Weak constraint data assimilation for tides in the Arctic Ocean

Kivman, G.

doi:10.1016/s0079-6611(98)00005-6

Cited by 9 publications

(4 citation statements)

References 19 publications

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“…In reality, uncertainty exists first of all about the magnitude of the errors, both for the model and the data. The relative amplitude of the assumed errors in the in- (Foreman et al 1980;Kivman 1997). In our case, spurious small scale baroclinic vertical modes appear in the solution for low w o .…”

Section: Computations With Synthetic Data: Effect Of the Ob Conditionmentioning

confidence: 63%

The M2 Internal Tide off Oregon: Inferences from Data Assimilation

Kurapov

Egbert

Allen

et al. 2003

Journal of Physical Oceanography

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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.

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Section: Computations With Synthetic Data: Effect Of the Ob Conditionmentioning

confidence: 63%

The M2 Internal Tide off Oregon: Inferences from Data Assimilation

Kurapov

Egbert

Allen

et al. 2003

Journal of Physical Oceanography

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“…Open boundary conditions at the small northern boundary of the domain in the Arctic were specified elevations, taken from the global FES94 solution [ Le Provost et al , 1994]. Tests with variants, including the Arctic assimilation solutions of Kivman [1997], and a rigid wall at the top of the domain, showed that elevations outside the Arctic were nearly independent of the details in these boundary conditions. Recent modifications to our modeling code allow more general spherical coordinate systems with both poles over land, and make time stepping of the SWE over the full globe possible.…”

Section: Hydrodynamic Modelingmentioning

confidence: 99%

Numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum

2004

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[1] A hydrodynamic model incorporating a self-consistent treatment of ocean selfattraction and loading (SAL), and a physically based parameterization of internal tide (IT) drag, is used to assess how accurately barotropic tides can be modeled without benefit of data, and to explore tidal energetics in the last glacial maximum (LGM). M 2 solutions computed at high resolution with present day bathymetry agree with estimates of elevations from satellite altimetry within 5 cm RMS in the open ocean. This accuracy, and agreement with atlimetric estimates of energy dissipation, are achieved only when SAL and IT drag are included in the model. Solutions are sensitive to perturbations to bathymetry, and inaccuracies in available global databases probably account for much of the remaining error in modeled elevations. The %100 m drop in sea level during the LGM results in significant changes in modeled M 2 tides, with some amplitudes in the North Atlantic increasing by factors of 2 or more. Dissipation is also significantly changed by the drop in sea level. If IT drag estimated for the modern ocean is assumed, dissipation increases by about 50% globally, and almost triples in the deep ocean. However, IT drag depends on ocean stratification, which is poorly known for the LGM. Tests with modified IT drag suggest that the tendency to a global increase in dissipation is a robust result, but details are sensitive to stratification. Significant uncertainties about paleotides thus remain even in this comparatively simple case where bathymetry is well constrained.

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“…Those are taken to be sufficiently small. Based on experience, assuming overly long model error decorrelation length scales may degrade the quality of data inversion [e.g., Kivman , ]. However, it is important to mention that assuming uncorrelated errors (e.g.,

C_{h} = σ_{h}^{2} I

, where I is the unity matrix) would yield a singular correction (a linear combination of structures such as that shown in Figure ).…”

Section: Discussionmentioning

confidence: 99%

Bathymetry correction using an adjoint component of a coupled nearshore wave‐circulation model: Tests with synthetic velocity data

Kurapov

Özkan-Haller

2013

JGR Oceans

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[1] The impact of assimilation of wave-averaged flow velocities on the bathymetric correction is studied in tests with synthetic (model-generated) data using tangent-linear and adjoint components of a one-way coupled nearshore wave-circulation model. Weakly and strongly nonlinear regimes are considered, featuring energetic unsteady along-beach flows responding to time-independent wave-averaged forcing due to breaking waves. It is found that assimilation of time-averaged velocities on a regular grid (mimicking an array of remotely sensed data) provides sensible corrections to bathymetry. Even though the wave data are not assimilated, flow velocity assimilation utilizes adjoint components of both the circulation and wave models. The representer formalism allows separating contributions of these two components to the bathymetric correction. In a test case considered, involving a beach with an alongshore varying bar, the adjoint wave model contribution was mainly to determine the cross-shore position of the bar crest. The adjoint circulation model provided an additional contribution, mostly adding to alongshore variability in the shape of the bar. The array mode analysis reveals that there are very few modes that can be effectively corrected, given the assumed data error level. Bathymetry perturbations associated with these modes are a mixture of near-coast intensified modes as well as modes extending their influence to deep water (along the background wave characteristics). Additional tests show the utility of different observational arrays in providing the bathymetric correction.

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Weak constraint data assimilation for tides in the Arctic Ocean

Cited by 9 publications

References 19 publications

The M2 Internal Tide off Oregon: Inferences from Data Assimilation

The M2 Internal Tide off Oregon: Inferences from Data Assimilation

Numerical modeling of the global semidiurnal tide in the present day and in the last glacial maximum

Bathymetry correction using an adjoint component of a coupled nearshore wave‐circulation model: Tests with synthetic velocity data

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