Internal tide generation from non-uniform barotropic body forcing

CE Papoutsellis, MJ Mercier… - Journal of Fluid …, 2023 - cambridge.org
Journal of Fluid Mechanics, 2023cambridge.org
We model linear, inviscid, internal tides generated by the interaction of a barotropic tide with
one-dimensional topography. Starting from the body-forcing formulation of the hydrodynamic
problem, we derive a coupled-mode system (CMS) using a local eigenfunction expansion of
the stream function. For infinitesimal topography, we solve this CMS analytically, recovering
the classical weak topography approximation (WTA) formula for the barotropic-to-baroclinic
energy conversion rate. For arbitrary topographies, we solve this CMS numerically. The …
We model linear, inviscid, internal tides generated by the interaction of a barotropic tide with one-dimensional topography. Starting from the body-forcing formulation of the hydrodynamic problem, we derive a coupled-mode system (CMS) using a local eigenfunction expansion of the stream function. For infinitesimal topography, we solve this CMS analytically, recovering the classical weak topography approximation (WTA) formula for the barotropic-to-baroclinic energy conversion rate. For arbitrary topographies, we solve this CMS numerically. The CMS enjoys faster convergence with respect to existing modal solutions and can be applied in the subcritical and supercritical regimes for both ridges and shelf profiles. We show that the non-uniform barotropic tide affects the baroclinic field locally over topographies with large slopes and we study the dependence of the radiated energy conversion rate on the criticality. We show that non-radiating or weakly radiating topographies are common in the subcritical regime. We also assess the region of validity of the WTA approximation for the commonly used Gaussian ridge and a compactly supported bump ridge studied here for the first time. Finally, we provide numerical evidence showing that in the strongly supercritical regime, the energy conversion rate for a ridge (respectively shelf) approaches the value obtained by the knife-edge (respectively step) topography.
Cambridge University Press
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