Observations of large-amplitude mode-2 nonlinear internal waves on the Australian north west shelf

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Large-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-thewater-column moorings spaced 600m apart in a triangular configuration. The moorings were deployedfor 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.

Original languageEnglish
Pages (from-to)309-328
Number of pages20
JournalJournal of Physical Oceanography
Volume49
Issue number1
DOIs
Publication statusPublished - 1 Jan 2019

Fingerprint

nonlinear wave
internal wave
internal tide
pycnocline
Froude number
tidal cycle
train
dry season
monsoon
stratification
deep water
kinematics
temperature

Cite this

@article{9b43c97f8ea84502954bff3c58969e18,
title = "Observations of large-amplitude mode-2 nonlinear internal waves on the Australian north west shelf",
abstract = "Large-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-thewater-column moorings spaced 600m apart in a triangular configuration. The moorings were deployedfor 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.",
keywords = "Australia, Continental shelf/slope, In situ oceanic observations, Internal waves, Regional models, Solitary waves",
author = "Rayson, {Matthew D.} and Jones, {Nicole L.} and Ivey, {Gregory N.}",
year = "2019",
month = "1",
day = "1",
doi = "10.1175/JPO-D-18-0097.1",
language = "English",
volume = "49",
pages = "309--328",
journal = "Journal of Physical Oceanography",
issn = "0022-3670",
publisher = "American Meteorological Society",
number = "1",

}

TY - JOUR

T1 - Observations of large-amplitude mode-2 nonlinear internal waves on the Australian north west shelf

AU - Rayson, Matthew D.

AU - Jones, Nicole L.

AU - Ivey, Gregory N.

PY - 2019/1/1

Y1 - 2019/1/1

N2 - Large-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-thewater-column moorings spaced 600m apart in a triangular configuration. The moorings were deployedfor 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.

AB - Large-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-thewater-column moorings spaced 600m apart in a triangular configuration. The moorings were deployedfor 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.

KW - Australia

KW - Continental shelf/slope

KW - In situ oceanic observations

KW - Internal waves

KW - Regional models

KW - Solitary waves

UR - http://www.scopus.com/inward/record.url?scp=85060951018&partnerID=8YFLogxK

U2 - 10.1175/JPO-D-18-0097.1

DO - 10.1175/JPO-D-18-0097.1

M3 - Article

VL - 49

SP - 309

EP - 328

JO - Journal of Physical Oceanography

JF - Journal of Physical Oceanography

SN - 0022-3670

IS - 1

ER -