An increase in the amount of stratospheric aerosol due to the Pinatubo eruption (June 12--15, 1991, 15.14¿N, 120.35¿E) was observed from the end of June by a lidar in NIES, Tsukuba (36¿N, 140¿NE). The first arrival of volcanic aerosol layers was observed just above the tropopause on June 28, 1991, only two weeks after the eruption. Aerosol layers higher than 20 km appeared sporadically in July and August, reflecting the inhomogeneity of aerosol distribution.

After the change in the wind system from summer easterlies to winter westerlies, the main body of the volcanic aerosol layer made its appearance over Tsukuba. The integrated backscattering coefficient (IBC) increased in winter as a result of transportation of aerosols from the tropical region. The IBC, which can be converted to optical thickness, exceeded the level of the value observed after the El Chichon eruption. ¿American Geophysical Union 1993