Quantifying the summertime response of the Austral jet stream and hadley cell to stratospheric ozone and greenhouse gases

Edwin P. Gerber, Seok Woo Son

Research output: Contribution to journalArticle

Abstract

The impact of anthropogenic forcing on the summertime austral circulation is assessed across three climate model datasets: the Chemistry-Climate Model Validation activity 2 and phases 3 and 5 of the Coupled Model Intercomparison Project. Changes in stratospheric ozone and greenhouse gases impact the Southern Hemisphere in this season, and a simple framework based on temperature trends in the lower polar stratosphere and upper tropical troposphere is developed to separate their effects. It suggests that shifts in the jet stream and Hadley cell are driven by changes in the upper-troposphere-lower-stratosphere temperature gradient. The mean response is comparable in the three datasets; ozone has chiefly caused the poleward shift observed in recent decades, while ozone and greenhouse gases largely offset each other in the future. The multimodel mean perspective, however, masks considerable spread in individual models' circulation projections. Spread resulting from differences in temperature trends is separated from differences in the circulation response to a given temperature change; both contribute equally to uncertainty in future circulation trends. Spread in temperature trends is most associated with differences in polar stratospheric temperatures, and could be narrowed by reducing uncertainty in future ozone changes. Differences in tropical temperatures are also important, and arise from both uncertainty in future emissions and differences in models' climate sensitivity. Differences in climate sensitivity, however, only matter significantly in a high emissions future. Even if temperature trends were known, however, differences in the dynamical response to temperature changes must be addressed to substantially narrow spread in circulation projections.

Original languageEnglish (US)
Pages (from-to)5538-5559
Number of pages22
JournalJournal of Climate
Volume27
Issue number14
DOIs
StatePublished - Jul 2014

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Keywords

  • Anthropogenic effects
  • Atmospheric circulation
  • Climate change
  • Climate models
  • Southern Hemisphere
  • Stratophere-troposphere coupling

ASJC Scopus subject areas

  • Atmospheric Science

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