Southern hemisphere sea-surface temperatures and their contemporary and lag association with New Zealand temperature and precipitation

The influence of sea-surface temperature (SST) anomalies on New Zealand climate variations is examined systematically, using data for the period 1949–1991. New Zealand temperature and precipitation anomalies, both monthly and seasonal, are represented in terms of rotated EOF patterns, the time series of which are then cross-correlated against sea-surface temperature data for an extensive region of the Southern Hemisphere. Relationships with mean sea level pressure anomalies in the Australasian region are examined to clarify significant associations found. Monthly lead and lag cross-correlations suggest that sea temperatures in the immediate vicinity of New Zealand are responding to atmospheric circulation variations, a result that is consistent with many similar studies elsewhere regarding midlatitude sea temperature anomalies. New Zealand temperatures, particularly in the North Island, are also significantly correlated to the previous month's sea-surface temperature anomaly in the western Tasman Sea and south of Australia, but only in autumn months (March, April, May). Subsequent analysis suggests the most likely cause of this is atmospheric forcing in the antecedent month. On the seasonal time scale, a number of SST–New Zealand climate lag relationships are found, many of which appear to be related to ENSO variations. However, tropical Indian Ocean SSTs unrelated to ENSO are prominent in the autumn–winter period. One phase of this teleconnection pattern is for warmer Indian Ocean waters in autumn to be followed by a stronger subtropical ridge just north of North Island in winter, stronger westerly flow over the country, higher South Island temperatures, more rainfall in west South Island districts and drier conditions in other areas of the country exposed to the north and east.