Work

Extreme Weather in the Southern Hemisphere in Early 2022

Year: 2025

Type: article

Abstract: In early 2022, several exceptionally extreme weather events struck the Southern Hemisphere. Deadly floods affected eastern Australia and South Africa, and an unprecedented heat wave in East Antarctica broke global temperature anomaly records. This study presents a multiscale analysis of the atmospheric processes leading to these extreme events ranging from local to planetary scales. While the subtropical flood events were associated with slow-moving circulation patterns with moderate departures from climatology, the Antarctic heat wave was unprecedented with surface temperatures and atmospheric moisture content breaking records in observation-based data since 1979. Despite the variety in weather type and region, all three extreme events share a common origin in extratropical Rossby wave breaking modulated by tropical variability on intraseasonal-to-interannual time scales. Equatorward wave breaking steered moisture transport from nearby oceans toward the subtropical flood regions favored by anticyclonic circulation anomalies in the midlatitudes and a poleward-displaced midlatitude jet. Enhanced tropical convection over the Indian Ocean promoted poleward–eastward Rossby wave propagation, eventuating in poleward wave breaking that forced an intrusion of exceptionally warm and moist air masses into the Antarctic continent. At seasonal time scales, large parts of the study regions experienced record-breaking surface weather associated with the influence of La Niña, setting up favorable circulation patterns for heavy precipitation over the eastern Australian and South African coasts and heat wave occurrence over East Antarctica’s interior. This study contributes to an improved process understanding of extreme weather events in the Southern Hemisphere with implications for weather and climate prediction of such events. Significance Statement Within a 2-month period in early 2022, eastern Australia and South Africa incurred unprecedented flood impacts and Antarctica experienced a heat wave, breaking global temperature anomaly records. Our collaborative effort investigates the local and remote atmospheric processes, leading to these extreme events. We find that all three extreme weather events have a common origin in wave breaking in the midlatitude circulation influenced by tropical weather and climate variability. Future research evaluating the simulation of these processes in weather and climate models is an important step toward improving predictions and projections of extreme weather with high impacts on society and the polar cryosphere.

Source: Bulletin of the American Meteorological Society

DOI: 10.1175/bams-d-23-0141.1