Geoscience Reference
In-Depth Information
Figure 2.26.
Mean annual cycle of cloud cover (total cloud and low cloud, in %) for
the Atlantic sector of the Arctic Ocean based on ICOADS data through 1995 (by the
authors).
much of the tropospheric water vapor; and (3) in accord with the surface-based
ICOADS observations, cloud cover is particularly extensive in the Atlantic sector
for all months.
Based on surface observations, Eastman and Warren (
2010a
) show a positive
trend in Arctic Ocean cloud cover, linked to the observed decline in sea ice extent.
The relationship, however, is complex. Whereas sea ice loss may promote more
cloud cover, changes in cloud cover will also influence the ice cover. A key issue
regarding the latter is the nature of the cloud radiative forcing. As already intro-
duced, whereas clouds reduce the shortwave radiation flux to the surface, largely
through their high albedo, they increase the longwave flux to the surface. It appears
that, except in summer, the net effect of clouds is to warm the surface (the long-
wave effect wins), and the cloud changes identified by Warren and Eastman (
2010a
)
appear to have a net warming effect. This finds support in the study of J. Francis
and E. Hunter (
2006
) based on infrared sounding data from satellites. We return the
issue of cloud radiative forcing in
Chapter 5
.
2.3.7
Precipitation
Arctic precipitation is another key climate variable, which, like cloud cover, is still
inadequately determined. The density of observing stations is generally quite low,
