02 Sep 2022
02 Sep 2022
Status: this preprint is currently under review for the journal WCD.

Anomalous subtropical zonal winds drive decreases in southern Australian frontal rain

Acacia Sarah Pepler and Irina Rudeva Acacia Sarah Pepler and Irina Rudeva
  • Australian Bureau of Meteorology, Melbourne, Australia

Abstract. Cold fronts make a significant contribution to cool season rainfall in the extratropics and subtropics. In many regions of the Southern Hemisphere the amount of frontal rainfall has declined in recent decades, but there has been no change in frontal frequency. We show that for southeast Australia this contradiction cannot be explained by changes in frontal intensity or moisture at the latitudes of interest. Rather, declining frontal rainfall in southeast Australia is associated with weakening of the subtropical westerlies in the mid troposphere, which is part of a hemispheric pattern of wind anomalies that modifies the extratropical zonal wave 3. Fronts that generate rainfall are associated with strong westerlies that penetrate well into the subtropics, and the observed decrease in frontal rainfall in southern Australia can be linked to a decrease in the frequency of fronts with strong westerlies at 25° S.

Acacia Sarah Pepler and Irina Rudeva

Status: open (until 26 Oct 2022)

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Acacia Sarah Pepler and Irina Rudeva

Acacia Sarah Pepler and Irina Rudeva


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Short summary
In recent decades, cold fronts have rained less often in southeast Australia, which contributes to decreasing cool season rainfall. The largest changes in front dynamics are found to the north of the area where rain changes. Wet fronts have strong westerly winds that reach much further north than dry fronts do, and these fronts are becoming less common, linked to weakening subtropical winds and changes in the southern hemisphere circulation.