Momentum and Kinetic Energy Budgets of Simulated Supercell Thunderstorms

Abstract

The results of numerical simulations of severe thunderstorms with rotating updrafts and supercell characteristics are analyzed to determine their sources, sinks, and transports of momentum and kinetic energy. Two simulations are used, one initiated in an idealized environment with unidirectional shear, and the other simulating a real tornadic storm in an environment with a curved hodograph. For the unidirectional shear storm, we carry out the analysis at 10-minute intervals throughout the 2.5 hour duration of the simulation, during which the storm develops a fairly steady amplitude after the first hour but continues to grow in areal extent and in disturbance kinetic energy. We analyze just one time level for the tornadic storm. For both storms the vertical flux of horizontal momentum is strongly down the velocity gradient, and the corresponding rate of transfer of disturbance kinetic energy from the mean flow is comparable to that of buoyant energy release. The mean-flow kinetic energy is in both cases partially restored by a gravity wave-generated pressure gradient, which may be considered as an interaction with the environment. The energy budget analysis detects evidence of excessively large artificial damping in the simulation. Comparison with an observational budget by Coover et al. provides further evidence of excessive dissipation.