Submesoscale Coherent Vortices in the Gulf Stream

Gula, Jonathan; Blacic, T. M.; Todd, Robert E.

doi:10.1029/2019gl081919

Cited by 47 publications

(64 citation statements)

References 47 publications

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“…It should be noted that the experiments presented in this study are based on synthetic SWOT observations from a state-of-the-art high resolution submesoscale permitting ocean model simulation (NEMO-NATL60). However, this model simulation does not account for the high frequency internal tides that will affect SWOT SSH signals at scales <100 km [15,16]. It is unclear how the efficiency of the method presented in this study would be affected by the representation of high frequency internal tides in the model.…”

Section: Discussionmentioning

confidence: 97%

“…Note, however, that internal tides are not represented in this simulation. Several studies suggest that internal tides will strongly impact the SSH SWOT signal [15,16], but what the impact will precisely be and whether we will be able to separate the internal tide signal from the balanced circulation remain open questions. Assessing whether the method proposed herein will be effective in the presence of internal tides is therefore left to future studies.…”

Section: Introductionmentioning

confidence: 99%

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Reduction of Spatially Structured Errors in Wide-Swath Altimetric Satellite Data Using Data Assimilation

et al. 2019

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The Surface Water and Ocean Topography (SWOT) mission is a next generation satellite mission expected to provide a 2 km-resolution observation of the sea surface height (SSH) on a two-dimensional swath. Processing SWOT data will be challenging because of the large amount of data, the mismatch between a high spatial resolution and a low temporal resolution, and the observation errors. The present paper focuses on the reduction of the spatially structured errors of SWOT SSH data. It investigates a new error reduction method and assesses its performance in an observing system simulation experiment. The proposed error-reduction method first projects the SWOT SSH onto a subspace spanned by the SWOT spatially structured errors. This projection is removed from the SWOT SSH to obtain a detrended SSH. The detrended SSH is then processed within an ensemble data assimilation analysis to retrieve a full SSH field. In the latter step, the detrending is applied to both the SWOT data and an ensemble of model-simulated SSH fields. Numerical experiments are performed with synthetic SWOT observations and an ensemble from a North Atlantic, 1/60° simulation of the ocean circulation (NATL60). The data assimilation analysis is carried out with an ensemble Kalman filter. The results are assessed with root mean square errors, power spectrum density, and spatial coherence. They show that a significant part of the large scale SWOT errors is reduced. The filter analysis also reduces the small scale errors and allows for an accurate recovery of the energy of the signal down to 25 km scales. In addition, using the SWOT nadir data to adjust the SSH detrending further reduces the errors.

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Section: Discussionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Reduction of Spatially Structured Errors in Wide-Swath Altimetric Satellite Data Using Data Assimilation

et al. 2019

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“…These authors show that relaxing the QG assumptions in an idealized model of the ocean interior leads to the emergence of large Rossby number and energetic frontogenesis driven by mesoscale eddies. Seismic imaging has also long revealed the existence of ageostrophic mesoscale eddies (50-100 km) in the ocean interior (Biescas et al 2008;Menesguen et al 2009;Barbosa Aguiar et al 2015), such as the subsurface anticyclones of the North Atlantic Ocean known as ''meddies'' (Armi et al 1988) or the coherent eddies of the Gulf Stream (Gula et al 2019). In addition, two recent in situ studies diagnosed strong upward vertical heat fluxes in the ocean interior (Siegelman et al 2020;Yu et al 2019), believed to be produced by ageostrophic dynamics.…”

Section: Introductionmentioning

confidence: 99%

Energetic Submesoscale Dynamics in the Ocean Interior

Siegelman

2020

Journal of Physical Oceanography

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Submesoscale ocean processes, characterized by order-1 Rossby and Richardson numbers, are currently thought to be mainly confined to the ocean surface mixed layer, whereas the ocean interior is commonly assumed to be in quasigeostrophic equilibrium. Here, a realistic numerical simulation in the Antarctic Circumpolar Current, with a 1/48° horizontal resolution and tidal forcing, is used to demonstrate that the ocean interior departs from the quasigeostrophic regime down to depths of 900 m, that is, well below the mixed layer. Results highlight that, contrary to the classical paradigm, the ocean interior is strongly ageostrophic, with a pronounced cyclone–anticyclone asymmetry and a dominance of frontogenesis over frontolysis. Numerous vortices and filaments, from the surface down to 900 m, are characterized by large Rossby and low Richardson numbers, strong lateral gradients of buoyancy, and vigorous ageostrophic frontogenesis. These deep submesoscales fronts are only weakly affected by internal gravity waves and drive intense upward vertical heat fluxes, consistent with recent observations in the Antarctic Circumpolar Current and the Gulf Stream. As such, deep submesoscale fronts are an efficient pathway for the transport of heat from the ocean interior to the surface, suggesting the presence of an intensified oceanic restratification at depth.

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“…Near 31.5° N, 79° W, a prominent topographic feature is present off the coasts of South Carolina and Georgia: the Charleston Bump. Above it, the flow is shallow (O(500) m) and intense (O(1) m s −1 ) even at the bottom, thus providing a context of strong current-topography interaction 10 and conditions that are favorable for the generation of lee waves 11 .…”

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confidence: 99%

Interaction of the Gulf Stream with small scale topography: a focus on lee waves

Marez

Lahaye

Gula

2020

Sci Rep

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the generation of lee waves in the Gulf Stream along the U.S. seaboard is investigated using high resolution realistic simulations. the model reproduces the surface signature of the waves, which compares favourably with observations from satellite sun glitter images in the region. in particular, a large number of internal waves are observed above the charleston Bump. these waves match well with the linear theory describing topographically-generated internal waves, which can be used to estimate the associated vertical transport of momentum and energy extracted from the mean flow. Finally, small scale topographic features are shown to have a significant impact on the mean flow in this region of the Gulf Stream, and the specific role of lee waves in this context is outlined.

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Submesoscale Coherent Vortices in the Gulf Stream

Cited by 47 publications

References 47 publications

Reduction of Spatially Structured Errors in Wide-Swath Altimetric Satellite Data Using Data Assimilation

Reduction of Spatially Structured Errors in Wide-Swath Altimetric Satellite Data Using Data Assimilation

Energetic Submesoscale Dynamics in the Ocean Interior

Interaction of the Gulf Stream with small scale topography: a focus on lee waves

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