Speaker: Tim Duda (WHOI)
Title: Internal tide radiation from the Gulf of Maine: Modal ray refraction in baroclinic Gulf Stream currents
The interaction with the Gulf Stream of southward-radiating internal tides generated by the strong resonant tides of the Gulf of Maine, observed in tide-inclusive HYCOM model fields, is examined with new ray-based wave propagation techniques. One interesting feature is that upstream semidiurnal internal tidal energy flux is seen in the main jet of the current. An explanation of the flux pattern within the Gulf Stream is that internal wave modal rays can be strongly redirected by baroclinic currents, and even ducted by baroclinic current jets that are directed counter to the modal propagation direction (i.e., when the waves travel upstream). This ducting behavior is analyzed and explained here with ray-based wave propagation studies for internal wave modes with anisotropic wavenumbers, as occur in mesoscale background flow fields. Two analysis tools are introduced and then used: the generalized Jones equation governing modal properties, and ray equations that are suitable for studying waves with anisotropic wavenumbers.