IMPACT OF STRATOSPHERIC VOLCANIC AEROSOLS ON CLIMATE - EVIDENCE FOR AEROSOL SHORTWAVE AND LONGWAVE FORCING IN THE SOUTHEASTERN US

Major volcanic eruptions inject massive amounts of dust and gases into the lower stratosphere and upper troposphere. Stratospheric volcanic aerosols can scatter incoming solar radiation to space, increasing pla netary albedo, reducing the total amount of solar energy reaching the troposphere and the earth's surface, and decreasing the daytime maximu m temperature (aerosol shortwave forcing). They can also absorb and sc atter outgoing terrestrial longwave radiation, increasing the nighttim e minimum surface temperature (longwave forcing). However, persuasive evidence of climate response to this forcing has thus far been lacking . Here we examine patterns of annual and seasonal variations in mean m aximum and minimum temperature trend during the periods 1992-1994 and 1985-1987 relative to that during the period 1988-1990 at 47 stations in the southeastern U.S. For evidence of such climate responses. The s tratospheric volcanic aerosol optical depths over the southeastern U.S . during the period 1985-1994 were inferred from the Stratospheric Aer osol and Gases Experiment (SAGE) II satellite extinction measurement. After the long-term trend signals are removed, it is shown that the do minant decreasing trend of mean maximum temperature and the dominant i ncreasing trend of mean minimum temperature over periods 1992-1994 and 1985-1987 relative to that over the period 1988-1990 are consistent w ith the distribution of stratospheric volcanic aerosols and prediction s from aerosol radiative forcing in the southeastern U.S. (C) 1997 Els evier Science Ltd.