Assimilating along-track SLA data using the EnOI in an eddy resolving model of the Agulhas system

Backeberg, Björn; Counillon, François; Johannessen, Johnny A.; Pujol, Marie–Isabelle

doi:10.1007/s10236-014-0717-6

Cited by 32 publications

(68 citation statements)

References 44 publications

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“…The different levels of variability in the Agulhas leakage between ORCA025 and ORAs may be attributed to the impacts of the SLA assimilation (Backeberg et al, 2014). However, even among ORAs these Agulhas patterns differ; for example, the weaker contributions in ORAP5 may be due to smoothing from the superobservation method applied to the altimeter data (Mogensen et al, 2012), as also noted by Masina et al (2015).…”

Section: Temporal Variabilitymentioning

confidence: 79%

South Atlantic meridional transports from NEMO-based simulations and reanalyses

2018

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Abstract. The meridional heat transport (MHT) of the South Atlantic plays a key role in the global heat budget: it is the only equatorward basin-scale ocean heat transport and it sets the northward direction of the global cross-equatorial transport. Its strength and variability, however, are not well known. The South Atlantic transports are evaluated for four state-of-the-art global ocean reanalyses (ORAs) and two free-running models (FRMs) in the period 1997-2010. All products employ the Nucleus for European Modelling of the Oceans (NEMO) model, and the ORAs share very similar configurations. Very few previous works have looked at ocean circulation patterns in reanalysis products, but here we show that the ORA basin interior transports are consistently improved by the assimilated in situ and satellite observations relative to the FRMs, especially in the Argo period. The ORAs also exhibit systematically higher meridional transports than the FRMs, which is in closer agreement with observational estimates at 35 and 11 • S. However, the data assimilation impact on the meridional transports still greatly varies among the ORAs, leading to differences up to ∼ 8 Sv and 0.4 PW in the South Atlantic Meridional Overturning Circulation and the MHTs, respectively. We narrow this down to large inter-product discrepancies in the western boundary currents (WBCs) at both upper and deep levels explaining up to ∼ 85 % of the inter-product differences in MHT. We show that meridional velocity differences, rather than temperature differences, in the WBCs drive ∼ 83 % of this MHT spread. These findings show that the present ocean observation network and data assimilation schemes can be used to consistently constrain the South Atlantic interior circulation but not the overturning component, which is dominated by the narrow western boundary currents. This will likely limit the effectiveness of ORA products for climate or decadal prediction studies.

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Section: Temporal Variabilitymentioning

confidence: 79%

South Atlantic meridional transports from NEMO-based simulations and reanalyses

2018

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“…A regional configuration of the HYCOM model is used, which has been previously shown to represent the Agulhas system well (Backeberg 2014). HYCOM combines isopycnic-coordinate and fixed grid ocean circulation within its primitive equation framework (Bleck 2002 found that the AGUa0.10 simulation has a salinity bias which is further discussed later.…”

Section: Hycom Outputsmentioning

confidence: 99%

“…State-of-the-art high-resolution ocean hindcasts are now able to reproduce the turbulent processes of the Agulhas Current realistically, despite remaining biases in their mean circulation and thermohaline properties (Loveday et al 2014;Backeberg et al 2012;Backeberg 2014). However how well these simulations compare with regard to AL has not yet been investigated.…”

Section: Introductionmentioning

confidence: 99%

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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“…There are seven papers on analysis of model outputs, data-assimilation or numerical methods (Backeberg et al 2014;Chang and Oey 2014;Dominicis et al 2014;Hjelmervik and Hjelmervik 2014;Miyama and Miyazawa 2014;Xu and Oey 2014;Wang et al 2014a). Three of the papers address air-sea interactions and upper layer physics (Broström et al 2014;Esau 2014;Troitskaya et al 2014).…”

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confidence: 99%

“…Physical-biological processes in a coastal system are addressed in Guo et al (2014) and overflows between ocean basins is the topic in Cuthbertson et al (2014). Backeberg et al (2014) configured a regional HYCOM (Hybrid Coordinate Ocean Model) to test the Ensemble Optimal Interpolation (EnOI) data assimilation scheme to simulate the Agulhas Current system and associated mesoscale eddies. The inner nested model has a resolution of 10 km with 30 hybrid layers, and along-track sealevel anomaly data is used for assimilation.…”

mentioning

confidence: 99%