UNUSUALLY SMALL ANTARCTIC OZONE HOLE THIS YEAR ATTRIBUTED TO EXCEPTIONALLY STRONG STRATOSPHERIC WEATHER, NOAA and NASA REPORT
September 30, 2002 — Scientists from NOAA and NASA confirmed today that this September the ozone hole over the Antarctic is not only much smaller than it was in 2000 and 2001, but that the ozone hole split into two separate holes during late September. (Click NOAA satellite image for larger view of Antarctic ozone hole taken Sept. 29, 2002. Click here for latest look at ozone hole.)
Estimates of the area of the Antarctic Ozone Hole (defined as the region with total column ozone below 220 Dobson Units) from the NASA Earth Probe Total Ozone Mapping Spectrometer (EPTOMS) and the NOAA-16 Solar Backscatter Ultraviolet instrument (SBUV/2) for the last two weeks are around 15 million square kilometers (6 million square miles), well below the values of more than 24 million square kilometers (9 million square miles) observed during the past six years for the same time of year. The scientists stressed that the smaller hole is due to this year’s peculiar stratospheric weather patterns and may not be an indication that the ozone layer is recovering.
Paul Newman, a lead researcher on ozone at NASA’s Goddard Space Flight Center, Greenbelt, Md., said that this year, warmer than normal temperatures around the edge of the polar vortex that forms annually in the stratosphere over Antarctica, are responsible for the smaller ozone loss.
“The Southern Hemisphere’s stratosphere was unusually disturbed this year,” said Craig Long, meteorologist at the NOAA Climate Prediction Center. The unusual weather patterns were so strong this year that the ozone hole split into two pieces during the late September period. The NOAA 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,” Long said.
At South Pole Station, balloon-borne ozone measuring instruments launched by the NOAA Climate Monitoring and Diagnostics Laboratory reveal the vertical structure of the developing ozone hole. Bryan Johnson, a researcher with CMDL, said that the main ozone depletion region (from 7 to 14 miles above the Earth) has large ozone losses, similar to the last few years. Above 15 miles altitude, measurements show higher than normal ozone concentrations and higher temperatures. The combination of these layers indicate that total ozone levels in a column of atmosphere will be higher than observed during the last few years, Johnson said. However, some layers may still show complete ozone destruction by early October, when ozone depletion is greatest.
In 2001, the Antarctic ozone hole reached a maximum size of more than 26.5 million square kilometers (10.2 million square miles), larger than the entire area of North America, including the U.S., Canada and Mexico combined. In the year 2000, it briefly approached 30 million square kilometers (11.5 million square miles). The last time the ozone hole was as small as it is this year was in 1988, and that was also due to warm temperatures.
“While chlorine and bromine chemicals cause the ozone hole, the temperature is also a key factor in ozone loss,” Newman said. The main reason why the ozone hole is smaller this year than last is simply higher temperatures, and the higher temperatures are caused by the disturbed stratospheric weather conditions. The Montreal Protocol and its amendments banned chlorine-containing chlorofluorocarbons (CFCs) and bromine-containing halons in 1995, because of their destructive effect on the ozone layer. However, CFCs and halons are extremely long-lived and still linger at high concentrations in the atmosphere.
Typically in the Southern Hemisphere the coldest temperatures over the South Pole 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 typically start to warm and the ozone layer starts to recover.
The stratosphere is an atmospheric layer about 6 to 30 miles above the Earth's surface where the ozone layer is found. The ozone layer prevents the sun's harmful ultra-violet radiation from reaching the Earth's surface. Ultra-violet radiation is a primary cause of skin cancer. Without upper-level ozone, life on Earth would be non-existent.
NOAA and NASA continuously observe Antarctic ozone with a combination of ground, balloon and satellite based instruments. This year the Total Ozone Mapping Spectrometer (TOMS) on NASA’s Earth Probe satellite and the NOAA-16 SBUV/2 (Solar Backscatter Ultraviolet instrument) are joined by the recently launched NOAA-17 SBUV/2. The NOAA satellites are operated by the NOAA National Environmental Satellite, Data, and Information Service. The scientists will continue to observe the atmospheric dynamics and thermal structure of the polar vortex using data collected by NASA and NOAA’s polar-orbiting satellites.