Trend analysis of 41 years of sunshine duration data for Turkey

Accurate knowledge of solar irradiation reaching the earth s surface is one of the most important pieces of information to use in global warming studies. In this respect, trend analysis of solar irradiation data for the long term is an essential evaluation method of climate change. Sunshine duration data have been recorded for many years, directly correlated to solar irradiation. Therefore, trend analysis of sunshine duration data is also an important research topic of climate change. Global research from di erent regions of the earth showed diming (1950s to about 1980s) and brightening (about 1980s to recent years) periods in solar irradiation. The present work aims to obtain the trends of the measured sunshine duration over Turkey. Seasonal and yearly bright sunshine hours of 36 selected stations are used and quite similar trends are seen. A decreasing trend (between 1970 to about 1990) is clearly identi ed for most of the stations. Nevertheless, the increasing period after 1990 is not so clear; however, we observed either zero trend variation or a reduction in the rate of decrease of sunshine duration for most of the locations. The decreasing period might be attributed to human-induced air pollution.