Program

Vertical mixing is a prominent problem in ocean and modeling today.  It is poorly represented in ocean and climate models, which also ignore critical latitude effects.  Critical latitude is the latitude where the inertial frequency equals the tidal frequency and differs for each tidal constituent.  Critical latitudes strongly influences generation and propagation of internal tides and are the turning latitudes for Poincaré waves of their respective frequencies.  Using a model, latitude effects on tidal interactions with a seamount were examined by changing the latitude from 20o-38o.   The critical latitude was found to strongly influence propagation of internal tides, the spectral content of the internal wave field, barotropic and baroclinic mean flows, diffusivities, and the temperature and salinity fields.  The strongest effects occurred in the 6o poleward of the K1 critical latitude.  Here, the semidiurnal tides, harmonics and high frequencies were enhanced, stronger barotropic and baroclinic mean velocities developed, particularly in the cross-slope direction, more energy was transferred to the harmonics and higher frequencies, particularly in the along-slope direction, diffusivities increased, and the location of mixing in the water column shifted, inducing mixing through the thermocline and warming from 500-1000 m water depth.  Spectral techniques indicate that most of these impacts are the result of non-linear wave-wave interactions and resonant phenomena.   There was no evidence of parametric subharmonic instabilities. Further than 6o poleward of the K1 critical latitude, these effects ceased.  Similar effects also occurred poleward of the latitude, which equaled the combined period of the M2 and K1 tides.