Distribution of net radiation

The net allwave radiation (or more simply net radiation) is the sum of the shortwave and longwave fluxes (Equation 5.1). Fields of net radiation based on ISCCP-D for the four mid-season months are provided in Figure 5.6. Values across the Arctic are negative from October through March. During polar darkness, the fields are of course essentially identical to those for the net longwave flux. For April, the ISCCP-D fields indicate that net radiation is slightly positive over the Arctic Ocean. The downwelling solar flux is significant for this month, with central Arctic values ranging from 100 to 130 W m-2 (Figure 5.1). However, the high albedo of the surface means that most of this solar

Kolorowanki Druku Trudne
Figure 5.6 Mean monthly net allwave radiation at the surface (W m 2) for the four mid-season months based on ISCCP-D data (courtesy of J. Key, NOAA, Madison, WI).

energy is lost back to space. June values of net radiation (not shown) over the central Arctic Ocean are about 80-95 Wm-2 compared to about 85-100 W m-2 in July. This asymmetry with respect to solar declination is largely due to albedo. While solar radiation peaks in June, this is offset by the lower albedo in July. Over land areas, the flux peaks in June. July fluxes over land areas typically range from 115 to 140 W m-2.

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