Internal Wave Energy

   One of the most promising applications of seismic oceanography is its potential to measure internal wave energy.  Internal waves are gravity waves in the ocean's interior that displace water upward and downward (much like the familiar ocean-surface waves whose displacements cause, among other things, seasickness).  Internal waves are important for many reasons, chief among them their likely role in causing diapycnal mixing (a key cog in machine of climate regulation by the ocean).

   In 2005, Ilker Fer and I published in GRL (download here) the first paper showing that the undulations observed in seismic reflections from inside the ocean actually provide a means of quantifying internal wave energy.   For the non-oceanographer, this can be easily understood by an analogy.  Picture the surface of the ocean on a calm day:  you'll see lots of long-wavelength, low amplitude swells.  On a windy, stormy day, in contrast, you'd see a very different ocean, with lots of closely spaced, steep, high-amplitude waves and whitecaps.  A seismic reflection can be viewed as a cross-sectional view of a layer in the ocean, complete with its upheavals (and "downheavals") from internal waves.  Tracking reflections and performing a Fourier transform produces a quantitative measure of internal wave energy.  What Ilker and I did was to show that such an approach produced a plot that matches the canonical Garrett-Munk internal wave spectrum of the ocean:

Holbrook_Fer_Fig3

(Click on the image to see a larger version.)


   My students and I are currently working hard to extend this approach to produce, among other things, maps of internal wave energy over entire seismic lines.   Stay tuned for more.


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