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Séminaires

Par Webmaster Legos Dernière modification 07/02/2012 11:59

Jeudi 21 Juin - Séminaire Pléiades

Par SEMSOU Dernière modification 09/04/2018 11:21
Quand ? Le 21/06/2018,
de 10:00 à 12:00
Où ? salle Coriolis
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Philippe Kubik, Céline Angelelis, Delphine Fontannaz

CNES

 

Titre: Séminaire Pléiades

 

Résumé: Lors d’une réunion que nous avions eue fin 2017 à propos des données Pléiades (https://pleiades.cnes.fr/) et de leur usage dans nos travaux sur les questions côtières et le littorales, certaines personnes ont exprimé un besoin d’informations sur cette mission. En réponse à cette demande, vous êtesi invité à réserver la matinée du jeudi 21/06 à 10h00 à midi en salle Coriolis pour assister à un séminaire sur cette mission spatiale et ses données.

Durant de ce séminaire, 3 présentations d’environ 20 minutes chacune seront faites par des collègues du CNES très impliqués sur le sujet Pléiades qu’ils aborderont selon 3 volets :

1. Les caractéristiques du système imageur et ses performances, par Philippe Kubik (responsable du service Qualité Images, Direction des Systèmes Orbitaux)

2. Un inventaire des usages actuels de ces images et leur positionnement dans les bases de données thématiques, par Céline Angelelis (responsable du service Analyse et Algorithmes, Direction des Systèmes Orbitaux)

3. L’organisation et les règles de mise à disposition des images, par Delphine Fontannaz du service Missions Terre et Atmosphère (Direction du Numérique et de l’Exploitation des Opérations).

Merci donc d’inscrire ce séminaire au solstice de votre agenda !

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Lundi 11 Juin - Regional to mesoscale organization of the primary productivity and the oxygen minimum zone in the Peru-Chile upwelling system

Par SEMSOU Dernière modification 25/05/2018 09:32
Quand ? Le 11/06/2018,
de 11:00 à 12:00
Où ? salle Jules Verne
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Pierre-Amaël Auger

Instituto Milenio de Oceanografia, Valparaiso, Chile

 

 

Title:  Regional to mesoscale organization of the primary productivity and the oxygen minimum zone in the Peru-Chile upwelling system

Abstract: Primary productivity and oxygen availability are key drivers for fish communities and the biological carbon pump in the ocean. First results of current projects which explore the organization, from regional to mesoscale, of primary productivity and the oxygen minimum zone (OMZ) in the Peru-Chile upwelling system (PCUS) are presented. ROMS-PISCES physical-biogeochemical modeling (now CROCO platform) is used to explore the mechanisms behind the observed ocean variability.
At regional scale, the model brings a new hypothesis to explain the meridional variability of the coastal upwelling productivity and its offshore extension in the coastal transition zone (CTZ). Iron limitation of the phytoplankton growth is indeed suggested to play a key role in the coastal upwelling of the PCUS. In the model, the iron limitation of coastal productivity (0-70 km from the coast) mostly relies on the iron inputs from the bottom sediments. These inputs likely depend on the contact time of upwelled waters with the sediments, and then on the continental shelf width. The offshore phytoplankton biomass (70-200 km from the coast) is mosty driven by the injection of living organisms from the coast, which itself relies on coastal productivity and cross-shore transport processes such as mesoscale eddies and filaments. The coastal productivity and offshore extension in the CTZ then depends on the continental shelf width and cross-shore exchange processes. The interaction between iron limitation and the level of eddy/filament activity may actually drive the regional distribution of plankton biomass in the PCUS. In recent years, quasi-zonal mesoscale jet-like features or striations have been ubiquitously detected in the time-mean circulation of the world ocean. Off central Chile (southern PCUS), striations were attributed to the organization of the mesoscale eddy field in preferred eddy tracks. Yet, their impact on biogeochemistry has not been assessed yet. In the CTZ, the model reproduces the surface chlorophyll striations detected in satellite records of ocean color. The interaction between preferred eddy tracks and sharp background gradients of biogeochemical properties seems to structure at mesoscale the mean horizontal distribution of the plankton biomass in the CTZ and the OMZ. The respective contributions of eddy trapping and eddy advection (stirring) to these striations are examined.


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Vendredi 18 Mai - Relationship between warm water volume and El Niño–Southern Oscillation: physical interpretation and asymmetry

Par SEMSOU Dernière modification 17/05/2018 09:17
Quand ? Le 18/05/2018,
de 14:00 à 15:00
Où ? salle Lyot
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Yann Planton

LOCEAN


Titre: Relationship between warm water volume and El Niño–Southern Oscillation: physical interpretation and asymmetry


Résumé: El Niño–Southern Oscillation (ENSO) is the dominant mode of interannual climate variability, with large environmental impacts at the global scale. With anomalous warming of up to 4°C in the eastern equatorial Pacific, extreme El Niño, such as in late 1982, 1997 and 2015, involve a complete re-organization of tropical convection with outsized societal impacts relative to moderate El Niño. Despite an improved understanding of ENSO dynamics over the past decades, predicting ENSO’s amplitude remains a challenge, especially at long lead-times. The recharge oscillator theory highlighted the role of the oceanic heat content averaged over the equatorial Pacific as a robust precursor of ENSO several seasons ahead, providing some hope to improve long-lead time ENSO forecasts. The water warmer volume (WWV), proxy of the equatorial Pacific heat content, is the most widely used precursor of ENSO. The standard interpretation of this lead relation in the context of the recharge oscillator theory is that anomalous easterlies during a La Niña, favour a slow recharge of the equatorial Pacific that will later favour a transition to El Niño. Using idealised experiments with a linear continuously stratified (LCS) ocean model, we demonstrate that WWV in spring mostly reflects the fast Kelvin wave response to wind anomalies during the early months of the year. It is hence not an appropriate index of the slow recharge invoked in the recharge oscillator. The evolution of the heat content over the western equatorial Pacific (WWVW) is dominated by the forced Rossby wave response to wind anomalies over the previous 10 months. WWVW hence involves a longer-term recharge than WWV, thus we recommend using WWVW rather than WWV as an index for the slow recharge before the spring predictability barrier. The recharge oscillator theory is however essentially linear and does not account for the potential asymmetries existing between El Niño and La Niña events. Yet, observations suggest that the ocean preconditioning is a more efficient predictor for La Niña than for El Niño events. Because of large uncertainties related to the short observational record, we analyse this asymmetry in a set of pre-industrial control experiments from eleven coupled models, selected for their capability to simulate observed ENSO variability. As suggested by observations, the discharge one year before ENSO peak in these models is a significantly better precursor of La Niña occurrence and amplitude than the recharge for El Niño. This asymmetry likely arises from (1) the asymmetry of the ocean preconditioning that promotes a larger influence on La Niña (larger discharge) than on El Niño (weaker recharge) and from (2) a nonlinear Bjerknes feedback that promotes the growth of El Niño rather than La Niña.

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