A Quasi-Lagrangian Study of the Barotropic Jet Stream

David D. Houghton National Center for Atmospheric Research, Boulder, Colo.

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Abstract

A quasi-Lagrangian formulation for an inviscid barotropic fluid is presented and shown to afford a convenient basis for analysis of certain ageostrophic jet flows. Material fines serve as the references to delineate the north-south variations in the fluid, and Eulerian representation is used in the east west direction. Several desirable features are shown for the use of material lines in this manner. First, by orienting the lines approximately parallel to the jet axis, flows with finite horizontal curvature may be represented simply. This is illustrated by a development with east-west variations represented by only two harmonies and a mean. The solution of this semi-spectra model agrees closely with a non-spectral numerical solution for over three days. Second, the Lagrangian movement of the material lines gives an indication of non-linear adjustment motions and demonstrates a mixing in the fluid.

Abstract

A quasi-Lagrangian formulation for an inviscid barotropic fluid is presented and shown to afford a convenient basis for analysis of certain ageostrophic jet flows. Material fines serve as the references to delineate the north-south variations in the fluid, and Eulerian representation is used in the east west direction. Several desirable features are shown for the use of material lines in this manner. First, by orienting the lines approximately parallel to the jet axis, flows with finite horizontal curvature may be represented simply. This is illustrated by a development with east-west variations represented by only two harmonies and a mean. The solution of this semi-spectra model agrees closely with a non-spectral numerical solution for over three days. Second, the Lagrangian movement of the material lines gives an indication of non-linear adjustment motions and demonstrates a mixing in the fluid.

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