Formation of Small-Scale Cyclones in Numerical Simulations of Synoptic-Scale Baroclinic Wave Life Cycles: Secondary Instability at the Cusp

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  • 1 University of Toronto, Department of Physics, Toronto, Ontario, Canada
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Abstract

An examination of high-resolution simulations of nonlinear baroclinic wave evolution, based upon the nonhydrostatic anelastic equations, has revealed the occurrence of frontal instabilities following cutoff of the primary wave occlusion. The frontal waves are shallow and have horizontal scales of approximately 700 km. They derive their energy from both baroclinic and barotropic energy conversions and it is suggested that they may owe their existence to the instability of a strip of anomalously large potential vorticity that develops along the surface front. The issue of the fundamental mechanism is complicated somewhat because such secondary cyclogenesis events occur at the frontal “cusp,” a location in which the flow is highly nonparallel.

Abstract

An examination of high-resolution simulations of nonlinear baroclinic wave evolution, based upon the nonhydrostatic anelastic equations, has revealed the occurrence of frontal instabilities following cutoff of the primary wave occlusion. The frontal waves are shallow and have horizontal scales of approximately 700 km. They derive their energy from both baroclinic and barotropic energy conversions and it is suggested that they may owe their existence to the instability of a strip of anomalously large potential vorticity that develops along the surface front. The issue of the fundamental mechanism is complicated somewhat because such secondary cyclogenesis events occur at the frontal “cusp,” a location in which the flow is highly nonparallel.

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