Surface signature of Mediterranean water eddies in the Northeastern Atlantic: effect of the upper ocean stratification

Bashmachnikov, Igor; Carton, Xavier

doi:10.5194/os-8-931-2012

Cited by 28 publications

(46 citation statements)

References 41 publications

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“…A key consideration is that a meddy does not travel as an isolated feature but strongly influences the waters above and below (Siedler et al 2005, Bashmachnikov andCarton 2012), to the point that a substantial portion of the water column moves almost jointly with the meddy, behaving very like a Taylor column (Pedlosky 1979, e.g.). However, the water on top of the meddy does not behave as a perfect Taylor column, as otherwise these waters would remain unchanged from the location where the meddy was originally formed, i.e.…”

Section: Discussionmentioning

confidence: 99%

Interaction of Mediterranean Water lenses with Antarctic Intermediate Water off Northwest Africa

Machín¹,

Pelegrí²

2016

Sci. Mar.

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Summary:Mediterranean Water lenses (meddies) in the eastern North Atlantic, north of the Canary Islands, appear to often have their salty and nutrient-poor core accompanied by relatively fresh and nutrient-rich waters on top. We describe several occurrences of freshwater halos and berets for meddies sampled north of the Canary Islands-with instrumented moorings, Argo floats and oceanographic cruises-and identify the source of these fresh anomalies as diluted Antarctic Intermediate Water (AAIW). We propose that this capping takes place off Northwest Africa, as the southward-advected meddy interacts with the northward-advected AAIW. This interpretation is consistent with a simple analysis of the relevant advectivediffusive time scales associated with the passage of meddies under a layer of AAIW, and suggests that meddies may be a mechanism for AAIW export far into the North Atlantic Ocean.Keywords: meddies; Antarctic Intermediate Water; eastern North Atlantic. Interacción de remolinos de agua mediterránea con Agua Intermedia Antártica al noroeste de ÁfricaResumen: Los Meddies en el Atlántico Norte oriental, al norte de las Islas Canarias, a menudo parecen tener su núcleo salado y pobre en nutrientes acompañado de aguas relativamente frescas y ricas en nutrientes en la parte superior. Se describen varios casos de halos y boinas de agua dulce para meddies muestreados al norte de las Islas Canarias -con instrumentos anclados, perfiladores Argo y campañas oceanográficas-identificando así el origen de estas anomalías frescas como Agua Intermedia Antártica (AIAA) diluida. Proponemos que esta interacción se lleva a cabo en el noroeste de África, cuando el meddy advectado hacia el sur interactúa con el AIAA advectada hacia el norte. Esta interpretación es coherente con un simple análisis de las escalas de tiempo advectivo-difusivas asociadas con el paso de meddies bajo una capa de AIAA, y sugiere que los meddies pueden ser un mecanismo para exportar AIAA hacia el océano interior en el Atlántico Norte.Palabras clave: meddies; agua intermedia antártica; Atlántico Norte oriental.Citation/Como citar este artículo: Machín F

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Section: Discussionmentioning

confidence: 99%

Interaction of Mediterranean Water lenses with Antarctic Intermediate Water off Northwest Africa

Machín¹,

Pelegrí²

2016

Sci. Mar.

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“…Yet, as the Meddy sinks deeper, how will the sea surface, containing its signal, change? As discussed in section 1, detecting Meddies using along track satellite altimetry is possible due to the Meddy's vorticity essentially being propagated to the sea surface, creating sea level anomaly sometimes as large as 12 cm [Bashmachnikov and Carton, 2012]. Figure 6b shows the time series of sea surface height anomaly along the path of AMUSE float am110.…”

Section: Horizontal and Vertical Displacement Of A Meddymentioning

confidence: 99%

“…In other words, upperlayer stratification can significantly reduce the intensity of the signal as it reaches the sea surface. The relative vorticity of their surface signals was, on average, from 20.05 to 20.10f (where f is the coriolis parameter, Bashmachnikov and Carton [2012]). Using along-track altimetry, Oliveira et al [2000] showed a 5-10 cm sea level anomaly, and Bashmachnikov and Carton [2012] also reported that the sea level anomaly over Meddies was 6-12 cm with a 70 km Meddy radius for a homogeneous upper layer.…”

Section: Introductionmentioning

confidence: 99%

“…The relative vorticity of their surface signals was, on average, from 20.05 to 20.10f (where f is the coriolis parameter, Bashmachnikov and Carton [2012]). Using along-track altimetry, Oliveira et al [2000] showed a 5-10 cm sea level anomaly, and Bashmachnikov and Carton [2012] also reported that the sea level anomaly over Meddies was 6-12 cm with a 70 km Meddy radius for a homogeneous upper layer. Later, Bashmachnikov et al [2013] reported examples of vertical profiles of temperature and salinity showing the uplift of isopycnals above a Meddy compared with the surrounding ocean (their Figure 1).…”

Section: Introductionmentioning

confidence: 99%

“…Meddy location observations were made based on the fact that the mechanism of generation of a Meddy surface signal is the compression of the upper-layer vorticity tubes by a moving Meddy, resulting from the conservation of the upper-layer potential vorticity [Bashmachnikov et al, 2009;Bashmachnikov and Carton, 2012;Bashmachnikov et al, 2013Bashmachnikov et al, , 2014, resulting in a weaker signal at the surface. In other words, upperlayer stratification can significantly reduce the intensity of the signal as it reaches the sea surface.…”

Section: Introductionmentioning

confidence: 99%

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An analysis of the evolution of Meddies in the North Atlantic using floats and multisensor satellite data

Ienna

Yan

2015

JGR Oceans

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Previous studies focusing on the remote detection of Mediterranean Eddies (Meddies) have reported that the isopycnal surface changes derived from satellite multisensor measurements at the approximate depth of 400 m can be used to sense the presence of underlying Meddies. While the isopycnal surface near that depth does indeed reveal the locations of Meddies, an analysis of isopycnal surface changes in response to the evolution of Meddies has yet to be made. Accordingly, this research focuses on analyzing the relationship between isopycnal surface changes and the evolution of Meddies. The vertical isopycnal surface variability of Meddies, which is directly related to contributions from rotational velocity, interior thermal variation, and vertical displacement of Meddies, is observed and studied using float observations from A Mediterranean Undercurrent Seeding Experiment (AMUSE). The contributions of each of the three aforementioned parameters are estimated, enabling us to understand their relative role in changing the isopycnal surface above Meddies. Furthermore, in order to further understand Meddies' evolution and their associated forcing, the dominant frequencies of their horizontal and vertical displacements, as well as the sea surface height variability above the Meddy, are analyzed using the Hilbert-Huang Transform. Finally, the horizontal and the vertical eddy viscosity dissipation of Meddies is computed and compared with a theoretical model. The empirical horizontal and the vertical eddy viscosities are found to be 7 3 10 6 cm 2 s 21 and 200 cm 2 s 21 , respectively. This study will therefore contribute to understanding how the isopycnal surface is related to the presence of Meddies, what frequencies dominate its variability, and the values of eddy viscosity which can be used for a numerical model.

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Characteristics of surface signatures of Mediterranean water eddies

2014

Self Cite

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In this work, we obtain new results on the manifestation of meddies (or of other deep eddies)at the sea-surface, further developing the results by Bashmachnikov and Carton (2012). The quasigeostrophic equations are used to describe a near-axisymmetric vortex in the upper ocean, forced at its lower boundary by the isopycnal elevation of a moving meddy. The solution thus obtained provides a better approximation of the characteristics of meddy surface signals. The results show that in subtropics large meddies with dynamic radius R m ! 30 km are always seen at the sea-surface with AVISO altimetry, that medium-size meddies with R m 5 20 km may be seen at the sea-surface only if they are sufficiently shallow and strong, while small meddies with R m 5 10 km generally cannot be detected with the present accuracy of altimetry data. The intensity of meddy surface signals decreases to the south with the decrease of the f = N ratio. The seasonal variation in intensity of the surface signal for northern meddies (45 N) is on the order of 2-3 cm, but for subtropical meddies (35 N) it can be on the order of 5-10 cm. The radii of meddy surface signals range from 1 to 2 times the radii of the corresponding meddies. For most of the observed subtropical meddies, the upper limit should be used. Numerical experiments show that surface signals of meddies translated with b-drift are efficiently dispersed by the radiation of Rossby waves. At the same time, for meddies translated by a background current, the surface signal does not show strong dissipation.

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Surface signature of Mediterranean water eddies in the Northeastern Atlantic: effect of the upper ocean stratification

Cited by 28 publications

References 41 publications

Interaction of Mediterranean Water lenses with Antarctic Intermediate Water off Northwest Africa

Interaction of Mediterranean Water lenses with Antarctic Intermediate Water off Northwest Africa

An analysis of the evolution of Meddies in the North Atlantic using floats and multisensor satellite data

Characteristics of surface signatures of Mediterranean water eddies

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