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Solar radiation at the surface in the Baltic Proper

Keevallik S., Loitjärv K.

Oceanologia

2010

No. 52 (4)

583-597

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.

Solar radiation fluxes at the surface of the Baltic Proper. Part 2. Uncertainties and comparison with simple bulk parametrisations

Isemer H. J., Rozwadowska A.

Oceanologia

1999

No. 41 (2)

147-185

An adjusted version of the semi-empirical model developed by Rozwadowska (1991) was applied to calculate monthly and annual estimates of incident solar radiation fluxes at the surface of the Baltic Proper during 1980 to 1992 using voluntary observing ship meteorological observations from COADS as input data. The semi-empirical model was specifically calibrated using measurements from the Baltic Proper region. In Part 1 of this study we described the resulting solar radiation flux climatology for the Baltic Proper as well as for its three sub-basins. In this second part, we give estimates of the overall random and systematic errors of the climatological flux results, apply simple bulk parametrisations to the same COADS ship observations, and compare the results with those of the semi-empirical model presented in Part 1. This comparison shows that bulk parametrisations calibrated both in purely marine and in continental environments elsewhere on the globe produce surface radiation climates over the Baltic Proper which deviate systematically, in a seasonally and regionally varying manner, from the results of the semi-empirical model. We present evidence to show that the differences found may be due both to physical reasons and to problems with the calibration methodology. This indicates that the atmospheric conditions over the Baltic Sea require specific, regionally calibrated models and parametrisations for solar surface radiation. We suggest that international efforts be made in order, firstly, to build up inventories and accessible data compilations of existing surface radiation records from the Baltic Sea, and secondly, to initiate additional surface radiation measurement activities based on internationally accepted and co-ordinated strategies. The planned intensive observational and modelling phase of BALTEX scheduled for the years 1999 to 2001 (BRIDGE) would be an ideal start for such initiatives.