Geoscience Reference
In-Depth Information
Figure 5.1.
Mean monthly downwelling solar radiation at the surface (Wm
−2
) for
March through October, based on ISCCP-D satellite data (courtesy of J. Key, NOAA,
Madison, WI).
circles). This illustrates the dominant effects of the strong latitudinal decrease in
the clear-sky downward solar radiation for these months. April through August are
dominated by a strong asymmetric pattern. Greenland shows a pronounced peak
over its central portions from April through August. This manifests the high eleva-
tion - the atmospheric path length is smaller and the central portions of the ice sheet
are often relatively cloud free. Fluxes decrease sharply toward the Atlantic side of
the Arctic, largely because of increasing cloud fraction (
Figure 2.24
) as well as
greater cloud optical thickness.
There is also some tendency in summer for mean monthly fluxes to increase with
latitude; most apparent in June, the month of maximum radiation. For this month,
the clear-sky downward solar flux at the surface exhibits a marked increase of about
20 W m
−2
, from 65
o
N to 90
o
N. The high values over the central Arctic Ocean also
manifest the effects of the high albedo of the sea ice surface in promoting multiple
scattering between the surface and clouds. For June, ISCCP-D fluxes over the high-
