26 Jul 2022
26 Jul 2022
Status: this preprint is currently under review for the journal WCD.

Revisiting the wintertime emergent constraint of the Southern Hemispheric midlatitude jet response to global warming

Philipp Breul1, Paulo Ceppi1,2, and Theodore Gordon Shepherd3 Philipp Breul et al.
  • 1Department of Physics, Imperial College London, London, United Kingdom
  • 2Grantham Institute, Imperial College London, London, United Kingdom
  • 3Department of Meteorology, University of Reading, Reading, United Kingdom

Abstract. Most climate models show a poleward shift of the southern hemispheric jet in response to climate change, but the inter-model spread is large. In an attempt to constrain future jet responses, past studies have identified an emergent constraint between the climatological jet latitude and the future jet shift in austral winter. However, we show that the emergent constraint only arises in the zonal mean, and not in separate halves of the hemisphere. This can be explained by the presence of a double jet structure in the Pacific region, making the zonal mean jet latitude a poorly defined quantity that does not represent the latitude of a zonally coherent structure during this season. The usefulness of the emergent constraint is therefore questionable. This finding can further explain the prior finding among CMIP5 and CMIP6 ensembles that the meridional structure of the zonal-mean zonal wind response does not change with climatological jet latitude but stays fixed.

Philipp Breul et al.

Status: open (until 06 Sep 2022)

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Philipp Breul et al.

Philipp Breul et al.


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Short summary
Accurately predicting the response of the mid-latitude jet stream to climate change is very important, but climate models show a variety of possible scenarios. Previous work has identified a relationship between climatological jet latitude and future jet shift in the southern hemispheric winter. However, we show that the jet latitude is not a well-defined metric in in austral winter, due to zonal asymmetries in the mid-latitude jet. The usefulness of the relationship is therefore questionable.