HR: 10:42h
AN: A22D-02 INVITED    [Abstracts]
TI: Cancellation of aerosol indirect effects in stratocumulus through cloud thinning
AU: * Wood, R
EM: robwood@atmos.washington.edu
AF: University of Washington, Atmospheric Sciences Box 351640 University of Washington, Seattle, WA 98195, United States
AB: It is generally assumed, and climate models show, that suppression of precipitation by increasing atmospheric aerosols results in an increased cloud albedo (e.g. increased cloud thickness, liquid water content, coverage, lifetime) in addition to that expected from the Twomey effect. However, recent high resolution model results and some observations challenge this notion. Here, I demonstrate that partial cancellation of the Twomey effect by the suppression of precipitation can be found in even the simplest of physical cloud models (mixed layer model) allowing an exploration of the factors that determine the strength of the aerosol indirect effect (AIE) in stratocumulus clouds. The results show that in order for a model to successfully represent AIEs it must be able to correctly treat (a) the response of precipitation to both cloud droplet concentration and liquid water content; (b) the entrainment process; (c) evaporation in the layer below cloud. The ability of our current generation of climate models to adequately resolve these processes is questionable.
UR: http://www.atmos.washington.edu/~robwood/papers/mlm/aie.pdf
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting