Kidson’s Synoptic Weather Types and Surface Climate Variability over New Zealand
Daily synoptic classifications developed by Kidson in the late 1990s have been updated through mid-2010. This paper documents the update in terms of the relative frequency of occurrence of the synoptic types and associated regimes, demonstrating that on average, synoptic type frequencies have not changed significantly over the past decade, although some long-term trends in occurrence frequency have been reported elsewhere. The regimes are associated in dynamically reasonable ways to the phase of the ENSO cycle and to the polarity of the SAM, with more zonal flow during El Niño and more blocking types during La Niña, more trough types during the negative SAM and more zonal and blocking types during the positive SAM. The synoptic types and regimes are closely associated with coherent daily climate anomalies, as illustrated using the highresolution Virtual Climate Station Network dataset. The mean magnitude of the daily climate anomalies associated with the Kidson types and regimes is much larger than suggested by Kidson’s original results, because Kidson’s results were based on regional averages and mixtures of the effects of different regimes within months.