Baroclinic Motions and Energetics as Measured by Altimeters

Wunsch, Carl

doi:10.1175/jtech-d-12-00035.1

Cited by 23 publications

(18 citation statements)

References 24 publications

(29 reference statements)

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“…Considering a period superior to 1 year (interannual), H as 10 3 m, a Brunt-V€ ais€ al€ a frequency of 0.2 cycles per hour (in the range of the lowest measured values in the abyssal Pacific; cf. Wunsch [2013] and Levitus [1982]) and a typical q value equal to 1027 kg m 23 , equation (B5) scales as:…”

Section: Appendix B: On the Relationship Between Vertical Energy Fluxmentioning

confidence: 99%

Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific

et al. 2017

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The question of how energy is redistributed in the ocean has renewed the interest for the processes leading to midlatitude subthermocline variability at low frequency. Here we investigate a process that has been disregarded although potentially relevant for climatic studies dealing with the planetary energy budget. The focus is on the Southeastern Pacific where an efficient oceanic teleconnection takes place, linking the remote surface equatorial momentum forcing with the subthermocline through the vertical propagation of low‐frequency long‐wavelength extratropical Rossby waves (ETRW). A high‐resolution model is used to document the vertical energy flux associated with ETRW at interannual to decadal time scales. The analysis of a long‐term (1958–2008) simulation reveals that the vertical energy flux can be interpreted to a large extent as resulting from the coastally forced ETRW as far south as 35°S, so that heat content variability can be predicted along theoretical trajectories originating from the coast below the thermocline. It is shown that the vertical energy flux associated with the El Niño Southern Oscillation forms beams below the thermocline that account for a large fraction of the total vertical energy flux at interannual time scales. Extreme El Niño events are the dominant contributor to this flux, which is hardly impacted by mesoscale activity. The energy beams experience a dissipation processes in the ocean below 1000 m that is interpreted as resulting from vertical turbulent diffusion. Our results suggest that the ETRW at ENSO time scales are strongly dissipated at the surface but still can modulate the heat content in the deep ocean of the Southeastern Pacific.

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Section: Appendix B: On the Relationship Between Vertical Energy Fluxmentioning

confidence: 99%

Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific

et al. 2017

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“…The eigenvalue equation can be solved by numerical method [Wunsch, 1975[Wunsch, , 2013. The vertical modal structure and its corresponding eigenvalue speed are obtained for each baroclinic mode.…”

Section: Baroclinic Mode and Phase Speedmentioning

confidence: 99%

“…The subsurface displacement of internal tides can be derived from the SSH amplitude following the vertical modal structures [Zhao and Alford, 2009;Wunsch, 2013]. According to the dispersion relation, the subsurface pressure anomalies and horizontal currents are also obtained.…”

Section: Plane Wave Fitmentioning

confidence: 99%

Internal tide radiation from the Luzon Strait

2014

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The M 2 , K 1 , and O 1 internal tides originating in the Luzon Strait are investigated using the sea surface height measurements by multiple satellites ERS-2, Envisat, TOPEX/Poseidon, Jason-1/2, and Geosat Follow-On. A plane wave fit method is used to resolve multiple internal tides in arbitrary horizontal directions. The Luzon Strait is an energetic internal tide generation site, and radiates internal tides both westward into the South China Sea (SCS) and eastward into the western Pacific (WP). In the SCS, the K 1 and O 1 internal tides propagate over 1600 km, reaching the Vietnam coast; in the WP, they propagate over 2500 km and arrive to the Mariana Ridge and Guam. The K 1 and O 1 internal tides refract toward the Equator during propagation. The M 2 internal tides in the SCS bifurcate into two beams. The northwestward beam is coincident with the frequent occurrence of internal solitary waves in this region, implying their causative relation. The phase speeds inferred from the altimetric along-beam propagation agree with the theoretical values. Due to the influence of the Earth's rotation, the K 1 and O 1 phase speeds decrease remarkably from high to low latitudes. For the diurnal internal tides, the eastward radiation is about 50% greater than the westward radiation. For M 2 , the westward radiation is about two times the eastward radiation. The altimetric energy fluxes are about 50% of those in numerical model simulations.

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“…That ageostrophic motions may contribute significantly to the upper-ocean variability should not be a surprise (e.g., Ferrari and Wunsch 2010;Wunsch 2013). Analysis of a global model with embedded tides suggests that high-frequency motions significantly flatten the near-surface spectra (Richman et al 2012).…”

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confidence: 99%

Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

Rocha

Chereskin

Gille

et al. 2016

Journal of Physical Oceanography

243

300

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This study discusses the upper-ocean (0-200 m) horizontal wavenumber spectra in the Drake Passage from 13 yr of shipboard ADCP measurements, altimeter data, and a high-resolution numerical simulation. At scales between 10 and 200 km, the ADCP kinetic energy spectra approximately follow a k 23 power law. The observed flows are more energetic at the surface, but the shape of the kinetic energy spectra is independent of depth. These characteristics resemble predictions of isotropic interior quasigeostrophic turbulence. The ratio of across-track to along-track kinetic energy spectra, however, significantly departs from the expectation of isotropic interior quasigeostrophic turbulence. The inconsistency is dramatic at scales smaller than 40 km. A Helmholtz decomposition of the ADCP spectra and analyses of synthetic and numerical model data show that horizontally divergent, ageostrophic flows account for the discrepancy between the observed spectra and predictions of isotropic interior quasigeostrophic turbulence. In Drake Passage, ageostrophic motions appear to be dominated by inertia-gravity waves and account for about half of the near-surface kinetic energy at scales between 10 and 40 km. Model results indicate that ageostrophic flows imprint on the sea surface, accounting for about half of the sea surface height variance between 10 and 40 km.

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Baroclinic Motions and Energetics as Measured by Altimeters

Cited by 23 publications

References 24 publications

Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific

Vertical energy flux at ENSO time scales in the subthermocline of the Southeastern Pacific

Internal tide radiation from the Luzon Strait

Mesoscale to Submesoscale Wavenumber Spectra in Drake Passage

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