The Southern Oscillation and New Zealand Weather

Abstract

Correlation coefficients between the Tahiti-Darwin Southern Oscillation Index (SOI) and pressure fields in the New Zealand area show a negative SOI to be associated with anomalous southwest flow on a yearly average basis, but reveal a strong seasonal variation in the correlation pattern. Difference fields between composites for negative and positive phases of the SO show similar seasonal variations. The SOI is significantly correlated in the southern summer with a zonal index at sea level over New Zealand and in winter with a meridional index. Correlations are strongest near zero lag, with persistence as the main contributor to lagged correlations. Temperature spatially averaged over New Zealand as a whole has a year-round positive correlation with the SOI. Contemporary correlations are strongest, with some indication of significant lag relationships other than those due to persistence. Rainfall spatially averaged over the country is less strongly correlated with the SOI. Regional temperature and rainfall correlations, and composite anomalies for different phases of the SO, reflect the interaction of different flow anomalies and New Zeland's orography.