Watching the Antarctic ozone hole
Scientists at the Royal Netherlands Meteorological Institute (KNMI) are tracking a developing ozone hole over the Antarctic using data from the GOME instrument aboard ESA's ERS-2 satellite.
Their maps and atmospheric profiles show that the hole appeared and began to grow in mid-August, and has now spread to cover an area of about 25 million km², with nearly 25 million tonnes of ozone lost. This extraordinary view of the emerging phenomenon in the Antarctic atmosphere is a product of a unique service developed by KNMI and ESA scientists, which harnesses satellite monitoring to high-speed computing to deliver global ozone maps processed in only a few hours.
Ozone helps to shield the Earth's surface from the harmful ultraviolet light rays of the sun. It is destroyed by chemical reactions with chemicals in the atmosphere - the halogen gases chlorine and bromine, and man-made CFCs. In the months of Antarctic winter, a giant swirl of circulating wind develops around the South Pole, trapping a mass of air at its heart - the eye of the storm - over Antarctica. As this still 'island' of air chills, clouds form releasing halogens. When the sun's warmth returns in Spring, its energy 'activates' these halogen atoms, which then voraciously react with the ozone, destroying it, and opening the so-called hole. In fact, the 'hole' is a thinning of the ozone layer, rather than its complete destruction.
The development of the ozone hole over the Antarctic was first spotted in the early 1980s, when its depth and extent grew rapidly, but looking back through earlier data suggests that it first appeared in 1976. The unusual atmospheric conditions over Antarctica amplify the effect of the mechanism which causes ozone depletion, so the Antarctic hole is really an early warning signal of what could happen world wide if levels of halogens and CFCs in our atmosphere continue to climb unchecked.
Monitoring the Antarctic ozone hole was only one of the reasons for developing the rapid delivery service. "The main reason for making this service available is to enable the creation of improved weather forecasts," says Ronald van der A, a senior project scientist at KNMI. "Ozone moves with the wind in the high atmosphere - we call it a stratospheric tracer. Because we can generate these three-dimensional profiles quickly, we can create moving maps from a series of snapshots, and so start to model the behaviour of the stratosphere much more accurately. We can also see events developing quickly, so if we spot a hole appearing, we can alert local scientists who can then monitor the event hour by hour using equipment carried aboard specially-launched balloons, called sondes."
Scientists emerging from their winter isolation at Antarctic bases to launch sondes will monitor the growth of the hole alongside their colleagues at KNMI who are using the GOME fast delivery service. The next few weeks will tell whether the 2001 hole overtakes previous years in extent or depth.
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