Idealized Simulations of Supercell Thunderstorm Interactions Near Stationary Boundaries

Supercell thunderstorms are characterized by a deep, persistently rotating mesocyclone, and are well-known for their production of severe weather, including large hail, gusty winds, and/or tornadoes. The structure, intensity, severe weather production, and longevity of a supercell thunderstorm is heavily influenced by its surrounding environment. Frontal boundaries are synonymous with strongly heterogeneous environments, and have been demonstrated to augment severe weather production as a result of supercell-boundary interactions. The goal of this study is to better understand the dynamical processes that result in storm enhancement as a result of boundary interactions, with a focus on supercells near stationary boundaries. Traditional idealized simulations of supercell-boundary interactions (i.e., two disparate environments placed next to each other), though useful, can be challenging to determine clean cause and effect due to frontal circulations associated with a horizontally-heterogeneous environment in the base-state environment. Additionally, there is a loss of control due the inability to independently specify the frontal gradients without also changing the magnitude and nature of the circulations. In the present study, these problems are addressed through the use of base-state substitution, wherein the base-state environment is temporally varied while maintaining a horizontally homogeneous environment throughout the model domain; a boundary interaction is simulated by rapidly changing the background environment, using timelines consistent with the nature of the interaction. The base-state environments used were rooted in observed cases of supercells interacting with stationary boundaries in the Great Plains. A random set of 7 supercell thunderstorms interacting with stationary boundaries from Magee and Davenport (2020) were identified. The timing of the first tornado report from each case was used to then measure the gradient of the stationary boundary; one sounding was selected to represent the warm side of the boundary, and another on the cold side of the boundary. These soundings were then used to create composite environments representing a realistic gradient in thermodynamic and dynamic quantities across a stationary boundary. A series of experiments will be shown that demonstrate the impact of these varying environments on the intensity and evolution of a supercell thunderstorm.