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Reconsideration of Orlanski's instability theory of frontal waves

Published online by Cambridge University Press:  26 April 2006

Keita Iga
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Abstract

This paper complements the instability theory of frontal waves investigated by Orlanski (1968), and reinterprets the unstable modes obtained. First, the stability of a frontal model is reconsidered by using a matrix method. The major part of Orlanski's (1968) result is verified but some flaws are found in some parameter regions: unstable modes do not exist over the entire Ri–Ro region. Also, the features of the neutral waves in the one-layer subsystems are studied, in order to determine the instability of the full two-layer system. As a result, the unstable mode called the (B)-mode by Orlanski (1968) and suggested by Sakai (1989) to be Rossby-Kelvin instability caused by a resonance between a Rossby wave and a gravity wave, proves to be a geostrophic unstable mode caused by resonance between a Rossby wave and the Rossby-gravity mixed mode. In addition, some of the analytical conclusions about the stability of this frontal model are explained by the features of the neutral waves in the one-layer subsystem.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 255 , October 1993 , pp. 213 - 236
Copyright
© 1993 Cambridge University Press

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