The impact of variations in upper-level shear on simulated supercell storms

Numerous observational and numerical studies have highlighted the critical role that vertical wind shear plays in the organisation of deep moist convection. However, the vast majority of this work has focused on shear in the lowest 6 km of the atmosphere. It has been suggested that upper-level storm-relative flow (a function both of the deep-layer shear and storm motion) is an important control on the precipitation distribution in supercell storms, giving rise to the familiar ‘classic', ‘low-precipitation' and ‘high-precipitation' morphologies. In the present study, the specific role of upper-level shear (that above 6 km) is isolated using idealized simulations. It is found that as upper-level shear increases, the simulated storms become larger, with more intense precipitation and associated stronger outflow winds. These changes (which are consistent across a range of model and environmental configurations) result from an increase in updraft mass flux, which leads to enhanced precipitation production and, in turn, stronger downdrafts. At the time of writing, work is ongoing to determine the mechanisms responsible for updraft intensification; however, preliminary results suggest that changes in the linear dynamic perturbation pressure forcing (associated with interactions between the updraft and upper-level shear) may be an important component. Findings from the completed investigation will be presented and discussed in the context of forecasting supercells and their associated hazards.