The stratosphere—a layer of the atmosphere that occurs from 10-30 miles above the ground—was unusually cold this past spring. Though these colder than normal temperatures did not affect conditions on the ground, they did impact the layer of ozone that protects Earth from the Sun’s harmful ultraviolet radiation. Chlorine molecules in the stratosphere are usually no threat to the ozone layer—except in extremely cold temperatures where they react, changing from inert forms of chlorine to highly reactive forms. Once the polar night ends (the period of time whereby the pole receives no daylight for weeks at a time), the presence of the reactive chlorine along with sunlight are able to break the bonds that hold the ozone molecule together. An ozone hole—or thinning of the ozone layer—may form if these reactions occur over large areas. Currently, the ozone layer over the South Pole is transitioning from winter to spring, and is experiencing the same, dramatic ozone depletion as was seen in the North Pole six months ago.
Usually the North Pole does not get cold enough for these reactions to occur, but this year’s January through March temperatures did provide the proper conditions for ozone depletion. These images show the large areas of the stratosphere that experienced colder than average temperatures (colored blue) in January-March of 2011, using data from the Microwave Sounding Unit (MSU) and Advanced Microwave Sounding Unit (AMSU) on board the NOAA POES satellites. The historical average is calculated over the 1978 - 2011 period. Atmospheric temperature data from MSU and AMSU provide one of the longest, and most complex continuous records of satellite data, dating back to 1978 and spanning 14 different satellites. The data from each satellite must be inter-calibrated to provide reliable climate data records.
On October 27, 2011, the NASA NPP satellite will launch, carrying the Advanced Technology Microwave Sounder. The ATMS sensor will continue the 33 year data record of MSU/AMSU and will be used by NOAA to continue to provide accurate weather forecasts, along with better understanding of the dynamics of the atmosphere.