A Two-Layer Model Study of the Combined Barotropic and Baroclinic Instability in the Tropics

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  • 1 Department of Geophysical Sciences, The University of Chicago, Chicago, IL 60637
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Abstract

The stabilities of shear zone and jet type mean currents with both horizontal and vertical shears in the tropics am investigated by the use of two-level linearized primitive equations. The results show that the main source of instability is the horizontal shear, and the influences of the mean vertical shear and stable stratification are to restrict the disturbance either to the upper or to the lower level. The β-effect stabilizes the shear flow and the westerly jet but it destabilizes the easterly jet, and the CISK mechanism is significant only when the surface layer is well mixed.

The jet profile is most unstable when its center is located from 6° to 10° from the equator, and the maximum intensity of the disturbance occurs on the side of the jet where the absolute vorticity of the mean flow is small. The first effect mentioned above is significant for the mean position of the ITCZ through the feedback mechanism.

Abstract

The stabilities of shear zone and jet type mean currents with both horizontal and vertical shears in the tropics am investigated by the use of two-level linearized primitive equations. The results show that the main source of instability is the horizontal shear, and the influences of the mean vertical shear and stable stratification are to restrict the disturbance either to the upper or to the lower level. The β-effect stabilizes the shear flow and the westerly jet but it destabilizes the easterly jet, and the CISK mechanism is significant only when the surface layer is well mixed.

The jet profile is most unstable when its center is located from 6° to 10° from the equator, and the maximum intensity of the disturbance occurs on the side of the jet where the absolute vorticity of the mean flow is small. The first effect mentioned above is significant for the mean position of the ITCZ through the feedback mechanism.

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