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  • Author or Editor: J. P. Koermer x
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V. E. Kousky and J. P. Koermer

Abstract

The atmospheric Kelvin wave is modeled with nonlinear terms included. Forcing from below leads to a Kelvin wave similar to that observed. The nonlinear terms lead to an asymmetry in the wave, producing a zone of strong vertical shear in association with the westerly shear zone. Dissipation was not included in the model to limit the degree of asymmetry or buildup of vertical shear.

Observational evidence indicates that clear-air turbulence (CAT) eventually breaks out, thus causing the waves to suddenly dissipate. It is inferred that, at the time of dissipation, large amounts of westerly momentum are supplied to the mean flow and that this is responsible for the downward propagation of the westerly shear zone.

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J. P. Koermer, A. Kasahara, and S. K. Kao

Abstract

A primitive equation spectral model using spherical harmonics is formulated to study dynamic interactions between the troposphere and stratosphere in association with sudden stratospheric warmings. Using sigma coordinates for five tropospheric layers and log-pressure coordinates for 26 stratospheric and mesospheric layers separate model equations for each system are combined to form single matrix governing equations. The gradual introduction of large scale topography to balanced initial states representative of observed mean winter conditions in the Northern Hemisphere is used for the generation of planetary waves during 40-day time integrations. Results of these integrations indicate that stratospheric warnings can be simulated by this orographic forcing and that mean momentum flux divergence due to zonal mean motion appears to be an essential mechanism of these simulated sudden warmings. It was found that the strength of the polar night jet can be, a determining factor whether a warming becomes “major” or “minor.”

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