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EJSSM 11.3: The Sensitivity of Deep Ascent of Cold-Pool Air to Vertical Shear and Cold-Pool Buoyancy

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#1 Roger Edwards

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Posted 27 July 2016 - 11:36 PM

EJSSM forum comments are welcome on this article by Houston (2016).





The tilting and stretching of solenoidally generated vorticity that is hypothesized to be a necessary
condition for supercell tornadogenesis is predicated on the presence of ascent of cold-pool air. Results are
presented from experiments designed to test the sensitivity of this ascent to the temperature deficit of the
cold pool and the environmental vertical shear. Experiments use idealized 2D numerical simulations
involving a density current and a parameterized non-rotating deep convective updraft. Experiments
conducted with only the density current demonstrate that simulated cold-pool upward motion generally
exhibits a highly correlated direct relationship to both environmental vertical shear and cold-pool
temperature deficit. Thus, despite increased negative buoyancy, colder cold pools are theoretically
characterized by faster ascent of cold-pool air. In the presence of the parameterized, non-rotating, deep
convective updraft, cold-pool upward motion is found to exhibit a strong linear relationship to both
environmental shear and cold-pool temperature deficit. A cold-pool tracer is also used to measure the
depth of transport of cold-pool air. Maximum tracer depth is found to increase linearly with environmental
vertical shear but is found to decrease with increasing cold-pool temperature deficit. These sensitivities are
attributed to the degree of phasing between deep positively buoyant ascent and the density current
dynamics: for stronger shear and smaller cold-pool temperature deficits, the deep updraft and the gust front
remain in close proximity, resulting in deep transport of cold-pool air.


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