Characteristics of the Sea Breeze System in Perth, Western Australia, and its Effect on the Nearshore Wave Climate

Abstract

The coastline of Perth, Western Australia, is subjected to one of the strongest and most consistent sea breeze systems in the world. Using forty-nine years of wind data collected at Perth airport (about 20 km inland) it was found that almost 200 sea breezes are experienced per year with an average wind speed at mid-afternoon (15:00 hrs) of 5.7 m/s. At the coastline, sea breeze velocities are 1.4 times greater than 20 km inland and in the summer months, when the sea breeze system is best developed, sea breeze velocities frequently exceed 10 m/s. A significant feature of the sea breeze is that it blows obliquely-onshore, rather than onshore. The importance of the sea breeze is clearly indicated in spectra of the wind speed showing a significant spectral peak at the diurnal frequency. Spectral analysis of hourly inshore wave data also revealed a diurnal spectral peak, suggesting a forcing of the wave conditions by the sea breeze. It is concluded that the diurnal sea breeze system can have a major impact on the incident wave climate, and hence nearshore processes, of sheltered coastal environments in tropical and subtropical regions.