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| Registros recuperados: 12 | |
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| Sevellec, Florian; Huck, Thierry. |
| A weakly damped mode of variability, corresponding to the oceanic signature of the Atlantic multidecadal oscillation (AMO) was found through the linear stability analysis of a realistic ocean general circulation model. A simple two-level model was proposed to rationalize both its period and damping rate. This model is extended here to three levels to investigate how the mode can draw energy from the mean flow, as found in various ocean and coupled models. A linear stability analysis in this three-level model shows that the positive growth rate of the oscillatory mode depends on the zonally averaged isopycnal slope. This mode corresponds to a westward propagation of density anomalies in the pycnocline, typical of large-scale baroclinic Rossby waves. The... |
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| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00281/39189/37745.pdf |
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| Lobelle, D.; Beaulieu, C.; Livina, V.; Sevellec, Florian; Frajka‐williams, E.. |
| Determining whether the Atlantic Meridional Overturning Circulation (AMOC)'s transport is in decline is challenging due to the short duration of continuous observations. To estimate how many years are needed to detect a decline, we conduct a simulation study using synthetic data that mimics an AMOC time series. The time series' characteristics are reproduced using the trend, variance, and autocorrelation coefficient of the AMOC strength at 26.5°,N from 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) models under the RCP8.5 future scenario, and from RAPID observations (2004‐‐2018). Our results suggest that the 14‐year RAPID length has just entered the lower limits of the trend’s `detection window’ based on synthetic data generated using CMIP5... |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00655/76661/77797.pdf |
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| Sevellec, Florian; Huck, Thierry; Jelloul Mahdi, Ben. |
| Centennial oscillations of the ocean thermohaline circulation are studied in a 2-D latitude-depth model under mixed boundary conditions (i.e. restoring surface temperature and prescribed freshwater flux). The oscillations are revealed through linear stability analysis of a steady state obtained in a single hemisphere configuration. A density variance budget is performed and helps determine the physical processes sustaining these oscillations: the restoring surface temperature appears as a source of density variance - this is a consequence of positively-correlated temperature and salinity anomalies. A minimal model, the Howard-Malkus loop oscillator, enables us to understand physically the oscillatory and growth mechanisms. The centennial oscillation is... |
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| Ano: 2006 |
URL: http://archimer.ifremer.fr/doc/2006/publication-6335.pdf |
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| Sevellec, Florian; Huck, Thierry; Colin De Verdiere, Alain. |
| The freshwater flux intensity is used as the main control parameter to destabilize the ThermoHaline Circulation (THC): as it increases, the classical bifurcation scenario, thermal stable steady state, millennial oscillation and haline stable steady state are reproduced in a 2D zonally-averaged ocean model under mixed boundary conditions. Both bifurcations arise through global bifurcations leading to an infinite period of the limit cycle. Here we highlight a centennial oscillation important for the instability of the thermal phase of the millennial oscillation and which could be considered as a precursor to the collapse of the THC. It is suggested that the existence or the absence of this centennial oscillation leads to dramatic changes in the collapse time... |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00038/14912/12623.pdf |
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| Liu, Wei; Fedorov, Alexey; Sevellec, Florian. |
| We explore the mechanisms by which Arctic sea ice decline affects the Atlantic meridional overturning circulation (AMOC) in a suite of numerical experiments perturbing the Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next similar to 100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in... |
| Tipo: Text |
Palavras-chave: Arctic; Meridional overturning circulation; Climate models. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00599/71107/69388.pdf |
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| Sevellec, Florian; Drijfhout, Sybren S.. |
| In a changing climate, there is an ever-increasing societal demand for accurate and reliable interannual predictions. Accurate and reliable interannual predictions of global temperatures are key for determining the regional climate change impacts that scale with global temperature, such as precipitation extremes, severe droughts, or intense hurricane activity, for instance. However, the chaotic nature of the climate system limits prediction accuracy on such timescales. Here we develop a novel method to predict global-mean surface air temperature and sea surface temperature, based on transfer operators, which allows, by-design, probabilistic forecasts. The prediction accuracy is equivalent to operational forecasts and its reliability is high. The post-1998... |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00454/56545/58254.pdf |
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| Hochet, Antoine; Huck, Thierry; Arzel, Olivier; Sevellec, Florian; Colin De Verdiere, Alain; Mazloff, Matthew; Cornuelle, Bruce. |
| The North Atlantic is characterized by basin-scale multidecadal fluctuations of the sea surface temperature with periods ranging from 20 to 70 years. One candidate for such a variability is a large-scale baroclinic instability of the temperature gradients across the Atlantic associated with the North Atlantic Current. Because of the long time scales involved, most of the studies devoted to this problem are based on low resolution numerical models leaving aside the effect of explicit meso-scale eddies. How high-frequency motions associated with the meso-scale eddy field affect the basin-scale low-frequency variabiliy is the central question of this study. This issue is addressed using an idealized configuration of an Ocean General Circulation Model at... |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00635/74701/74640.pdf |
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| Stephenson, Dafydd; Muller, Simon; Sevellec, Florian. |
| Water mass ventilation provides an important link between the atmosphere and the global ocean circulation. In this study, we present a newly developed, probabilistic tool for offline water mass tracking. In particular, NEMOTAM, the tangent-linear and adjoint counterpart to the NEMO ocean general circulation model, is modified to allow passive-tracer transport. By terminating dynamic feedbacks in NEMOTAM, tagged water can be tracked forward and backwards in time as a passive dye, producing a probability distribution of pathways and origins, respectively. Upon contact with the surface, the tracer is removed from the system, and a record of ventilation is produced. Two test cases are detailed, examining the creation and fate of North Atlantic Subtropical Mode... |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00588/69980/67888.pdf |
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| Registros recuperados: 12 | |
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