Publications

Export 2 results:
Sort by: Author Title Type [ Year  (Desc)]
2015
Johnston, TMS, Rudnick DL, Kelly SM.  2015.  Standing internal tides in the Tasman Sea observed by gliders. Journal of Physical Oceanography. 45:2715-2737.   10.1175/jpo-d-15-0038.1   AbstractWebsite

Low-mode internal tides are generated at tall submarine ridges, propagate across the open ocean with little attenuation, and reach distant continental slopes. A semidiurnal internal tide beam, identified in previous altimetric observations and modeling, emanates from the Macquarie Ridge, crosses the Tasman Sea, and impinges on the Tasmanian slope. Spatial surveys covering within 150 km of the slope by two autonomous underwater gliders with maximum profile depths of 500 and 1000 m show the steepest slope near 43 degrees S reflects almost all of the incident energy flux to form a standing wave. Starting from the slope and moving offshore by one wavelength (similar to 150 km), potential energy density displays an antinode-node-antinode-node structure, while kinetic energy density shows the opposite. Mission-mean mode-1 incident and reflected flux magnitudes are distinguished by treating each glider's survey as an internal wave antenna for measuring amplitude, wavelength, and direction. Incident fluxes are 1.4 and 2.3 kW m(-1) from the two missions, while reflected fluxes are 1.2 and 1.8 kW m(-1). From one glider surveying the region of highest energy at the steepest slope, the reflectivity estimates are 0.8 and 1, if one considers the kinetic and potential energy densities separately. These results are in agreement with mode-1 reflectivity of 0.7-1 from a model in one horizontal dimension with realistic topography and stratification. The direction of the incident internal tides is consistent with altimetry and modeling, while the reflected tide is consistent with specular reflection from a straight coastline.

2010
Rainville, L, Johnston TMS, Carter GS, Merrifield MA, Pinkel R, Worcester PF, Dushaw BD.  2010.  Interference Pattern and Propagation of the M(2) Internal Tide South of the Hawaiian Ridge. Journal of Physical Oceanography. 40:311-325.   10.1175/2009jpo4256.1   AbstractWebsite

Most of the M(2) internal tide energy generated at the Hawaiian Ridge radiates away in modes 1 and 2, but direct observation of these propagating waves is complicated by the complexity of the bathymetry at the generation region and by the presence of interference patterns. Observations from satellite altimetry, a tomographic array, and the R/P FLIP taken during the Farfield Program of the Hawaiian Ocean Mixing Experiment (HOME) are found to be in good agreement with the output of a high-resolution primitive equation model, simulating the generation and propagation of internal tides. The model shows that different modes are generated with different amplitudes along complex topography. Multiple sources produce internal tides that sum constructively and destructively as they propagate. The major generation sites can be identified using a simplified 2D idealized knife-edge ridge model. Four line sources located on the Hawaiian Ridge reproduce the interference pattern of sea surface height and energy flux density fields from the numerical model for modes 1 and 2. Waves from multiple sources and their interference pattern have to be taken into account to correctly interpret in situ observations and satellite altimetry.