Diagnosing indicators of large-scale forcing of east-coast cyclogenesis

Abstract

Small-scale, intense extra-tropical cyclones that develop near the east coast of Australia, commonly referred to as east coast lows, are of critical importance to the eastern seaboard. The rainfall that they generate, combined with the topography of the Great Dividing Range, can cause severe inundation as well as replenish reservoirs. The storm- to hurricane-force winds sometimes generated pose a major hazard to commercial shipping and recreational boating, as well as to onshore infrastructure, while the ocean waves and storm-surge generated can cause severe coastal erosion. Accurate forecasts of the precise locations and magnitudes of east coast lows are vital for community preparedness for individual events. Additionally, knowledge of the climatological distribution of the environments in which east coast lows occur is essential if changes in their occurrence frequency or severity are to be assessed under future climate scenarios. Most climatological or classification studies of east coast lows have focused on their surface synoptic weather patterns, or on their effects (e.g. rainfall). While some studies have qualitatively described the upper-tropospheric wave/jet structures of particular events, hitherto no systematic studies of upper-tropospheric patterns of cyclogenetic forcing have been presented, yet there is subjective evidence that the development of most major east coast lows is associated with the movement of a high amplitude upper-tropospheric trough system over eastern Australia. In this paper a number of upper-tropospheric diagnostic quantities that might provide a basis for preparing a climatology of large-scale drivers of east-coast cyclogenesis will be presented for a number of major east coast low events. A preliminary climatology of these diagnostic quantities, based on ERA-Interim reanalyses, will also be presented. The application of these diagnostics to GCM simulations of past and future climates will be discussed