Numerical analysis of shedding vortices past a simplified supercell storm

On 5th September 2015 a supercell storm occurred in the Gulf of Naples, with exceptional intensity for the Mediterranean area. During this event, the development of shedding vortices was observed past the storm, resembling the von Kármán vortex street (VKVS) typical of flows interacting with solid cylindrical obstacles. However, in this case no solid obstacles are present, suggesting that the storm itself, with its strong vertical updraft, acted as an obstacle to the tropospheric wind, triggering the vortices. This meteorological phenomenon, which has never been reported in literature, is analysed in this work by setting a Large-Eddy Simulation, a high-resolution numerical approach, with the open-source software OpenFOAM. The simulation reproduces a simplified supercell structure, starting from the classical problem of a buoyant jet in crossflow (BJICF). The initial conditions and the computational grid geometry are estimated from ERA5 reanalysis dataset and data from satellite and ground radar collected during the event. Starting from a coarse grid and gradually improving the resolution, the contributions of buoyancy, updraft rotation and variation of updraft diameter are investigated, running the final simulations with 250m resolution. The results reproduce the essential features of the storm and the presence of shedding vortices in the wake, showing differences and similarities with the real case: the simulated vortices have alternate rotation, pronounced vertical development, distance from the central axis coherent with observations, but the shedding period does not match with the real event. Furthermore, the difference is pointed out between the process of formation of the simulated vortices, ascribable to the entrainment of crossflow air into the updraft giving rise to vertical helicoidal motions similar to the counter-rotating vortices in the BJICF, and the one typical of VKVS past a solid body, originating from the viscous boundary layer of the obstacle.