A modeling study of aerosol effects on cloud radiative property and precipitation

Abstract

A two-moment (mass and number) warm cloud scheme together with ground and aircraft measurements over Beijing is used in a regional model to study the effects of aerosols on cloud radiative property and precipitation. Using a prescribed tri-modal lognormal aerosol size distribution, the aerosol numbers are calculated from prognostic aerosol masses, for which advection, diffusion, and cloud drop activation/deactivation are considered. Specifically, the accumulation mode of a tri-lognormal aerosol size distribution is fitted to the aircraft measured values for a cold front case passed through northern China during June 25-26, 2005. In the simulations, the warm cloud scheme simulates explicitly the cloud drops and subsequently affects the radiative heating and cooling, and circulations. Simulations with different initial conditions for being fitted with aircraft measurements, continental and maritime aerosol numbers were conducted. It is found that more aerosols result in more but smaller cloud drops and more cloud water, leading to an increase in albedo. The effects on rains are complex: smaller cloud drops have less efficient coagulation for raindrop to form (autoconversion), leading to fewer raindrop numbers and less rainwater; while more cloud water enhances the accretion for raindrop growth. Nevertheless, for the whole cloud system, the impact of increasing aerosols inhibits precipitation. © 2010 Science in China Press and Springer Berlin Heidelberg.