Squall line study

Doubled-domain size test
Doubled-domain		 Low level vorticity structure
Vorticity structure		 The real world
Observed cases of interest
low-vertical-shear case
Low-shear simulations		 moderate-vertical-shear case
Moderate-shear results		 2-D modeled front evolution
Idealized 2-D front
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Severe thunderstorms often occur along mesoscale boundaries such as fronts and drylines. Truly isolated severe convection is rare in the sense that mid-tropospheric forcing or low-level boundaries are absent. Are these mesoscale processes of any importance other than assisting parcels to condensation and subsequent convective initiation?

This study is designed to investigate the longer-term role of the forcing and the more realistic environments which accompany it. We have found this role may be significant - storms simulated with and without the mesoscale environments differ, even though their local buoyancy and shear profiles are the same.

The forcing here is a cold front, modeled in two dimensions with the same cloud model. Unlike the (even more..) idealized cold front (right-bottom panel above), the front in this case was simulated (again, in 2-D) with surface (semi- slip) drag and crude lower stratosphere present. The evolution of the vertical velocity field (domain: 4000 km wide by 18 km high) is depicted here (mpeg, 225k) | (MooV, 1.9 MB). The broad region of rising motion ahead of the surface front collapses to a narrow updraft at the leading edge, eventually taking on a "split updraft" shape.

The initiation procedure results in frontal forcing (based on a collapsed Eady wave, but with a tropopause and variable stratification and shear) as well as desired along-front profiles of buoyancy and shear. The result is a somewhat complete initial state with which to study squall lines.

Brian F. Jewett | bjewett@ncsa.uiuc.edu | homepage