Washington: NASA scientists have found that declining chlorine in the stratosphere has not yet caused a recovery of the ozone hole - formed annually over Antarctica.
Two new studies showed that signs of recovery are not yet present, and that temperature and winds are still driving any annual changes in ozone hole size.
Natalya Kramarova, of NASA`s Goddard Space Flight Center in Greenbelt, Maryland, tackled the 2012 ozone hole, the second-smallest hole since the mid 1980s. To find out what caused the hole`s diminutive area, she turned to data from the NASA-NOAA Suomi National Polar-orbiting Partnership satellite, and gained the first look inside the hole with the satellite`s Ozone Mapper and Profiler Suite`s Limb Profiler.
Next, data were converted into a map that shows how the amount of ozone differed with altitude throughout the stratosphere in the center of the hole during the 2012 season, from September through November.
The map revealed that the 2012 ozone hole was more complex than previously thought. Increases of ozone at upper altitudes in early October, carried there by winds, occurred above the ozone destruction in the lower stratosphere.
Separate research led by Susan Strahan, also NASA`s Goddard, tackled the holes of 2006 and 2011 - two of the largest and deepest holes in the past decade.
The researchers were surprised to find that the holes of 2006 and 2011 contained different amounts of ozone-depleting chlorine.
The researchers next used a model to simulate the chemistry and winds of the atmosphere. Then they re-ran the simulation with the ozone-destroying reactions turned off to understand the role that the winds played in bringing ozone to the Antarctic.
Results showed that in 2011, there was less ozone destruction than in 2006 because the winds transported less ozone to the Antarctic - so there was less ozone to lose. This was a meteorological, not chemical effect. In contrast, wind blew more ozone to the Antarctic in 2006 and thus there was more ozone destruction.