MMM Seminar: Impacts of Environmental Dry Air on Deep Convective Downdrafts and Cold Pools in Simula

Speaker: Christopher Nowotarski, University of Texas A&M

Downdrafts in deep moist convection and their associated near-surface outflow (i.e., cold pools) are integral to the organization of convection and the formation of severe thunderstorm hazards.   Such downdrafts and cold pools are largely driven by hydrometeor loading and latent cooling from melting or evaporating hydrometeors.   While prior work has focused on how low-level static stability and relative humidity in the near-storm environment modulate these features, there is relatively less understanding of how dry air in the free troposphere affects downdrafts and cold pools relative to dryness in the boundary layer.    Furthermore, many simulation-based studies have relied on a limited range of highly idealized analytic thermodynamic environments.  

This talk will explore how the magnitude of dryness as well as the vertical distribution of dry air can influence downdrafts and cold pools in idealized simulations of supercell thunderstorms as well as multicell storms in a less sheared environment.  Free tropospheric and boundary layer relative humidity are modified both systematically and through selection of real-storm environments with a range of free-tropospheric and boundary layer relative humidity. Results highlight the importance of the balance between precipitation production and latent cooling in dictating downdraft and cold pool properties.    Impacts of dry-air modulation of downdrafts and cold pools for tornadoes and nontornadic damaging wind and forecasting implications of these hazards will also be presented.  The importance and challenges of simulating storms over a wider variety of realistic environments will also be discussed.