EVOLUTION OF SOLAR RADIATIVE EFFECTS OF MOUNT-PINATUBO AT GROUND-LEVEL

The field research reported here contributes to the documentation on t he effect of stratospheric aerosols produced by the 1991 eruption of M ount Pinatubo. Using ground-based data obtained at 2 radiometric stati ons, located at very different latitudes (Estonia and Spain), we have studied the evolution of the Pinatubo eruption effects. Following the eruption of Mount Pinatubo there is a significant reduction in direct solar radiation, of about 10% in Almenria (Spain) and 7% in Tiirikoja (Estonia). The maximum reduction, of about 15% and 9% respectively, is measured during the 1991-92 winter. The aerosol optical depth in Alme ria presents, aside from the seasonal dependence, evident influences d ue to the volcanic aerosol cloud. We have tried to isolate this last e ffect. As a result, we have found that the 1991/1992 winter presented the maximum volcanic effects, with a decay along 1992 and a recovery i n the 1992/1993 winter. These results are in agreement with more sophi sticated studies of the aerosol cloud effects. By the 1993-1994 winter , our analysis shows evidence of a recovery of pre-eruption conditions confirmed by the aerosol optical depth behaviour during 1994. The ana lysis of Tiirikoja data set using an atmospheric integral transparency coefficient leads to similar results. The volcanic aerosol effect sho ws an exponential decay in both locations estimated at 8.6+/-1.9 month s for Almeria and 8.9 +/- 3.5 months for Tiirikoja.