Understanding Subtropical MCSs in Argentina Using WRF

Subtropical South America is home to some of the world’s most intense convection, particularly near the Andes and Sierras de Córdoba mountain ranges of Argentina. Convective cells typically initiate along the foothills due to the combined influence of complex topography, the South American low-level jet, large-scale support, and the diurnal cycle. As storms mature and propagate eastward, they grow upscale to much larger horizontal dimensions and frequently develop into mesoscale convective systems (MCSs). These MCSs have substantial socioeconomic impacts on the region’s cities and agriculture due to the damaging hail, winds, and rainfall often associated with various stages of an MCS. The distinguishing factor of these MCSs relative to those in other more studied locations (i.e., the U.S.) is their tendency to “backbuild,” or remain convectively tied, to the eastern edge of the foothills terrain as they grow and propagate eastward. To investigate this unique characteristic, the Weather Research and Forecasting model is used to perform simulations of a long-lasting, backbuilding MCS in Argentina testing different microphysics schemes: Morrison, Thompson, and NSSL. Analysis shows that all three simulations featured backbuilding convection tied to the Sierras de Córdoba, similar trends in updraft velocity and depicted three waves of convection, two of which were likely related to the diurnal cycle. The simulation with Morrison microphysics featured the broadest areal extent of moderate to intense rainfall, while the Thompson simulation produced the broadest extent of forecast hail. Morrison sustained convection and the most robust cold pool east of the Sierras de Córdoba throughout the simulation. Future work will assess output from other microphysics and planetary boundary layer parameterization options and continue to explore likely causes of the three waves of enhanced convection.