KINETIC ENERGY GENERATION AND DISSIPATION IN THE LARGE-SCALE ATMOSPHERIC CIRCULATION

ERNEST C. KUNG Geophysical Fluid Dynamics Laboratory, Environmental Science Services Administration, Washington, D.C

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Abstract

The kinetic energy budget and dissipation are studied in their various partitionings, using daily aerological (wind and geopotential) data from the network over North America for six months.

The total kinetic energy dissipation is partitioned into vertical mean flow and shear flow and also into planetary boundary layer and free atmosphere. Furthermore, the dissipations in the vertical mean flow and shear flow are partitioned separately into components contributed by the boundary layer and free atmosphere. Two important terms in the total kinetic energy equation in determining the total dissipation are the generation and outflow. Two important terms in the mean flow kinetic energy equation in determining the mean flow dissipation are the conversion between the vertical shear and mean flows and the outflow. The mean flow and shear flow dissipations seem to have numerical values of the same order of magnitude. The evaluated boundary layer dissipation and free atmosphere dissipation indicate that the latter is at least, as important as the former. It is also shown that the mean flow dissipation is mainly contributed from the free atmosphere while the shear flow dissipation is contributed from the boundary layer and free atmosphere in the same order of magnitude. The evaluated dissipation values and related kinetic energy parameters are presented and examined in detail.

Of special interest in this study is the direct evaluation of the kinetic energy generation due to the work done by the horizontal pressure force. Daily variation of the generation at different pressure levels seems to suggest three different modes of the generation cycle in the upper, mid, and lower troposphere. Clear vertical profiles of the generation from the surface to the 100-mb. level are obtained; it is shown that strong generation takes place in the upper and lower troposphere while the generation in the mid troposphere is very weak. It is also suggested that there may be an approximate balance of the kinetic energy generation and dissipation in the boundary layer.

Abstract

The kinetic energy budget and dissipation are studied in their various partitionings, using daily aerological (wind and geopotential) data from the network over North America for six months.

The total kinetic energy dissipation is partitioned into vertical mean flow and shear flow and also into planetary boundary layer and free atmosphere. Furthermore, the dissipations in the vertical mean flow and shear flow are partitioned separately into components contributed by the boundary layer and free atmosphere. Two important terms in the total kinetic energy equation in determining the total dissipation are the generation and outflow. Two important terms in the mean flow kinetic energy equation in determining the mean flow dissipation are the conversion between the vertical shear and mean flows and the outflow. The mean flow and shear flow dissipations seem to have numerical values of the same order of magnitude. The evaluated boundary layer dissipation and free atmosphere dissipation indicate that the latter is at least, as important as the former. It is also shown that the mean flow dissipation is mainly contributed from the free atmosphere while the shear flow dissipation is contributed from the boundary layer and free atmosphere in the same order of magnitude. The evaluated dissipation values and related kinetic energy parameters are presented and examined in detail.

Of special interest in this study is the direct evaluation of the kinetic energy generation due to the work done by the horizontal pressure force. Daily variation of the generation at different pressure levels seems to suggest three different modes of the generation cycle in the upper, mid, and lower troposphere. Clear vertical profiles of the generation from the surface to the 100-mb. level are obtained; it is shown that strong generation takes place in the upper and lower troposphere while the generation in the mid troposphere is very weak. It is also suggested that there may be an approximate balance of the kinetic energy generation and dissipation in the boundary layer.

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