Barotropic and Baroclinic Tides in the Central North Pacific Ocean Determined from Long-Range Reciprocal Acoustic Transmissions

Dushaw, Brian D.; Howe, Bruce M.; Cornuelle, Bruce D.; Worcester, Peter F.; Luther, Douglas S.

doi:10.1175/1520-0485(1995)025<0631:babtit>2.0.co;2

Cited by 181 publications

(143 citation statements)

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“…Given this evidence that the time series of amplitude modulations derived from the tide gauges are properly reflecting internal tide modulations, we can now examine the lowfrequency modulations seen in the long tide gauge records in order to evaluate the suggestion of Dushaw et al [1995] that the internal tide is coherently generated along the Hawaiian Ridge. We interpret such a coherence in the low-frequency modulations as being due to the fact that the internal tide amplitude varies as the stratification (depth of the pycnocline) changes and therefore expect that the low-frequency modulations in the M2 amplitude series should positively correlate with stratification changes that act to deepen the pycnocline.…”

Section: Resultsmentioning

confidence: 99%

“…We focus on the north side of the ridge simply to maximize our signal to noise ratio. The second reason for focusing on the northern side of the ridge is that the signals observed by Dushaw et al [1995] are to the north of the ridge, and we are attempting to evaluate the possibility that generation on the northern side of the ridge can indeed account for their observations. Sea level data are available from four gauges along the main part of the Hawaiian Island chain (Figure 1) We also use data from an array of IES instruments that were moored near the HOT site (Figure 1).…”

Section: Datamentioning

confidence: 99%

“…Given the modulations in the M 2 internal tide derived from the tide gauges, we then exploit the fact that the tide gauge records are >20 years long and look at the coherence along the ridge of the lowest-frequency modulations. We assume that if the lowest-frequency (i.e., decadal) modulations in the internal tide generated at the ridge are coherently generated along the ridge, then it is reasonable to expect that the mean internal tide observed by Dushaw et al [1995] would also be coherent spatially. This is, in fact, what we find, which we propose as evidence supporting the interpretation of Dushaw et al [1995].…”

Section: Introductionmentioning

confidence: 99%

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Coherence of internal tide modulations along the Hawaiian Ridge

Mitchum¹,

Chiswell²

2000

J. Geophys. Res.

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Abstract. Long time series of sea level from tide gauges along the north side of the Hawaiian Ridge and shorter series of dynamic heights inferred from inverted echo sounders moored just north of the main Hawaiian Islands are examined for evidence of internal tides at the M 2 frequency. We find that the amplitudes and phases of the M 2 tidal components have low-frequency variability, which is consistent with a superposition of an internal tide with the larger barotropic tide. Further, the low-frequency variability is correlated with low-frequency changes in the depth of the pycnocline, which suggests a simple physical mechanism to account for the low-frequency modulations in the internal tidal amplitude. These modulations are coherent for long distances along the Hawaiian Ridge, indicating a coherent generation of the internal tide that is consistent with acoustic observations in the North Pacific and with recent analyses of sea surface heights from satellite altimetry. intercomparisons are important given that the scale of the temporal modulations of the internal tide is only of the order of 1 cm and also because the interpretation of the tide gauge series depends on a highly simplified model of the internal tide generation process. However, we are able to show that the model of the generation process and the analysis method we derive yield a remarkable degree of consistency between these two independent sets of measurements during the relatively brief period when the IES measurements are available. This consistency gives us the confidence necessary to assess the interannual to decadal modulations in the internal tidal amplitude using the tide gauge data only, and these intercomparisons are described in some detail. Given the modulations in the M 2 internal tide derived from the tide gauges, we then exploit the fact that the tide gauge records are >20 years long and look at the coherence along the ridge of the lowest-frequency modulations. We assume that if the lowest-frequency (i.e., decadal) modulations in the internal tide generated at the ridge are coherently generated along the ridge, then it is reasonable to expect that the mean internal tide observed by Dushaw et al. [1995] would also be coherent spatially. This is, in fact, what we find, which we propose as evidence supporting the interpretation of Dushaw et al. [1995].At the same time that we initially undertook these analyses, one of us (G. T. M.) also began collaborating on a complementary analysis of these signals using sea surface heights from the TOPEX/Poseidon (T/P) altimeter. That analysis is quite different, relying on wavenumber structure for separating the baroclinic from the barotropic tides, and is complementary to the work described here in that the T/P and the Dushaw et al.[1995] analyses both focus on the mean internal tide. Preliminary results of the T/P analysis have been published [Ray and Mitchurn, 1996Mitchurn, , 1997, and a similar conclusion can be made from this very different analysis. Taken all together, these analyses provid...

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Section: Resultsmentioning

confidence: 99%

Section: Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Coherence of internal tide modulations along the Hawaiian Ridge

Mitchum¹,

Chiswell²

2000

J. Geophys. Res.

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“…The generation of internal tidal waves in the ocean results primarily from interaction processes between the barotropic tide and the bottom topography; these lead to periodical vertical displacements of isopycnals [Siedler and Paul, 1991; Vlasenko and Morozov, 1993;Dushaw et al, 1995]. While semidiurnal internal waves are found almost everywhere in the world ocean [Morozov, 1995], their greatest amplitudes are usually observed near submarine ridges and continental slopes [Holloway, 1984[Holloway, , 1993Sherwin, 1988;Pingree and New, 1995].…”

Section: Introductionmentioning

confidence: 99%

Internal tides observed at 2°S–156°E by in situ and TOPEX/POSEIDON data during the Coupled Ocean‐Atmosphere Response Experiment (COARE)

Gourdeau¹

1998

J. Geophys. Res.

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Abstract. During the enhanced monitoring phase of the Coupled Ocean-Atmosphere Experiment (COARE), semidiurnal baroclinic tides were observed. At 2øS-156øE (1739 m depth) the Tropical Atmosphere-Ocean (TAO) mooring outfitted with additional sensors from surface to bottom provides an interesting tool for describing the internal tides. M2, S2, and N2 baroclinic components were detected, explaining 59% of the semidiurnal variance on surface dynamic height. At the semidiurnal frequency, vertical displacements of isopycnals, highly variable in time, can reach 30 m and are mostly a combination of the M2, S2, and N2 internal waves. The two first baroclinic modes explain 70% of the variance in vertical displacement. M2 and S2 internal waves have different vertical structure: M2 resembles the first baroclinic mode and S2 resembles the second baroclinic mode. The M2 and S2 internal waves projected on their respective baroclinic mode are highly related to the modeled barotropic tide. Two TOPEX/POSEIDON tracks cross over the mooring every 10 days, and the internal wave signature can be expected in sea level along the tracks despite the weakness of the signal. Sea level spectra along both ascending and descending tracks show the existence of energy around the 250 km and the 120 km wavelength, respectively, which is in accordance with a first baroclinic wave propagating northeastward, as suggested in previous studies. From wavelet transform, the baroclinic tide signatures on the ascending (descending) track are centered around 2.5øS (3.5øS) with a 1 ø (2 ø) latitudinal extension, respectively, limited to the Ontong Java Plateau. We confirm the northeastward propagation of the baroclinic tides, and their source could be a series of islands parallel to the Kilinailau Trench or the large sloping topography between the Kilinailau Trench and the Ontong Java Plateau. IntroductionThe generation of internal tidal waves in the ocean results primarily from interaction processes between the barotropic tide and the bottom topography; these lead to periodical ver-

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“…Then Schott [1977] and Hendry [1977] detected energetic coherent (phase locked relative to the barotropic tide) baroclinic tidal waves in the North Atlantic. More recently, Dushaw et al [1995], Feng et al [1998], Chiswell and Moore [1999], Chiswell [2000Chiswell [ , 2002, and Cummins et al [2001] observed baroclinic components that were coherent with the barotropic tide in the near field, but gradually decayed with distance from the generation area because of topographic scattering and density variations. Thus both ''coherent'' (phase-locked) and ''incoherent'' (random) baroclinic components exist, but their relative contribution depends on stability of horizontal and vertical stratification and on distance from the generation source.…”

Section: Introductionmentioning

confidence: 99%

Barotropic and baroclinic tidal currents on the Mackenzie shelf break in the southeastern Beaufort Sea

2004

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[1] Tidal currents near the outer shelf break of the Mackenzie Shelf in the southern Beaufort Sea were examined using year-long (1987)(1988) current measurements from the upper ($35 m) and lower ($150 m) layers at four sites along the southeast (SS1), northeast (SS2), north central (SS3), and northwest (SS4) perimeter of the shelf. At all stations, semidiurnal currents were dominant, and upper layer currents were approximately double those observed in the lower layer. Maximum M 2 currents were observed above the sharp northeastern corner of the Mackenzie Shelf (6.0-7.5 cmÁs À1 ), while in the Mackenzie Canyon they were negligible. Diurnal currents were weaker and depth uniform; maximum K 1 currents (1.5-3.0 cmÁs À1 ) were found in the eastern part of the shelf. Diurnal and lower layer semidiurnal currents were in good agreement with those computed numerically by Kowalik and Proshutinsky [1994], indicating that these currents are essentially barotropic. In contrast, upper layer semidiurnal currents were mainly baroclinic. About 74% of the total energy of semidiurnal currents was associated with baroclinic coherent (phase-locked) tidal currents, while barotropic (12%), baroclinic incoherent (7%), and inertial (7%) components are the remaining semidiurnal currents in this area. High baroclinic generation coefficients (the ratio of locally generated baroclinic waves to barotropic waves) for stations SS2 and SS3 (about 7.0-8.0 in comparison with 0.3 for SS1 and SS4) located near the northeastern Mackenzie Shelf identify this region as a probable generation source of intensive internal tidal waves, which become then locally resonantly trapped between the shelf and the critical latitudes.

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Barotropic and Baroclinic Tides in the Central North Pacific Ocean Determined from Long-Range Reciprocal Acoustic Transmissions

Cited by 181 publications

References 0 publications

Coherence of internal tide modulations along the Hawaiian Ridge

Coherence of internal tide modulations along the Hawaiian Ridge

Internal tides observed at 2°S–156°E by in situ and TOPEX/POSEIDON data during the Coupled Ocean‐Atmosphere Response Experiment (COARE)

Barotropic and baroclinic tidal currents on the Mackenzie shelf break in the southeastern Beaufort Sea

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