Journal of the Meteorological Society of Japan. Ser. II
Online ISSN : 2186-9057
Print ISSN : 0026-1165
ISSN-L : 0026-1165
A Preliminary Study on the Stability of a Baroclinic Flow in Cyclostrophic Balance
Yoshihisa Matsuda
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1984 Volume 62 Issue 5 Pages 791-796


We investigate the stability of a baroclinic flow in which a centrifugal force acting on the zonal flow cannot be neglected compared to the Coriolis force. It is found that in the governing equations of this problem, the coefficient which corresponds to the Coriolis parameter in the usual baroclinic instability theory becomes a function of height, and the wave number in the longitudinal direction (k) becomes an independent external parameter. When the value of the Rossby number (R0=k/_??_ ΔH, here Δ is a vertical shear of the basic zonal flow and H is a depth of the layer) is small, the dynamic balance of the basic flow is always in the vicinity of pure geostrophic balance, so that the departure of eigenvalues obtained from pure geostrophic case remains small. For R0 larger than about 3.0, with an increase of ΔH, the dynamic balance of the basic flow is continuously changed from geostrophic balance to cyclostrophic one. It is found that in the balance close to the latter, there appear unstable waves which have fairly larger growth rate than unstable waves appearing in the usual baroclinic instability.

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