HR: 0800h
AN: A11A-0037    [Abstracts]
TI: Indirect effects of mineral dust on warm clouds
AU: * Min, Q
EM: min@asrc.cestm.albany.edu
AF: State University of New York, 251 Fuller Road, Albany, NY 12203,
AU: Li, R
EM: Rui_li@asrc.cestm.albany.edu
AF: State University of New York, 251 Fuller Road, Albany, NY 12203,
AU: Harrison, L
EM: lee@asrc.cestm.albany.edu
AF: State University of New York, 251 Fuller Road, Albany, NY 12203,
AU: Lin, B
EM: bing.lin@nasa.gov
AF: NASA Langley Research Center, Hampton, Hampton, VA 23681,
AU: Joseph, E
EM: ejoseph@howard.edu
AF: Howard University, Washington, Washington, DC 20059,
AB: Cloud evolution is affected profoundly by aerosols and associated microphysical processes and by cloud dynamics and thermodynamics. To isolate dynamic influences from microphysical impacts, we stratify warm cloud measurements of MODIS, AMSR, and CERES in four key ways: cloud precipitation regime, cloud top temperature (or height), cloud liquid water path, and aerosol number concentration. We found that correlations, which appear to demonstrate Twomey effect, strongly depend on the cloud precipitation regime and cloud top height. Our estimated aerosol indirect effect (AIE) for precipitating clouds with cloud top height above the freezing level is -0.14 (r=0.75, p<0.03) while the AIE for shallow precipitating clouds is not statistically significant. In contrast, for non-precipitating clouds, clouds that directly interact with the dust layer show strong Twomey effects with AIE of -0.15 (r=0.89, p<0.01), while clouds with cloud top above the freezing level show insignificant Twomey effects. We also estimate radiation forcing of dust aerosols directly from satellite measurements. The direct shortwave (SW) radiation effect of Saharan dusts at solar zenith angle of 21.6¡ã is 47.96+6.21 wm-2 per unit AOD with correlation coefficient of 0.88. The indirect SW forcing of Saharan dust is 34.44+4.91 wm-2 per unit AOD for clouds with LWP of 100 gm-2. Our study points out the importance of cloud dynamics and aerosol vertical transport on the aerosol indirect effect. Without carefully segregating cloud precipitation regime and cloud top height, the estimated AIE can vary substantially and have much smaller correlation coefficients.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0321 Cloud/radiation interaction
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting