Investigating the Geographic Controls of Severe Local Storm Environments: From Real World to Reduced Complexity

Severe Local Storms (SLS), such as severe thunderstorms and tornadoes, pose significant risk to life and property in the United States. 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 is in part 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.

This work investigates the relative role of elevated terrain upstream and the Gulf of Mexico to the generation of SLS environments in the United States using a variety of experiments in the Community Atmosphere Model version 6 (CAM6). First, component denial CAM6 simulation experiments are performed with topography over removed over North America as well as where the Gulf of Mexico is converted to land, and the results are compared to a CAM6 control simulation of current climate following the Atmospheric Model Intercomparison Project (AMIP) protocols for 1980 thru 2014. We analyze the response in both environments favorable for severe local storm activity and key larger-scale features known to help generate these environments. This work indicates that topography is crucial for inland SLS environments but perhaps not for their existence in general (e.g., near the Gulf of Mexico). Second, reduced-complexity experiments in which idealized land and terrain features are imposed within the CAM6 aquaplanet configuration are performed to further isolate the influence of these geographic features. Both sets of simulation experiments build understanding of the geographic controls of SLS environments in the Earth’s climate system.