Topographical Influences on a Subtropical South American Mesoscale Convective System

Satellite radar observations indicate subtropical South America is a hotspot for meteorological extremes such as tornadoes, large hail, lightning and flash flooding. These intense storms are most commonly located near the Sierras de Cordoba (SDC), a secondary mountain range east of the Andes mountains. The primary focus of this study is to analyze and understand the role of the SDC initiating and maintaining a mesoscale convective system (MCS). In order to study these interactions, the WRF-ARW model was used to conduct two experiments: one control simulation and one simulation with the SDC removed from the topography of South America. From these experiments, it was observed that cold pools from an MCS along the SDC dam up and promote continued convective initiation along the terrain from lifting along the leading edge of the cold pool. When the cold pool expands horizontally, the SDC become a physical barrier and keeps the moist air from mixing with the drainage flow from the Andes. Additionally, the SDC was found to play a crucial role in the separation of the MCS cold pool and mid-level dry air flowing over the Andes. When the SDC are present in the model, there is an ideal balance of moist air from the cold pool and mid-level dry air entering the rear inflow region of the MCS, which enhances evaporative cooling and strengthens the cold pool. When the SDC are removed, the dry air is able to descend farther into the MCS, undercutting and weakening the system. Having the SDC present allows for the back-building of convection and keeps the MCS tied to the topography, a unique feature of convection within this region.