The Influence of Boundary-Layer Shear and Static Stability on Low-Level Vertical Accelerations in a Supercell
Naval Postgraduate School Monterey United States
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It is well documented that tornadoes are formed from a special breed of rotating thunderstorms called supercells, and that tornadogenesis is a result of several factors, one of which is the vertical stretching of low-level vorticity. Not as well understood are the factors that contribute to vertical acceleration of low-level vorticity in the updraft region of a supercell to support tornadogenesis. This paper examined the influence ofcombining both low-level shear and low-level static stability on low-level vertical accelerations using idealized simulation from Cloud Model 1 CM1. A matrix of simulations varied the low-level shear and the low-level convective inhibition CIN in order to parse out the dynamic response of these parameters on the low-level forcing. When shear was added to simulations, there was a consistent positive response to thelow-level dynamic forcing when low-level CIN was increased, there was a consistent negative response to the low-level buoyant forcing. Despite the chaotic nature of a supercell environment, a balance can be achieved in the lower atmosphere where the low-level CIN can counteract the low-level shear and inhibit the vertical stretching of vorticity. Since this phenomenon is associated with tornadogenesis, a correlation can be made between the ratio of low-level static stability to low-level shear and its effect on tornado formation.
- Fluid Mechanics