Solar radiation at the surface in the Baltic Proper

Radiation data recorded at 12 sites around the central part of the Baltic Sea during 1996-2000 drawn from the BALTEX (Baltic Sea Experiment) meteorological data archives are used to study the spatio-temporal variability of daily global radiation totals. The annual average daily global radiation total varies from about 10 MJ m-2 at Visby (on Gotland) and Kołobrzeg (on the coast of Poland) to less than 9 MJ m-2 at Zi-la-ni (inland Latvia), Šilute. (Lithuania) and Jokioinen (Finland). The monthly average daily global radiation total over the whole region extends from 0.93 in December to 19.0 in June. The variability in global radiation is analysed on the basis of the fraction of the daily total at the top of the atmosphere. The spatial and temporal variability is the least in August - this shows that the variation in the cloud cover and atmospheric properties at this time of year is the smallest. The spatial correlation is the strongest between the two Finnish stations - Vantaa and Jokioinen. It is also high between Stockholm and Norrköping, on the east coast of Sweden. The correlation coefficients are the largest over the whole area in April. Radiation data from coastal stations are compared with an earlier parameterization based on ship observations (Rozwadowska & Isemer 1998, Isemer & Rozwadowska 1999). It is concluded that in climatological research, actinometric data from Visby can be used to characterize the radiation field over the northern part of the Baltic Proper and those from Kołobrzeg to characterize the radiation field over the southern part of this sea.