Subsurface geostrophic velocities inference from altimeter data: Application to the Sicily Channel (Mediterranean Sea)

Nardelli, Bruno Buongiorno; Cavalieri, Olga; Rio, Marie-Hélène; Santoleri, Rosalia

doi:10.1029/2005jc003191

Cited by 28 publications

(28 citation statements)

References 32 publications

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“…Our transport‐like approach allowed to better quantify the different AW related flows while taking into account the strong bathymetry constraints of the SC. This transport‐like approach appears globally efficient, as the long‐term averaged transport budgets gave low residuals, at least for the boxes over the deepest areas, and mean transports are in the range of previous estimates for the AC flow (0.5–1.5 Sv) at the entrance or inside the SC (e.g., Astraldi et al, ; Buongiorno Nardelli et al, ; Onken et al, ; Sammari et al, ). Budget uncertainties for boxes 3 and 5 over shallow areas, however, show the limits of such altimetry‐derived approach, requiring thus to be discussed in‐depth.…”

Section: Discussionmentioning

confidence: 94%

“…This estimate is reduced to 0.56 Sv with the 12 months low‐pass filter in Figure , but Figure shows that monthly estimates rather varies over the range of previous estimates. On the other hand, a mean baroclinic AW transport of 0.49 Sv is given in Korres et al () through the SC, while the few estimates of Buongiorno Nardelli et al () varies from 0.43 to 1.43 Sv for a 0–300 dbar vertical section over the deepest part of track 059. Likewise, the northern inflow of track 237 (ATC) shows values during 2003 in agreement with the transport estimate of Ben Ismail et al () from in situ geostrophic and adjusted currents over the 0–150 m layer.…”

Section: Discussionmentioning

confidence: 99%

“…More information about the sampling details of the oceanographic cruises (periods, number of casts, and stations) can be found in the SeaDataNet website or in Sammari et al () and Ben Ismail et al (). Based on the classical dynamic method (Schilchtholz, ), the temperature and salinity fields of the available CTD data are used to compute the surface dynamic heights and estimate the in situ surface geostrophic currents, as in Ben Ismail et al (), with a 320 m reference level for the deeper CTD casts (300 dbar in Buongiorno Nardelli et al, ) and the bottom depth for those on shallower bathymetry.…”

Section: Methodsmentioning

confidence: 99%

“…This time shift between both estimates varies from few hours to 4 days in our case (see Figures and ), and the larger it gets, the most significant differences are noted. This time shift would be particularly constraining such comparisons in an area of marked mesoscale variability like the Central Mediterranean Sea (e.g., Buongiorno Nardelli et al, ).…”

Section: Transport‐like Analysismentioning

confidence: 99%

“…In the case of the Sicily Strait, the LIW and AW flows being opposite, there is a no motion layer signing their interface as shown in Buongiorno Nardelli et al (). Assuming this AW/LIW interface as a reference depth, any projection of surface velocity values down to it should be able to reproduce grossly the baroclinic component of the AW related flow.…”

Section: Transport‐like Analysismentioning

confidence: 99%

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Interannual Variations of Surface Currents and Transports in the Sicily Channel Derived From Coastal Altimetry

et al. 2017

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A 20 year coastal altimetry data set (X‐TRACK) is used, for the first time, to gain insight into the long‐term interannual variations of the surface circulation in the Sicily Channel. First, a spectral along with a time/space diagram analysis are applied to the monthly means. They reveal a regionally coherent current patterns from track to track with a marked interannual variability that is unequally shared between the Atlantic Tunisian Current and Atlantic Ionian Stream inflows in the Sicily Channel and the Bifurcation Tyrrhenian Current outflow northeast of Sicily. Second, an empirical altimetry‐based transport‐like technique is proposed to quantify volume budgets inside the closed boxes formed by the crossing of the altimetry tracks and coastlines over the study area. A set of hydrographic measurements is used to validate the method. The inferred altimetry transports give a well‐balanced mean eastward Atlantic Waters baroclinic flow of 0.4 Sv and standard deviations of 0.2 Sv on a yearly basis throughout the Sicily Channel and toward the Ionian Sea, which is fairly coherent with those found in the literature. Furthermore, the analysis allows to quantify the intrusions of Atlantic Waters over the Tunisian Shelf (0.12 ± 0.1 Sv) and highlights two main modes of variability of the main surface waters path over the Sicily Channel through the Bifurcation Atlantic Tunisian Current and Atlantic Ionian Stream systems. Some physical mechanisms are finally discussed with regards to changes in the observed currents and transports.

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Section: Discussionmentioning

confidence: 94%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Transport‐like Analysismentioning

confidence: 99%

Section: Transport‐like Analysismentioning

confidence: 99%

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Interannual Variations of Surface Currents and Transports in the Sicily Channel Derived From Coastal Altimetry

et al. 2017

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Southern Ocean Mixed‐Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

et al. 2017

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The depth of the upper ocean mixed layer provides fundamental information on the amount of seawater that directly interacts with the atmosphere. Its space‐time variability modulates water mass formation and carbon sequestration processes related to both the physical and biological pumps. These processes are particularly relevant in the Southern Ocean, where surface mixed‐layer depth estimates are generally obtained either as climatological fields derived from in situ observations or through numerical simulations. Here we demonstrate that weekly observation‐based reconstructions can be used to describe the variations of the mixed‐layer depth in the upper ocean over a range of space and time scales. We compare and validate four different products obtained by combining satellite measurements of the sea surface temperature, salinity, and dynamic topography and in situ Argo profiles. We also compute an ensemble mean and use the corresponding spread to estimate mixed‐layer depth uncertainties and to identify the more reliable products. The analysis points out the advantage of synergistic approaches that include in input the sea surface salinity observations obtained through a multivariate optimal interpolation. Corresponding data allow to assess mixed‐layer depth seasonal and interannual variability. Specifically, the maximum correlations between mixed‐layer anomalies and the Southern Annular Mode are found at different time lags, related to distinct summer/winter responses in the Antarctic Intermediate Water and Sub‐Antarctic Mode Waters main formation areas.

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Three‐Dimensional Ageostrophic Motion and Water Mass Subduction in the Southern Ocean

2018

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Vertical velocities at the ocean mesoscale are several orders of magnitude smaller than corresponding horizontal flows, making their direct monitoring a still unsolved challenge. Vertical motion is generally retrieved indirectly by applying diagnostic equations to observation‐based fields. The most common approach relies on the solution of an adiabatic version of the Omega equation, neglecting the ageostrophic secondary circulation driven by frictional effects and turbulent mixing in the boundary layers. Here we apply a diabatic semigeostrophic diagnostic model to two different 3‐D reconstructions covering the Southern Ocean during the period 2010–2012. We incorporate the effect of vertical mixing through a modified K‐profile parameterization and using ERA‐interim data, and perform an indirect validation of the ageostrophic circulation with independent drifter observations. Even if horizontal gradients and associated vertical flow are likely underestimated at 1/4° × 1/4° resolution, the exercise provides an unprecedented relative quantification of the contribution of vertical mixing and adiabatic internal dynamics on the vertical exchanges along the Antarctic Circumpolar Current. Kinematic estimates of subduction rates show the destruction of poleward flowing waters lighter than 26.6 kg/m3 (14 ÷ 15 Sv) and two main positive bands associated with the Antarctic Intermediate Water (7 ÷ 11 Sv) and Sub‐Antarctic Mode Waters (4 ÷ 7 Sv) formation, while Circumpolar Deep Water upwelling attains around 3 ÷ 6 Sv. Diabatic and adiabatic terms force distinct spatial responses and vertical velocity magnitudes along the water column and the restratifying effect of adiabatic internal dynamics due to mesoscale eddies is shown to at least partly compensate the contribution of wind‐driven vertical exchanges to net subduction.

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Subsurface geostrophic velocities inference from altimeter data: Application to the Sicily Channel (Mediterranean Sea)

Cited by 28 publications

References 32 publications

Interannual Variations of Surface Currents and Transports in the Sicily Channel Derived From Coastal Altimetry

Interannual Variations of Surface Currents and Transports in the Sicily Channel Derived From Coastal Altimetry

Southern Ocean Mixed‐Layer Seasonal and Interannual Variations From Combined Satellite and In Situ Data

Three‐Dimensional Ageostrophic Motion and Water Mass Subduction in the Southern Ocean

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