HR: 16:45h
AN: A14A-04    [Abstracts]
TI: Examination of cumulus cloud contamination on aerosol retrieval from Terra instruments over ocean
AU: * Zhao, G
EM: gyzhao@atmos.uiuc.edu
AU: Di Girolamo, L
EM: larry@atmos.uiuc.edu
AB: Large quantitative discrepancy in aerosol climatologies derived from the passive satellite sensors has long been recognized. One of the major factors causing this discrepancy is hypothesized to be small cumuli, because cumuli tend to partially fill satellite fields-of-view (pixels) and these partially cloudy pixels may or may not be used for aerosol retrieval depending on the quality of the cloud screening algorithm for each satellite instrument. However, examining the quality of a cloud screening algorithm requires the knowledge of the true cloud fields, which can only be provided from coincident high resolution satellite images. Fortunately, with the coincident 15 m observation from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), cumulus cloud contamination on aerosol retrieval can now be examined for both the Moderate Resolution Imaging SpectroRadiometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR) aboard Terra satellite. From Sep. to Dec. 2004, 124 ASTER scenes containing only cumuli over the tropical western Atlantic were collected with overlapped MODIS and MISR observations. The average cloud fraction of all the ASTER scenes examined is 8.6%, half of which is contributed from clouds less than 2 km in diameter. With reference to ASTER, 9.6% of MISR 1.1 km pixels used to retrieve aerosol properties, which are reported at 17.6 x 17.6 km2 regions, contain some clouds, but 86% of the cloud-contaminated pixels have a cloud fraction less than 1% of a pixel area. The information on which 1 km pixels were used in the MODIS aerosol retrieval is not available, making the assessment of cloud contamination on the MODIS aerosol retrieval difficult. However, when comparing to MODIS at pixel level, MISR aerosol optical depth is only 0.02 larger than MODIS on average with a standard deviation of 0.015. Although our results reveal that cumulus cloud contamination is not a major factor that causes the large discrepancy in aerosol climatologies, it is noticed that both aerosol optical depth and Angstrom exponent do have a correlation with the spatial distribution of cumuli.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0321 Cloud/radiation interaction
DE: 0399 General or miscellaneous
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting