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ON THE ENERGY EXCHANGE BETWEEN THE BAROCLlNlC AND BAROTROPIC COMPONENTS OF ATMOSPHERIC FLOW

A. WIIN-NIELSENNational Center for Atmospheric Research, Boulder, Colo. and Department of Meteorology and Oceanography, University of Michigan, Ann Arbor, Mich.

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MARGARET DRAKENational Center for Atmospheric Research, Boulder, Colo.

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Abstract

The energy conversion between the vertical shear flow and the vertical mean flow has been computed using atmospheric data from the isobaric surfaces: 850, 700,500, 300, and 200 mb. In comparison with earlier calculations based on a smaller vertical resolution (2 levels) and a smaller sample, it is found that the new calculations give larger numerical values in better agreement with the results of numerical experiments concerning the general circulation of the atmosphere. The energy transformation has been computed in the wave number regime, and it is found that the medium-scale waves are responsible for the major portion of the transformation.

The amounts of energy in the baroclinic component (the vertical shear flow) and the barotropic component (the vertical mean flow) have been computed as a function of wave number. It is found that the kinetic energy in the barotropic component is about 2.6 times the kinetic energy in the baroclinic component. The partitioning of the kinetic energy between the zonal flow and the eddies is such that the eddies contain more energy than the zonal flow. This result applies for the vertical shear flow as well as the vertical mean flow and is in contrast to the results obtained from numerical experiments regarding the general circulation.

The present computations include only the energy calculations which would be present in a quasi-non-divergent model. Later calculations will provide estimates of the remaining term of the energy conversion.

Abstract

The energy conversion between the vertical shear flow and the vertical mean flow has been computed using atmospheric data from the isobaric surfaces: 850, 700,500, 300, and 200 mb. In comparison with earlier calculations based on a smaller vertical resolution (2 levels) and a smaller sample, it is found that the new calculations give larger numerical values in better agreement with the results of numerical experiments concerning the general circulation of the atmosphere. The energy transformation has been computed in the wave number regime, and it is found that the medium-scale waves are responsible for the major portion of the transformation.

The amounts of energy in the baroclinic component (the vertical shear flow) and the barotropic component (the vertical mean flow) have been computed as a function of wave number. It is found that the kinetic energy in the barotropic component is about 2.6 times the kinetic energy in the baroclinic component. The partitioning of the kinetic energy between the zonal flow and the eddies is such that the eddies contain more energy than the zonal flow. This result applies for the vertical shear flow as well as the vertical mean flow and is in contrast to the results obtained from numerical experiments regarding the general circulation.

The present computations include only the energy calculations which would be present in a quasi-non-divergent model. Later calculations will provide estimates of the remaining term of the energy conversion.

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