Geoscience Reference
In-Depth Information
Figure 5.10.
Mean monthly total cloud radiative forcing at the surface (Wm
−2
) for
the four mid-season months based on ISCCP-D data (courtesy of J. Key, NOAA,
Madison, WI).
radiation, albedo, incoming shortwave radiation, and incoming longwave radiation.
The SHEBA results are given along with estimates from several other studies. The
reader is referred to Persson et al. (
2002
) for details.
The annual cycle of net radiation at the SHEBA site shows a peak of about 80
W m
−2
in July, and a minimum of about −15 W m
−2
in January, the latter of course
driven by the longwave deficit. Note how the July maximum in net radiation coin-
cides with the July minimum in surface albedo (of about 0.56), rather than the June
maximum in the downward shortwave radiation (of about 280 W m
−2
). This is in
agreement with the satellite-based results presented earlier. It is estimated that for
ice of 1-2 m thick (as in the SHEBA region), during July and August, from 1-7
W m
−2
of solar radiation penetrates the ice into the ocean. The incoming longwave
flux varies between 150 W m
−2
in December to about 300 W m
−2
during July and
August. As discussed, this reflects the seasonality in lower-tropospheric air tem-
perature, water vapor content, and cloud cover. Although the general shapes of the
annual cycles at the SHEBA site are similar to those from previous estimates, there
