Acoustic Tomography in the Canary Basin: Meddies and Tides

Type Article
Date 2017-11
Language English
Author(s) Dushaw Brian1, Gaillard FabienneORCID2, Terre Thierry2
Affiliation(s) 1 : Nansen Environm & Remote Sensing Ctr, Bergen, Norway.
2 : Univ Brest, CNRS, Lab Oceanog Phys & Spatiale, IFREMER,IRD,IUEM, Plouzane, France.
Source Journal Of Geophysical Research-oceans (2169-9275) (Amer Geophysical Union), 2017-11 , Vol. 122 , N. 11 , P. 8983-9003
DOI 10.1002/2017JC013356
WOS© Times Cited 1
Keyword(s) Meddy, acoustic tomography, Canary Basin, Mediterranean water, internal tides
Abstract

An acoustic propagation experiment over 308-km range conducted in the Canary Basin in 1997–1998 was used to assess the ability of ocean acoustic tomography to measure the flux of Mediterranean water and Meddies. Instruments on a mooring adjacent to the acoustic path measured the southwestward passage of a strong Meddy in temperature, salinity, and current. Over nine months of transmissions, the acoustic arrival pattern was an initial broad stochastic pulse varying in duration by 250 to 500 ms, followed eight stable, identified ray arrivals. Small-scale sound speed fluctuations from Mediterranean water parcels littered around the sound channel axis caused acoustic scattering. Internal waves contributed more modest acoustic scattering. Based on simulations, the main effect of a Meddy passing across the acoustic path is the formation of many early-arriving, near-axis rays, but these rays are thoroughly scattered by the small-scale Mediterranean water fluctuations. A Meddy decreases the deep-turning ray travel times by 10–30 ms. The dominant acoustic signature of a Meddy is therefore the expansion of the width of the initial stochastic pulse. While this signature appears inseparable from the other effects of Mediterranean water in this region, the acoustic time series indicates the steady passage of Mediterranean water across the acoustic path. Tidal variations caused by the mode-1 internal tides were measured by the acoustic travel times. The observed internal tides were partly predicted using a recent global model for such tides derived from satellite altimetry.

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