Impact of Orography on Updraft Rotation in Simulated Supercells

This study addresses the sensitivity of near-ground rotation in supercells to changes in topography over the southeast United States. In particular, ARW-WRF simulations will be presented in which the topography has been modified in various ways, including increases or total elimination of the topographic relief. A number of VORTEX-SE and other cases will be analyzed. Storm-scale differences will be explored using idealized simulations with the Bryan Cloud Model 1 (CM1), initialized with base-state environments retrieved from the WRF simulations. The main hypothesis based on preliminary simulations is that the impact of orography on supercell occurrence is rather small if the synoptic-scale environment is abundantly supportive of supercells (i.e., large CAPE and large vertical wind shear), which usually involves strong synoptic-scale forcing. In situations with weak synoptic-scale forcing, mesoscale augmentations of CAPE and shear due to the orography may have a much larger impact. Examples showing each scenario will be presented, storm behavior will be explained, and implications for forecasting such events will be discussed.