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Atmospheric Composition

The level and distribution of modeled relative humidity (and consequently, water uptake) is the major contributor to the large spread in modeled aerosol radiative forcing associated with sulfate aerosols. Unfortunately, the effect of water uptake on aerosols throughout the atmospheric column is not monitored at the present time, so global aerosol models are left unchecked. Global aerosol modelers rely almost exclusively upon aerosol optical thickness (AOT) and aerosol Angstrom exponent to test the accuracy of their aerosol modules; although these are valuable tools that provide some information about aerosol mass and size at ambient relative humidities, they do not provide information about the aerosol water content, or the dry aerosol mass. The aerosol polarimetry sensor (APS) level-3 aerosol product provides real refractive indices (at a minimum of three wavelengths) and single-scatter albedo for each of the fine and coarse aerosol modes; this allows the retrieval of the aerosol water uptake and hygroscopicity for each mode. Additionally, we retrieve dry AOT and dry particulate mass, and aerosol liquid water path from the other aerosol optics properties provided by the APS (i.e., AOT, effective radius, and effective variance). These constraints will be valuable for separating discrepancies associated with aerosol mass (or emissions) from discrepancies associated with aerosol hygroscopic growth. The objectives of this proposal are to 1.) modify our current aerosol water uptake retrieval so that it is suitable for the Glory satellite product, 2.) validate the research code at AERONET sites that are located near long-term surface measurements of f(RH) and with suitable aircraft profiles from field missions, and 3.) apply the retrieval to the Glory Aerosol Polarimetry Sensor (APS) data product (processing at least one year of data), and make the results publicly available. The retrieval described in this proposal finally provides a check for the water uptake modules of global aerosol models, which modelers can use to constrain their hygroscopic growth parameterizations. This will result in improved aerosol radiative forcing calculations, but there are other important applications as well. For instance, aerosol water uptake is also important for aerosol-cloud interaction studies, and dry aerosol mass is important for air quality assessment (especially if the Glory data set overlaps with the CALIPSO data set, which can provide the fraction of particulate matter located near the surface). Finally, this retrieval enables regional and seasonal observations of aerosol water content and growth for the entire globe.

Project PI: Gregory Schuster/NASA Langley Research Center

NASA Langley Research Center Mail Stop 420 VA 23681-2199 Hampton United States

Phone: (757) 864-1486

Email: Gregory.L.Schuster@nasa.gov

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Started: Sep 27, 2010

Last Activity: Jan 04, 2011

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