Meteorological observing and climate in the British Antarctic Territory and South Georgia: Part 1

Antarctica is a huge continent covering a similar area to the whole of Europe. It rises steeply from sea level at the coast to a vast ice plateau lying above 2000m and covering more than half the continent. The mean altitude of the continent is 2300m and the plateau reaches above 4000m at its highest. The Vinson Massif in the Ellsworth Mountains, which rises to 5140m, is the highest point of the continent. Fringing the continent are many floating ice shelves, some of which have recently broken up in response to local climate change (Abdalati, 2006). Most manned stations are at coastal sites, primarily so that stores can easily be transported to the station. All the British stations are in the British Antarctic Territory at near-coastal locations. This means that in some ways their weather is not a true representation of the continent as a whole, as it is much milder due to the influence of the sea. Automatic stations are much more widely spread across the continent and give a broader picture of the meteorology; however their record length is much shorter and they are not discussed in detail in this paper. The International Geophysical Year (IGY) of 1957/1958 provided a big impetus towards setting up continuously operated stations; more than 40 were set up, of which over a dozen are still operating today. This was the peak of manned observation in Antarctica, and since then the number of staffed stations has declined, although this is offset by an increasing number of automatic stations. Table 1 gives details of the British stations that have operated since 1903, with Figure 1 showing those currently active. A further boost to the observing network has taken place for the International Polar Year (IPY) of 2007/2008. Meteorological observations in Antarctica are of great research interest, particularly in studies of climate change. The Antarctic Peninsula region has been one of the fastest-warming regions of the planet over the last 50 years. Meteorological observations are made regularly throughout the day at most manned stations. Surface temperature, humidity, sunshine, pressure, and wind speed and direction are largely measured by automated instruments but an observer is needed to estimate the visibility and the amount, type and height of clouds, although automatic instruments are being introduced that report visibility and cloud base. The observer also needs to keep note of the weather: rain, snow, fog, gale etc., as well as more unusual phenomena such as diamond dust, haloes, mirages and the aurora australis. The observations are expressed in a numeric code and sent via geostationary satellites to meteorological centres, largely in the Northern Hemisphere, on the Global Telecommunications System (GTS), the meteorological equivalent of the Internet. At the centres, thousands of other observations from all over the world, along with data from aircraft, balloons and satellites are processed by super-computers and used to create weather forecasts. The cold atmosphere of the Antarctic makes it a good place to see some of the more unusual meteorological phenomena. Halo phenomena (Figure 2) are caused by reflection and refraction of light from the sun or moon by ice crystals in the atmosphere. They may take the form of rings, arcs, pillars or bright spots. Haloes can be seen from most countries and are normally formed by high, thin clouds. In the Antarctic another phenomena called ‘diamond dust’ also produces them. Here, because the air is so cold, ice can crystallize out of clear air near the ground. As the crystals tumble slowly to the ground, they catch and reflect the sunlight like thousands of tiny diamonds. They are not a significant source of precipitation, but do change the radiative properties of the atmospheric boundary layer and hence affect the overall mass-balance.