The Role of Mesoscale Eddies in the General Circulation of the Ocean—Numerical Experiments Using a Wind-Driven Quasi-Geostrophic Model

Holland, William R.

doi:10.1175/1520-0485(1978)008<0363:tromei>2.0.co;2

Cited by 397 publications

(249 citation statements)

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“…Consequently, chaotic behavior can be observed that leads to a mesoscale flow besides the large-scale double-gyre circulation. It is characterized by eddies, which exhibit notable local differences in velocity, temperature, and SSH, and they may also influence the large-scale flow (Holland 1978). This underlines the model's high-dimensional dynamics, which is important concerning the aim of our study.…”

Section: Model Initialization and Truth Runmentioning

confidence: 81%

Assessment of a Nonlinear Ensemble Transform Filter for High-Dimensional Data Assimilation

Tödter

Kirchgessner

Nerger

et al. 2016

Monthly Weather Review

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This work assesses the large-scale applicability of the recently proposed nonlinear ensemble transform filter (NETF) in data assimilation experiments with the NEMO ocean general circulation model. The new filter constitutes a second-order exact approximation to fully nonlinear particle filtering. Thus, it relaxes the Gaussian assumption contained in ensemble Kalman filters. The NETF applies an update step similar to the local ensemble transform Kalman filter (LETKF), which allows for efficient and simple implementation. Here, simulated observations are assimilated into a simplified ocean configuration that exhibits globally highdimensional dynamics with a chaotic mesoscale flow. The model climatology is used to initialize an ensemble of 120 members. The number of observations in each local filter update is of the same order resulting from the use of a realistic oceanic observation scenario. Here, an importance sampling particle filter (PF) would require at least 10 6 members. Despite the relatively small ensemble size, the NETF remains stable and converges to the truth. In this setup, the NETF achieves at least the performance of the LETKF. However, it requires a longer spinup period because the algorithm only relies on the particle weights at the analysis time. These findings show that the NETF can successfully deal with a large-scale assimilation problem in which the local observation dimension is of the same order as the ensemble size. Thus, the second-order exact NETF does not suffer from the PF's curse of dimensionality, even in a deterministic system.

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Section: Model Initialization and Truth Runmentioning

confidence: 81%

Assessment of a Nonlinear Ensemble Transform Filter for High-Dimensional Data Assimilation

Tödter

Kirchgessner

Nerger

et al. 2016

Monthly Weather Review

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“…Laplacian lateral heat diffusion tends to suppress the formation of mesoscale eddies by diminishing baroclinic signals at that scale, thus making it more difficult for baroclinic instabilities to overcome diffusive damping [Holland and Batteen, 1986]. Biharmonic diffusion, on the other hand, tends to allow the formation of mesoscale instabilities because it tends to damp at scales smaller than mesoscale eddies [Holland, 1978]. As a result, the use of biharmonic lateral diffusion should allow mesoscale eddy generation via barotropic (horizontal shear) and/or baroclinic (vertical shear) instability mechanisms.…”

Section: Heat and Momentum Diffusionmentioning

confidence: 99%

Wind‐forced modeling studies of currents, meanders, and eddies in the California Current system

Batteen¹

1997

J. Geophys. Res.

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Abstract. This process-oriented study of the California Current system (CCS) uses a high-resolution, multilevel, primitive equation ocean model on a/3 plane to isolate the response of that eastern boundary oceanic regime to temporal and spatially varying wind forcing. To study the generation, evolution, and maintenance of many of the observed features such as currents, meanders, and eddies in the CCS, the model is forced from rest with seasonal climatological winds. In response to the prevailing wind direction, surface equatorward currents develop, along with upwelling of cooler water along the coast and a poleward undercurrent. Baroclinic/barotropic instabilities in the equatorward surface current and poleward undercurrent result in the generation of meanders near the coast.As the meanders intensify, cold upwelling filaments develop along the coast and subsequently extend farther offshore. In time, the meanders form both cyclonic and anticyclonic eddies, which subsequently propagate farther offshore,, Longer. simulation

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“…They find that the stability analysis can correctly identify regions of instability best when the analysis is applied to instantaneous currents rather than time-mean ones and when the eddying flow is not too complicated or 'turbulent'. Many of the time-averaged solutions by HOLLAND (1977b) show no sources of instability, a fact that may influence how best to apply simple stability theory to actual ocean currents. HARRISON and ROBINSON (1978) developed an interpretation of the role of Reynolds stress-mean flow interaction work in open regions of a turbulent fluid flow, so that kinetic energy budgets over open regions can be studied.…”

Section: Eddy-resolving Oceanic General Circulation Modelsmentioning

confidence: 99%

The Mid-Ocean Dynamics Experiment

1978

Deep Sea Research

153

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Abstract--The Mid-Ocean Dynamics Experiment (MODE-1) was designed to investigate mid-ocean mesoscale eddies. An intensive and extensive program of measurements in three spatial dimensions and time was undertaken in an area southwest of Bermuda from March through mid-July 1973. Principal components of the experiment were an array of moored current meters and temperature-pressure recorders, hydrographic stations, drifting neutrally buoyant floats at 1500 m tracked by SOFAR, and acoustic and electromagnetic profilers. During MODE-1 a smaller scale survey relying on ship-tracked neutrally buoyant floats, a conductivity-temperature (CTD) survey, and a moored current meter array, MINIMODE, was carried out. The experiment was preceded by MODE-0, consisting of measurements by a series of moored current meters and other instruments in the general area selected for MODE-1.MODE-I observations were generally within a 300-km radius circle centered at 26°N, 69°40'W, with a greater concentration of observations in the interior ofthe circle. The region covers varied topography, wit h a flat abyssal plain sloping upward to t he continental rise in t he western half and rough topography in the eastern half.Descriptive, dynamical, numerical results of the experiment are presented. It is concluded that midocean eddies are part of an energetic and structured variability field superimposed on the weaker gyrescale mean circulation. In the western North Atlantic there is a band of eddy variability of around 100-day period and 70-km scale in which currents are horizontally nearly isotropic; vertical scales are of the order of the depth. The experiment provided conclusive evidence of the existence of mid-ocean eddies and serves as the basis for future experiments, such as POLYMODE, to extend our knowledge of these systems.DURING the past decade, physical oceanographers have directed a considerable effort to exploring and modeling mid-ocean mesoscale 'eddies', which are fluctuating current cells extending throughout the water column. Eddies occur irregularly throughout the World's oceans. They have swirl speeds of 5 to 50 cm s-1, and space-time scales of tens to hundreds of kilometers and weeks to months. Associated with the horizontal currents are fluctuating vertical displacements of up to several hundred meters in the main thermocline. Eddies, where they exist, usually dominate the mid-ocean flow.Understanding the eddies and their role in the general circulation has emerged as a central problem in ocean circulation dynamics. Moreover, understanding eddy dynamics is a prerequisite for both valid modeling of large-scale exchanges of momentum and energy, heat and salt, geochemicals, nutrients and other passive solutes, and for realistic coupled ocean-atmospheric models necessary for longer range weather prediction and climate modeling.

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The Role of Mesoscale Eddies in the General Circulation of the Ocean—Numerical Experiments Using a Wind-Driven Quasi-Geostrophic Model

Cited by 397 publications

References 0 publications

Assessment of a Nonlinear Ensemble Transform Filter for High-Dimensional Data Assimilation

Assessment of a Nonlinear Ensemble Transform Filter for High-Dimensional Data Assimilation

Wind‐forced modeling studies of currents, meanders, and eddies in the California Current system

The Mid-Ocean Dynamics Experiment

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