Edited by Rachel Duncan 4th Edition ISBN 0-907649-91-2 London ...

1.3.4 Precipitation
Figure 1: Wind Chill Index
The Polar Environment 9
High latitude areas are often deserts due to the limited capacity of cold air to hold
moisture. The northern part of Greenland is one example but the most extreme case is
Antarctica where annual precipitation may be 30–40cm around the coasts but only 5–10cm
inland. Even on sunny days blowing snow (spin drift) can impede travel. Most of the snow
causing loss of visibility is old snow raised from the surface by wind with speeds as low as
10 knots obscuring ground features and crevasses. A speed of 30 knots causes blizzards
and complete loss of visibility.
1.3.5 Visibility
Under good weather conditions polar air can produce visibility limited only by the
curvature of the Earth and beyond by refraction. The estimation of distance by eye is thus a
matter requiring extreme caution by the inexperienced. Objects are likely to be much
further away than you may think. A further complication may be caused by mirage, in
which distant objects are apparently raised above their natural position by instability in the
air above relatively warmer surfaces. Icebergs in open ocean are often seen raised, while
early sightings of the Antarctic continent may have been confused by this phenomenon.
This is known as Fata Morgana and is the opposite type of mirage to that experienced in
hot deserts. On the Arctic Ocean, the presence of open water can be deduced from shadows
of the dark surface water on the underside of clouds.
1.4 Climatic differences
The principal difference between the two polar regions is that the north polar region is an
ocean surrounded by (more or less) elevated land masses, while the south polar region is
itself an elevated land mass. In winter, sea ice extends the ice- covered areas and thus heat
loss, especially around Antarctica where the ice covered area approximately doubles. In
summer the melting of sea ice from the Arctic Ocean allows significant heat exchange
which is not nearly so significant in the continental mass of Antarctica. These geographical
factors cause the Antarctic region to have mean temperature values below those of the