Cyclogeostrophic balance in the Mozambique Channel

Penven, Pierrick; Halo, Issufo; Pous, Stéphane; Marié, Louis

doi:10.1002/2013jc009528

Cited by 49 publications

(64 citation statements)

References 28 publications

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“…For anticyclonic features with large g 0 leading to large u g , the sum under the square root sign can become negative as r gets close to zero. This effect was noted in Penven et al [2014], who showed that for large g 0 , the gradient wind equation has no solution for small radii. The fact that the solution only exists within a limited range should be taken into consideration when calculations are completed.…”

Section: Idealized Casementioning

confidence: 86%

Analysis of ageostrophy in strong surface eddies in the Atlantic Ocean

Douglass

Richman

2015

JGR Oceans

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Strongly nonlinear surface eddies are identified and analyzed in a general circulation model. Agulhas rings and Gulf Stream cold-core eddies are examples of eddies that cannot be properly characterized using linear geostrophic dynamics. These eddies are compact, highly circular, persistent in time, and travel long distances while maintaining their characteristics. The nonlinear eddies can be identified by a large Rossby number and high circularity. The majority of the anomalous eddies are anticyclones. Calculation of the balance of forces on these eddies demonstrates that the centrifugal force associated with strong curvature is significant, and the force balance shifts from geostrophy toward a gradient wind balance. Using geostrophy instead of the gradient wind balance produces large errors in estimates of rotational velocity of these eddies. The gradient wind velocity can be calculated from geostrophic velocity and eddy radius. Comparison between the results demonstrates that even when only sea surface height and associated geostrophic velocities are available, strongly nonlinear eddies can be identified and properly characterized. This analysis is then applied to altimetric maps of sea surface height. Nonlinear eddies are present in the altimetric maps, but are less common and not as strongly nonlinear. This analysis demonstrates that by properly accounting for the dynamics of the eddy field, a more complete statistical description including nonlinear terms can be obtained from readily available observations.

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Section: Idealized Casementioning

confidence: 86%

Analysis of ageostrophy in strong surface eddies in the Atlantic Ocean

Douglass

Richman

2015

JGR Oceans

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“…This latter force needs to be taken into account, otherwise, the velocity is underestimated for anticyclones and overestimated for cyclones [Elliott and Sanford, 1986;Penven et al, 2014]. The cyclostrophic velocities v c can be retrieved by solving the quadratic equation expressing the gradient wind balance in a cylindrical coordinate system: To infer cyclostrophic velocities, (1) the eddy center position and (2) absolute geostrophic velocities have to be determined.…”

Section: Appendix A: Solving the Gradient Wind Balance With Glidersmentioning

confidence: 99%

Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

et al. 2016

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Since 2010, an intense effort in the collection of in situ observations has been carried out in the northwestern Mediterranean Sea thanks to gliders, profiling floats, regular cruises, and mooring lines. This integrated observing system enabled a year‐to‐year monitoring of the deep waters formation that occurred in the Gulf of Lions area during four consecutive winters (2010–2013). Vortical structures remnant of wintertime deep vertical mixing events were regularly sampled by the different observing platforms. These are Submesoscale Coherent Vortices (SCVs) characterized by a small radius (∼5–8 km), strong depth‐intensified orbital velocities (∼10–20 cm s−1) with often a weak surface signature, high Rossby (∼0.5) and Burger numbers O(0.5–1). Anticyclones transport convected waters resulting from intermediate (∼300 m) to deep (∼2000 m) vertical mixing. Cyclones are characterized by a 500–1000 m thick layer of weakly stratified deep waters (or bottom waters that cascaded from the shelf of the Gulf of Lions in 2012) extending down to the bottom of the ocean at ∼2500 m. The formation of cyclonic eddies seems to be favored by bottom‐reaching convection occurring during the study period or cascading events reaching the abyssal plain. We confirm the prominent role of anticyclonic SCVs and shed light on the important role of cyclonic SCVs in the spreading of a significant amount (∼30%) of the newly formed deep waters away from the winter mixing areas. Since they can survive until the following winter, they can potentially have a great impact on the mixed layer deepening through a local preconditioning effect.

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“…Momentum equations can be then easily solved, giving rise to the gradient wind solution (e.g., Holton, 1992). This provides a first correction to the geostrophic velocities derived from altimetry, which can be up to 50 % of the geostrophic velocity in intense vortices (Penven et al, 2014). This correction, which depends on the curvature of the streamlines, can be implemented using the iterative method proposed by Endlich (1961) and Arnason et al (1962):…”

Section: Currents From Sea Surface Heightmentioning

confidence: 99%

“…The iterations stop once the velocity increment falls below a threshold or it starts to increase (Penven et al, 2014).…”

Section: Currents From Sea Surface Heightmentioning

confidence: 99%

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

Isern‐Fontanet

Ballabrera-Poy

Turiel

et al. 2017

Nonlin. Processes Geophys.

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Abstract. Ocean currents play a key role in Earth's climate -they impact almost any process taking place in the ocean and are of major importance for navigation and human activities at sea. Nevertheless, their observation and forecasting are still difficult. First, no observing system is able to provide direct measurements of global ocean currents on synoptic scales. Consequently, it has been necessary to use sea surface height and sea surface temperature measurements and refer to dynamical frameworks to derive the velocity field. Second, the assimilation of the velocity field into numerical models of ocean circulation is difficult mainly due to lack of data. Recent experiments that assimilate coastal-based radar data have shown that ocean currents will contribute to increasing the forecast skill of surface currents, but require application in multidata assimilation approaches to better identify the thermohaline structure of the ocean. In this paper we review the current knowledge in these fields and provide a global and systematic view of the technologies to retrieve ocean velocities in the upper ocean and the available approaches to assimilate this information into ocean models.

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Cyclogeostrophic balance in the Mozambique Channel

Abstract: Three methods are proposed for the inclusion of inertia when deriving currents from sea surface height (SSH)

Cited by 49 publications

References 28 publications

Analysis of ageostrophy in strong surface eddies in the Atlantic Ocean

Analysis of ageostrophy in strong surface eddies in the Atlantic Ocean

Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

Remote sensing of ocean surface currents: a review of what is being observed and what is being assimilated

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