AN ESTIMATION OF THE RADIATIVE EFFECT IN THE STRATOSPHERE DUE TO THE PINATUBO AEROSOL

The global distribution of the Pinatubo aerosol in the stratosphere is constructed for optical thickness at 1 mu m by combining satellite da ta and lidar data for one year, from June 1991 to June 1992, following the eruption. The distribution, averaged for every two months, is com posed of the data from Stratospheric Aerosol and Gas Experiment II bet ween about 70 degrees N and 70 degrees S and the data from other satel lites and lidar measurements at high latitudes and in the tropical low er stratosphere. Radiative heating rate due to the Pinatubo aerosol is calculated combining this distribution at 1 mu m with the radiative p roperties of observed sulfate aerosols. Sulfate aerosol does not absor b substantially but only scatters solar radiation, thereby producing v ery weak warming of about 0.02 Kday(-1) in the upper stratosphere due to ozone absorption of aerosol-reflected radiation. Terrestrial radiat ion brings a warming of about 0.1 Kday(-1) to the aerosol layer in low and middle latitudes, and very weak cooling at high latitudes. The ne t effect is, then, brought about by terrestrial radiation. Stratospher ic temperature change is also calculated using a fixed dynamical heati ng model. In low latitudes, the middle stratospheric temperature rises rapidly by about 2 K during the first 40 days, following which the wa rming slows down and its axis moves northward to about 15 degrees N. T he largest warming of 3 K appears in the axis latitude after 10 months and the second largest warming of 2.9 K at 5 degrees S after 12 month s.