Ozone depletion in the stratosphere above the Antarctic generally peaks in October or November at a height of roughly 18 km, whereas tropospheric cooling tends to lag behind, reaching a maximum in December – January. With this in mind, scientists had proposed that the troposphere might be more sensitive to depletion of ozone lower down in the stratosphere, which also peaks in December – January.
But now a UK-US team has modelled the effects of ozone depletion at different levels in the stratosphere and found that ozone loss in the lower stratosphere (near the tropopause region between the troposphere and stratosphere) has no significant effect on tropospheric temperatures.
"Lower stratospheric ozone changes (below 164 hPa) aren't the driver for tropospheric response in Antarctica and this is contrary to the suggestion made in the World Meteorological Organization Scientific Assessment of Ozone Depletion: 2006," Sarah Keeley of the University of East Anglia, UK, told environmentalresearchweb.
Keeley and researchers from the University of East Anglia, UK, Colorado State University, US, NOAA Earth System Research Laboratory, US, and the University of Leeds, UK, used the Hadley Centre Atmospheric model HadSM3-L64. They ran a control experiment with ozone concentrations comparable to those in the 1970s and three perturbation experiments – one with ozone depletion to late 1990s levels throughout the depth of the stratosphere, one with depletion below 164 hPa and one with depletion above 164 hPa. The team chose 164 hPa as the level separating the lower and middle stratosphere.
Keeley says that the team's findings have implications for understanding the mechanisms of stratosphere–troposphere coupling and the drivers of atmospheric circulation change in the southern hemisphere.
"The mechanism underlying these tropospheric responses, and the reason for its lag compared to the stratospheric forcing, remain open to debate," they have written in a paper in Geophysical Research Letters.
Now members of the group will look at changes in circulation with increases of greenhouse gases and the recovery of the ozone hole during the next century.