The impact of convection-permitting simulation on the mesoscale structures of two severe synoptic-scale cyclones on the south-southeast coast of Brazil in 2023 austral winter

Synoptic-scale cyclones in the southwestern South Atlantic Ocean often result in heavy rainfall, strong winds, sudden temperature drops, and other abrupt changes that affect important metropolitan areas along the south-southeastern coast of Brazil. Despite notable advancements in understanding these systems, numerical simulations continue to face difficulties in accurately reproducing cyclone-induced rainfall and intense winds. Therefore, the aim of this study is to assess the ability of convection-permitting scale simulations (CP) with a spatial resolution of 3 km, to reproduce the mesoscale structures associated with two extratropical cyclones that caused multiple fatalities in the southern Brazil in June and July of 2023. Regional Climate Model (RegCM) version 5 is configured in CP mode and runned continuously from May to July 2023 in a large domain (lon: -81.12 to -33.09; lat: -48.45 to -10.47). The first month is considered a spin-up period. Precipitation simulated in CP mode is compared with locally observed data and with satellite estimates. The comparison with observations indicates that the resolution refinement and the use of cloud microphysics in CP simulation develop many of the cyclone mesoscale structures generating intense precipitation events. The authors thank CNPq, FAPESP and FAPEMIG for their financial support.