Observations of enhanced nonlinear instability in the surface reflection of internal tides. Issue 8 (29th April 2013)

• Record Type: Journal Article
• Authors: Xie, Xiaohui; Shang, Xiaodong; van, Hans; Chen, Guiying
• Is Part Of: Geophysical research letters. Volume 40:Issue 8(2013:Apr.)
• Page Start: 1580
• Page End: 1586
• Publication Date: 2013-04-29
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/grl.50322
• Languages: English
• ISSNs: 0094-8276

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p id="grl50322-para-0001">[1] Enhanced vertically standing waves formed by the superposition of two upward and downward going near‐diurnal (<italic>D</italic>₁) waves are observed during one semidiurnal (<italic>D</italic>₂) spring tide in an approximately 75 day long velocity record from the northeastern South China Sea. Bicoherence estimates suggest that the enhanced <italic>D</italic>₁ waves are likely due to nonlinear parametric subharmonic instability of <italic>D</italic>₂ internal tides. The timescale for energy growth by an order of magnitude is about 2.5 days for these waves. In addition to subharmonics, higher harmonics <italic>D</italic>₄ (=<italic>D</italic>₂ + <italic>D</italic>₂) and a mean flow are generated by a different nonlinear interaction during the same <italic>D</italic>₂ spring tide. The separation of coherent from incoherent internal tidal signals and a rotary spectral decomposition in the vertical direction reveal that <italic>D</italic>₂ waves with opposite vertical propagation directions in the region of internal tide reflection from the surface may be responsible for the pronounced nonlinear instability.</p> </abstract>