Observations of the Tasman Sea internal tide beam

Amy F. Waterhouse, Samuel M. Kelly, Zhongxiang Zhao, Jennifer A. Mackinnon, Jonathan D. Nash, Harper Simmons, Dmitry Brahznikov, Luc Rainville, Matthew Alford, Rob Pinkel

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Low-mode internal tides, a dominant part of the internal wave spectrum, carry energy over large distances, yet the ultimate fate of this energy is unknown. Internal tides in the Tasman Sea are generated atMacquarie Ridge, south of New Zealand, and propagate northwest as a focused beam before impinging on the Tasmanian continental slope. In situ observations from the Tasman Sea capture synoptic measurements of the incident semidiurnal mode-1 internal-tide, which has an observed wavelength of 183 km and surface displacement of approximately 1 cm. Plane-wave fits to in situ and altimetric estimates of surface displacement agree to within a measurement uncertainty of 0.3 cm, which is the same order of magnitude as the nonstationary (not phase locked) mode-1 tide observed over a 40-day mooring deployment. Stationary energy flux, estimated from a plane-wave fit to the in situ observations, is directed toward Tasmania with a magnitude of 3.4±.4kWm-1, consistent with a satellite estimate of 3.9±2.2kWm-1. Approximately 90% of the timemean energy flux is due to the stationary tide. However, nonstationary velocity and pressure, which are typically 1/4 the amplitude of the stationary components, sometimes lead to instantaneous energy fluxes that are double or half of the stationary energy flux, overwhelming any spring-neap variability. Despite strong winds and intermittent near-inertial currents, the parameterized turbulent-kinetic-energy dissipation rate is small (i.e., 10-10Wkg-1) below the near surface and observations of mode-1 internal tide energy-flux convergence are indistinguishable from zero (i.e., the confidence intervals include zero), indicating little decay of the mode-1 internal tide within the Tasman Sea.

Original languageEnglish (US)
Pages (from-to)1283-1297
Number of pages15
JournalJournal of Physical Oceanography
Volume48
Issue number6
DOIs
StatePublished - Jun 1 2018

Bibliographical note

Funding Information:
Acknowledgments. A. F. Waterhouse and S. M. Kelly acknowledge funding from NSF-OCE1434722 and NSF-OCE1434352 as well as ship time aboard the R/V Falkor supported by the Schmidt Ocean Institute. LR and ZZ acknowledge NSF-OCE1129246. HLS and DB acknowledge support from the Tasman Sea Tidal Dissipation Experiment (TTIDE) NSF Grants OCE1130048. We are grateful to our collaborative T-TIDE scientists and, in particular, Gunnar Voet who deployed the A1 mooring from the R/V Revelle as well as the scientists and volunteers aboard the R/V Falkor: Pete Strutton, Randall Lee, Spencer Kawamoto, Gabriela Pilo, Ryan McDougall-Fisher, Hayley Dosser, Judy Lemus, Annalena Lochte, and Danielle Mitchell. Shipboard LADCP observations are available from the Interdisciplinary Earth Data Alliance (https://doi.org/10.1594/IEDA/322415; https://doi.org/ 10.1594/IEDA/322414). We thank two anonymous reviewers for their comments, which helped to improve the manuscript.

Keywords

  • In situ oceanic observations
  • Internal waves
  • Mixing
  • Satellite observations
  • Tides

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