Abstract
The aerosol optical thickness of the atmosphere was measured using a spectropyrheliometer at Tsukuba for three winter seasons from October 1980 to March 1983. The optical thickness was abnormally large in the ('82-'83) winter, because of the enhancement of the stratospheric aerosols due to the volcanic eruptions of El Chichon. Size distributions of aerosols in the vertical air column were inferred, which show characteristic features of bimodal distribution for the pre-E1 Chichon season and power law distribution for the post-E1 Chichon season. Optical properties of the El Chichon volcanic aerosols have been estimated; the stratospheric optical thickness was about 0.1 on the wavelength average in the ('82-'83) winter, and aerosol size distributions were relatively monodispersive with a mode radius around 0.3μm. Possible effects of the enhanced stratospheric aerosols on the solar radiation budget were estimated and compared with available observations. The El Chichon induced aerosols in the ('82-'83) winter could reduce the total solar radiation on the ground by as much as 3-4% on cloudless days, and enhance the spherical albedo by about 10%.
