Climate of the polar realms - The Global Climate System: Patterns, Processes, and Teleconnections - page 159

shallow and discontinuous, permafrost is melting. However, these occur-
rences are a function not solely of observed temperature increase, but also
of the snow cover. Snow cover insulates the soil from the air, hence the
amount as well as the distribution over the season are important. A heavy
snowfall in autumn will insulate the soil from the cold winter air temperature.
A similar snowfall in spring will have much less of an effect on the soil
temperature.
The katabatic wind, which dominates the surface climate of Antarctica, is
widespread in Greenland. However, neither the persistence nor the intensity
is as high as in Antarctica. Greenland's surface radiation budget is less
negative, and further, the fetch area does not have the same dimension as in
Antarctica. A smaller cousin of this wind is the glacier wind, which is often
observed on mountain glaciers. The air directly over the glacier surface is
cooled by the snow and ice, while the air in the surrounding valley warms up
during a summer day. The air over the glacier being colder (heavier) starts
moving down the glacier, a phenomenon well known to mountaineers.
5.8.3 Sea ice
The annual variation in sea ice extent is much less pronounced in the Arctic
when compared to Antarctica. This is, of course, an effect of the geography,
as the Arctic Ocean is surrounded to a great extent by land masses. The
greatest variation is found in the peripheral seas, namely the Sea of Okhotsk,
the Bering Sea, Chukchi Sea, Davis Strait, Baffin Bay, Greenland Sea,
Norwegian Sea and Barents Sea. Some of these areas are located south of the
Arctic Circle, and do not belong to the Arctic proper. In the Arctic Ocean the
sea ice is mostly multi-year ice with a thickness of about 3 m. In summer, it
melts at the surface, and in winter new ice is formed at the bottom; Russian
scientist have been especially active in this field (Makshtas 1991 ).
Observations from land and from ships go back to the nineteenth century,
but systematic high quality satellite observations have been obtained for
about three decades. The annual maximum in ice extent for the Arctic
Ocean and the adjacent seas is normally reached in February with 14 mil-
lion km 2 , the minimum in late August with about half this value.
A number of sea ice studies have been carried out, and the majority of these
show a decrease in ice concentration, both for the Arctic Ocean and for the
surrounding seas; however, the variations in ice extent are large from year to
year. Further, the ice thickness has decreased, as shown by submarine cruises
below the sea ice and anchored buoys, both being equipped with upward
looking sonar (Rothrock et al. 1999 ). On the other hand, a more recent study
doubts the magnitude of the frequently cited rapid thinning of sea ice
(Holloway and Sou 2002 ) and states that the volume of sea ice in 2000 was