Climate of the polar realms - The Global Climate System: Patterns, Processes, and Teleconnections - page 137

45.78W) is located, at which systematic measurements have been carried out
since 1905. It is, of course, located north of the Antarctic Circle, hence not a
proper polar station. The temperature record displayed an increase of 1.8 8C
for the last 98 years. The accepted worldwide value is 0.6 8C. This higher
value is in good agreement with models, which predict an enhancement in
temperature change for polar regions. The Peninsula showed even higher
values, and for the coastal stations of Antarctica proper, warming was
observed, the magnitude of which varies from station to station. Further, it
is, of course, difficult to deduce long-term temperature trends from shorter
and non-identical time periods, as temperature change with time is seldom
linear. However, a mean of about 2 8C for the last century could be obtained.
There are only two long-term interior stations: Vostok (3488 m) and Pole
Station (2835 m). The distance between the stations is 1260 km and both are
located on the high plateau of East Antarctica. While Vostok shows an
increase in temperature with time, similar to those observed for the coastal
stations, Pole Station recorded a decrease in temperature. When analyzing the
data, obvious errors in the measurements could not be detected. It is possible
to explain the opposing trend between the coastal and interior stations as due
to changed advection of warm air from the north, in which the lapse rate could
be modified. However, the observed opposing trends of the two inland
stations are difficult to explain; both stations are located at similar altitudes
over uniform surfaces of snow, hence microclimatology cannot be the culprit.
The air above the surface of Antarctica cools due to the negative radiation
balance. As the solar radiation is mostly reflected, it is unable to balance the
continuous losses in the infrared region. This process develops an inversion,
which means that the air at the surface is colder than the air above. These
inversions are common all over Antarctica, but especially well developed in
the interior in winter, in the absence of solar radiation. Phillpot and Zillman
( 1970 ) were the first to carry out a systematic study of the inversion strengths
for the Antarctic continent, which are a unique feature of Antarctica insofar as
frequency and strength are concerned. At lower latitudes inversions are less
steep and mostly limited to nighttime and winter.
Katabatic winds
If terrain is sloped, cold air close to the surface will start flowing downhill due
to its higher density, and the so-called katabatic wind is formed. Eventually,
an equilibrium between slope angle, inversion strength, and Coriolis force
will be established, which was first modeled by Ball ( 1957 ). Katabatic winds
are very common in Antarctica, and can reach very high wind speeds due to
the low roughness of the snow surface, the large fetch often in excess of
1000 km, a persistent strong inversion, and funneling due to topographic
features. They normally have their maximum speed during winter, when