Climate of the polar realms - The Global Climate System: Patterns, Processes, and Teleconnections - page 131

Chapter 5
Climate of the polar realms
5.1 Introduction
Gerd Wendler, University of Alaska
The polar regions are defined as the areas north of the Arctic Circle and south
of the Antarctic Circle. These regions represent the sinks in the global energy
system of planet Earth. They have a number of common characteristics such
as cold temperatures, ice covered oceans, glaciers and ice sheets. Both areas
display an extreme seasonal variation in day length, with continuous daylight
and darkness of up to six months. However, there are also large differences
between the two regions, which are caused mainly by their geographic
settings. In the Arctic there is a centrally located Arctic Ocean, which is
surrounded by continents, while in Antarctica there is a centrally located con-
tinent, which is surrounded by oceans. Consequences of this are that Antarctica
is covered by an ice sheet, and only some 2%of its area is ice free, while the only
extensive ice sheet in the north can be found in Greenland. Owing to the high
altitude of Antarctica - it has the highest mean elevation of all continents due to
the snowand ice accumulation - the temperatures drop to very lowvalues and in
Vostok, a Russian inland station, a minimum temperature of 89.5 8C has been
observed, the coldest temperature measured on Earth. This value is much lower
than anything measured in the Arctic, where the coldest temperatures are found
in Siberia. Sea ice is, on average, much thinner in the Southern Ocean, which at
first glance might be surprising. However, here the sea drifts steadily north into
the South Pacific, Indian and South Atlantic Oceans where it melts. In contrast
to this, the Arctic Ocean has a much thicker ice cover and multi-year sea ice is
common, as the continents prevent a southward drift with the exception of the
Bering Strait and the Northern Atlantic Ocean.
The temperature differences between the tropics (see Chapter 3 ) and the
polar regions are, of course, the driving force of the general circulation
systems. In Figure 5.1 the radiative budget on top of the atmosphere is
shown, the tropics and the subtropics being the areas with an energy surplus.
The energy is lost in mid-latitudes and especially in polar regions. The
resultant poleward energy transfer for equilibrium, both by the atmosphere
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