Investigating Cold Pool Impacts on Supercell Thunderstorm Development and Updraft Characteristics

Previous studies have investigated how moisture and/or vertical wind shear variations impact supercell thunderstorm dynamics, while others have stated the importance of the cold pool for squall line maintenance. However, no previous studies that we are aware of have explicitly analyzed the role the cold pool plays in impacting supercell development, sustenance, and strength. This project aims to fill in the gaps to the fundamental questions surrounding what role the cold pool plays in getting a supercell to develop and maintain itself, how the cold pool affects the strength and structure of the supercell, and how important the cold pool is in redirecting inflow air into the updraft compared to what is being dynamically “sucked up” by the mesocyclone itself.

A suite of 72 idealized simulations were conducted using Cloud Model 1 (CM1), with half of the simulations having a cold pool while the other half utilized a modified version of the Morrison two-moment microphysics scheme in which evaporation of rain and melting of hail were turned off across the entire domain at model initialization, effectively “turning off” the cold pool. Additional modifications were made to free tropospheric relative humidity, lifting condensation level height, and vertical wind shear of the model base state to determine the robustness of our findings across different environments.

Sustained supercells developed in both cold-pool and non-cold-pool simulations with similar updraft widths and strengths, suggesting that the cold pool plays a relatively minor, albeit non-zero, role in tilting inflow air into the updraft. Low-level rotation was more pronounced in cold pool supercell simulations, supporting past work highlighting the importance of baroclinic vorticity generation in low-level mesocyclone formation. Of the additional environmental modifications tested, free tropospheric relative humidity appeared to have the largest impact on storm development with cold pool simulations exhibiting stronger and faster storm motions in more moist environments owing to stronger cold pools.