The role of atmospheric forcings and WRF physical set-up on convective initiation over Córdoba, Argentina

Abstract

The accurate determination of the location and timing of convective initiation (CI) is a crucial aspect of forecasting and high impact weather warning systems associated with deep convection. Central Argentina, particularly the Sierras de Córdoba (SDC), is characterized by the regular occurrence of deep convective cells that reach supercell characteristics producing large hail and occasionally tornadoes. In order to analyze the sensitivity of the CI over SDC, an ensemble of 12 simulations with the WRF model at convection-permitting resolution (3 km.) was carried out to study a marginal supercell initiated on October 17, 2017 at the SDC foothills. The ensemble was built using 3 different microphysics (MP) parameterizations (WSM6, Thompson and Morrison) and 2 planetary boundary layer (PBL) parameterizations (Yonsei University and Mellor Yamada Janjic). Also, the sensitivity of initial and boundary conditions is considered by forcing the model with 2 different global analyses: the European Centre for Medium-Range Weather Forecast (ECMWF) model, and the Global Data Assimilation System (GDAS). The two different forcing data show low-level moisture differences, which later modulate the life-cycle of the simulated cells. A tracking algorithm was used to capture their life-cycle, and CI was detected at both the hills and the plains. Simulations forced with ECMWF analyses tend to show better results with characteristics closer to the ones observed including: initiation over the eastward slope of SDC, stronger cells and slow propagation. Among all simulations analyzed, the best performance was obtained with the combination of Thompson MP and Yonsei University PBL schemes.