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Free Content Linear planetary wave dynamics in a 2.5-layer ventilated thermocline model

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Linear planetary wave dynamics in a 2.5-layer ventilated thermocline model is investigated by a local eigenvalue analysis and simple numerical computations. It is known that there are two types of waves in this system; we refer to one of them as the N-mode (Non-Doppler shift mode), which propagates almost westward, and the other as the A-mode (Advection mode), which propagates almost along the second layer basic current. First, we study the local longwave dynamics, assuming that the wavelength is much longer than the deformation radius and shorter than the gyre scale. It is shown that the N-mode and the A-mode cannot neatly be separated in the ventilated zone, and even in the Rhines and Young pool, a compact A-mode disturbance cannot exist by itself. When anomalous Ekman pumping is applied in the ventilated zone, the N-mode is generated in the forcing region, and the A-mode is generated at the wave front of the N-mode. For diabatic forcing, a similar phenomenon occurs. It is also found that the shadow zone is unstable to longwave disturbances. Secondly, the wave behavior in the linear planetary geostrophic model is numerically investigated. The main features can be interpreted by the local wave dynamics, and the disturbances around the maximum amplitudes are dominated by the waves whose wavenumber vectors are perpendicular to the second layer potential vorticity contours. The amplitude changes during the wave propagation are also discussed. Finally, the effects of the finite wavelength are studied. The N-mode is strongly dispersive at the scale of the Rossby deformation radius, while the A-mode is weakly dispersive. It is also shown that the ventilated zone is unstable to shortwave disturbances, although it is stable to longwave disturbances.

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Document Type: Regular Paper

Publication date: May 1, 2002

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  • The Journal of Marine Research, one of the oldest journals in American marine science, publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. Biological studies involving coupling between ecological and physical processes are preferred over those that report systematics. The editors strive always to serve authors and readers in the academic oceanographic community by publishing papers vital to the marine research in the long and rich tradition of the Sears Foundation for Marine Research. We welcome you to the Journal of Marine Research.
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