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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. Plain Language Summary: Extra‐tropical cyclones play a major role in the circulation within the atmosphere, acting to transfer heat toward the poles. Here we assess the representation of extreme precipitation within extra‐tropical cyclones. By applying a threshold for precipitation that changes with geographic location, we are able to determine how extreme precipitation varies within a cyclone‐centered coordinate system. When breaking cyclones into lifecycle stages representing deepening, peak intensity and decay, we find that extreme precipitation occurs most often as the cyclone is developing. The area of the cyclone relevant for extremes reduces toward the cyclone center as the threshold for determining extreme precipitation increases. Extreme precipitation weakens at a higher rate as cyclones becomes more intense, highlighting the importance of extremes in the growth phase of the cyclone. Key Points: We detail a new methodology to assess precipitation extremes within cyclone composites using a spatially dependent precipitation thresholdExtreme precipitation occurs preferentially and makes up a larger fraction of total accumulation before cyclones reach peak intensityExtreme precipitation is more constrained around the cyclone center and weakens more rapidly over time compared to moderate precipitation [ABSTRACT FROM AUTHOR]

ABSTRACT New insight is provided regarding 21st century projections of synoptic scale atmospheric circulation over the New Zealand region. Daily mean sea level pressure patterns from a number of general circulation models ( GCMs) participating in the 5th Coupled Model Intercomparison Project ( CMIP5) were analysed through a self-organizing map ( SOM) technique. In terms of simulating the synoptic climatology found in reanalyses, an initial model evaluation revealed quite substantial differences in model skill. Generally, those models with relatively high horizontal atmospheric resolution skilfully simulated the historical frequency and mean lifetime of large scale synoptic patterns over this region. Analysing future projections under this smaller subset of better-performing models indicated robust and quite substantial increases in the annual frequency of widespread anticyclonic conditions over New Zealand, accompanied by a general decrease in widespread low pressure. These projected changes in frequency of synoptic occurrences become the most pronounced towards the end of the 21st century and for winter, whereas changes in the average synoptic pattern lifetime remain small. While not robust for all models in this subset, significant 21st century trends in the intensification of geostrophic westerly flow conditions within certain synoptic patterns were also found. Linking synoptic patterns to surface climate variables has also provided evidence that these circulation changes may collectively manifest as a significant non-uniform climatic change across New Zealand. These findings should encourage further focused studies on circulation-relevant applications and impacts in a climate change context. [ABSTRACT FROM AUTHOR]

The article investigates the association between the extratropical Southern Hemisphere and the decadal variability in the Pacific Ocean. It discusses a pattern of coherent large-scale anomalies and trends in cyclone and anticyclone behavior in light of the climate variability in the Pacific Ocean over the ERA40 reanalysis period. The two representative Pacific Ocean indices are the Pacific Decadal and Interdecadal Oscillations. Although global warming and related changes in the Southern Annular Mode may also help explain the observed behavior, the large-scale response provides a new insight and would be of considerable interest for further modeling studies.