Climate of extremes - Antarctica: Global Science from a Frozen Continent - page 116

Figure 4.13 Schematic of the north - south and

vertical winds over the Antarctic and mid-latitudes
of the southern hemisphere. The Antarctic katabatic
winds are seen as winds blowing from 90ºS to 65ºS
in the lowest part of the atmosphere. Where these
winds encounter the southward flowing mid-
latitude winds strong rising motion occurs, which
creates cloudy conditions near the Antarctic coast.

ning characteristic of the Antarctic climate and are
common over much of the Antarctic due to the coincidence of very cold air near
the surface and the presence of sloping terrain over much of the continent. These
katabatic winds initially

Katabatic winds are a de

flows straight downhill,
but eventually this wind is turned to the left due to the rotation of the planet. The
result is air that spirals down and to the left from the high interior of the continent.
Just as with

flow straight downhill, much as water

flowing water the katabatic winds are channelled by the underlying ice
topography resulting in them converging into in the ice sheet. The speed of

these winds increases with decreasing temperature and with increasing terrain slope,
but will also increase at locations where air from a large region is channelled through a
small area. One of these locations is at Cape Denison, where Sir Douglas Mawson

' valleys '

s
Australasian Antarctic Expedition spent two years from 1912 through 1913. As the
quote at the start of this chapter indicates, the winds at this location were unrelenting.
Peak winds in excess of 50m s 1 were not uncommon and the highest monthly
mean wind speed observed by Mawson

'

s party was 35m s 1 .
Adding to the misery of the strong winds experienced by Mawson

'

is party is
the fact that strong winds over a snow surface can result in dense blowing and
drifting snow and blizzard conditions. A blizzard occurs when strong winds result
in blowing snow that reduces horizontal visibility, and can occur even if no new
snow is falling. The frequent blizzard conditions which Mawson

'

' is party experienced

led Mawson to refer to Cape Denison as the .

The combination of steep topography and cold, dense air which engenders
katabatic winds can also cause barrier winds to develop. A barrier wind occurs when
cold, dense air blows towards a barrier, such as a high mountain range. Easterly
winds persist around the edge of the Antarctic continent. These winds eventually
encounter the Antarctic Peninsula, a steep mountainous barrier. The cold easterly
winds are slowed and eventually blocked by this terrain, increasing the air pressure

' Home of the Blizzard '