, Warren M. Washington, David D. Houghton, Robert T. Ryan, Donald R. Johnson, Margaret A. LeMone, Alexander E. MacDonald, Richard E. Hallgren, and Kenneth C. Spengler
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EXECUTIVE COMMITTEE, David D. Houghton, Paul D. Try, Warren M. Washington, Robert T. Ryan, Margaret A. LeMone, Richard S. Greenfield, Richard E. Hallgren, and Kenneth C. Spengler
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EXECUTIVE COMMITTEE, Robert T. Ryan, Warren M. Washington, Donald R. Johnson, William D. Bonner, Margaret A. LeMone, Ronald D. McPherson, Richard E. Hallgren, and Kenneth C. Spengler
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EXECUTIVE COMMITTEE, Donald R. Johnson, Robert T. Ryan, William D. Bonner, James R. Mahoney, Kristina B. Katsaros, Ronald D. McPherson, Richard E. Hallgren, and Kenneth C. Spengler
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John T. Sullivan, Timothy Berkoff, Guillaume Gronoff, Travis Knepp, Margaret Pippin, Danette Allen, Laurence Twigg, Robert Swap, Maria Tzortziou, Anne M. Thompson, Ryan M. Stauffer, Glenn M. Wolfe, James Flynn, Sally E. Pusede, Laura M. Judd, William Moore, Barry D. Baker, Jay Al-Saadi, and Thomas J. McGee

Abstract

Coastal regions have historically represented a significant challenge for air quality investigations because of water–land boundary transition characteristics and a paucity of measurements available over water. Prior studies have identified the formation of high levels of ozone over water bodies, such as the Chesapeake Bay, that can potentially recirculate back over land to significantly impact populated areas. Earth-observing satellites and forecast models face challenges in capturing the coastal transition zone where small-scale meteorological dynamics are complex and large changes in pollutants can occur on very short spatial and temporal scales. An observation strategy is presented to synchronously measure pollutants “over land” and “over water” to provide a more complete picture of chemical gradients across coastal boundaries for both the needs of state and local environmental management and new remote sensing platforms. Intensive vertical profile information from ozone lidar systems and ozonesondes, obtained at two main sites, one over land and the other over water, are complemented by remote sensing and in situ observations of air quality from ground-based, airborne (both personned and unpersonned), and shipborne platforms. These observations, coupled with reliable chemical transport simulations, such as the National Oceanic and Atmospheric Administration (NOAA) National Air Quality Forecast Capability (NAQFC), are expected to lead to a more fully characterized and complete land–water interaction observing system that can be used to assess future geostationary air quality instruments, such as the National Aeronautics and Space Administration (NASA) Tropospheric Emissions: Monitoring of Pollution (TEMPO), and current low-Earth-orbiting satellites, such as the European Space Agency’s Sentinel-5 Precursor (S5-P) with its Tropospheric Monitoring Instrument (TROPOMI).

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