An Assessment of Extra‐Tropical Cyclone Precipitation Extremes Over the Southern Hemisphere Using ERA5

Abstract

ERA5 reanalysis is used to examine extreme precipitation using a spatially dependent precipitation threshold applied within a cyclone compositing framework. This is used to account for regional variation in precipitation generating processes within Southern Hemisphere mid‐latitude cyclones across the cyclone lifecycle. The spatial extent of extreme precipitation is limited to a smaller region around the cyclone center compared to non‐extreme precipitation, though extreme precipitation displays a good spatial correlation with non‐extreme precipitation. Extreme precipitation occurs more often during the deepening phase of the cyclone before it reaches peak intensity. Precipitation occurrence at the 90th and 98th percentiles reduces to 46% and 30% of the deepening value across the cyclone lifecycle, averaged over the composite. Precipitation fraction at the 90th and 98th percentile reduces to 80% and 60% of the deepening value. Our methodology provides a quantitative assessment of precipitation extremes both spatially and temporally, within a cyclone compositing framework.