83rd Annual

Thursday, 13 February 2003: 1:30 PM
Application of Satellite Precipitation Measurements in a Study of Aerosol Removal Rates
Eric M. Wilcox, SIO/Univ. of California, La Jolla, CA; and V. Ramanathan
The highly variable distribution of aerosol source, modification, and sink processes requires that studies of regional- or global-scale aerosol distributions be done with the aid of a chemical transport model. This study aims to improve upon simulations of aerosol transport by integrating a high resolution, 3-hourly, multi-platform satellite precipitation dataset into the wet deposition scheme of the MATCH chemical transport model. Precipitation is the dominant contributor to the removal of aerosol, acting through both the removal of cloud drops seeded by aerosol particles, as well as the collision of raindrops with particles below cloud. To date, budget studies of aerosol species have relied upon numerical representations of precipitation typical of climate models, which in the tropics are primarily parameterizations of deep, moist convection. Significant biases in the spatial and temporal distributions of precipitation in a modern convection parameterization are apparent when compared with satellite observations of precipitation, for example underestimating the occurrence of extreme precipitation events relative to drizzle events. Furthermore, assumptions are often made about the fraction of each model grid cell occupied by precipitation, which are completely unconstrained by observations. Such biases can be corrected with the application of available satellite datasets. This study focuses on aerosol emitted from the Indian Subcontinent during the winter monsoon and transported south over the Indian Ocean before encountering extensive deep convection along the Inter-Tropical Convergence Zone. Comparisons with published aerosol distributions from the Indian Ocean Experiment (INDOEX) will be made. The effect of biases in simulated precipitation distributions on the lifetime of aerosol particles will be investigated by comparing the removal rate using a convection parameterization to the simulation using observed precipitation. In addition to improving estimates of the aerosol removal rate, an important consideration is the amount of aerosol that manages to avoid scavenging and is thereby made available for transport to the upper-troposphere where it can be efficiently transported thousands of kilometers.

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