Geoscience Reference
In-Depth Information
Figure 24.2
Important physical limits in the
Antarctic: the 10°C January
isotherm, the Antarctic
convergence and the northern
limit of pack ice in winter.
Antarctic convergence
10°C January isotherm
Antarctic circle
Winter pack ice
Australia
Permanent pack ice
Pacific Ocean
Ross Sea
West
Antarctica
East
Antarctica
South
America
Weddell
Sea
Falkland
Islands
Southern
Ocean
South
Georgia
Indian Ocean
0
1000
Atlanti c Ocean
km
The climate of Antarctica is dominated by the vast and
deep ice sheet covering over 97 per cent of the continent.
At the end of winter there is a belt of sea ice averaging up
to 1 m in thickness covering about 20 M km
2
of the
southern ocean, but a large proportion of this melts in
summer. The ice plateau reaches over 3,500 m in height,
so its climate is severe. At the south pole the mean summer
temperature is only -28
C, dropping to -58
C in winter
and -89
CLIMATE
Mountain meteorology
Mountains cover 20 per cent of Earth's terrestrial
surface, yet mountain weather and climate often receive
scant attention beyond their role in generating major
disturbances in planetary atmospheric waves and the
phenomena of valley winds. Comprehensive mountain
meteorological data are limited by mountain remoteness,
low population density and instrumental failure due to the
harsh climate. Beyond a systematic decline in temperature
with altitude and a parallel tendency towards higher
relative humidity, cloud cover and precipitation, moun-
tain
topoclimates
provide a mosaic of rapid spatial and
seasonal change. They are difficult to map accurately
and many parameters are susceptible to significant feed-
back from the geomorphic and vegetation surfaces which
they promote. However, we must grasp their climatic
character to understand the true nature of mountain
environments.
C has been recorded in midwinter at Vostok
(3,500 m). Around the coastal margins the southern
westerlies provide some warmer influence and much more
precipitation. Mean summer temperatures are near
freezing point and mean annual precipitation can reach
800 mm. It is a cloudy zone with much pressure and
weather variability associated with the migrating pressure
systems. One of the noteworthy features of the Antarctic
climate is the katabatic wind. It blows like a density
current of cold air off the ice sheet and merges with the
tropospheric polar vortex. Locally these winds can be
funnelled into the coastal valleys to give extreme climatic
conditions. At Cape Denison (67
S, 143
E), average daily
wind speeds of
18 m s
-1
were recorded on over 60 per
cent of days between 1912 and 1913.
