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A tale of two quasi-linear convective systems, their mesoscale structure and moisture sources
16 June 2021 @ 2:00 pm - 3:00 pm
Much of the heavy and extreme rainfall in the Melbourne region occurs on days with linearly organized precipitation. These systems are typically convective in nature and frequently associated with cold fronts. Of course, not every linear (or quasi-linear) convective system (QLCS) leads to extreme rainfall. Those that do, tend to be larger and more intense, move slower, and have a greater degree of along-line propagation than other QLCSs. It is useful to understand the processes that support extreme rainfall in organized convection, for prediction of both near-term and future extreme rainfall, and Melbourne’s topography makes it different from many of the regions where QLCSs have been studied more extensively (e.g. the Great Plains region of the US).
On each of the 7 and 8 of December 2010, a QLCS passed through the Melbourne region. Both QLCSs resembled classic systems on radar, but heavy rainfall was much more widespread on the second day. The goals of this work are to 1) understand the processes that drive these seemingly similar QLCSs, and 2) explore the relationship between the convective inflow layer and moisture sources. To this end, we have analyzed a high-resolution (~1 km) ‘full physics’ WRF-ARW simulation that captures both events. We find that the mesoscale flow in both cases generally is explainable by existing theory, and that the second QLCS has stronger large scale and mesoscale forcing. Consequently, parcels are lifted over a deeper layer. We also find that parcels nearer to the surface come from the north and east (over the Tasman), while those from more elevated layers come from the west (west-southwest of Perth).
Brief Biography: Stacey is currently a Postdoctoral Research Fellow with the ARC Centre of Excellence for Climate Extremes and the School of Geography, Earth, and Atmospheric Sciences at the University of Melbourne. She completed a BS (2012) and MS (2014) in meteorology at the University of Oklahoma and a PhD in atmospheric science at Colorado State University (2018). Most of her work has focused on using both observations and models to better understand the convective and mesoscale processes that lead to extreme rainfall. Stacey first became fascinated by (terrified of) storms at an early age (6), and has been trying to understand them ever since.