Sea Breeze Climatology and Nearshore Processes along the Perth Metropolitan coastline, Western Australia

摘要

The Perth metropolitan coastline is characterised by one of the strongest and most consistent sea breeze systems in the world. In contrast to the 'classic' sea breeze system, characterised by sea breezes blowing in the onshore direction, the sea breeze in Perth blows in a predominantly alongshore direction. Each year, around 200 sea breezes are experienced with an average wind speed of 5.7 m/s. Sear breezes in summer are stronger and more persistent than in winter. The importance of the sea breeze is clearly indicated by wind spectra showing significant spectral peaks at the diurnal frequency. The sea breeze system directly forces the incident wave field and induces a diurnal cycle of nearshore change by causing: (1) an increase in wave height; (2) a decrease in wave period; (3) an intensification of the nearshore currents; and (4) an increase in suspended sediment levels and suspended sediment transport. In addition, the seasonal variation in sea breeze activity, with frequent and strong sea breezes in summer and infrequent and weaker sea breezes in winter, is responsible for a seasonal change in the littoral drift direction. In summer, longshore sediment transport is towards the north and causes baches located south of structures or headlands to widen considerably. In winter, when littoral drift is towards the south due to northwesterly storms, beaches located north of structures or headlands will become wider. It is further demonstrated that strong sea breeze activity is common along the entire Western Australian coastline, implying that the results obtained for the Perth metropolitan coastline can be applied to some extent to the netire state.