HR: 10:20h
AN: A32B-01 INVITED     [Abstracts]
TI: Aerosols, Clouds and Global Dimming
AU: * Ramanathan, V
EM: vram@fiji.ucsd.edu
AF: Scripps Institution of Oceanography, University of California at san Diego, 2500 Gillman Ave, La Jolla, CA 92093 United States
AU: Kim, D
EM: dkim@ucsd.edu
AF: Scripps Institution of Oceanography, University of California at san Diego, 2500 Gillman Ave, La Jolla, CA 92093 United States
AU: Chung, C
EM: cchung@ucsd.edu
AF: Scripps Institution of Oceanography, University of California at san Diego, 2500 Gillman Ave, La Jolla, CA 92093 United States
AU: Podgorny, I
EM: ipodgorny@ucsd.edu
AF: Scripps Institution of Oceanography, University of California at san Diego, 2500 Gillman Ave, La Jolla, CA 92093 United States
AB: Several studies have reported that there was a large reduction of surface solar radiation worldwide during the 1950s to 1980s, as large as 5 to 10 W.m-2 and a partial recovery of this dimming during the following decades. If this was indeed the case on a global scale, then this dimming trend from the 1950s to the end of the twentieth century must have played a large role in the observed surface temperature trends. Given the uncertainties in surface and satellite solar radiation measurements, we need independent determination of the magnitude and causes of the dimming trends. In this study we explore if trends in radiative forcing due to aerosols, particularly soot and dust, can account for the observed dimming. We include both the direct and the indirect effect of aerosols as well as the observed trends in cloudiness. Satellite based Aerosol data from MODIS, CERES and AVHRR are combined with surface based observations (AERONET and GEBA), field observations (INDOEX, ACE-Asia) and aerosol assimilation models (GOCART) to estimate the global reduction of solar radiation from aerosols and clouds over selected land and oceanic regions of the globe for the last several decades. Our focus is on Asia, N. America, Indian and Pacific oceans where data are available from aircraft, surface and satellites. For the regions investigated in this study, the surface dimming can range from -5 to -20 W.m-2 for the entire twentieth century, while the trends for particular decadal periods depend on the assumed emission histories for aerosols, particularly black carbon. Long range transport of aerosols from populated regions to the marine environment, several thousand kilometers away, is the major factor contributing to the global nature of the dimming. While, the present data and models are not of sufficient accuracy to confirm the observed trends in global dimming, this study clearly shows that global dimming is a major factor in the observed temperature trends. For example, we show that over S. Asia and Indian Ocean, it is nearly impossible to explain the observed trends (for 1950 to 2000) in temperatures and rainfall without accounting for the effects of global dimming.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting