Antarctic Ozone Hole Shrinks, Divides in Two

GREENBELT, Maryland, September 30, 2002 (ENS) - The ozone hole over the Antarctic this September is not only smaller than it was in 2000 and 2001, but has split into two separate holes, according to scientists in the United States and Europe.

Every year since 1979, the return of sunlight to the high latitudes of the Southern Hemisphere has produced massive depletion of ozone over Antarctica. This year, the hole is smaller than at any time since 1988, atmospheric scientists say.


Ozone depletion over Antarctica September 24, 2002 (Photo courtesy NASA's Goddard Space Flight Center)
Scientists from the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) say the smaller ozone hole over the Antarctic is due to this year's warm stratospheric weather patterns.

Paul Newman, a lead ozone researcher at NASA's Goddard Space Flight Center, Greenbelt, Maryland, said this year, warmer than normal temperatures around the edge of the polar vortex are responsible for the smaller ozone loss.

"The Southern Hemisphere's stratosphere was unusually disturbed this year," said Craig Long, meteorologist at NOAA's Climate Prediction Center.

The unusual weather patterns were so strong, the ozone hole split into two pieces during late September.

The Climate Prediction Center has been monitoring and studying the ozone since the early 1970s. "This is the first time we've seen the polar vortex split in September," said Long.

"This breakdown is occurring exceptionally early in the year, about two months earlier than normal," confirmed Henk Eskes, a senior scientist at the Royal Netherlands Meteorological Institute. "The depth of the ozone hole this year also is unusually small, about half that recorded in 2001."

Last September, the Antarctic ozone hole was larger than the combined area of the United States, Canada and Mexico - about 24 million square kilometers (nine million square miles).

This year it measures about 15 million square kilometers (6 million square miles) - a little larger than Antarctica.

The stratosphere is that part of the atmosphere about six to 30 miles above the Earth's surface where the ozone layer is found. The ozone layer prevents much of the sun's harmful ultraviolet radiation from reaching the Earth's surface. Ultraviolet radiation is a primary cause of skin cancer.

Since the early 1980s, the Antarctic ozone hole has developed every year starting in August or September. Depletion is caused by chlorine compounds such as chlorofluorocarbons, or CFCs, which had been used as refrigerants, solvents and foam blowing agents, and bromine compounds such as halons used to extinguish fires.

Ozone depletion occurs only at very low temperatures under the influence of solar radiation. As a result, the ozone hole only appears over the cold region of Antarctica, when the sun returns after the polar winter.


Ozone hole over Antarctica, September 2000. (Photo courtesy NASA's GSFC)
The coldest temperatures over the South Pole typically occur in August and September. Thin clouds form in these cold conditions, and chemical reactions on the cloud particles help chlorine and bromine gases to rapidly destroy ozone.

By early October, temperatures usually begin to warm, and thereafter the ozone layer starts to recover.

The Montreal Protocol and its amendments banned some chlorine and bromine compounds in 1995, because of their destructive effect on the ozone layer. But CFCs and halons still linger at high concentrations in the atmosphere.

Although the ozone hole is smaller this year, scientists are warning that a single year's unusual pattern does not make a long term trend.

Despite the optimistic forecast, Eskes warned the possibility that one of the two remnants will strengthen and form a new ozone hole "cannot be excluded."

The Dutch national research and information center for climate, climatic change and seismology, uses data from the European Space Agency's Global Ozone Monitoring Experiment instrument onboard the ERS-2 satellite to generate daily global ozone analyses and nine day ozone forecasts.

NOAA and NASA continuously observe Antarctic ozone with a combination of ground, balloon, and satellite based instruments.