AN AUTOMATED PROCEDURE FOR THE IDENTIFICATION OF SYNOPTIC TYPES APPLIED TO THE NEW-ZEALAND REGION

Cluster analysis has been applied to 9 years of daily 1000 hPa analyse s for 1980-1988 over the New Zealand region. The resulting 13 synoptic groupings are characterized mainly by high-pressure cells and pressur e gradients reflecting the predominant wind directions. Low-pressure c entres are not well represented, presumably because of their smaller h orizontal scale and lower frequency of occurrence. Seasonal variations in cluster frequency over this period typically differ by a factor of two. The most persistent patterns are associated with highs to the so uth of New Zealand, whereas the transitions between clusters show the familiar sequence of eastward-propagating high-pressure cells interspe rsed with troughs. It is anticipated that these synoptic classificatio ns will prove helpful in interpreting inter-annual climate fluctuation s, in validating the performance of climate models for the New Zealand region and in providing improved guidance to forecasters. Their appli cation to the analysis of daily and monthly variations in climatic ele ments is described in a companion paper.