Energy cascades in the baroclinic ocean wind-driven double gyre problem
Seminar Room 1, Newton Institute
AbstractCo-author: David Straub
We consider the classic baroclinic quasigeostrophic wind-driven ocean double gyre problem over a range of deformation radii, wind stress amplitudes, and bottom friction coefficients with an aim of understanding transfer of energy across scales. In this beta-plane basin setting, we find significant differences from classic studies of gestrophic turbulence, which generally assume zonal periodicity. In a basin geometry, the beta term (related to a latitudinal dependence in the Corioils parameter) can play a key role. For example, it can be the dominant term allowing for energy transfer between the basin scale and the baroclinic mesoscale. We also find that barotropization of baroclinic mesoscale energy forces the barotropic mode at scales where the barotropic mode is most energetic. Related to this, the barotropic nonlinear inverse energy cascade does not extend between mesoscale injection and large scale dissipation wavenumbers, as is often assumed. Instead, it is part of a ``double cascade" of barotropic energy in which the nonlinear inverse cascade is nearly offset by a forward cascade associated with the beta term. This is particularly evident in weak bottom drag simulations, for which a time eddy-mean flow decomposition reveals the double cascade to beassociated with the eddy-only terms.
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