Stratospheric influence on circulation changes in Southern Hemisphere troposphere in coupled climate models

The recent intensification of the circumpolar circulation in the SH troposphere in summer and autumn has been attributed to external forcing such as stratospheric ozone depletion and greenhouse gas (GHG) increases. Several studies have shown that climate models are able to simulate observed changes when forced by observed ozone trends or combined ozone and GHG trends. However, as some of these studies suffered from erroneously specified forcing, the reason for the circulation intensification remains debatable. Here, we re-approach this issue using data from 21 CMIP3 models. We demonstrate that only models that include ozone depletion simulate downward propagation of the circulation changes from the stratosphere to the troposphere similar to that observed, with GHG increases causing significant Antarctic geopotential height trends only in the lower troposphere. These changes are simulated by the majority of the ozone-forced models except those with the lowest vertical resolution between 300 hPa and 10 hPa. Citation: Karpechko, A. Yu., N. P. Gillett, G. J. Marshall, and A. A. Scaife (2008), Stratospheric influence on circulation changes in the Southern Hemisphere troposphere in coupled climate models, Geophys. Res. Lett., 35, L20806, doi: 10.1029/2008GL035354.

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