New telescope aids climate studies

Anew telescope recently installed on the Davis LIDAR (Light Detection and Ranging), is enhancing the quality of climate-related data collected by the instrument. The new data will be used in the international Climate and Weather of the Sun-Earth System Programme to examine large-scale climate processes in the Antarctic atmosphere.

The LIDAR uses laser light to remotely sense atmospheric temperature as well as the properties of aerosols (fine solid particles and large molecules) from near the ground to about 100 km altitude. The new telescope allows us to collect more laser light that is scattered back from the atmosphere than before, extending the altitude range of the instrument and reducing the amount of time needed to attain more precise measurements.

One focus of the LIDAR research programme is on the temperature structure of the atmosphere. In the figure (right), temperatures obtained by the LIDAR above 25 km altitude are shown combined with measurements from balloons (radiosondes), flown by the Bureau of Meteorology. Part of the seasonal cycle in the lower atmosphere can be seen, with temperatures cooling to as low as -95°C during winter. At altitudes above 45 km, warm summer temperatures earlier in the year gave way to considerable variability, particularly in late winter and early spring. During July and August, the variability was associated with ‘planetary-scale’ waves which periodically influenced temperatures above Davis every 15 days or so. These waves are natural atmospheric oscillations that arise in the polar region due to climate processes occurring in the lower atmosphere.

It is becoming apparent that planetary-scale waves propagating in the stratosphere (10–50 km above the Earth) can influence weather patterns at the surface. This is important in developing long-range weather and climate forecasts, as planetary wave propagation at high latitudes is expected to be influenced by changes in atmospheric circulation associated with global warming and ozone depletion. Indeed, changing rainfall patterns in Australia have been linked with a shift in stratospheric circulation patterns over Antarctica.

The LIDAR will continue this observing programme during 2006, when an additional telescope will be installed to further investigate stratospheric processes.

ANDREW KLEKOCIUK, JOHN INNIS and ANDREW CUNNINGHAM, Ice, Oceans, Atmosphere and Climate Programme, AAD

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