The evolution and energetics of large amplitude nonlinear internal waves on the Portuguese shelf

Abstract. We revisit experimental studies performed by Ekman on dead-water (Ekman, 1904) using modern techniques in order to present new insights on this peculiar phenomenon. We extend its description to more general situations such as a three-layer fluid or a linearly stratified fluid in presence of a pycnocline, showing the robustness of dead-water phenomenon. We observe large amplitude nonlinear internal waves which are coupled to the boat dynamics, and we emphasize that the modeling of the wave-induced drag requires more analysis, taking into account nonlinear effects. Dedicated to Fridtjöf Nansen born 150 yr ago (10 October 1861).

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Observations of Large-Amplitude Mode-2 Nonlinear Internal Waves on the Australian North West Shelf

Journal of Physical Oceanography ◽

10.1175/jpo-d-18-0097.1 ◽

2019 ◽

Vol 49 (1) ◽

pp. 309-328 ◽

Cited By ~ 10

Author(s):

Matthew D. Rayson ◽

Nicole L. Jones ◽

Gregory N. Ivey

Keyword(s):

Internal Waves ◽

Large Amplitude ◽

Transition Period ◽

Local Mode ◽

Driving Mechanism ◽

Length Scale ◽

North West ◽

Nonlinear Internal Waves ◽

Mode 2 ◽

Amplitude Mode

AbstractLarge-amplitude mode-2 nonlinear internal waves were observed in 250-m-deep water on the Australian North West shelf. Wave amplitudes were derived from temperature measurements using three through-the-water-column moorings spaced 600 m apart in a triangular configuration. The moorings were deployed for 2 months during the transition period between the tropical monsoon and the dry season. The site had a 25–30-m-amplitude mode-1 internal tide that essentially followed the spring–neap tidal cycle. Regular mode-2 nonlinear wave trains with amplitudes exceeding 25 m, with the largest event exceeding 50 m, were also observed at the site. Overturning was observed during several mode-2 events, and the relatively high wave Froude number and steepness (0.15) suggested kinematic (convective) instability was likely to be the driving mechanism. The presence of the mode-2 waves was not correlated with the tidal forcing but rather occurred when the nonlinear steepening length scale was smaller than the distance from the generation region to the observation site. This steepening length scale is inversely proportional to the nonlinear parameter in the Korteweg–de Vries equation, and it varied by at least one order of magnitude under the evolving background thermal stratification over the observation period. Despite the complexity of the internal waves in the region, the nonlinear steepening length was shown to be a reliable indicator for the formation of large-amplitude mode-2 waves and the rarer occurrence of mode-1 large-amplitude waves. A local mode-2 generation mechanism caused by a beam interacting with a pycnocline is demonstrated using a fully nonlinear numerical solution.

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Shoaling of large-amplitude nonlinear internal waves at Dongsha Atoll in the northern South China Sea

Continental Shelf Research ◽

10.1016/j.csr.2012.01.010 ◽

2012 ◽

Vol 37 ◽

pp. 1-7 ◽

Cited By ~ 28

Author(s):

Ke-Hsien Fu ◽

Yu-Huai Wang ◽

Louis St. Laurent ◽

Harper Simmons ◽

Dong-Ping Wang

Keyword(s):

South China Sea ◽

Internal Waves ◽

South China ◽

Large Amplitude ◽

Northern South China Sea ◽

Nonlinear Internal Waves ◽

China Sea ◽

Dongsha Atoll

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Observations of Large-Amplitude Nonlinear Internal Waves from a Drifting Array: Instruments and Methods

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2010jtecho774.1 ◽

2010 ◽

Vol 27 (10) ◽

pp. 1711-1731 ◽

Cited By ~ 12

Author(s):

L. R. Centurioni

Keyword(s):

South China Sea ◽

Time Scales ◽

Internal Waves ◽

South China ◽

Large Amplitude ◽

The South China Sea ◽

Nonlinear Internal Waves ◽

China Sea ◽

Drifting Buoy ◽

The Waves

Abstract This paper presents a novel methodology applied to the observation of large-amplitude nonlinear internal waves in the upper ocean from an array of drifting instruments. The characteristics of the instrument used—an Autonomous Drifting Ocean Station with acoustic current profilers (ADOS-A), which is a drifting buoy with a 200-m-long thermistor chain, several profiling acoustic current meters, and a GPS—are discussed. The ADOS-A is lightweight and relatively inexpensive and can be deployed from aircrafts or from ships of opportunity. Three packets of large-amplitude, nonlinear internal waves were observed in the South China Sea. The speed and the direction of propagation of the waves are accurately determined and their characteristics and evolution over space and time scales comparable with those of the waves, as they propagate through the array, are discussed.

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