Planetary Waves and Ozone Holes

Newman was the lead author of a paper published in September 2001 which presents satellite and meteorological data linking planetary waves to bursts of warming registered in the Arctic - a connection that scientists long-ago recognised but have only now quantified. (His paper appeared in the September 16th issue of Journal of Geophysical Research - Atmospheres.)

"Typically a wave will warm the polar region by 5° to 10° C," Newman continued. "A 'warm' polar stratosphere is typically in the temperature range -73° to -63° C. Of course, as soon as the wave has dissipated, the polar region begins to cool down again."

Credit: Lamont Poole, NASA Dangerous beauty. Polar stratospheric clouds (PSCs) are common in Antarctica, but a rare sight in the Arctic. They form when temperatures in the stratosphere become extremely cold - below -78° C. PSCs spell trouble for ozone; tiny ice crystals and droplets within the clouds provide surfaces where CFCs are converted into ozone-destroying molecules.

Indeed, planetary waves in the northern hemisphere don't always heat the stratosphere enough to prevent substantial ozone destruction. In 1997, for example, the waves were weak because of capricious weather. That triggered a rare springtime ozone hole over the Arctic.

Scientists are concerned that climate change could make such times more common. "If our models of Arctic stratospheric cooling are correct, we would expect lower ozone values across the Arctic during this century," says Newman.

It so happens that stratospheric cooling can be a curious result of global warming. Greenhouse gases, which trap the heat radiating from Earth's surface in the lowest layer of the atmosphere, reduce the heat that reaches the stratosphere. In effect, greenhouse gases cool the stratosphere by insulating it from the warmer Earth below.