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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.

Solar radiation fluxes at the surface of the Baltic Proper. Part 1. Mean annual cycle and influencing factors

Rozwadowska A., Isemer H. J.

Oceanologia

1998

No. 40 (4)

307-330

Meteorological observations made on board Voluntary Observing Ships in the period 1980-1992 are used to estimate the climatological characteristics of the solar radiation flux at the surface of the Baltic Proper. A semi-empirical model developed for the Baltic region is used. Monthly and annual means of solar radiation fluxes reaching the sea surface, averaged over the northern, southern and western parts of the Baltic Proper are calculated. Seasonal and interannual variability of the fluxes as well as the impact of both meteorological and astronomical factors on the monthly and annual means of the fluxes are also analysed. The annual mean irradiance for the entire Baltic Proper is estimated at 117 ( ±4) W m-2. The long-term monthly means for this area vary from 12 (±4) W m-2 in December to 241 (±21) W m-2 in June.