Computations of the energy flux to mixing processes via baroclinic wave drag on barotropic tides

Abstract

The geographical distribution of barotropic to baroclinic transfer of tidal energy by baroclinic wave drag in the abyssal ocean is estimated. Using tidal velocities from a state-of-the-art numerical tidal model, the total loss of barotropic tidal energy in the deep ocean (between 70°S and 70°N and at depths greater than 1000 m) is estimated to be about 0.7 TW ( M 2) corresponding to a mean value of the energy flux ( e) of 2.4×10 −3 W/m 2. The distribution of e is however highly skewed with a median of about 10 −6 W/m 2. Only 10% of the area is responsible for more than 97% of the total energy transfer. To assess the possible influence of the relatively coarse bathymetry representation upon the present estimate, complementary calculations using better resolved sea floor topography are carried out over a control area around the Hawaiian Ridge. There are no major differences between the results achieved using the two different bathymetry databases. Fluxes of about 16 GW or 6×10 −3 W/m 2 are computed in both cases, and the main contributions to the total fluxes originate in the same range of e-values and cover equally large parts of the total area. It is not clear whether the present model is valid at flat or subcritical bottom slopes. However, for the Hawaiian region, only 2% of the total energy flux as calculated in the present study originates in areas of critical and subcritical slopes.