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Atmospheric Composition

We propose to use measurements from the Aerosol Polarimetry Sensor (APS) to investigate and improve our characterization of ice particle scattering properties, and in particular the degree to which ice particles should be roughened in scattering models. Roughening can occur because of riming or air bubbles within the ice particles. Smooth-faced ice particles have more complex scattering phase functions and higher values of the asymmetry factor than roughened particles. Recent POLDER data analyses indicate the importance of polarized radiances, particularly the degree of linear polarization, to this investigation. The work outlined in this proposal provides the basis for a more consistent retrieval of ice cloud microphysical and optical properties for A-Train satellite instruments taking measurements in the visible and shortwave infrared (SWIR) part of the spectrum. Given our involvement with the MODIS Science Team, we are in a unique position to assess the consistency of MODIS and MODIS-like ice cloud retrievals with observations from APS. In comparison with POLDER (up to 14 angles/scene with polarimetry at wavelengths of 0.443, 0.670, and 0.865 microns), APS will provide polarimetry at much higher along-track angular resolution (up to 250 angles/scene) at higher spectral resolution, including SWIR spectral channels that cover the atmospheric window channels used for the standard MODIS cloud retrievals. Specific goals of our proposal are to: 1. generate ice cloud bulk scattering models for appropriate APS and MODIS visible and SWIR channels based on new databases of ice particle scattering properties for smooth particles and particles with various amounts of surface roughening, 2. Perform polarized radiative transfer simulations, 3. develop software to co-locate MODIS and APS data in collaboration with Dr. Jerome Riedi (Univ. Lille), paying particular attention to the significance and impact of varying pixel size on the interpretation of multiangle measurements, 4. intercompare APS spectral multiangular views (total radiance and polarization). Due to the shortened time for this proposed project (1.5 years), we anticipate analysis of just a limited number of case study scenes with different ice cloud generation mechanisms (e.g., tropical anvil cirrus, synoptic cirrus, etc.) to assess ice model/phase function consistency as well as compare with MODIS. Other A-Train sensors will be used to determine appropriate case study scenes (MODIS, CALIPSO, CloudSat). Our investigation of the total radiance and polarization data from ice clouds based on APS will provide valuable insight to the remote sensing of ice cloud microphysical and optical properties and could result in improvements to narrowband and broadband numerical models that employ parameterizations of ice cloud shortwave radiative properties. This proposal includes synergistic efforts from three groups (Texas A&M;, ice particle scattering; UW-Madison/SSEC, bulk ice cloud optical models and co-location; NASA GSFC, cloud retrieval algorithm development and analysis). Due to a high level of codependence, we have combined the various efforts into a single proposal per advice from the NASA Radiation Science Program (RSP) Manager. With further advice, we have included a 3-year budget in the event that additional funding support becomes available, with which we would develop a more robust global co-location algorithm and move from a select number of case studies to regional and global studies.

Project PI: Bryan Baum/Space Science and Engineering Center, University of Wisconsin, Madison

Space Science and Engineering Center University of Wisconsin-Madison 1225 West Dayton St. Madison, WI 53706

Phone: (608) 263-3898

Fax: (608) 262-5974

Email: bryan.baum at ssec.wisc.edu

http://www.ssec.wisc.edu/~baum/

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Started: Sep 27, 2010

Last Activity: Jan 04, 2011

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