Influence of the Antarctic Circumpolar Wave upon New Zealand temperature and precipitation during autumn-winter

Abstract

Autumn-winter temperature and precipitation records at 34 stations over New Zealand from 1982 to 1995 are found by empirical orthogonal function (EOF) analysis to fluctuate together with 3-6-yr quasi periodicity similar to that associated with the Antarctic Circumpolar Wave (ACW), which propagates slowly eastward past New Zealand in its global traverse around the Southern Ocean. By allowing these EOF time sequences to represent New Zealand temperature and precipitation indices, both the positive temperature index related to warm sea surface temperature (SST) anomalies around New Zealand and the positive precipitation index related to warm (cool) SST anomalies north and east (south and west) of New Zealand are found. These warm (cool) SST anomalies are associated with poleward (equatorward) meridional surface wind (MSW) anomalies, the same as observed in association with the ACW. When warm (cool) SST and poleward (equatorward) MSW anomalies are located north (south) of New Zealand, then anomalous low-level wind convergence occurs over New Zealand, and when they are located east (west) of New Zealand, then anomalous cyclonicity occurs over New Zealand, both during years of anomalously high autumn-winter precipitation over New Zealand. Regular eastward propagation of the ACW past New Zealand suggests that covarying SST and MSW anomalies (and New Zealand autumn-winter temperature and precipitation) can be predicted 1-2 yr into the future. The authors test for this by utilizing the eastward propagation of the ACW contained in the dominant extended EOF mode of SST anomalies upstream from New Zealand to predict SST indices in the western South Pacific that are linked statistically to New Zealand temperature and precipitation indices. At 0-yr lead, this statistical climate prediction system nowcasts the observed sign of New Zealand temperature (precipitation) indices 12 (12) years out of the 14-yr record, explaining 50% (62%) of the interannual variance for each index. At 1-yr lead, it hindcasts the observed sign of New Zealand temperature (precipitation) indices 12 (13) years out the 14-yr record, explaining 24% (74%) of the interannual variance. At 2-yr lead, hindcasting is insignificant. This hindcast skill at 1-yr lead suggests that prediction of interannual climate variability over New Zealand may depend more upon predicting the amplitude and phase of the ACW than upon predicting it for tropical ENSO.