Lidar measurements of stratospheric aerosol content and depolarization ratios after the eruption of El Chichón volcano: measurements at Nagoya, Japan

Abstract

An enormous increase in backscattered light from the stratospheric aerosol layer was observed after the El Chichón eruption by using a ruby lidar in Nagoya, Japan (35°N, 137ºW). An apparent increase in depolarization ratio was also observed in the lower part of the main aerosol layer for severa months after the eruption. The increase in depolarization ratio indicates the existence of non-spherical particles such as silicate particles. The depolarization ratio decreased to only a few percent, which suggests that almost all particles were spherical, after the end of September. Even several months after the eruption, aerosols in the easterly wind region above 20 km were still distributed inhomogeneously. After the wind system changed into the winter system, the aerosol layer showed only one broad peak and it seems that aerosols were distributed zonally homogeneously. An effective vertical diffusion coefficient was estimated on the basis of the data obtained after September and the value of about 3 x 103 cm 2 /s was obtained.