Climate of extremes - Antarctica: Global Science from a Frozen Continent - page 129

Box 4.6 Weather forecasting for a mid-winter rescue flight to

the South Pole

In addition to crosswinds and reduced visibility, the extremely cold temperatures
at the South Pole also present a signi

cant aviation hazard. At very cold

temperatures the hydraulic fluid used in aircraft to operate rudders and wing

flaps begins to congeal and cannot be used, making landing or taking-off
impossible. As a result of the cold temperatures, the normal flight season at the

South Pole is quite restricted (October to February). When the last

flight leaves in

February no further flights will arrive for 9months. During the winter of 2001,

the doctor at South Pole station, Dr Ronald Shemenski, began to suffer from
pancreatitis and gallstones. Medical treatment for this was not possible on the
station, and he needed to be evacuated during the winter.
The United States Antarctic Program contracted with Kenn Borek Air Ltd. of
Canada to carry out the rescue

flights using ski-equipped Twin Otter aircraft.
Two Twin Otter aircraft departed Canada in April of 2001 and ew south to

Punta Arenas, Chile and then on to the British station of Rothera on the
Antarctic Peninsula. The flight from Rothera to the South Pole is a 10-hour ight

in a Twin Otter, and the aircraft waited at Rothera for a forecast of suitable
weather for a round trip. Both United States and British weather forecasts relied
on weather observations and a suite of numerical weather prediction models to
make their forecast for this unprecedented mid-winter

flight to the South Pole.
One of the Twin Otter aircraft arrived at the South Pole on 24 April, with the
second Twin Otter aircraft staying at Rothera to provide support in case of
problems. The Twin Otter returned to Rothera, with Dr Shemenski on 26 April,
approximately 34 hours after ight

would not have been possible without an accurate weather forecast that was able
to predict a lull in the winds, and blowing snow at the South Pole that lasted only
slightly longer than the length of the mission.

first leaving Rothera. This mid-winter rescue

The Antarctic ozone hole

In 1985 British scientists announced the discovery of reduced amounts of ozone over
the Antarctic continent during the spring months. Surface-based observations of
ozone conducted at Halley station indicated that ozone amounts had been
decreasing since 1977, but there was concern that satellite measurements of ozone
made during the same time period did not indicate a similar decrease. Upon closer
inspection of the satellite data it was found that the algorithm used to process the
satellite data was rejecting the low ozone values observed by the satellite as the values