Regional influence of climate patterns on the wave climate of the southwestern Pacific: The New Zealand region

Abstract

This work investigates how the wave climate around New Zealand and the southwest Pacific is modulated by the Pacific Decadal Oscillation (PDO), El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Zonal Wave-number-3 Pattern (ZW3), and Southern Annular Mode (SAM) during the period 1958–2001. Their respective climate indices were correlated with modeled mean wave parameters extracted from a 45 year (1957–2002) wave hindcast carried out with the WAVEWATCH III model using the wind and ice fields from the ERA-40 reanalysis project. The correlation was performed using the Pearson's correlation coefficient and the wavelet spectral analysis. Prior to that, mean annual and interannual variabilities and trends in significant wave height (Hs) were computed over 44 years (1958–2001). In general, higher annual and interannual variabilities were found along the coastline, in regions dominated by local winds. An increasing trend in Hs was found around the country, with values varying between 1 and 6 cm/decade at the shoreline. The greatest Hs trends were identified to the south of 48°S, suggesting a relationship with the positive trend in the SAM. Seasonal to decadal time scales of the SAM strongly influenced wave parameters throughout the period analyzed. In addition, larger waves were observed during extreme ENSO and IOD events at interannual time scale, while they were more evident at seasonal and intraseasonal time scales in the correlations with the ZW3. Negative phases of the ZW3 and ENSO and positive phases of the IOD, PDO, and SAM resulted in larger waves around most parts of New Zealand.