HR: 0800h
AN: A11A-0034    [Abstracts]
TI: Modeling Aerosol Effects on Shallow Cumuli and Turbulent Activities Under Various Meteorological Conditions
AU: * Wang, H
EM: Hailong.Wang@noaa.gov
AF: University of Illinois, 105 S Gregory Street, Urbana, IL 61801, United States
AU: * Wang, H
EM: Hailong.Wang@noaa.gov
AF: Cooperative Institute for Research in Environmental Sciences (CIRES), NOAA, 325 Broadway,R/CSD3, Boulder, CO 80302, United States
AU: McFarquhar, G M
EM: mcfarq@atmos.uiuc.edu
AF: University of Illinois, 105 S Gregory Street, Urbana, IL 61801, United States
AB: To determine conditions over the Indian Ocean for which cloud fields are most susceptible to modification from aerosols and to study how turbulent activities and shallow cumuli vary for different meteorological scenarios, the National Center for Atmospheric Research Eulerian-semi-Lagrangian (EULAG) three-dimensional large-eddy simulation model was initialized using data collected during the Indian Ocean Experiment (INDOEX). Radiosonde data were used to construct 6 soundings encompassing the range of temperature and humidity observed in the trade-wind boundary layer. By then adding the characteristics (height, depth and strength) of either a typical transition layer (TL), a strong inversion layer (IL) or no stable layer a total of 18 meteorological scenarios were produced. Separate simulations were conducted using EULAG assuming pristine and polluted conditions (i.e., cloud droplet number concentrations, aerosol extinction profiles and single-scattering albedos) using INDOEX observations. For the range of meteorological conditions observed during INDOEX, sensitivity studies showed that the semi- direct effect always dominated indirect effects, producing a positive daytime mean net indirect forcing varying between 0.2 and 4.5 W m-2. The simulations showed that changes in the environmental relative humidity (RH) and the presence of the TL had critical impacts on the cloud properties, turbulence and lateral detrainment rates, and on how aerosols affect these quantities. The net indirect forcing was larger when the RH was higher and in the absence of any dry and stable layers. It was reduced to less than 1.2 W m-2 when the TL was present. The impact of the IL was dependent on convective strength which increases with increasing RH. In fact, changes in meteorological factors had larger impacts on the simulated cloud properties than did the presence of anthropogenic aerosols, indicating large uncertainties can be introduced when solely using observations of aerosols and clouds made under different meteorological conditions to quantify aerosol effects.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting