Observational Study of a Multiple Microburst-Producing Storm Part III:Vorticity Budgets

Abstract

A vorticity component and budget analysis in three dimension is conducted for the subcloud layer of two microburst-producing storms using dual-Doppler de­ rived winds. This study examines the vorticity associated with a single microburst­ producing storm which occurred on 14 July 1982 and a multiple microburst­ producing storm which occurred on 5 August 1982 in Colorado.
Results show that horizontal vorticity centers are coincident with strong hor­izontal gradients of vertical velocity and with areas of strong vertical shear. These gradients are maximized along the edges of downrushing air and along gust fronts. Regions of high speed low-level winds have a core horizontal vorticity above them.
A vorticity budget analysis of the advection, divergence and tilting terms, comprising the vorticity component equations, shows the magnitude of these terms to be greater in the microburst domain than in the storm domain. This indicates that the strongest forcing and advection takes place within small regions of the storms. The diverging out ow of the microburst in both cases weakens any existing positive vorticity in the microburst region (z < 1 km).
The differences in storm structure allow examination of the vorticity of a simple, nearly circular-symmetric microburst and that of a microburst within a complicated flow field. This leads to different voricity distributions and budgets.

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