Characterizing the semidiurnal internal tide off <scp>T</scp>asmania using glider data

Boettger, Daniel; Robertson, Robin; Rainville, Luc

doi:10.1002/2015jc010711

Cited by 14 publications

(13 citation statements)

References 26 publications

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“…The change in wavelength between the north and south part of the track (Figure a) indicates the spatial variability of the internal tide properties. Both of these attributes are consistent with in situ observations in this region [ Wolanski and Pickard , ; Boettger et al ., ].…”

Section: Regional Examplesmentioning

confidence: 99%

Mapping the nonstationary internal tide with satellite altimetry

Zaron

2017

JGR Oceans

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Temporal variability of the internal tide has been inferred from the 23 year long combined records of the TOPEX/Poseidon, Jason‐1, and Jason‐2 satellite altimeters by combining harmonic analysis with an analysis of along‐track wavenumber spectra of sea‐surface height (SSH). Conventional harmonic analysis is first applied to estimate and remove the stationary components of the tide at each point along the reference ground tracks. The wavenumber spectrum of the residual SSH is then computed, and the variance in a neighborhood around the wavenumber of the mode‐1 baroclinic M2 tide is interpreted as the sum of noise, broadband nontidal processes, and the nonstationary tide. At many sites a bump in the spectrum associated with the internal tide is noted, and an empirical model for the noise and nontidal processes is used to estimate the nonstationary semidiurnal tidal variance. The results indicate a spatially inhomogeneous pattern of tidal variability. Nonstationary tides are larger than stationary tides throughout much of the equatorial Pacific and Indian Oceans.

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Section: Regional Examplesmentioning

confidence: 99%

Mapping the nonstationary internal tide with satellite altimetry

Zaron

2017

JGR Oceans

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“…1a). A Kongsberg Seaglider (SG613;Eriksen et al, 2001) was deployed from NRV Alliance between 2 and 5 June 2017 during the fourth Marine Autonomous Systems in Support of Marine Observations mission (MASSMO4). The glider was navigated from the deeper waters of the Faroe-Shetland Channel (FSC) to the WTR and held station for 40 h by a short oceanographic mooring, deployed 5 days previously from MRV Scotia (Fig.…”

Section: Observationsmentioning

confidence: 99%

“…The acoustic current meter was configured with a 10 min sampling interval and linearly downsampled onto the same 20 min sampling interval as the ADCP. Good velocity data were recovered for all depth levels between 85 and 705 m, as well as 780-785 m. In addition to the ADCP and current meter measurements, horizontal velocity was inferred from GPS position and the Seaglider flight model using a dive-average current method (DAC; Eriksen et al, 2001;Frajka-Williams et al, 2011). DAC was only calculated for dives deeper than 500 m so that values were representative of the majority of the water column.…”

Section: Data Processingmentioning

confidence: 99%

“…Ocean gliders have previously been used to observe internal waves and internal tides Rainville et al, 2013;Boettger et al, 2015;Hall et al, 2017a), including the calculation of energy fluxes using current velocity measurements from gliders equipped with ADCPs . However, ADCPs are not routinely integrated with commercially available glider platforms (Seaglider, Slocum, and SeaExplorer), in part due to their higher power requirement.…”

Section: Introductionmentioning

confidence: 99%

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Internal tide energy flux over a ridge measured by a co-located ocean glider and moored acoustic Doppler current profiler

2019

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Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring–neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being “fished out” by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimize these risks, with u measured by a low-frequency acoustic Doppler current profiler (ADCP) moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the semidiurnal internal tide radiating from the Wyville Thomson Ridge in the North Atlantic. The observed energy flux (4.2±0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by subsampling potential density in an idealized internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (<10 %) if all the glider data are contained within a “watch circle” with a diameter smaller than 1∕8 the mode-1 horizontal wavelength of the internal tide. Energy flux is biased low because the glider samples density with a broad range of phase shifts, resulting in underestimation of vertical isopycnal displacement and available potential energy. The negative bias increases with increasing watch circle diameter. If watch circle diameter is larger than 1∕8 the mode-1 horizontal wavelength, the negative bias is more than 3 % and all realizations within the 95 % confidence interval are underestimates. Over the Wyville Thomson Ridge, where the semidiurnal mode-1 horizontal wavelength is ≈100 km and all the glider dives are within a 5 km diameter watch circle, the observed energy flux is estimated to have a negative bias of only 0.4 % and an error of less than 3 % at the 95 % confidence limit. With typical glider performance, we expect energy flux error due to imperfect co-location to be <10 % in most mid-latitude shelf slope regions.

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“…These include: (1) physical and biogeochemical studies of offshore eddies (Baird et al, 2011), (2) characterization of internal tides and sediment resuspension (Boettger et al, 2015;Pattiaratchi and De Oliveira, 2016), and (3) examination of the influence of the East Australian Current on shelf dynamics (Schaeffer and Roughan, 2015). Schaeffer et al (2016) compiled a shelf climatology using Slocum glider data, and Jones et al (2012) 2016).…”

Section: Science Highlightsmentioning

confidence: 99%