PROPERTIES OF MOUNT-PINATUBO AEROSOLS AS DERIVED FROM NIMBUS-7 TOTAL OZONE MAPPING SPECTROMETER MEASUREMENTS

The perturbations to the radiances measured by the Nimbus 7 total ozon e mapping spectrometer (TOMS) during the 18 months after the eruption of Mount Pinatubo are used to derive weekly zonal mean values for the stratospheric aerosol optical thickness at 312.5 nm and zonal-mean val ues for the area-weighted or effective radius. The method uses the TOM S observations, on both sides of the orbital track, of the detailed st ructure in the backscattering region of the aerosol-scattering phase f unction. Spatial and temporal evolution of the aerosol optical thickne ss and effective radius is obtained for the tropical region (25 degree s N to 25 degrees S) during most of the period mid-July 1991 to Decemb er 1992. The largest derived value of optical thickness was 0.22 (+36% /-10%), obtained for the latitude zone from 5 degrees to 15 degrees S at the end of July 1991. By the end of 1992, tropical optical depths v aried from 0.02 to 0.06 over the 25 degrees N to 25 degrees S geograph ical area. The main source of uncertainty in the derived optical depth is the altitude of the aerosol layer. The inferred time evolution of the effective radius clearly shows an increase in particle size. At th e end of July 1991, effective radius values of about 0.5 mu m were der ived, while in the fall of 1992, these values were between 0.7 and 1.4 mu m. Corrections and error estimates are obtained for the measured o zone amounts. The zonal average retrieved ozone amounts corrected for the presence of aerosols are within 1% of the uncorrected zonal averag es. Individual scan angles can have ozone amount corrections of +/-3%, with a nadir view correction of 2%.