The seasonal ozone declines continue.

It's that time of year again, when the ozone over Antarctica grows almost as sparse as the hair on a balding man's head and provides little more protection against the sun's cancer-causing rays.

So far, however, this year's ozone measurements are producing a confused picture. Data taken from a U.S. spectrometer flown aboard a Russian satellite suggest that the protective layer has thinned almost as much as it did last October, researchers told SCIENCE NEWS. But data from instruments on balloons sent into the stratosphere hint that things aren't that bad.

The ozone layer helps guard Earth from the sun's damaging ultraviolet radiation. In the spring, when sunlight finally reaches Antarctica, the protective blanket of gas thins as light activates chlorine and bromine particles, which help break apart ozone molecules. By November, as the polar stratosphere warms, the hole begins to mend. Concentrations of ozone should bottom out around Oct. 10, says Samuel J. Oltmans of the National Oceanic and Atmospheric Administration in Boulder, Colo.

Last October's record-breaking 70 percent drop in ozone probably resulted in part from the dose of sulfur dioxide that Mt. Pinatubo shot into the stratosphere when it erupted in 1991 (SN: 10/16/93, p.247).

In the last 2 weeks, the low recorded by researchers using the balloon instruments was 103 Dobson units of ozone -- about 10 percent more than last year at the same time, Oltmans says. This slight increase doesn't suggest a permanent comeback for ozone, he warns. The data have a margin of error of plus or minus 4 Dobson units.

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Satellite records suggest that the rate of ozone decline has almost matched last year's, says Arlin J. Krueger of NASA's Goddard Space Flight Center in Greenbelt, Md. He and his colleagues recorded a low of 100 Dobson units of ozone on Sept. 30 and expect it will drop to last year's low of 90, he says. The margin of error is 10 Dobson units.

The ozone hole has become more extensive in the past few years. It now covers about 23 million square kilometers, roughly the size of North America.