Hanno Ohvril

Column Transparency and Precipitable Water in Estonia: Variability During the Last Decades Hanno Ohvril

Multiannual changes in atmospheric column transparency, based on measurements of direct solar radiation and precipitable water express various tendencies in climatic changes. Time series of atmospheric transparency are calculated for Estonian, Spanish, Russian and Kyrgyzian stations covering together a 70-year period. The comparison of time series revealed that decrease in ransparency during 1962?1984 coincides with extensive development of industry, energetics, transport and agriculture. The trend ends with a steep decline of transparency after a series of volcanic eruptions of Soufriere (1979), St. Helens (1980), Alaid (1981) and El Chichón (1982). From 1984 to 1990 the atmosphere remarkably restored its clarity, almost reaching the level of the 1960s. Following the eruption of Mt. Pinatubo (1991), there was the most significant reduction in transparency of the postwar period. The clearing from 1993 evidently indicates a decrease in the content of aerosol particles and, besides the absence of volcanic activity, may therefore be also traced to changes in technology, to general industrial and agricultural decline in the former USSR and Eastern Europe.