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| False-color view of total ozone over the Antarctic pole. The purple and blue colors are where there is the least ozone, and the yellows and reds are where there is more ozone. [IMAGE/GFX: NASA Ozone Watch] |
Washington: The average area covered by the Antarctic ozone hole this
year was the second smallest in the last 20 years, according to data from NASA
and National Oceanic and Atmospheric Administration (NOAA) satellites.
Scientists attribute the change to warmer temperatures in the Antarctic lower
stratosphere.
The ozone hole reached its maximum size Sept. 22, covering
8.2 million square miles (21.2 million square kilometers), or the area of the
United States, Canada and Mexico combined. The average size of the 2012 ozone
hole was 6.9 million square miles (17.9 million square kilometers). The Sept.
6, 2000 ozone hole was the largest on record at 11.5 million square miles (29.9
million square kilometers).
"The ozone hole mainly is caused by chlorine from
human-produced chemicals, and these chlorine levels are still sizable in the
Antarctic stratosphere," said NASA atmospheric scientist Paul Newman of
NASA's Goddard Space Flight Center in Greenbelt, Md. "Natural fluctuations
in weather patterns resulted in warmer stratospheric temperatures this year. These
temperatures led to a smaller ozone hole."
The ozone layer acts as Earth's natural shield against
ultraviolet radiation, which can cause skin cancer. The ozone hole phenomenon
began making a yearly appearance in the early 1980s. The Antarctic ozone layer
likely will not return to its early 1980s state until about 2065, Newman said.
The lengthy recovery is because of the long lifetimes of ozone-depleting
substances in the atmosphere. Overall atmospheric ozone no longer is declining
as concentrations of ozone-depleting substances decrease. The decrease is the
result of an international agreement regulating the production of certain
chemicals.
This year also showed a change in the concentration of ozone
over the Antarctic. The minimum value of total ozone in the ozone hole was the
second highest level in two decades. Total ozone, measured in Dobson units
(DU), reached 124 DU on Oct. 1. NOAA ground-based measurements at the South
Pole recorded 136 DU on Oct. 5. When the ozone hole is not present, total ozone
typically ranges from 240-500 DU.
This is the first year growth of the ozone hole has been
observed by an ozone-monitoring instrument on the Suomi National Polar-orbiting
Partnership (NPP) satellite. The instrument, called the Ozone Mapping Profiler
Suite (OMPS), is based on previous instruments, such as the Total Ozone Mapping
Spectrometer (TOMS) and the Solar Backscatter Ultraviolet instrument (SBUV/2),
which have flown on multiple satellites. OMPS continues a satellite record
dating back to the early 1970s.
In addition to observing the annual formation and extent of
the ozone hole, scientists hope OMPS will help them better understand ozone
destruction in the middle and upper stratosphere with its Nadir Profiler. Ozone
variations in the lower stratosphere will be measured with its Limb Profiler.
"OMPS Limb looks sideways, and it can measure ozone as
a function of height," said Pawan K. Bhartia, a NASA atmospheric physicist
and OMPS Limb instrument lead. "This OMPS instrument allows us to more
closely see the vertical development of Antarctic ozone depletion in the lower
stratosphere where the ozone hole occurs."
NASA and NOAA have been monitoring the ozone layer on the
ground and with a variety of instruments on satellites and balloons since the
1970s. Long-term ozone monitoring instruments have included TOMS, SBUV/2,
Stratospheric Aerosol and Gas Experiment series of instruments, the Microwave
Limb Sounder, the Ozone Monitoring Instrument, and the OMPS instrument on Suomi
NPP. Suomi NPP is a bridging mission leading to the next-generation
polar-orbiting environmental satellites called the Joint Polar Satellite
System, which will extend ozone monitoring into the 2030s.