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Development of radiation fields and baroclinic eddies in a β-plane

Published online by Cambridge University Press:  19 April 2006

C. L. Tang
C. L. Tang
Affiliation:
Bedford Institute of Oceanography, Dartmouth, N.S., Canada
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Abstract

The evolution of an eddy in a two-layer shear flow and the radiation field generated by the eddy are investigated by solving the initial value problem. The solution indicates that two wave regimes with different characteristics exist in the x/t plane, where t is the time and x is the distance from the initial disturbance. The near-field (small x/t) behaviour depends critically on the stability of the shear. In a baroclinically stable shear flow, the radiation field of the baroclinic waves is confined to a region the boundary of which expands linearly with time. If the shear flow is baroclinically unstable, the eddy gradually evolves from an isotropic structure into a wave packet that grows exponentially and expands as the square root of time. The far field (large x/t) consists mainly of long barotropic Rossby waves. As x/t increases, the effect of the mean currents becomes weaker and the motion becomes increasingly barotropic in character. If we consider the strong boundary current as a source of baroclinic energy in the ocean, the far-field results show that the mid-ocean eddies can reach large amplitudes independent of the mean currents. The transient motion (small x and t) of the eddy is examined by numerically computing the stream function from the solution. The results show that the combined actions of baroclinic instability and wave dispersion cause an initially isotropic eddy to remain roughly isotropic for a relatively long period of time. This suggests that the initial development of unstable eddies cannot be neglected in studying the meridional scale of the eddy field in the atmosphere. Application of the model to study the dispersion of wind-generated Rossby waves is discussed.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 93 , Issue 2 , 26 July 1979 , pp. 379 - 400
Copyright
© 1979 Cambridge University Press

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