Frontogenesis in a Moist Semigeostrophic Model

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  • 1 National Center for Atmospheric Research, Boulder, CO 80307
  • | 2 Department of the Geophysical Sciences, The University of Chicago, Chicago, IL 60637
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Abstract

Analytic solutions are obtained for a prototype semigeostrophic frontal model in which cumulus heating is parameterized by applying the conventional wave-CISK scheme and the scheme of Mak in the geostrophic coordinate. Such heating schemes give rise to a vertically tilted heating distribution as suggested by observational evidence of clouds in frontal zones. The wave-CISK scheme produces a larger influence than the Mak scheme and preferentially excites smaller-scale components of the solution. Both schemes generate a significant frontogenetic development at higher levels over the front, although their impact on the temperature near the surface is smaller. The various facets of the model solutions for moist frontogenesis are compared with those for dry frontogenesis. The main differences are the significant enhancement by the heating of frontogenesis aloft and the nongeostrophic component of the circulation. Specifically, the magnitude of the ascending motion over the surface cold front can be readily increased several fold, and its length scale reduced to be comparable to that of the front itself. The propagation of the cold front into the warm sector is also slightly enhanced as a result of the heating.

Abstract

Analytic solutions are obtained for a prototype semigeostrophic frontal model in which cumulus heating is parameterized by applying the conventional wave-CISK scheme and the scheme of Mak in the geostrophic coordinate. Such heating schemes give rise to a vertically tilted heating distribution as suggested by observational evidence of clouds in frontal zones. The wave-CISK scheme produces a larger influence than the Mak scheme and preferentially excites smaller-scale components of the solution. Both schemes generate a significant frontogenetic development at higher levels over the front, although their impact on the temperature near the surface is smaller. The various facets of the model solutions for moist frontogenesis are compared with those for dry frontogenesis. The main differences are the significant enhancement by the heating of frontogenesis aloft and the nongeostrophic component of the circulation. Specifically, the magnitude of the ascending motion over the surface cold front can be readily increased several fold, and its length scale reduced to be comparable to that of the front itself. The propagation of the cold front into the warm sector is also slightly enhanced as a result of the heating.

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