On the Inertial Stability f the Equatorial Middle Atmosphere

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  • 1 Department of Atmospheric Sciences, University of Washington, Seattle 98195
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Abstract

A theory of inertial instability on the equatorial beta-plane is developed with application to the inertial stability of the equatorial middle atmosphere at the solstices. It is shown that the stability of this region depends primarily on two unknowns. First, there is the question of whether eddy diffusion can be regarded as stabilizing, or whether this diffusion actually arises from the instability itself. Second, because the diabatic circulation would appear to induce a cross-equatorial shear much greater than that observed, or than that modeled in Holton and Wehrbein (1980), it appears that the gravity wave-induced decelerations would he crucial to the stability of this flow. Unfortunately, the parameterization scheme of Leovy (1964) designed to mimic this effect obscures the issue, since this “frictional drag” concept is invalid on a local basis (Lindzen, 1981).

The expected structure and vertical wavelength of the equatorial inertial instability is discussed in the context of this simple model. Predicted vertical wavelengths also depend on the unknown factors listed above. The greatest likelihood of an observable inertial instability would be in the winter tropical mesosphere, within 10° of the equator.

Abstract

A theory of inertial instability on the equatorial beta-plane is developed with application to the inertial stability of the equatorial middle atmosphere at the solstices. It is shown that the stability of this region depends primarily on two unknowns. First, there is the question of whether eddy diffusion can be regarded as stabilizing, or whether this diffusion actually arises from the instability itself. Second, because the diabatic circulation would appear to induce a cross-equatorial shear much greater than that observed, or than that modeled in Holton and Wehrbein (1980), it appears that the gravity wave-induced decelerations would he crucial to the stability of this flow. Unfortunately, the parameterization scheme of Leovy (1964) designed to mimic this effect obscures the issue, since this “frictional drag” concept is invalid on a local basis (Lindzen, 1981).

The expected structure and vertical wavelength of the equatorial inertial instability is discussed in the context of this simple model. Predicted vertical wavelengths also depend on the unknown factors listed above. The greatest likelihood of an observable inertial instability would be in the winter tropical mesosphere, within 10° of the equator.

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