The Mass, Absolute Angular Momentum and Kinetic Energy Budgets of Model-Generated Extratropical Cyclones and Anticyclones

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  • 1 Australian Numerical Meteorology Research Centre, Melbourne, Australia
  • | 2 Deaprtment of Meteorology and Space and Engineering Center, University of Wisconsin, Madison 53706
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Abstract

The budgets of mass, absolute angular momentum and kinetic energy for two model-generated cyclones and one anticyclone are examined using a sigma-coordinate framework which moves with the center of the MSL pressure extremum. The mass budgets for all three cases show a concentration of lateral mass transport in the surface boundary layer and at a level near 200 mb. The spin up of the low troposphere during cyclogenesis results from the dominance of the mean mode of lateral transport of absolute angular momentum. The spin up of the upper troposphere results from the combined influence of an inward eddy mode of lateral transport and vertical transport of absolute angular momentum. The eddy mode of lateral transport is determined by the configuration of the upper level flow (particularly jet streaks) and is enhanced by frontogenesis in the low and mid-troposphere as these regions spin up. The increase of kinetic energy in the low troposphere during cyclogenesis results from the dominance of local generation by cross-isobar flow toward the center of the developing vortex. In the upper troposphere the kinetic energy budget is not related uniquely to the development or decay of the surface cyclone. While the anticyclone, to a large extent, displays similar behavior to the cyclone, the eddy mode of lateral transport of angular momentum in the upper troposphere is not enhanced by lower level frontogenetic effects, as in the case of the cyclone.

Abstract

The budgets of mass, absolute angular momentum and kinetic energy for two model-generated cyclones and one anticyclone are examined using a sigma-coordinate framework which moves with the center of the MSL pressure extremum. The mass budgets for all three cases show a concentration of lateral mass transport in the surface boundary layer and at a level near 200 mb. The spin up of the low troposphere during cyclogenesis results from the dominance of the mean mode of lateral transport of absolute angular momentum. The spin up of the upper troposphere results from the combined influence of an inward eddy mode of lateral transport and vertical transport of absolute angular momentum. The eddy mode of lateral transport is determined by the configuration of the upper level flow (particularly jet streaks) and is enhanced by frontogenesis in the low and mid-troposphere as these regions spin up. The increase of kinetic energy in the low troposphere during cyclogenesis results from the dominance of local generation by cross-isobar flow toward the center of the developing vortex. In the upper troposphere the kinetic energy budget is not related uniquely to the development or decay of the surface cyclone. While the anticyclone, to a large extent, displays similar behavior to the cyclone, the eddy mode of lateral transport of angular momentum in the upper troposphere is not enhanced by lower level frontogenetic effects, as in the case of the cyclone.

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