Linear Dynamic Pressure Explains the Persistence of the Rear Flank Downdraft in Supercells

Supercells are a highly organized form of thunderstorm, with structure that persists over relatively long periods of time. Part of this persistent structure is a feature referred to as the “rear flank downdraft” (RFD). There is a bevy of prior research on short duration downdraft surges in this region, yet ample room for a dynamic understanding of RFD persistence remains. Bulk analysis of numerous Lagrangian trajectories within simulations of supercells across environments with varied wind shear and lifted condensation level (LCL) shows that reductions in the vertical perturbation pressure gradient acceleration (VPPGA) are primarily responsible for the downward acceleration of near-surface downdrafts in the RFD region. Time averaged and updraft centered composites suggest that linear-dynamic VPPGA, resulting from interactions between environmental vertical wind shear and the low-level supercell updraft, explains the persistence of downdrafts in a supercell’s RFD region.