AGS-PRF: Impacts of Microphysics and Cold Pool Thermodynamics on Supercell Tornadogenesis: Comparisons of Numerical Simulations with VORTEX2 Observations

Dawson Daniel T, Norman OK

Investigators

Abstract

The violent and ephemeral tornado remains one of the most challenging subjects of study in the atmospheric sciences. Tornadogenesis, maintenance, intensification and decay mechanisms are all characteristics that are still poorly understood. Each of these issues were primary motivations for the recent VORTEX2 (hereafter, V2) field campaign that took place during the Spring of 2009 and 2010 in the Great Plains of the United States. Unprecedented data on many tornadic and nontornadic supercells were acquired over the length of the project, which included rich mobile radar data, high density in situ surface observations, and proximity soundings. Within the context of this project, the surface in situ observations of surface temperature and moisture in the cold pools of the surveyed storms, as well as disdrometer observations of dropsize distributions (DSDs) coupled with polarimetric radar data, are of primary interest. Research over the past decade has indicated a clear empirical signal for tornadogenesis, intensity, and longevity to be strongly influenced by the thermodynamic properties of the associated storm cold pool. In particular, tornadoes are more likely to form, persist, and intensify, when the surface temperature and moisture deficits (relative to a suitable undisturbed near-storm environment) in the cold pool are relatively small. This research aims to investigate the causative mechanisms for this empirical correlation through an idealized numerical modeling approach. The work will leverage several diverse cases from the V2 field program to aid in initialization and verification of the model simulations. As such, it will sample a fairly large parameter space that was spanned by the V2 cases. Intellectual Merit: The research is expected to provide new insights into the relationship between supercell cold pools and tornado activity through the following means: 1) Understanding the sensitivity of cold pool thermodynamics to the microphysical processes of water loading, evaporation, and melting utilizing sophisticated microphysics parameterization packages, and the variance across the spectrum of cases provided by V2; 2) Assessing the impact of variation in the thermodynamic properties of the cold pools on tornadoes, and improving physical understanding of this connection; 3) Verifying microphysical parameterizations through comparison with disdrometer and polarimetric radar data. Broader Impacts: The results of this research are expected to improve our ability to understand supercell storm characteristics that are most likely to produce significant tornadoes, and thus it will have a direct impact on the lives of the millions of U.S. citizens threatened or affected by tornadoes each year. The comparison between model representations of microphysical processes and the rich polarimetric radar and disdrometer datasets available from the V2 will help identify avenues for improvement of these parameterizations and thus have direct implications for forecasts of precipitation from severe convection and the associated risks of flooding and hail damage.