Translation, decay and splitting of Agulhas rings in the southeastern Atlantic Ocean

Schouten, Mathijs W.; Ruijter, W. P. M. de; Leeuwen, Peter Jan van; Lütjeharms, J. R. E.

doi:10.1029/1999jc000046

Cited by 171 publications

(191 citation statements)

References 35 publications

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“…7) suggesting that this is the dominant time scale of variability. This time scale is comparable to the frequency of shedding of Agulhas rings as estimated from observations (Schouten et al 2000). That all hindcast simulations share this common feature (which also comes out when using Putrasahan et al 2015 method, not shown), despite differences in spatial characteristics along Goodhopeline, is a major finding of this study.…”

Section: Temporal Variability Of Agulhas Leakagesupporting

confidence: 64%

“…We aim to determine below if they also contribute to the temporal variability of AL. According to previous studies using satellite observations, Agulhas rings are shed from the retroflection at a rate of 5-6 per year (Schouten et al 2000;van Aken et al 2003;Doglioli et al 2006). Note that, according to the recent analysis by Elipot and Beal (2015), this largely exceeds the number of mesoscale meanders observed within the Agulhas Current at 34 • S, which suggests that other local or remote mechanisms predominantly control ring shedding and eventually Agulhas leakage variability.…”

Section: Temporal Variability Of Agulhas Leakagementioning

confidence: 96%

“…They have an average radius of 150-200 km and surface velocities which exceed 1 m/s (Schouten et al 2000;van Aken et al 2003). Rings are shed on average every 2-3 months at a rate of 5-6 per year but there can be sustained periods with no rings produced (Schouten et al 2000). They are not easily measured, as turbulence in the Cape Basin leads to the decay of rings (Boebel et al 2003).…”

Section: Introductionmentioning

confidence: 99%

“…AL is primarily rendered by Agulhas rings, large structures that act as vehicles transporting warm, salty water from the Indian Ocean to the South Atlantic. They have an average radius of 150-200 km and surface velocities which exceed 1 m/s (Schouten et al 2000;van Aken et al 2003). Rings are shed on average every 2-3 months at a rate of 5-6 per year but there can be sustained periods with no rings produced (Schouten et al 2000).…”

Section: Introductionmentioning

confidence: 99%

“…They are not easily measured, as turbulence in the Cape Basin leads to the decay of rings (Boebel et al 2003). As one ring is estimated to carry a volume transport of 0.5-1.5 Sv (Schouten et al 2000), with only 5-6 rings per year, rings cannot be the only vehicle of exchange as alone they cannot produce the estimated 15 Sv of transport reported by Richardson (2007). The extra contribution is likely provided through sub-mesoscale processes including filaments and jets (Lutjeharms and Cooper 1996) and by a background flux component (Loveday et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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Spatio-temporal characteristics of Agulhas leakage: a model inter-comparison study

et al. 2016

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west of the southern tip of Africa , is used to identify features that are robust regardless of the model used and takes into account the thermohaline biases of each model. When determined by a passive tracer method, 60 % of the magnitude of Agulhas leakage is captured and more than 80 % of its temporal fluctuations, suggesting that the method is appropriate for investigating the variability of Agulhas leakage. In all simulations but one, the major driver of variability is associated with mesoscale features passing through the section. High resolution (<1/10 • ) hindcast models agree on the temporal (2-4 cycles per year) and spatial (300-500 km) scales of these features corresponding to observed Agulhas Rings. Coarser resolution models (<1/4 • ) reproduce similar time scale of variability of Agulhas leakage in spite of their difficulties in representing the Agulhas rings properties. A coarser resolution climate model (2 • ) does not resolve the spatio-temporal mechanism of variability of Agulhas leakage. Hence it is expected to underestimate the contribution of Agulhas Current System to climate variability.

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Section: Temporal Variability Of Agulhas Leakagesupporting

confidence: 64%

Section: Temporal Variability Of Agulhas Leakagementioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Spatio-temporal characteristics of Agulhas leakage: a model inter-comparison study

et al. 2016

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Agulhas ring formation as a barotropic instability of the retroflection

Weijer

Zharkov²,

Nof

et al. 2013

Geophysical Research Letters

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Agulhas Leakage is an important link in the global ocean circulation, as it transfers a significant volume of relatively warm and salty water from the Indian Ocean to the Atlantic Ocean. The main route of this transfer is through the shedding of large Agulhas rings from the Agulhas retroflection. In this paper we study the dynamics of the ring formation process by analyzing the stability of the Indian/Atlantic supergyre in a reduced gravity model. We show that the ring‒shedding process results from a barotropic instability of the steady circulation in the Agulhas retroflection region. The destabilizing mode appears to be linked to a Rossby basin mode of the combined South Indian/Atlantic basin, which is localized in the retroflection region by the background flow.

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Long‐lived mesoscale eddies in the eastern Mediterranean Sea: Analysis of 20 years of AVISO geostrophic velocities

et al. 2014

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We analyzed 20 years of AVISO data set to detect and characterize long-lived eddies, which stay coherent more than 6 months, in the eastern Mediterranean Sea. In order to process the coarse gridded (1=8 ) AVISO geostrophic velocity fields, we optimized a geometrical eddy detection algorithm. Our main contribution was to implement a new procedure based on the computation of the Local and Normalized Angular Momentum (LNAM) to identify the positions of the eddy centers and to follow their Lagrangian trajectories. We verify on two mesoscale anticyclones, sampled during the EGYPT campaign in 2006, that our methodology provides a correct estimation of the eddy centers and their characteristic radius corresponding to the maximal tangential velocity. Our analysis reveals the dominance of anticyclones among the longlived eddies. This cyclone-anticyclone asymmetry appears to be much more pronounced in eastern Mediterranean Sea than in the global ocean. Then we focus our study on the formation areas of long-lived eddies. We confirm that the generations of the Ierapetra and the Pelops anticyclones are recurrent and correlated to the Etesian wind forcing. We also provide some evidence that the smaller cyclonic eddies formed at the southwest of Crete may also be induced by the same wind forcing. On the other hand, the generation of long-lived eddies along the Libyo-Egyptian coast are not correlated to the local wind-stress curl but surprisingly, their initial formation points follow the Herodotus Trough bathymetry. Moreover, we identify a new formation area, not discussed before, along the curved shelf off Benghazi.

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Translation, decay and splitting of Agulhas rings in the southeastern Atlantic Ocean

Abstract: Abstract.All Agulhas rings that were spawned at the Agulhas retrofiection between 1993 and 1996 (a total of 21 rings) have been monitored using TOPEX/Poseidon satellite altimetry and followed as they moved through the

Cited by 171 publications

References 35 publications

Spatio-temporal characteristics of Agulhas leakage: a model inter-comparison study

Spatio-temporal characteristics of Agulhas leakage: a model inter-comparison study

Agulhas ring formation as a barotropic instability of the retroflection

Long‐lived mesoscale eddies in the eastern Mediterranean Sea: Analysis of 20 years of AVISO geostrophic velocities

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