Antarctic ozone bottoms at record low.

Antarctic Ozone Bottoms at Record Low

The infamous hole in the Antarctic ozone layer reached record proportions last week, providing a dramatic reminder of pollution's power to alter the atmosphere. The severe ozone loss largely confirms a prediction made earlier this year by a meteorologist who found a statistical connection between the tropical climate and the severity of polar ozone depletions.

Satellite measurements show that the ozone concentration in the Antarctic stratosphere -- 12 to 50 kilometers up -- reached 125 Dobson units on Oct. 4, a value on par with the record lows of 121 and 125 Dobson units set in 1987 and 1989 (SN: 9/29/90, p.198). "This is as big an ozone hole as we've seen in the past," says Arlin Krueger, of NASA's Goddard Space Flight Center in Greenbelt, Md.

Ozone molecules in the stratosphere protect life by absorbing damaging ultraviolet radiation from the sun. Every year since 1977, the ozone layer above the entire Antarctic continent has thinned dramatically during September, the beginning of springtime in that region.

The hole forms because extremely cold temperatures in this part of the stratosphere activate chlorine and bromine pollutants that chemically attack ozone molecules. Persisting for a month or two, the hole finally fills in when a breakdown of winter polar-wind patterns allows an influx of ozone-rich air.

The same pollutants are apparently thinning the ozone layer around the entire globe, although at a slower rate.

Even before ozone levels started dropping this year, meteorologist James K. Angell predicted severe depletions for 1990 in a paper published in the September GEOPHYSICAL RESEARCH LETTERS. Angell, who works at the National Oceanic and Atmospheric Administration in Silver Spring, Md., based the prediction on a statistical link he found between polar ozone loss and two variables: sea surface temperatures near the equator and a cyclic wind pattern called the Quasi-Biennial Oscillation (QBO).

The QBO refers to stratospheric winds that circle the equator and reverse direction about every 13 months. To examine the QBO since 1958, Angell used records of stratospheric temperatures over Singapore, which indicate the direction and strength of the equatorial stratospheric winds.

Angell concentrated on temperature measurements for June, July and August. He found that when both equatorial stratospheric and sea surface temperatures increased from one summer to the next, ozone depletions in October and November were worse than the year before.

Since both stratospheric and sea surface temperatures near the equator rose over the past year, Angell predicted severe depletions for 1990. Several researchers previously have sought a QBO-ozone connection, but none had looked at both winds and sea surface temperature.

Angell's discovery has intrigued scientists, who do not know why equatorial conditions should influence ozone loss in Antarctica. "At this point, there is no good dynamical explanation for the connection between the QBO and the ozone hole," says Paul Newman of NASA Goddard. If the statistical relationship proves real, it can help researchers model and predict polar ozone loss.