Geoscience Reference
In-Depth Information
Figure 5.6.
Mean monthly downwelling longwave radiation at the surface (Wm
−2
)
for the four mid-season months based on ISCCP-D data (courtesy of J. Key, NOAA,
Madison, WI).
The net longwave flux is negative in all months. Typical values over the Arctic
Ocean are −20 to −40 W m
−2
. Larger deficits are found over Greenland and land
areas, for the latter especially during summer. This implies that over land, summer
surface temperatures are fairly high while the lower troposphere remains fairly cool
and dry. The large deficits over Greenland in all months point to the high elevation
of the ice sheet. The smaller July deficits over sea ice of about −40 W m
−2
(relative
to land areas) are understood in that the melting sea fixes the skin temperature, lim-
iting the magnitude of the upward longwave flux.
5.6
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
