Impact of Pinatubo aerosols on the seasonal trends of global, direct and diffuse irradiance in two northern mid-latitude sites

Abstract

In June 1991, Mt Pinatubo's eruption in the Philippines ejected a staggering 20 million metric tons of SO 2 into the stratosphere which resulted in an aerosol cloud covering most of the Earth within a few months after the eruption. In this article we illustrate how the seasonal trends of global, direct and diffuse solar radiation were modified by the eruption in two mid-latitude sites in Europe and the U.S., totalling about 12 yr of hourly data. A spectacular increase in the diffuse fraction of solar radiation as opposed to a decrease in direct radiation which extended from late 1991 to mid 1993 was observed in both sites and for clear sky conditions. Global radiation was not altered significantly from these data sets. Sunphotometer measurements in one of the sites show the volcanic aerosols tripled the total atmospheric aerosol optical depth at 1 μm and approximately doubled the aerosol optical depth at 0.5 μm.