Enormous increase of volcanic clouds in the stratosphere over Fukuoka after April 1982

Abstract

Very large-increases of stratospheric aerosols caused by the eruption of Mexican volcano El Chichón in early April 1982 were observed by a Yag lidar system over Fukuoka (33°N) and the long term variation of the profiles for 15 months is presented. The densest aerosol layers were located in the altitude range from 20 to 30 km for the early six months and the lower rarer layers were located below the altitude about 20 km. The densest part gradually descended after October 1982 to about 20 km in January 1983, after merging with thelowerpart and remained there since that time. The descending velocity of the upper !ayer is about 1 km/month or less.The optical depth of the aerosol layers at the wavelength 0.55 μm attained maximum value about 0.3 for the period from December 1982 to February 1983 and then gradually decreased to 0.05 in July 1983. The eddy diffusion in the upper part is estimated to be extremely small for the period from April through October 1982 in the vertical and meridional directions. This finding can explain observed results consistently and supports the view originally proposed by Matsuno (1980).