Internal Tide Research

Tim Duda
Woods Hole Oceanographic Institution
Woods Hole MA 02543

Tim Duda cv/homepage hosted by Coastal and Ocean Fluids Lab



Internal gravity wave motions at or near tidal frequencies, usually if not always generated by the action of the ocean's surface tides, compose an important fraction of the internal velocity and shear budget in many areas. These waves are also precursors of nonlinear internal waves which appear throughout the world. The nonlinear waves appear as solitary waves or packets of waves, have time scales of minutes to tens of minutes, and length scales of hundreds of meters (wave width or crest-to-crest). By contrast, the internal tides have wavelengths of 30 to 100 km. There are numerous online resources providing further detail in on ocean internal waves ans internal tides. This compendium provides theoretical background as well as geographic information: (www.internalwaveatlas.com).

The interest of the WHOI Ocean Acoustics and Signals Lab in this class of ocean waves began grew during the mid 90's. The successful SWARM program (Shallow Water Acoustics in Random Medium) provided very good data showing the importance of nonlinear internal waves to the physics of underwater sound fluctuation. Since then, the 2001 ASIAEX and Shallow Water 2006 (SW06) programs have successfully collected good information on the phenomena.

At this time we are focused on explaining a poorly understood lack of correlation between the very regular tidal forcing currents and the somewhat irregular and difficult to predict internal tides and nonlinear wave packets.

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Examples of large internal tides and nonliner internal waves measured in the South China Sea Asiaex project are shown below. A the left, timeseries of isotherm heights are shown as color contours. The mooring locations are shoewn at the right. (click to enlarge) At the top of the page is a NASA Space Shuttle photograph of surface roughness of nonlinear waves, also in the Asian Seas area, caused by converging surface currents. This image from eol.jsc.nasa.gov also appears at www.internalwaveatlas.com.


Links:

WHOI Applied Ocean Physics and Engineering. Dept. (AOPE)
WHOI AOPE Coastal and Ocean Fluid Dynamics Lab Webpage
WHOI AOPE Ocean Acoustics and Signals Lab Webpage (My formal affiliation.)
NSF
 


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