Climate of extremes - Antarctica: Global Science from a Frozen Continent - page 124

Figure 4.20 Meteorologist Bob Bedner

releases a weather balloon at
Amundsen - Scott South Pole Station.
These balloon launches provide a
pro le of the atmosphere and aid with
weather forecasts. (Credit: Phillip
Marzette, NSF)

atmosphere changes or if the temperature of the air changes. Since this maximum
amount of water vapour decreases rapidly with decreasing temperature, at very cold
temperatures the atmosphere only needs to contain a very small amount of water
vapour in order to be saturated. As a result the Antarctic atmosphere can be dry in
an absolute sense, that is it can contain very little water vapour, but because the
temperature is so cold it can also have a very high relative humidity. The relative
humidity over the Antarctic continent is often 90% or greater.

Weather forecasting in the Antarctic

Modern weather forecasting, whether for the Antarctic or anywhere else on our
planet, relies on a combination of current weather observations, provided by surface
weather stations, weather balloons (radiosondes), and satellite observations,
predictions from computer models of the atmosphere, and human forecasters.
Uncertainties exist with all of these elements in the Antarctic, increasing the
dif culty of producing accurate weather forecasts.

There are approximately 100 surface weather observation points in the Antarctic
while there is an order of magnitude more weather observations over the United
States or Europe, both of which cover a smaller area than Antarctica. Since the
atmosphere is three-dimensional, weather forecasters need to consider not only the
surface weather but weather data through the depth of the troposphere. A key
method of obtaining this data is from radiosondes. Radiosondes are routinely
launched twice per day and make measurements of temperature, pressure, humidity,
wind speed and wind direction. There are fewer than 20 radiosonde sites in the