M 2 tidal dissipation around Vancouver Island: an inverse approach (original) (raw)
Related papers
Estimating Open-Ocean Barotropic Tidal Dissipation: The Hawaiian Ridge
Journal of Physical Oceanography, 2006
The generalized inverse of a regional model is used to estimate barotropic tidal dissipation along the Hawaiian Ridge. The model, based on the linear shallow-water equations, incorporates parameterizations for the dissipation of energy via friction in the bottom boundary layer and form drag due to internal waves generated at topographic slopes. Sea surface height data from 364 orbit cycles of the Ocean Topography Experiment (TOPEX)/Poseidon satellite mission are used to perform inversions at eight diurnal and semidiurnal tidal frequencies. It is estimated that the barotropic M 2 tide loses energy at a rate of 19 GW, of which 88% is lost within 250 km of the ridge, presumably via conversion to the internal or baroclinic tide. Uncertainty in the assumed model error and wave drag in the forward model suggest that M 2 dissipation values from 18 to 25 GW are consistent with the altimetric observations. Other barotropic tidal constituents are estimated to lose a total of 5.7 GW. The spatial distribution of barotropic dissipation along the ridge is similar to that inferred from three-dimensional primitive equation models, and it is largely insensitive to details of assumed model and data errors. Dissipation at semidiurnal frequencies is most intense at the French Frigate Shoals with lesser, but significant, contributions at other sites. Diurnal tidal dissipation is concentrated to the east of the French Frigate Shoals, at the Gardner Pinnacles. Further work with threedimensional models will be necessary to determine the fate of the energy that is removed from the barotropic tide.
A finite‐element tidal model for the southwest coast of Vancouver Island
Atmosphere-Ocean
A finite-element, barotropic, tidal model is developed for the southwest coast of Vancouver Island. The model is run with 10 tidal constituents and the results are compared with Flather's (1988) finite-difference model, and extensive tide-gauge and current-meter observations. Although sea-level amplitudes and phases are reproduced, on average, to within 0.4 cm and 0.6° for each constituent, the model currents do not compare as favourably. Evidence is shown that these inaccuracies are due to baroclinic effects that cannot be reproduced with a barotropic model. Tidal residuals calculated by the model demonstrate the existence of eddies off the tip of Cape Flattery and around the commercial fishing grounds at Swiftsure and Amphitrite Banks. RÉSUMÉ Un modèle des marées, à élément fini et barotrope est élaboré pour le sud-ouest de la côte de l'île de Vancouver. On utilise le modèle avec 10 constituants de la marée et les résultats sont comparés au modèle à différence finie de Flather (1988), et à des observations approfondies par indicateurs de marées et par des courantomètres. Bien que les amplitudes et les phases au niveau de la mer sont reproduites, en moyenne, à 0,4 cm et 0,6° près pour chacun des constituants, les courants du modèle ne se comparent pas avantageusement. On peut montrer que ces inexactitudes sont dues aux effets baroclines qui ne peuvent être reproduits avec un modèle barotrope. Les marées résiduelles calculées par le modèle font voir l'existence de tourbillons près de V extrémité du Flattery et près des zones de pêche commerciale sur les bancs Swiftsure et Amphritrite.
Tidal current energy assessment for Johnstone Strait, Vancouver Island
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, 2007
The maximum tidal power potential of Johnstone Strait, BC, Canada is evaluated using a two-dimensional finite element model (TIDE2D) with turbines simulated in certain regions by increasing the drag. Initially, side channels are closed off so that the flow is forced through one channel to test the validity of a general analytic theory [1] with numerical results. In this case, the modelled power potential of 886 MW agrees reasonably well with the analytic estimate of 826 MW. In reality, two main channels, Discovery Passage and Cordero Channel, connect the Pacific Ocean to the Strait of Georgia. Turbines are simulated in Johnstone Strait, northwest of the two main channels, and separately for Discovery Passage and Cordero Channel. Northwestern Johnstone Strait is similar to the one channel case as the flow must go through this channel, but Discovery Passage and Cordero Channel are different as the flow can be diverted away from the channel with the turbines and into the other channel....
A high-resolution assimilating tidal model for the northeast Pacific Ocean
Journal of …, 2000
Abstract. A high-resolution, nonlinear, barotropic, finite element tidal model lis developed for removing tidal elevations from satellite altimeter observations in■ he northeast Pacific Ocean. Surface elevations and currents for the constitutents IM2, 5г, N2, Ki-, K\, Oi, Pli and ...
Estuarine, Coastal and Shelf Science, 2003
The Great Bay Estuarine System, in New Hampshire, USA, has been the focus area for an attempt to develop a robust finite element method model for estuarine hydrodynamics. Past studies used a nonlinear, time stepping, kinematic model with limited success (Ip et al. Advances in fluid mechanics III, WIT, Southampton (2000) 569; Bilgili et al. J. Geophys. Res.-Oceans 107 (2002); Ertu¨rk et al. Estuar. Coast. Shelf Sci. 47 (1998) 119). We add dynamic physics (that is, local accelerations) for deep-water areas and keep kinematic physics (that is, without local and advective accelerations), with the inclusion of a porous medium beneath the open channel, for shallow and dewatering areas. The choice of which physics set to apply is made on an elemental depth dependent basis. The addition of the local acceleration terms for deep-water areas is seen to greatly improve accuracy in matching of tidal phasing over previous studies. Simulations involving M 2 /M 4 /M 6 tidal constituents result in strong agreement to observed data from the 1975 Great Bay field program (Ertu¨rk et al. Estuar. Coast. Shelf Sci. 17 (1983) 297), in terms of both tidal heights and cross-section averaged velocities. Comparisons with 10 tidal elevation observation stations and four cross-section averaged current transects show good agreement, displaying average normalized root mean square misfit values of 0.08 and 0.25, respectively. Study of the simulated momentum balance shows the size of the contributions from acceleration terms to be on the order of a third the size of the contributions from the pressure gradient and bottom stress terms. Although relatively small, they are observed to peak at the crucial time of tidal reversal. Application of the model for long-term simulation using an M 2 /N 2 /S 2 forcing shows the ability to realistically capture the spring-neap cycle. The tidally rectified flow is generally described as a constant spatial pattern with overall amplitude modulation following the spring-neap cycle.
The M 2 Internal Tide off Oregon: Inferences from Data Assimilation
Journal of Physical Oceanography, 2003
A linearized baroclinic, spectral-in-time tidal inverse model has been developed for assimilation of surface currents from coast-based high-frequency (HF) radars. Representer functions obtained as a part of the generalized inverse solution show that for superinertial flows information from the surface velocity measurements propagates to depth along wave characteristics, allowing internal tidal flows to be mapped throughout the water column. Application of the inverse model to a 38 km ϫ 57 km domain off the mid-Oregon coast, where data from two HF radar systems are available, provides a uniquely detailed picture of spatial and temporal variability of the M 2 internal tide in a coastal environment. Most baroclinic signal contained in the data comes from outside the computational domain, and so data assimilation (DA) is used to restore baroclinic currents at the open boundary (OB). Experiments with synthetic data demonstrate that the choice of the error covariance for the OB condition affects model performance. A covariance consistent with assumed dynamics is obtained by nesting, using representers computed in a larger domain. Harmonic analysis of currents from HF radars and an acoustic Doppler profiler (ADP) mooring off Oregon for May-July 1998 reveals substantial intermittence of the internal tide, both in amplitude and phase. Assimilation of the surface current measurements captures the temporal variability and improves the ADP/solution rms difference. Despite significant temporal variability, persistent features are found for the studied period; for instance, the dominant direction of baroclinic wave phase and energy propagation is always from the northwest. At the surface, baroclinic surface tidal currents (deviations from the depth-averaged current) can be 10 cm s Ϫ1 , 2 times as large as the depth-averaged current. Barotropic-to-baroclinic energy conversion is generally weak within the model domain over the shelf but reaches 5 mW m Ϫ2 at times over the slopes of Stonewall Bank.
Tidal dynamics in the Gulf of Maine and New England Shelf: An application of FVCOM
Journal of Geophysical Research, 2011
The unstructured-grid, Finite-Volume Community Ocean Model (FVCOM) was used to simulate the tides in the Gulf of Maine (GoM) and New England Shelf (NES) for homogeneous and summer stratified conditions. FVCOM captures the near-resonant nature of the semidiurnal tide and energy flux in the GoM and the complex dynamics governing the tide in the NES. Stratification has limited impact on tidal elevation, but can significantly modify the tidal current profile. Internal tides are energetic in the stratified regions over steep bottom topography, but their contribution to the total tidal energy flux is only significant over the northeast flank of Georges Bank. The model suggests that the tidal flushing-induced eddy east of Monomoy Island is the dynamic basis for the locally observed phase lead of the M 2 tide. The southward propagating tidal wave east of Cape Cod encounters the northeastward propagating tidal wave from the NES south of Nantucket Island, forming a zone of minimum sea level along a southeast-oriented line from Nantucket Island. These two waves are characterized by linear dynamics in which bottom friction and advection are negligible in the momentum balance, but their superposition leads to a strong nonlinear current interaction and large bottom stress in the zone of lowest sea elevation.
The effect of uncertain bottom friction on estimates of tidal current power
Royal Society Open Science, 2019
Uncertainty affects estimates of the power potential of tidal currents, resulting in large ranges in values reported for a given site, such as the Pentland Firth, UK. We examine the role of bottom friction, one of the most important sources of uncertainty. We do so by using perturbation methods to find the leading-order effect of bottom friction uncertainty in theoretical models by Garrett & Cummins (2005 Proc. R. Soc. A 461 , 2563–2572. ( doi:10.1098/rspa.2005.1494 ); 2013 J. Fluid Mech. 714 , 634–643. ( doi:10.1017/jfm.2012.515 )) and Vennell (2010 J. Fluid Mech. 671 , 587–604. ( doi:10.1017/S0022112010006191 )), which consider quasi-steady flow in a channel completely spanned by tidal turbines, a similar channel but retaining the inertial term, and a circular turbine farm in laterally unconfined flow. We find that bottom friction uncertainty acts to increase estimates of expected power in a fully spanned channel, but generally has the reverse effect in laterally unconfined farms....
3-D Modelling and Assessment of Tidal Current Resources in the Bay of Fundy, Canada
The Bay of Fundy, located between the Canadian Provinces of Nova Scotia and New Brunswick, is home to the world's largest tides and has long been identified as one of the world's premier resources of tidal energy. This paper describes the development of a high-resolution three-dimensional hydrodynamic model of tidal flows in the Bay of Fundy, and its application to help quantify and assess the kinetic energy resource throughout the Bay. Information on the scale and character of the tidal currents and the associated kinetic energy resource is presented herein for three of the most energetic parts of the Bay: near Long Island, Passamaquoddy Bay and Minas Passage (where a $70 million pre-commercial deployment of in-stream turbines is presently underway).