The evolution and structure of a tropical island sea/land-breeze system, northern Australia

Summary

This paper is concerned with sea/land-breeze systems over relatively flat tropical islands to the north of continental Australia. The purpose of this study is to contribute to the relatively small body of knowledge on tropical island sea/land-breeze systems in this region and to highlight their particular characteristics. The evolution and structure of coastal circulations over the Tiwi Islands, northern Australia are examined using observations made during the Maritime Continent Thunderstorm Experiment (MCTEX), November/December 1995. During the transition period between dry and wet (monsoon) seasons, strong diurnal surface heating dominates the local meteorology. Thermally modified pressure differences across the coastline are seen to control the timing, direction and intensity of local winds. The evolution and structure of the resulting circulations appear to be affected greatest by tropospheric stability and friction, while the Coriolis force, synoptic winds and topography are of much less importance in this case. Consequently, even small differences in surface properties seem to produce strong and well defined local wind circulations. The depth of the sea breeze averaged 1200 m, while the land breeze was considerably shallower (290 m). Return flows were evident in both circulations, although better defined in land breeze cases. Day to day variation in vertical structure was considerable and appeared to be controlled by stability in the lower troposphere. Spatial patterns of surface temperature, pressure and wind show formation of an island heat low by day and a cool high pressure centre at night, resulting in island scale convergence and divergence, respectively.