Evaluation of the ECMWF ocean reanalysis system ORAS4

Balmaseda, Magdalena; Mogensen, Kristian; Weaver, Anthony

doi:10.1002/qj.2063

Cited by 1,071 publications

(1,000 citation statements)

References 58 publications

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“…We use monthly fields of ocean temperature, wind stress, and heat flux from the Ocean Reanalysis System 4 (ORA-S4) of the European Centre for Medium-Range Weather Forecasts (ECMWF) [Balmaseda et al, 2013] [Carton and Giese, 2008] for the same time period as for ORA-S4, namely, 1958to 2009.4 is forced with 20CRv2 surface winds [Compo, 2011] and has 40 vertical levels and a horizontal resolution of 0.25°. We have calculated interannual anomalies by subtracting a mean seasonal cycle as well as the linear trend of the time series.…”

Section: Methodsmentioning

confidence: 99%

Symmetry of the Atlantic Niño mode

Lübbecke

McPhaden²

2017

Geophysical Research Letters

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El Niño–Southern Oscillation (ENSO) in the Pacific is asymmetric for warm and cold events with respect to amplitude, spatial patterns, and temporal evolution. Here the symmetry of the Atlantic Niño mode, which many previous studies have argued is governed by atmosphere‐ocean dynamics similar to those of ENSO, is investigated using two different ocean reanalysis products. Calculation of Bjerknes feedback terms for the Pacific reveals a pronounced asymmetry between warm and cold events, though unlike most previous studies, the largest asymmetry is found in the relationship between eastern Pacific thermocline depth and sea surface temperature anomalies. For the Atlantic, cold events are effectively mirror images of warm events with Bjerknes feedbacks of similar strength. The analysis supports not only the conclusion that Atlantic Niños are more symmetric than ENSO but also the hypothesis itself that the Bjerknes feedback is operative in the Atlantic given the strength of the relationship between the key variables involved.

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Section: Methodsmentioning

confidence: 99%

Symmetry of the Atlantic Niño mode

Lübbecke

McPhaden²

2017

Geophysical Research Letters

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“…In this simulation, we choose to prescribe a complete signal of Atlantic sea level to consider both local and global changes, at seasonal and interannual time scales. To achieve this, we use data from the ORAS4 global ocean reanalysis (Balmaseda et al 2013) which includes sea level contributions from ice sheet mass loss, glaciers ice melt, changes in land water storage, as well as global thermal expansion. ORAS4 provides Atlantic boundary conditions for SSH, temperature and salinity to the regional ocean model for the period 1980-2012.…”

Section: Med12-improved Dataset For the Atlanticmentioning

confidence: 99%

Improving sea level simulation in Mediterranean regional climate models

et al. 2017

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long-term regional simulations of the Mediterranean Sea do not integrate the full sea level information from the Atlantic, which is a substantial shortcoming when analysing Mediterranean sea level response. In the present study we analyse different approaches followed by state-of-the-art regional climate models to simulate Mediterranean sea level variability. Additionally we present a new simulation which incorporates improved information of Atlantic sea level forcing at the lateral boundary. We evaluate the skills of the different simulations in the frame of long-term hindcast simulations spanning from 1980 to 2012 analysing sea level variability from seasonal to multidecadal scales. Results from the new simulation show a substantial improvement in the modelled Mediterranean sea level signal. This confirms that Mediterranean mean sea level is strongly influenced by the Atlantic conditions, and thus suggests that the quality of the information in the lateral boundary conditions (LBCs) is crucial for the good modelling of Mediterranean sea level. We also found that the regional differences inside the basin, that are induced by circulation changes, are model-dependent and thus not affected by the LBCs. Finally, we argue that a correct configuration of LBCs in the Atlantic should be used for future Mediterranean simulations, which cover hindcast period, but also for scenarios.

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“…The following observational datasets are used: 1) SST from the Hadley Centre Sea Ice and SST dataset, version 1.1 (HadISST1.1), (Rayner et al 2003) during 1880-2013 on a 18 3 18 longitude-latitude grid and 2) upper-ocean temperature and surface wind stress from the European Centre for Medium-Range Weather Forecasts (ECMWF) Ocean Reanalysis System 4 (ORAS4) for the period 1960-2011 (Balmaseda et al 2013). ORAS4 assimilates temperature and salinity profiles and along-track altimeterderived sea level anomalies on a 18 3 18 longitude-latitude grid with progressively finer latitude resolution (0.38) in the tropics and 42 levels in the vertical (18 of which are in the upper 200 m).…”

Section: B Observational Datasetsmentioning

confidence: 99%

Nonlinear Controls on the Persistence of La Niña*

2014

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A large fraction (35%-50%) of observed La Niña events last two years or longer, in contrast to the great majority of El Niño events, which last one year. Here, the authors explore the nonlinear processes responsible for the multiyear persistence of La Niña in the Community Climate System Model, version 4 (CCSM4), a coupled climate model that simulates the asymmetric duration of La Niña and El Niño events realistically. The authors develop a nonlinear delayed-oscillator (NDO) model of the El Niño-Southern Oscillation (ENSO) to explore the mechanisms governing the duration of La Niña. The NDO includes nonlinear and seasonally dependent feedbacks derived from the CCSM4 heat budget, which allow it to simulate key ENSO features in quantitative agreement with CCSM4.Sensitivity experiments with the NDO show that the nonlinearity in the delayed thermocline feedback is the sole process controlling the duration of La Niña events. The authors' results show that, as La Niña events become stronger, the delayed thermocline response does not increase proportionally. This nonlinearity arises from two processes: 1) the response of winds to sea surface temperature anomalies and 2) the ability of thermocline depth anomalies to influence temperatures at the base of the mixed layer. Thus, strong La Niña events require that the thermocline remains deeper for longer than 1 yr for sea surface temperatures to return to neutral. Ocean reanalysis data show evidence for this thermocline nonlinearity, suggesting that this process could be at work in nature.

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Evaluation of the ECMWF ocean reanalysis system ORAS4

Cited by 1,071 publications

References 58 publications

Symmetry of the Atlantic Niño mode

Symmetry of the Atlantic Niño mode

Improving sea level simulation in Mediterranean regional climate models

Nonlinear Controls on the Persistence of La Niña*

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