Publication Date:
2016-10-12
Description:
Much research has focused on trends in the Southern Hemispheric circulation in austral summer (Dec-Jan-Feb) in the troposphere and stratosphere, while changes in other seasons have received less attention. Here we examine the seasonality and structure of observed changes in tropospheric and stratospheric winds, temperature, and ozone over the Southern Hemisphere. We find that statistically significant trends similar to those of the Antarctic summer season are also observed since 1979 in austral fall, particularly May, and are strongest over the Pacific sector of the hemisphere. We provide evidence for a significant shift in the position of the jet in May over the Pacific, and show that the strengthening and shifting of the jet has rendered the latitudinal distribution of upper tropospheric zonal wind more bimodal. The Antarctic ozone hole has cooled the lower stratosphere and strengthened the polar vortex. While the mechanism and timing are not fully understood, the ozone hole has been identified as a key driver of the summer season tropospheric circulation changes in several previous observational and modeling studies. We find that significant ozone depletion and associated polar cooling also occur in the lowermost stratosphere and tropopause region through austral fall, with spatial patterns that are coincident with the observed changes in stratospheric circulation. We also show that radiatively-driven temperature changes associated with the observed ozone depletion in May represent a substantial portion of the observed May cooling in the lowermost stratosphere, suggesting a potential for contribution to the circulation changes.
Print ISSN:
0894-8755
Electronic ISSN:
1520-0442
Topics:
Geography
,
Geosciences
,
Physics
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