December 12, 2013
NASA Data From Inside Ozone Hole Paint Complex Picture
Brett Smith for redOrbit.com - Your Universe Online
A small hole in the Earth’s protective ozone layer appears annually over Antarctica and scientists have found that the 2012 ozone hole was the second-smallest hole since the mid 1980s.
However, NASA scientists have also found that the hole in the ozone layer isn’t near to completely closing despite an international agreement to limit the emissions of ozone-depleting chlorofluorocarbons (CFC) more than 20 years ago – according to research being presented on Wednesday at the annual meeting of the American Geophysical Union in San Francisco.
"Ozone holes with smaller areas and a larger total amount of ozone are not necessarily evidence of recovery attributable to the expected chlorine decline," said Susan Strahan of NASA's Goddard Space Flight Center in Greenbelt, Md. "That assumption is like trying to understand what's wrong with your car's engine without lifting the hood."
Using data from the NASA-NOAA Suomi National Polar-orbiting Partnership satellite, Strahan and her NASA Goddard colleague Natalya Kramarova explicitly examined the 2012 hole to determine what caused its relatively smaller size.
The NASA scientists used the data to generate a map that shows how the amount of ozone changed with respect to altitude in the center of the hole from September through November 2012. The map revealed that increases in ozone higher in the stratosphere in early October took place above ozone destruction in the lower stratosphere.
"Our work shows that the classic metrics based on the total ozone values have limitations – they don't tell us the whole story," Kramarova said.
Strahan and Kramarova said their work has been submitted to the Atmospheric Chemistry and Physics journal for publishing.
As part of a separate project, Strahan also looked at the hole from 2006 and 2011 – two of the largest holes in the past that grew via different mechanisms. Initial observations made using data from NASA’s Aura satellite revealed that the two holes had different amounts of ozone-depleting chlorine.
Next, Strahan’s team created a computer model to replicate the chemistry and winds of the atmosphere. The model showed that there was less ozone destruction in 2011 than in 2006 because winds sent less ozone to the Antarctic – meaning there was less available ozone to be depleted. In 2006, wind blew more ozone to the Antarctic – resulting in more ozone destruction.
The NASA scientists said their study calls into question classic total column measurements that do not show the year-to-year variations in the two factors that control the ozone layer: atmospheric winds and the chemical activity of chlorine. They added that these forces will continue to dictate the size of the hole in the ozone layer until chlorine levels in the lower stratosphere drop below early 1990s levels – expected sometime after 2015.
"We are still in the period where small changes in chlorine do not affect the area of the ozone hole, which is why it's too soon to say the ozone hole is recovering," Strahan said. "We're going into a period of large variability and there will be bumps in the road before we can identify a clear recovery."