Understanding the Geographic Controls of Severe Local Storm Environments in the United States: Role of the Gulf of Mexico

Severe Local Storms (SLS), such as severe thunderstorms and tornadoes, pose significant risk to life and property in the United States every year. While these SLS events are small scale, they develop principally within favorable larger-scale environments (i.e., SLS environments). Why these large-scale environments are confined to specific regions of Earth, particularly the Eastern United States, is not well understood. This can, in part, be related to a limited fundamental knowledge of how the climate system creates SLS environment, which provides uncertainty in how SLS environments may be altered in a changing climate.

Previous research has identified the Gulf of Mexico as an important source of low-level moist warm air for the generation of SLS environments over the Eastern United States. This work investigates the role of this feature through “component denial” experiments in the Community Atmosphere Model version 5 (CAM5). In particular, CAM5 simulations where the Gulf of Mexico is converted to land is compared to a CAM5 control simulation of current climate following the Atmospheric Model Intercomparison Project (AMIP) protocols. In addition to exploring differences in general characteristics of the large-scale environments, SLS changes will be explored through standard large-scale environmental proxies for SLS activity that include convective available potential energy, vertical wind shear, and storm-relative helicity. This initial work is a crucial first step to building a reduced-complexity framework within CAM5 to quantify how land-ocean contrast and elevated terrain control SLS environments.