The impacts of oceanic deep temperature perturbations in the North Atlantic on decadal climate variability and predictability

Journal Article · Tue Dec 19 00:00:00 EST 2017 · Climate Dynamics

DOI:https://doi.org/10.1007/s00382-017-4016-z· OSTI ID:1507092

Germe, Agathe ^[1]; Sévellec, Florian ^[2]; Mignot, Juliette ^[3]; Fedorov, Alexey ^[4]; Nguyen, Sébastien ^[5]; Swingedouw, Didier ^[6]

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1. National Oceanography Centre, Southampton (United Kingdom); National Oceanography Centre, Water Front Campus, European Way, Southampton SO14 3ZH, UK
2. Univ. of Southampton, Southampton (United Kingdom)
3. Sorbonne Univ., Paris (France). LOCEAN Lab. Inst. Pierre-Simon Laplace (IPSL)
4. Yale Univ., New Haven, CT (United States)
5. Sorbonne Univ., Paris (France). LOCEAN Lab. Inst. Pierre-Simon Laplace (IPSL)
6. Univ. of Bordeaux, Pessac (France). Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC)

Decadal climate predictability in the North Atlantic is largely related to ocean low frequency variability, whose sensitivity to initial conditions is not very well understood. Recently, three-dimensional oceanic temperature anomalies optimally perturbing the North Atlantic Mean Temperature (NAMT) have been computed via an optimization procedure using a linear adjoint to a realistic ocean general circulation model. The spatial pattern of the identified perturbations, localized in the North Atlantic, has the largest magnitude between 1000 and 4000 m depth. In the present study, the impacts of these perturbations on NAMT, on the Atlantic meridional overturning circulation (AMOC), and on climate in general are investigated in a global coupled model that uses the same ocean model as was used to compute the three-dimensional optimal perturbations. In the coupled model, these perturbations induce AMOC and NAMT anomalies peaking after 5 and 10 years, respectively, generally consistent with the ocean-only linear predictions. To further understand their impact, their magnitude was varied in a broad range. For initial perturbations with a magnitude comparable to the internal variability of the coupled model, the model response exhibits a strong signature in sea surface temperature and precipitation over North America and the Sahel region. The existence and impacts of these ocean perturbations have important implications for decadal prediction: they can be seen either as a source of predictability or uncertainty, depending on whether the current observing system can detect them or not. In fact, comparing the magnitude of the imposed perturbations with the uncertainty of available ocean observations such as Argo data or ocean state estimates suggests that only the largest perturbations used in this study could be detectable. This highlights the importance for decadal climate prediction of accurate ocean density initialisation in the North Atlantic at intermediate and greater depths.

• Research Organization: Yale Univ., New Haven, CT (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
• Grant/Contract Number: SC0016538
• OSTI ID: 1507092
• Alternate ID(s): OSTI ID: 22854598
• Journal Information: Climate Dynamics, Journal Name: Climate Dynamics Journal Issue: 5-6 Vol. 51; ISSN 0930-7575
• Publisher: Springer-Verlag
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
Atlantic meridional overturning circulation
Decadal climate predictability
IPSL-CM5A
Initial condition uncertainties
Linear optimal perturbations
North Atlantic variability