Journal ArticleDOI
Significant dissipation of tidal energy in the deep ocean inferred from satellite altimeter data
Gary D. Egbert,Richard D. Ray +1 more
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Satellite altimeter data from Topex/Poseidon is used to map empirically the tidal energy dissipation and shows that approximately 1012 watts—that is, 1 TW, representing 25–30% of the total dissipation—occurs in the deep ocean, generally near areas of rough topography.Abstract:
How and where the ocean tides dissipate their energy are long-standing questions that have consequences ranging from the history of the Moon to the mixing of the oceans. Historically, the principal sink of tidal energy has been thought to be bottom friction in shallow seas. There has long been suggestive evidence, however, that tidal dissipation also occurs in the open ocean through the scattering by ocean-bottom topography of surface tides into internal waves, but estimates of the magnitude of this possible sink have varied widely. Here we use satellite altimeter data from Topex/Poseidon to map empirically the tidal energy dissipation. We show that approximately 10(12) watts--that is, 1 TW, representing 25-30% of the total dissipation--occurs in the deep ocean, generally near areas of rough topography. Of the estimated 2 TW of mixing energy required to maintain the large-scale thermohaline circulation of the ocean, one-half could therefore be provided by the tides, with the other half coming from action on the surface of the ocean.read more
Citations
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Journal ArticleDOI
Efficient Inverse Modeling of Barotropic Ocean Tides
TL;DR: In this paper, a relocatable system for generalized inverse (GI) modeling of barotropic ocean tides is described, where the GI penalty functional is minimized using a representer method, which requires repeated solution of the forward and adjoint linearized shallow water equations.
Journal ArticleDOI
A long-term numerical solution for the insolation quantities of the Earth
Jacques Laskar,Philippe Robutel,F. Joutel,Mickael Gastineau,Alexandre C. M. Correia,Alexandre C. M. Correia,Benjamin Levrard +6 more
TL;DR: In this article, a new solution for the astronomical computation of the insolation quantities on Earth spanning from −250 m to 250 m was presented, where the most regular components of the orbital solution could still be used over a much longer time span, which is why they provided here the solution over 250 m.
Journal ArticleDOI
Modelling the global ocean tides: modern insights from FES2004
TL;DR: A review of the state-of-the-art in the field of finite element solutions (FES) atlases can be found in this paper, where the authors introduce the FES2004 tidal atlas and validate the model against in situ and satellite data.
Journal ArticleDOI
The monsoon circulation of the Indian Ocean
TL;DR: In this article, the authors review observations, theory and model results on the monsoon circulation of the Indian Ocean and discuss possible physical mechanisms behind seasonal variability of the meridional overturning streamfunction and heat flux.
Journal ArticleDOI
Vertical mixing, energy, and the general circulation of the oceans
Carl Wunsch,Raffaele Ferrari +1 more
TL;DR: In particular, small-scale mixing processes are necessary to resupply the potential energy removed in the interior by the overturning and eddy-generating process as discussed by the authors, and it is shown that over most of the ocean significant vertical mixing is confined to topographically complex boundary areas implies a potentially radically different interior circulation than is possible with uniform mixing.
References
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Journal ArticleDOI
Abyssal recipes II: energetics of tidal and wind mixing
Walter Munk,Carl Wunsch +1 more
TL;DR: Using the Levitus climatology, the authors showed that 2.1 TW (terawatts) is required to maintain the global abyssal density distribution against 30 Sverdrups of deep water formation.
Journal ArticleDOI
TOPEX/POSEIDON tides estimated using a global inverse model
Abstract: Altimetric data from the TOPEX/POSEIDON mission will be used for studies of global ocean circulation and marine geophysics. However, it is first necessary to remove the ocean tides, which are aliased in the raw data. The tides are constrained by the two distinct types of information: the hydrodynamic equations which the tidal fields of elevations and velocities must satisfy, and direct observational data from tide gauges and satellite altimetry. Here we develop and apply a generalized inverse method, which allows us to combine rationally all of this information into global tidal fields best fitting both the data and the dynamics, in a least squares sense. The resulting inverse solution is a sum of the direct solution to the astronomically forced Laplace tidal equations and a linear combination of the representers for the data functionals. The representer functions (one for each datum) are determined by the dynamical equations, and by our prior estimates of the statistics or errors in these equations. Our major task is a direct numerical calculation of these representers. This task is computationally intensive, but well suited to massively parallel processing. By calculating the representers we reduce the full (infinite dimensional) problem to a relatively low-dimensional problem at the outset, allowing full control over the conditioning and hence the stability of the inverse solution. With the representers calculated we can easily update our model as additional TOPEX/POSEIDON data become available. As an initial illustration we invert harmonic constants from a set of 80 open-ocean tide gauges. We then present a practical scheme for direct inversion of TOPEX/POSEIDON crossover data. We apply this method to 38 cycles of geophysical data records (GDR) data, computing preliminary global estimates of the four principal tidal constituents, M(sub 2), S(sub 2), K(sub 1) and O(sub 1). The inverse solution yields tidal fields which are simultaneously smoother, and in better agreement with altimetric and ground truth data, than previously proposed tidal models. Relative to the 'default' tidal corrections provided with the TOPEX/POSEIDON GDR, the inverse solution reduces crossover difference variances significantly (approximately 20-30%), even though only a small number of free parameters (approximately equal to 1000) are actually fit to the crossover data.
Journal ArticleDOI
Spatial variability of turbulent mixing in the Abyssal Ocean
TL;DR: Ocean microstructure data show that turbulent mixing in the deep Brazil Basin of the South Atlantic Ocean is weak at all depths above smooth abyssal plains and the South American Continental Rise, which implies that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry.
Journal ArticleDOI
Evidence for slow mixing across the pycnocline from an open-ocean tracer-release experiment
Abstract: THE distributions of heat, salt and trace substances in the ocean thermocline depend on mixing along and across surfaces of equal density (isopycnal and diapycnal mixing, respectively). Measurements of the invasion of anthropogenic tracers, such as bomb tritium and 3He (see, for example, refs 1 and 2), have indicated that isopycnal processes dominate diapycnal mixing, and turbulence measurements have suggested that diapycnal mixing is small3,4, but it has not been possible to measure accurately the diapycnal diffusivity. Here we report such a measurement, obtained from the vertical dispersal of a patch of the inert compound SF6 released in the open ocean. The diapycnal diffusivity, averaged over hundreds of kilometres and five months, was 0.11 ± 0.02 cm2 s−1, confirming previous estimates1–4. Such a low diffusivity can support only a rather small diapycnal flux of nitrate into the euphotic zone; it justifies the neglect of diapycnal mixing in dynamic models of the thermocline25–27, and implies that heat, salt and tracers must penetrate the thermocline mostly by transport along, rather than across, density surfaces.
Journal ArticleDOI
Scaling turbulent dissipation in the thermocline
Abstract: By comparing observations from six diverse sites in the mid-latitude thermocline, we find that, to within a factor of 2, 〈eIW〉=7×10‐10〈N2/N02〉〈S104/SGM4〉 W kg‐1, where 〈eIW〉 is the average dissipation rate attributable to internal waves; N0 = 0.0052 s−1 is a reference buoyancy frequency; S10 is the observed shear having vertical wavelengths greater than 10 m; and SGM is the corresponding shear in the Garrett and Munk spectrum of internal waves. The functional form agrees with estimates by McComas and Muller and by Henyey, Wright, and Flatte of the rate of energy transfer within the internal wave spectrum, provided the energy density of the internal waves is treated as a variable instead of one of the constant parameters. Following Garrett and Munk, we assume that 〈S104/SGM4〉=〈EIW2/EGM2〉, where EIW is the observed energy density and EGM is the energy density used by Garrett and Munk. The magnitude of eIW is twice that of Henyey et al. and one third that of McComas and Muller. Thus the observations agree with predictions sufficiently well to suggest that (1) a first-order understanding of the link between internal waves and turbulence has been achieved, although Henyey et al. made some ad hoc assumptions and Garrett and Munk's model does not match important features in the internal wave spectrum reported by Pinkel, and (2) the simplest way to obtain average dissipation rates over large space and time scales is to measure 〈N2/N02〉〈S104/SGM4〉. Even though the observations were taken at latitudes of 42°−11.5°, the variability in the Coriolis parameter ƒ was too limited for a conclusive test of the ƒ dependence also predicted for 〈eIW〉 by the wave-wave interaction models. An exception to the scaling occurs east of Barbados in the thermohaline staircase that is apparently formed and maintained by salt fingers. Although e in the staircase is very low compared with rates at mid-latitude sites, it is 8 times larger than predicted for e due only to internal waves.
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Spatial variability of turbulent mixing in the Abyssal Ocean
Vertical mixing, energy, and the general circulation of the oceans
Carl Wunsch,Raffaele Ferrari +1 more