The Modification of Long Planetary Waves by Homogeneous Potential Vorticity Layers

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Abstract
A mechanism by which long planetary waves in the ocean may propagate significantly faster than the classical long baroclinic Rossby waves is investigated. The mechanism depends on the poleward thickening of intermediate density layers and the concomitant thinning of near-surface and deep layers. These features of the mass distribution are associated with the well-known homogenization of potential vorticity in intermediate density layers and with significantly elevated meridional potential vorticity gradients near the surface and somewhat at depth. The mechanism is explored in a simple three-layer model, in which the middle layer has zero potential vorticity gradient and is sandwiched between a surface layer with large potential vorticity gradient and a bottom layer with modest potential vorticity gradient. The effective phase speed of the planetary waves is merely the sum of the phase speeds of virtual baroclinic Rossby waves propagating on the individual layer interfaces as though the other inte... Abstract A mechanism by which long planetary waves in the ocean may propagate significantly faster than the classical long baroclinic Rossby waves is investigated. The mechanism depends on the poleward thickening of intermediate density layers and the concomitant thinning of near-surface and deep layers. These features of the mass distribution are associated with the well-known homogenization of potential vorticity in intermediate density layers and with significantly elevated meridional potential vorticity gradients near the surface and somewhat at depth. The mechanism is explored in a simple three-layer model, in which the middle layer has zero potential vorticity gradient and is sandwiched between a surface layer with large potential vorticity gradient and a bottom layer with modest potential vorticity gradient. The effective phase speed of the planetary waves is merely the sum of the phase speeds of virtual baroclinic Rossby waves propagating on the individual layer interfaces as though the other inte...

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