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SVALBARD – the most northerly outpost of Norway and home to some 3000 polar bears – is an isolated group of glacier-covered islands deep within the Arctic Circle. As we know only too well, glaciers haven’t been faring well in recent years. But it isn’t the state of the ice that is being monitored here. Instead, the vital climate change research being carried out is aimed high in the sky, to the mysterious region of the atmosphere known as the tropopause.
Stand on the surface of the Earth and your head is in the troposphere. Near the poles the troposphere is at its thinnest: about 9 kilometres thick. At the equator it is more like 17 kilometres. Above it is the stratosphere, and at the intersection between the two is the tropopause.
Monitoring the region is the SOUSY Svalbard Radar (SSR), an array of 96 Yagi antennas in Adventdalen on Spitsbergen Island, shown in the photo. SOUSY stands for sounding system: its job is to sound out the activity of the atmosphere, by measuring phenomena such as gravity waves and air turbulence. We need to know what the tropopause is doing because greenhouse gases have very different effects above and below it. “While increasing greenhouse gas concentrations contribute to warming the troposphere, the very same gases diffuse into the middle atmosphere where they act as refrigerants and therefore cause ‘global cooling’,” says Chris Hall of the University of Tromsø, Norway, who works on the SSR.
Since the altitude of the tropopause is affected both by warming from below and cooling from above it is particularly sensitive to radiative forcing, the amount of solar energy trapped in the atmosphere. “The SOUSY radar monitors parameters such as tropopause height 24/7,” says Hall. “A long-enough time series built up by this instrument helps us monitor and understand climate change in new ways.”