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2011
Zhao, ZX, Alford MH, Girton J, Johnston TMS, Carter G.  2011.  Internal tides around the Hawaiian Ridge estimated from multisatellite altimetry. Journal of Geophysical Research-Oceans. 116   10.1029/2011jc007045   AbstractWebsite

Satellite altimetric sea surface height anomaly (SSHA) data from Geosat Follow-on (GFO) and European Remote Sensing (ERS), as well as TOPEX/Poseidon (T/P), are merged to estimate M(2) internal tides around the Hawaiian Ridge, with higher spatial resolution than possible with single-satellite altimetry. The new estimates are compared with numerical model runs. Along-track analyses show that M(2) internal tides can be resolved from both 8 years of GFO and 15.5 years of ERS SSHA data. Comparisons at crossover points reveal that the M(2) estimates from T/P, GFO, and ERS agree well. Multisatellite altimetry improves spatial resolution due to its denser ground tracks. Thus M(2) internal tides can be plane wave fitted in 120 km x 120 km regions, compared to previous single-satellite estimates in 4 degrees lon x 3 degrees lat or 250 km x 250 km regions. In such small fitting regions the weaker and smaller-scale mode 2 M(2) internal tides can also be estimated. The higher spatial resolution leads to a clearer view of the M(2) internal tide field around the Hawaiian Ridge. Discrete generation sites and internal tidal beams are clearly distinguishable, and consistent with the numerical model runs. More importantly, multisatellite altimetry produces larger M(2) internal tidal energy fluxes, which agree better with model results, than previous single-satellite estimates. This study confirms that previous altimetric underestimates are partly due to the more widely spaced ground tracks and consequently larger fitting region. Multisatellite altimetry largely overcomes this limitation.

2003
Johnston, TMS, Merrifield MA.  2003.  Internal tide scattering at seamounts, ridges, and islands. Journal of Geophysical Research-Oceans. 108   10.1029/2002jc001528   AbstractWebsite

[1] The scattering of mode-1 internal tides from idealized Gaussian topography in a nonrotating ocean with constant and realistic stratifications is examined with a primitive equation numerical model. Incident mode-1 energy fluxes of 20 and 2000 W m(-1) are used to examine the linear regime and a more realistic situation. Simulations using two-dimensional or infinite ridges compare well with ray tracing methods and illustrate how the size and shape of the topography influence wave scattering. The height affects energy transmission and reflection, while the slope and width determine the conversion of low-mode internal tides into beams or higher modes. Three-dimensional topographic scattering is considered for seamounts, finite-width ridges, and islands. Scattering from finite ridges focuses wave energy directly downstream, while scattering from seamounts produces azimuthal energy dispersion. Scattering to higher wave modes occurs in the lee of near-critical and supercritical seamounts and ridges. Nonlinear interactions transfer energy into the mode-1 M-4 internal tide. The Mellor-Yamada level-2.5 submodel parameterizes turbulent mixing. For the near-critical and supercritical ridges with realistic stratification, elevated mixing is found over the leading edge of the topography and along a tidal beam up to the first surface bounce. A transition from a beam structure near the topography to a low-mode structure farther away occurs due to an increased contribution from the mode-1 internal tide as it refracts around the topography and not due to turbulent dissipation. Internal tide scattering at topography leads to a loss of energy to mixing and to a redistribution of energy flux in space, frequency, and mode number.