Lidar observation of the stratospheric aerosol layer over Okinawa, Japan, after the mt. Pinatubo volcanic eruption

Abstract

Stratospheric aerosols originating from Mt. Pinatubo (15.14°N, 120.35°E), which erupted violently on June 15, 1991, were observed by lidar at Naha (26.2°N, 127.7°E) on Okinawa Island. Aerosols had already reached Okinawa by mid September 1991, the start point of this observation series. The altitude range of the aerosol layer is from just above the tropopause to about 30 km. The total amount of aerosols began to increase in mid November corresponding to the appearance of layers at higher altitude, in the 30 to 33 km region, and maximum backscattering ratio 23.1 was observed at 25.8 km altitude on December 4, 1991. Depolarization ratio observations demonstrated that there were not only volcanic ash particles present but also spherical particles, probably sulphate droplets, from the start of this observation series. The highly depolarized region was observed on lower side of the layer and lower depolarization on the higher side. The depolarization ratio reached a peak value of 0.22 at about 16.4 km on November 18, 1991, and has gradually decreased since.