Numerical simulations of supercell interactions with thermal boundaries

Abstract

The association of tornadoes and tornadic thunderstorms with surface boundaries has been recognized for several decades. However, little has been done to study this phenomenon in a systematic manner. This study uses a numerical cloud model to examine the effects of the interaction of simulated supercede thunderstorms with thermal boundaries on storm morphology and low-level rotation. This study differs from previous supercede modeling studies that use homogeneous initial conditions. A non-homogeneous initial condition is used to permit the introduction of a low-level thermal boundary into the model domain. This study focuses solely on the effects from increased baroclinicity associated with the boundary. The results indicate that thermal boundaries have a significant influence on supercede morphology that is somewhat consistent with previous observational studies. The storms interacting with boundaries have 'stronger updrafts, stronger low-level mesocyclones, and storm morons that are altered by the boundary. Surprisingly supercedes interacting with boundaries take longer to develop low-level mesocyclones than the homogeneous simulation. This behavior appears to result from the presence of the mesoscale cool pool retarding rear flank downdrafts reaching the surface as readily as in the homogenous simulation.