Numerical Simulations of the Effects of Seamounts and Vertical Resolution on Strong Ocean Flows

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  • 1 Institute for Naval Oceanography, NSTL, Mississippi 39529
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Abstract

The effect of seamounts on Gulf Stream-like flow is examined using a quasi-geostrophic modal model that is spun-up from rest with idealized wind forcing. A flat-bottom simulation that resolves the flow with two vertical modes produces, on the average, a straight Gulf Stream-like jet across the domain along the latitude where the wind stress curl is zero. In a similar simulation that includes topographic effects, a chain of seamounts, approximately the width of the New England Seamounts, is responsible for a southward deflection of the jet as it passes over the seamounts. However, the seamounts do not appear to be a source mechanism for increased eddy activity. Simulations that include the effects of the second baroclinic mode produce a very different response from simulations that are resolved with the barotropic and first baroclinic mode only. Although 90% of the kinetic energy is contained in the two lowest modes, the higher modal interactions transfer energy to the lower modes and significantly alter the time evolution of those modes. In particular, the increased vertical shear due to the inclusion of the extra mode, enhances the energy transfer due to baroclinic instability by a factor of three relative to the 2-modal simulations and inhibits the zonal penetration of the Gulf Stream-like jet.

Abstract

The effect of seamounts on Gulf Stream-like flow is examined using a quasi-geostrophic modal model that is spun-up from rest with idealized wind forcing. A flat-bottom simulation that resolves the flow with two vertical modes produces, on the average, a straight Gulf Stream-like jet across the domain along the latitude where the wind stress curl is zero. In a similar simulation that includes topographic effects, a chain of seamounts, approximately the width of the New England Seamounts, is responsible for a southward deflection of the jet as it passes over the seamounts. However, the seamounts do not appear to be a source mechanism for increased eddy activity. Simulations that include the effects of the second baroclinic mode produce a very different response from simulations that are resolved with the barotropic and first baroclinic mode only. Although 90% of the kinetic energy is contained in the two lowest modes, the higher modal interactions transfer energy to the lower modes and significantly alter the time evolution of those modes. In particular, the increased vertical shear due to the inclusion of the extra mode, enhances the energy transfer due to baroclinic instability by a factor of three relative to the 2-modal simulations and inhibits the zonal penetration of the Gulf Stream-like jet.

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