When ocean tidal currents encounter undersea topography, waves called internal tides are generated.
These waves propagate into the ocean interior and can contribute significantly to oceanic mixing when they break, influencing how nutrients are distributed and how energy is transported throughout the ocean.
Understanding where this breaking occurs in the ocean is thus central to understanding the global climate system.
Prior models showed that a particular breaking mechanism known as "parametric subharmonic instability" (PSI) could in principle remove a large amount of energy from the internal tides at a "critical latitude" of 28.8 degrees North.
To test this notion, Alford et al. heavily instrumented a 1400-km (870-mile)-long line beginning at French Frigate Shoals, a major generation site at the Hawaiian Ridge, with the intention of tracking the internal tide's northward progress past the critical latitude.
They found strong evidence that PSI does occur, leading to intense alternating bands of clockwise-rotating velocity, but that the process appears not to substantially attenuate the internal tide (whose fate remains uncertain). However, PSI does appear to strongly affect the latitudinal distribution of internal wave energy.
Title: Internal waves across the Pacific
Authors: M. H. Alford: Applied Physics Laboratory, University of Washington, Seattle, Washington, U.S.A.; also at School of Oceanography, University of Washington, Seattle, Washington, U.S.A.; J. A. MacKinnon and Rob Pinkel: Scripps Institution of Oceanography, La Jolla, California, U.S.A.; Zhongxiang Zhao: Applied Physics Laboratory, University of Washington, Seattle, Washington, U.S.A.; Jody Klymak: School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada; Thomas Peacock: Mechanical Engineering, Massachusetts Institute of Technology, Cambridge Massachusetts, U.S.A.
Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL031566, 2007; http://dx.doi.org/10.1029/2007GL031566
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