Australian Rainfall and Surface Temperature Variations Associated with the Southern Hemisphere Annular Mode

TLDR

The Southern Hemisphere Annular Mode’s high‑index phase is marked by a poleward contraction of midlatitude westerlies, influencing recent trends in Australian rainfall and temperature. Daily variations in Australian rainfall and surface temperature linked to the SAM were documented from 1979 to 2005 using observational data. The high‑index SAM phase reduces winter rainfall in southeast and southwest Australia, increases summer rainfall on the southern east coast, and lowers weekly rainfall variance by up to ~15%—comparable to ENSO—while also producing low maximum temperatures in spring and summer across central and eastern subtropical Australia, with cooler regions experiencing higher rainfall.

Abstract

Abstract Daily variations in Australian rainfall and surface temperature associated with the Southern Hemisphere annular mode (SAM) are documented using observations for the period 1979–2005. The high index polarity of the SAM is characterized by a poleward contraction of the midlatitude westerlies. During winter, the high index polarity of the SAM is associated with decreased daily rainfall over southeast and southwest Australia, but during summer it is associated with increased daily rainfall on the southern east coast of Australia and decreased rainfall in western Tasmania. Variations in the SAM explain up to ∼15% of the weekly rainfall variance in these regions, which is comparable to the variance accounted for by the El Niño–Southern Oscillation, especially during winter. The most widespread temperature anomalies associated with the SAM occur during the spring and summer seasons, when the high index polarity of the SAM is associated with anomalously low maximum temperature over most of central/eastern subtropical Australia. The regions of decreased maximum temperature are also associated with increased rainfall. Implications for recent trends in Australian rainfall and temperature are discussed.