The Dynamics of Extreme-Rain-Producing Quasi Linear Convective Systems in Victoria, Australia

Abstract:

Quasi-linear convective systems (QLCSs) are a consistent and noticeable year-round feature of Melbourne, and the surrounding region of Victoria, Australia. These systems are typically convective in nature, frequently associated with cold fronts, and in some cases can lead to significant rainfall and flash flooding. Melbourne is geographically located in a region we know relatively little about, surrounded by modest terrain on three sides and the Southern Ocean coastline to the south; this makes it different from many of the regions where QLCSs have been studied more extensively (like the Great Plains region of the US). As organized convection still presents one of the greatest challenges for understanding the future of extreme precipitation, it is useful to explore how well existing fundamental theories of convective organization apply (or not), and what distinguishes extreme events from the rest. The goals of this work are to understand 1) What processes drive the pre-frontal/frontal convection in the Victoria region, 2) How these processes fit (or not) within existing understanding of QLCSs elsewhere, and 3) The role of moisture (emphasis on source and depth) in modulating the intensity of convection. To this end we are exploring the dynamics of four cases in great detail: two QLCSs with extreme rainfall, and two more typical ‘non-extreme’ cases. In each category, both pre-frontal and frontal cases analysed.