HR: 1340h
AN: A23C-0826    [Abstracts]
TI: The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations
AU: * Tao, W
EM: tao@agnes.gsfc.nasa.gov
AF: Code 912, Laboratory for Atmosphere, NASA, Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Li, X
EM: xli@agnes.gsfc.nasa.gov
AF: Code 912, Laboratory for Atmosphere, NASA, Goddard Space Flight Center, Greenbelt, MD 20771 United States
AU: Khain, A
AF: The Institute for Earth Sciences, The Hebrew University of Jerusalem, Jerusalem, 91904 Israel
AU: Simpson, J
AF: Code 912, Laboratory for Atmosphere, NASA, Goddard Space Flight Center, Greenbelt, MD 20771 United States
AB: Cloud microphysics are inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region, in the sub-tropics (Florida) and in the mid-latitude using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fewer droplets, larger sizes develop due to greater condensational and collection growth, leading to a broader size spectrum in comparison to the high CCN case. Forward and backward trajectory calculation are performed to identify the origin of clouds; and retrieve the dynamics, thermo-dynamic and CCN characteristics along the trajectory.
DE: 0305 Aerosols and particles (0345, 4801)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting