Evolution of a Southeast Australian Coastally Trapped Disturbance

Summary

 The southeast Australian coastally trapped disturbance (CTD) of 9–11 November 1982 that was previously studied by Holland and Leslie is re-visited. Additional observational data not considered by these authors and a numerical simulation using the Colorado State University Regional Atmospheric Modeling system (RAMS) are used for this purpose. Following initiation of the event on the south coast, mesoscale ridging propagated along the east coast to just north of Brisbane. Associated with the arrival of the event were a marked increase in surface pressure, drop in temperature and a shift and strengthening of the wind. While the simulation does not appear to capture the details of the boundary layer as well as one would like, it does represent the main features of the event, including the speed of propagation along the coast, reasonably well. Similar to the observed, the model event shows gravity current-like characteristics.

The significance of topographic variability (e.g., large gap in the coastal mountains at the Hunter Valley) is considered. It is suggested that the topography and ambient stratification in southeastern Australia are less favourable for CTD occurrence than those in southern Africa and western North America where these systems have been extensively studied. Consequently, when CTD do occur in southeastern Australia, the less pronounced topography and weaker stratification may enable local effects to mask the CTD signal to some extent, thereby posing challenges in observation and forecasting.