Session 10.6 Do supercell thunderstorms play a role in the equilibrium of the large-scale atmosphere?

Wednesday, 6 October 2004: 2:45 PM
Robert J. Trapp, Purdue University, West Lafayette, IN; and C. A. Doswell III and M. Huber

Presentation PDF (1.9 MB)

Supercell thunderstorm formation has traditionally been treated as the result of a one-way, non-scale interacting process. Specifically, supercells are regarded as products of a larger-scale environment, and are presumed to form only when certain combinations of environmental conditions exist. Additional or refined environmental conditions are required for supercell by-products such as hail, strong winds, and tornadoes.

We propose an alternative treatment of this problem, based on why the atmosphere requires supercell storms to form under such environmental conditions. In other words, what role do these storms have in larger-scale balances, and how does this feed back to the storm scale?

To illustrate this, consider the case of deep moist convection (DMC) in the tropics, which occurs or releases convective instability soon after the instability is created by larger-scale processes. Tropical DMC is responsible for much of the vertical transport of heat and moisture, and helps maintain the balance of the tropical atmosphere, under the influence of surface heat fluxes and radiation. In continental midlatitude regions, extratropical cyclones play the critical role in meridional (and also vertical) transport of heat and moisture. Accordingly, midlatitude DMC—which does not immediately release convective instability upon creation by larger-scale processes—may exist “whenever the redistribution of heat by synoptic-scale processes is not sufficient to mitigate the imbalances resulting from differential heating at the surface” (Doswell and Bosart 2001). Recalling the characteristic longevity and intensity of supercells, as well as their relative infrequency, it is plausible to extend this idea and argue that such storms exist when extraordinary imbalances exist and need be mitigated.

The ultimate goal of this study is to determine connections between supercell storms and the quasi-equilibrated state of the larger-scale atmosphere. The first step toward this goal is to quantify the unique effect of supercell (and tornadic) storms on their larger-scale environments. This will be addressed initially using WRF simulations of the extreme outbreak of tornadoes in the central United States during the period of 4-10 May 2003. Possible applications of the results to climate-change scenarios will be discussed.

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