HR: 09:15h
AN: A21H-05    [Abstracts]
TI: Asian Aerosols: A Geophysical Fluid Dynamics Laboratory general circulation model sensitivity study of model response to aerosol optical depth and aerosol absorption
AU: * Randles, C A
EM: cynema@alum.mit.edu
AF: Princeton University Atmospheric and Oceanic Sciences Program, 300 Forrestal Road, Sayre Hall, Princeton, NJ 08540, United States
AU: Ramaswamy, V
EM: V.Ramaswamy@noaa.gov
AF: Geophysical Fluid Dynamics Laboratory, 201 Forrestal Road, Princeton, NJ 08540, United States
AB: Atmospheric absorption by black carbon (BC) aerosol heats the atmosphere while simultaneously cooling the surface and reducing latent and sensible heat fluxes from the land. Recent studies have shown that absorbing BC aerosol can have a large impact on regional climates, including modification of the hydrological cycle. However, significant uncertainties remain with regards to (a) the total amount of all aerosol species and (b) the amount of aerosol absorption. Here we present a GCM sensitivity study focusing on the influences due to total aerosol amount and aerosol absorption in the south and east Asian regions. Six experiments are conducted to test the equilibrium response of the GFDL AM2 GCM (under conditions of prescribed, observed sea surface temperatures) to (i) changes in aerosol absorption caused by changes in BC aerosol amount, and (ii) aerosol extinction optical depth increases corresponding to the year 1990 relative to a control case of 1950. In order to systematically explore the uncertainties in aerosol loading and absorption, the sensitivity experiments are classified into four regimes: low extinction optical depth, low absorption; low extinction optical depth, high absorption; high extinction optical depth, low absorption; and high extinction optical depth, high absorption. Changes in surface temperature and changes in the hydrological cycle are generally insignificant when lower aerosol extinction optical depths are considered. For higher extinction optical depths, the change in the modeled regional circulation relative to the control circulation over south and east Asia is affected by the amount of aerosol absorption and contrasts sharply to the regional circulation change associated with increasing only scattering aerosols. When increasing absorbing aerosols over the region, low-level convergence and increases in vertical velocity overcome the stabilizing effects of the absorbing aerosol and enhance the monsoonal circulation and precipitation rate in northwestern India relative to the control run. In contrast, the presence of a purely scattering aerosol weakens the monsoonal circulation relative to the control run and inhibits precipitation in this same region. This study has potential implications for aerosol reduction strategies that seek to mitigate air pollution concerns. At higher optical depths, if absorbing aerosol is present, reduction of scattering aerosol alone may have a lesser effect on precipitation changes, implying that reductions in black carbon aerosol should be undertaken at the same time as reductions in sulfate aerosol.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 1610 Atmosphere (0315, 0325)
DE: 1854 Precipitation (3354)
DE: 3337 Global climate models (1626, 4928)
DE: 9320 Asia
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting