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Contrasting recent trends in Southern Hemisphere Westerlies across different ocean basins
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  • Darryn W. Waugh,
  • Antara Banerjee,
  • John C. Fyfe,
  • Lorenzo M Polvani
Darryn W. Waugh
Johns Hopkins University

Corresponding Author:waugh@jhu.edu

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Antara Banerjee
Cooperative Institute for Research in Environmental Sciences
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John C. Fyfe
Environment Canada
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Lorenzo M Polvani
Columbia University
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Abstract

Many studies have documented the trends in the latitudinal position and strength of the midlatitude westerly jet in the Southern Hemisphere. However, very little attention has been paid to the longitudinal variations of these trends. Here, we specifically focus on the zonal asymmetries in the southern jet trends between 1980-2018. Meteorological reanalyses show a robust strengthening and an equatorward shift of the annual-mean and springtime jet over the Pacific sector, in contrast to a weaker strengthening and poleward shift over the Atlantic and Indian Ocean sectors. The reanalysis trends fall within the ensemble spread for historical climate model simulations, showing that climate models are able to capture the observed trends. Climate model simulations indicate that the differential movement of the jet is a manifestation of internal variability and is not a forced response. Implications of these asymmetries for other components of the climate system are discussed.