Interannual variability and controls of the Sydney wave climate

Abstract

AbstractA multi‐decadal beach survey dataset at a coastal embayment in Sydney, Australia, identifies erosion/accretion cycles coinciding with phase shifts in the El Niño/Southern Oscillation (ENSO). In an attempt to explain the processes governing these cycles, this study explores the interannual variability and controls of the Sydney wave climate using ECMWF ERA‐40 and corrected ERA‐40 (C‐ERA‐40) reanalysis data. Comparisons with wave measurements collected by the Sydney waverider buoy show that these datasets represent the Sydney wave climate reasonably well, although westerly waves are significantly over‐predicted. Removing these values strengthens correlations between predicted and measured wave heights. A summary of the Sydney wave climate from 1957 to 2002 is presented, which highlights the high degree of variability in storm events. Controls of interannual variability are investigated by comparing values in Sydney with regional mean sea level pressure anomalies, the Southern Oscillation Index (SOI) and the Southern Annular Mode (SAM). Austral summer wave heights over this 45‐year period increase/decrease with positive/negative phases of the SOI and the SAM. An inverse relationship is found between wave directions and the SOI for the austral autumn and spring; and between wave directions and the SAM for the austral winter. Variability of storm events in Sydney is significantly correlated with the SOI, but not the SAM. In particular, La Niña phases are generally associated with longer duration, higher‐energy events from a more easterly direction when compared to those during El Niño phases. Copyright © 2009 Royal Meteorological Society