Abstract
Intense columnar vortices in a convecting layer are explored with direct numerical simulations that are otherwise similar to the large-eddy simulations of6, Q. J. R. Meteorol. Soc. 126, 2789–2810). With free-slip boundaries and a Rayleigh number of 106(4096 times critical), vortices similar to large dust devils are readily produced. The genesis, intensity and life cycle of these intense vortices (dust devils) are studied. The simulated dust devils last for the order of the over-turning time of the largest eddies. The intensity is limited by the hydrostatic pressure drop supported by the buoyancy confined in the core. The genesis of a simulated dust devil requires not only tilting of the baroclinically generated vorticity, but also a symmetry-breaking event that allows one sign of vorticity to become concentrated in an updraft. Such symmetry breaking is the rule with random initialization in the simulations. However, when initialization is restricted to certain Fourier modes, exceptions are found that produce only symmetric vortex couplets that are relatively weak.
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