Post-Volcanic Stratospheric Aerosol Decay as Measured by Lidar

Abstract

Liday observations of the stratosphere aerosol vertical distribution from October 1971 to July 1976 over midlatitude North America are presented. The results show the sudden increase in the stratospheric aerosol content after the eruption of the Volc´n de Fuego and its subsequent decline. The data are presented in terms of lidar scattering ratio profiles, vertically integrated aerosol backscattering, and rawinsonde temperature profiles. In the months immediately following the volcanic eruption, the lidar-derived aerosol structure is correlated with rawinsonde temperature structure showing the stratospheric temperature minimum occurring near the aerosol layer peak. Analysis of the time dependence of the integrated aerosol backscattering and the tropopause altitude indicates an approximate 0.9 correlation between aerosol loading and tropopause pressure. In addition, the integrated aerosol backscattering also showed some correlation with the minimum stratospheric temperature, i.e., a warmer stratospheric minimum is associated with a relatively higher aerosol loading. The lidar backscatter data also show that rapid decay of the stratospheric aerosol occurred over the late winter to early spring period and that the summer to fall interval was quite stable. For both winter to summer periods of 1975 and 1976 in approximate 40% decrease in the total integrated aerosol backscattering was observed, while from January 1975 to January 1976 a 65% decrease occurred. For the 19-month period from January 1975 to July 1976 the exponential l/e decay time for the integrated aerosol backscattering was 11.6 months.