Abstract
The spectral aerosol-optical-thicknesses (AOTs) of vertical air columns were measured by a ground-based multi-channel sunphotometer at Tsukuba (36.05°N, 140.13°E), Japan, during January through April of 1991 and 1992. The AOTs measured during the 1992 season were much larger, by as much as 0.1 to 0.2, than those in the 1991 season. This difference was mainly attributed to the enhancement of stratospheric aerosols caused by the Mt. Pinatubo eruptions in June 1991. The stratospheric AOTs exhibited a maximum during February 1992, which exceeded the maximum value observed in December 1982 for the El Chichon volcanic dust. The aerosol size distributions in the optically active size range were retrieved from the spectral. A fairly narrow mono-modal size distribution, having a mode radius of about 0. 6μm and an effective variance of less than 0.05, was retrieved for the Pinatubo volcanic aerosols. This mono-modal size distribution is similar to that estimated from Bishop's ring simulations (Asano, 1992).
