The Trade Wind Regime of eastern Australia

Despite their prevalence along much of the coastline and potential importance in the annual cycle of precipitation, the characteristics of the trade wind regime of eastern Australia and their associated temperature inversion are poorly understood. This region exemplifies conditions at the western flanks of the subtropical high pressure systems, where the trade winds vary considerably from classic models developed from observations in the eastern North Pacific and Atlantic oceans. Upper-air data from several observing stations along the coast of eastern Australia were analysed over the period 1976-2010 and a climatology of the trade winds and the basic characteristics of the trade wind inversion are presented. The trade wind regime dominates during the winter (late summer) in the deep tropics (subtropics) with its poleward fringe in southeastern Queensland. Interannual variability in the frequency of low-level wind directions associated with the trades has a strong linear relationship with the intensity of the subtropical ridge. The basic properties of the inversion (i.e. base height, strength, and thickness) are found to have a distinct annual cycle with a pattern that is largely independent of latitude. Monthly mean inversion base height and thermodynamic properties of the inversion (e.g. strength) have different annual cycles and vary independently of one another, contrary to research in other parts of the tropics. Interannual variations in inversion base height have the strongest linear relationship with the intensity and latitude of the subtropical ridge, while variations in the frequency of occurrence of the inversion are linearly related to the local sea surface temperature anomaly. This study elucidates the nature of the trade winds on the western flanks of the subtropical highs and, by developing a climatology of this weather regime, provides the foundation for a more complete understanding of precipitation in tropical Australia.