Diabatic Quasi-Geostrophic Surface Frontogenesis

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

Diabatic processes are included in a quasi-geostrophic model of surface frontogenesis due to an imposed horizontal deformation field. Analytic solutions are found for prescribed heating and for conditional instability of the second kind (CISK) parameterizations of cumulus convection.

The solutions for prescribed heating show that condensational heating has no direct effect on the surface potential temperature field. Indirectly this heating aloft may alter the surface frontogenesis by its induced ageostrophic horizontal divergences, but such an effect is estimated to be small Condensational heating does, however, increase the strength of the mid-tropospheric frontogenesis and intensifies the vertical velocity above the surface front.

In contrast prescribed boundary layer heating (e.g., surface heat transfer, subcloud evaporative cooling) modifies the surface temperature field directly and can also create a strong ageostrophic convergence near the ground.

Solutions for CISK heating parameterizations indicate that the heating and hence the ascending motion becomes concentrated in a narrow region on the warm side of the surface front. The dynamically induced heating is greater in magnitude and narrower in halfwidth for wave-CISK than for a CISK scheme proposed by Mak. An intermediate scheme which has features of both parameterizations is also studied.

Abstract

Diabatic processes are included in a quasi-geostrophic model of surface frontogenesis due to an imposed horizontal deformation field. Analytic solutions are found for prescribed heating and for conditional instability of the second kind (CISK) parameterizations of cumulus convection.

The solutions for prescribed heating show that condensational heating has no direct effect on the surface potential temperature field. Indirectly this heating aloft may alter the surface frontogenesis by its induced ageostrophic horizontal divergences, but such an effect is estimated to be small Condensational heating does, however, increase the strength of the mid-tropospheric frontogenesis and intensifies the vertical velocity above the surface front.

In contrast prescribed boundary layer heating (e.g., surface heat transfer, subcloud evaporative cooling) modifies the surface temperature field directly and can also create a strong ageostrophic convergence near the ground.

Solutions for CISK heating parameterizations indicate that the heating and hence the ascending motion becomes concentrated in a narrow region on the warm side of the surface front. The dynamically induced heating is greater in magnitude and narrower in halfwidth for wave-CISK than for a CISK scheme proposed by Mak. An intermediate scheme which has features of both parameterizations is also studied.

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