Antarctic ozone hole returns with a bang.Antarctic ozone hole ozone hole
An area of the ozone layer, such as the large area over Antarctica or the smaller area over the North Pole, that periodically becomes depleted of ozone. returns with a bang
'Tis the season for ozone depletion Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since around 1980; and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions over the Antarctic, and this year's ozone hole is developing at record speed. Ozone has rapidly dwindled in the Antarctic stratosphere despite weather conditions resembling those that checked the growth of an ozone hole in 1988.
'Tis also the season for satellite setbacks, and NASA's main ozone-sensing instrument is threatening to die of old age before the agency can launch a replacement -- a situation that would drastically hamper efforts to monitor ozone loss over the entire globe.
The stratospheric strat·o·spher·ic
1. Of, relating to, or characteristic of the stratosphere.
2. Extremely or unreasonably high: "money borrowed at today's stratospheric rates of interest" ozone layer ozone layer or ozonosphere, region of the stratosphere containing relatively high concentrations of ozone, located at altitudes of 12–30 mi (19–48 km) above the earth's surface. protects life on Earth by blocking out much of the sun's damaging ultraviolet radiation before it reaches the planet's surface. Every September since the late 1970s, the Antarctic has experienced a temporary but dramatic loss of ozone. The ozone hole develops because extremely cold conditions in the polar stratosphere help chlorine and bromine bromine (brō`mēn, –mĭn) [Gr.,=stench], volatile, liquid chemical element; symbol Br; at. no. 35; at. wt. 79.904; m.p. –7.2°C;; b.p. 58.78°C;; sp. gr. of liquid 3.12 at 20°C;; density of vapor 7. pollutants to destroy ozone through chemical processes.
Balloon measurements made above Antarctica's McMurdo Station McMurdo Station is the largest community in Antarctica (capable of supporting up to 1,258 residents) and a science research center operated by the United States through the United States Antarctic Program, a branch of the National Science Foundation. indicate that stratospheric ozone levels this year have dropped as swiftly as they did in 1987 and 1989 -- two years when ozone reached its lowest recorded level (SN: 10/14/89, p.246), says David J. Hofmann of the National Oceanic and Atmospheric Administration Noun 1. National Oceanic and Atmospheric Administration - an agency in the Department of Commerce that maps the oceans and conserves their living resources; predicts changes to the earth's environment; provides weather reports and forecasts floods and hurricanes and in Boulder, Colo.
In early September, the rate of ozone loss exceeded even that of 1987 and 1989, according to measurements by the Total Ozone Mapping Spectrometer The Total Ozone Mapping Spectrometer (TOMS) is a satellite instrument for measuring ozone values. Of the five TOMS instruments which were built, four entered successful orbit. (TOMS) aboard NASA's Nimbus 7 satellite. "It's clear that the ozone is somewhat lower this year than it was last year at the same time," says Arlin J. Krueger of the NASA NASA: see National Aeronautics and Space Administration.
in full National Aeronautics and Space Administration
Independent U.S. Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory established on May 1, 1959 as NASA's first space flight center. GSFC employs approximately 10,000 civil servants and contractors, and is located approximately 6.5 miles northeast of Washington, D.C. in Greenbelt, Md. TOMS data show that the minimum ozone level over Antarctica plummeted from 200 Dobson units in mid-August to 133 Dobson units in mid-September.
Ozone losses normally continue through the early part of October. Scientists say they cannot predict whether this year's ozone layer will thin to the same extent it did in 1987 and 1989, when levels reached a minimum value of around 103 Dobson units.
The amount of ozone lost so far this year already exceeds the total lost in 1988, a year when several large weather patterns formed in the Southern Hemisphere and disturbed the Antarctic vortex -- a ring of winds circling the pole that seal off the Antarctic stratosphere. In 1988, the weakened vortex let in winds from the midlatitudes, which kept the stratosphere relatively warm and inhibited the development of a strong ozone hole.
Similar but weaker weather patterns developed this year, disrupting the Antarctic vortex to some degree in late August and early September. Because dramatic ozone losses occurred during the same period, scientists now wonder whether weak atmospheric disturbances might sometimes enhance the growth of ozone holes.
At the same time, many researchers express concern that the aging TOMS instrument may be approaching death's door. Launched in 1978 with a planned lifetime of two years, the monitoring device is plagued by a rotating wheel that occasionally drifts out of sync with other parts. The problem has affected TOMS on and off since 1984, but this summer "was by far the most severe episode," says Krueger.
Data collected during these episodes remain usable, but eventually the drift will worsen and TOMS will send only static back to Earth. NASA plans to launch the old design model for TOMS on a Soviet satellite in 1991 as a stopgap until a new instrument goes up in 1993. Researchers want to check the calibration of the current TOMS against another model in order to resolve questions about how much the global ozone layer has thinned since the late 1970s, but if the present instrument fails before a replacement arrives, the calibration opportunity will be lost.