RELATIONSHIP OF NEW-ZEALAND DAILY AND MONTHLY WEATHER PATTERNS TO SYNOPTIC WEATHER TYPES

The effectiveness of the classification of daily mean sea-level pressu re patterns over New Zealand into 13 synoptic types by Kidson (1994) h as been tested through their relationship with daily and monthly varia tions in temperature, precipitation, sunshine, and daily wind run over the period 1980-1990. The mean anomalies of these weather elements fo r each synoptic class often showed spatially consistent patterns, with departures falling in the second and fourth (below normal and above n ormal) quintiles. These were readily interpretable in terms of the eff ects of advection, differences in static stability, and the influence of mountain ranges on the low-level circulation. On a monthly basis, 6 0 per cent of the variance in the frequencies of occurrence of the 13 synoptic types was found to be due to three significant EOFs. These fo rmed the basis of an iterative clustering process to group the flow pa tterns for the 11-year period into eight sets of monthly analogues or 'regimes', for which the composite patterns of the weather element wer e obtained. Overall, the results suggest that the synoptic classificat ions are likely to be helpful in specifying daily values of weather el ements, and in interpreting the monthly departures of the New Zealand climate. They should also prove useful in validating climate model per formance for the New Zealand region and in providing better detail of the regional climate changes likely to result from the greenhouse effe ct.