An analysis of the extinction of direct solar radiation on Mt. Kasprowy Wierch, Poland

Abstract

The study describes the extinction of direct solar radiation in a high mountainous region, as represented by the example of Mount Kasprowy Wierch (in the Tatra Mountains, Poland), in the period of 1964–2003. The location is specific due to its high elevation (1991ma.s.l.) and lack of significant local sources of industrial pollution. The data used for this study had been made available by the Institute of Meteorology and Water Management (Poland).The extinction of solar radiation was expressed by means of Linke's turbidity factor (TL2), the atmospheric transparency coefficient (p2) and Ångström's turbidity coefficient (βL2). Changes in individual optical characteristics of the atmosphere were presented in diurnal and annual courses and in distinguished long-term periods. In a diurnal course, the smallest extinction of solar radiation in the studied period occurred before midday (TL2=2.17), whereas in the afternoon its value increased (TL2=2.40). In an annual course, not unlike in a number of other locations where such studies had been carried out, the atmosphere was the most transparent to solar radiation in the winter (TL2=1.96) and the least in the summer (TL2=2.86). In a multi-annual course, divided into two long-term sub-periods, less extinction of solar radiation occurred in the second of these (1994–2003).Several factors, both natural and anthropogenic, contributed to the improvement in the optical state of the atmosphere in the second sub-period. A decrease in volcanic activity observed at that time is one significant natural factor, whereas in the case of the anthropogenic factors, a substantial reduction of atmospheric emissions resulting from social and political transformations in Central and Eastern Europe is an important aspect. These transformations had triggered considerable economic changes, with reduced emissions being one of the outcomes.The extinction of solar radiation was also juxtaposed with the prevailing air masses. The smallest atmospheric turbidity was found in arctic air masses (TL2=2.07), whereas the greatest turbidity was characteristic of tropical air masses (TL2=2.69).