2003b, 2008, Krężel et al. 2008, Krężel & Paszkuta 2011). Calculated in accordance with the above scheme, the magnitudes characterizing the solar radiation flux through the atmosphere to the Baltic Sea surface and the parameters governing its attenuation in the atmosphere, are illustrated in map form in Figure 3. The maps in Figures 3a to 3c quantitatively illustrate the reduction in the solar radiation flux diffusing through the SCH 900776 mw atmosphere to the sea surface

and show the relevant irradiance distributions in the Baltic area over practically the whole spectral range reaching the sea surface (strictly speaking the wavelength interval 300–4000 nm). These are therefore the distributions of the following values: the downward irradiance of a horizontal plane at the top of the atmosphere E↓OA ( Figure 3a); the downward irradiance at the sea surface of solar radiation reaching the sea surface through a real atmosphere but neglecting the effect of clouds E↓OS ( Figure 3b), and the downward irradiance at the sea surface under real conditions, that is, the effect of cloudiness is taken into account during the determination of E↓S ( Figure 3c). The other maps ( Figures 3d, 3e) show distributions

of the two most important optical properties of the atmosphere, i.e. those that most strongly differentiate the surface irradiance in various parts of the Baltic

Sea. The first of these properties is the aerosol optical thickness of the atmosphere ( PLX-4720 concentration Figure 3d), which is the principal factor reducing the downward irradiance from E↓OA to E↓OS. The second property is the downward irradiance transmittance through clouds ( Figure 3e), which quantifies the reduction in the downward irradiance at the sea surface due to clouds present in the sky at the time and site of measurement from E↓OS to E↓S. Characterizing the solar radiation influx through the atmosphere to the Baltic Paclitaxel order Sea surface and the parameters attenuating this irradiance in the atmosphere, the maps in Figure 3 merely illustrate certain cases of such processes. They are typical of the hours around noon on sunny spring or summer days, when the sky is cloudless or only slightly cloudy (there are clouds over only small areas of the sea). In this particular case (11:00 UTC on 24 April 2011) the irradiance transmittance by clouds over most of the Baltic was equal to or nearly 100%. It has to be borne in mind, however, that on most days in the Baltic Sea region at different times of the year, but especially in autumn and winter, the sky is often overcast. As a result, the real irradiance during a day, even around noon, is usually very much lower and may vary spatially to a great extent.