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 centre 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 a maximum depth.
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.