The sun is much more than a vital source of warmth and light. In the region between it and Earth, which we call geospace, is a constant stream of charged particles called the solar wind, flowing out from the sun at hundreds of kilometres a second. Most particles nearing our planet are deflected by Earth’s geomagnetic field, but in polar regions some plunge into our atmosphere, where they create auroras (aurora australis or southern lights in the Southern Hemisphere). The charged solar wind blowing past Earth also generates large voltages in the Antarctic atmosphere and forms huge convection cells (similar to a weather map's high and low pressure areas). These cells drive 7000 km/h winds in a region of the upper atmosphere called the ionosphere.
Occasionally, enormous eruptions on the sun blast billions of tonnes of matter into the solar wind which can wreak havoc on Earth, knocking out communications and navigation, and generating huge magnetic storms that can destroy satellites and even power grids. At such times the auroras expand out away from the polar regions and can even be seen as far north as Brisbane.
Understanding and predicting all these effects falls into a category of science now called ‘space weather’. Physicists from the Australian Antarctic Division and other Australian institutions have installed two radar instruments for studying space weather — a digital portable sounder (digisonde) at Davis, Antarctica, and the Tasman International Geospace Environment Radar (TIGER) in southern Tasmania.
The Davis digisonde is a high frequency radar system using radio waves to probe the ionosphere up to a height of around 600km. It ‘sounds’ the ionosphere to measure a vertical profile of ion concentration (an ionogram), which is used by Australia’s IPS Radio and Space Services to forecast space weather for communication and polar aviation purposes. The digisonde can also measure ionospheric wind speeds and identify disturbed regions.
TIGER is an over-the-horizon radar system whose beam, sweeping over the Southern Ocean, yields data on the ionosphere over thousands of square kilometres to the shores of Antarctica. Its location makes the TIGER radar ideal for keeping an eye on the auroral oval and polar convection patterns, potentially generating warnings of an approaching magnetic storm. Like the digisonde, TIGER can also measure upper atmosphere wind speeds and study irregularities there.
Both the digisonde and TIGER will further our understanding of processes in the Earth’s geospace environment, and be of major importance in the forecasting of space weather.