Séminaires

Upcoming seminars

Département de Géosciences

Date: March 3, 2020
Time: 11h
Location: Froidevaux – E314
By: Mathilde PASCAL (Santé Publique France)
Title: Changement climatique : le plus grand risque, et la plus grande opportunité pour la santé publique du 21ème siècle

CERES

Date: March 3, 2020
Time: 14h
Location: Froidevaux – E314
By: Régis Briday (UPEC) & Roland Séférian (Météo France)
Title: Géoingénierie, stockage du carbone et autres solutions « interventionnistes » pour lutter contre le changement climatique : quels espaces pour en débattre ?

Laboratoire de Géologie

Date: March 10, 2020
Time: 11h
Location: Froidevaux – E314
By: Magali Riesner (CEA)
Title: TBA

Laboratoire de Météorologie Dynamique

Date: March 11, 2020
Time: 11h
Location: Froidevaux – E314
By: Andrew Friedman (Univ Edinburgh)
Title: TBA

Laboratoire de Géologie

Date: March 17, 2020
Time: 11h
Location: Froidevaux – E314
By: Riccardo Asti (Géosciences Rennes)
Title: Rôle de l’héritage sur l’évolution structurale et thermique de la lithosphère pendant le rifting : l’exemple de la limite de plaque Ibérie-Eurasie
Abstract: Des questions importantes demeurent toujours sur le comportement rhéologique de la croûte pendant le rifting et sur les paramètres qui l’influencent. Les Pyrénées sont un endroit idéal pour étudier le style de déformation de la croute continentale pendant le rifting.
Des nouvelles observations de terrain associés à l’étude microscopique de la déformation crustale dans la partie occidentale de la Zone Nord Pyrénéenne montrent que à l’Albien-Cénomanien la partie distale de la marge nord-ibérique était constituée : (i) de manteau exhumé, (ii) de minces lentilles de croûte moyenne/supérieure déformées ductilement pendant le rifting et (iii) de sédiments des séries pré- et syn-rift thermométamorphisés et désolidarisées de leur socle crustal au niveau des évaporites triasiques (Keuper). Les conditions de déformation de la croûte sont en facies schistes verts et on remarque l’absence de roches dérivées de la croute profonde (granulites).
Un étude pétrochronologique effectué sur des roches de croûte inférieure montre que la croûte continentale pyrénéenne était déjà réduite à un épaisseur d’une vingtaine de kilomètres au Permien inf., suite à la phase d’effondrement de la Chaîne Varisque. Ensuite, pendant la phase de rifting crétacée, une déformation ductile en facies amphibolite à très faible profondeur se localise dans la croûte profonde en relation avec l’exhumation finale du manteau.
L’extension tardi- à post-varisque de la région péri-pyrénéenne contrôle l’évolution mésozoïque de la lithosphère dans ce secteur, déterminant un layering rhéologique de la croûte qui va contrôler l’évolution structurale et thermique pendant la phase de rifting Jurassique sup. – Crétacé inf. Des modèles numériques, en accord avec les observations de terrain, montrent que le set up pré-rift permet la déposition d’épaisses séries syn-rift dans un contexte de type sag. Le découplage au niveau des évaporites pré-rift permet à la couverture sédimentaire de rester dans la partie centrale du rift pendant qu’on amincit la croûte continentale en dessous et d’atteindre des conditions de thermicité élevées. Cela favorise aussi un style d’amincissement principalement ductile de la croûte continentale.
Cette configuration ne concerne pas seulement la zone des Pyrénées, mais tout le domaine qui va de la Chaîne Ibérique à la Flexure Celtaquitaine. Cela permet à cette région d’accommoder la déformation liée aux mouvements relatifs entre l’Ibérie et l’Europe sur une grande étendue, plutôt que le long d’une limite de plaque étroite localisée au niveau des Pyrénées. Ce domaine correspond grosso modo au bassin d’avant-pays carbonifère de la Chaîne Varisque dans ce secteur, suggérant qu’il y a un contrôle déterminant de l’héritage varisque sur l’évolution tectonique et topographique de ce secteur sur un très long intervalle de temps.

Laboratoire de Météorologie Dynamique

Date: March 18, 2020
Time: 11h
Location: Froidevaux – E314
By: Sébastien Fromang (LSCE)
Title: The influence of the MJO on the NAO: insights inferred from idealized numerical experiments
Abstract:
Several observational studies have shown that the North Atlantic Oscillation (NAO) is influenced by the Madden-Julian Oscillation (MJO): the positive (negative) phase of the NAO is favored 10-15 days after enhanced (reduced) convection is located over the Indian Ocean, a configuration known as MJO phase 3 (phase 6). Using a quasi-geostrophic model on the sphere, we investigate the dynamical origin of this influence. We find that the MJO excites a stationary Rossby wave that propagates over the North Pacific all the way to the North Atlantic and influences the storm tracks location and properties over both oceans basins. In accordance with observations, it results in an increase by about 30% of the positive (negative) phase of the NAO following phase 3 (phase 6) of the MJO. A PV budget will be described that helps understand the dynamical origin of that lagged correlation, while the limits and perpectives of this work will be discussed during the last part of the presentation.

CERES

Date: March 24, 2020
Time: 14h
Location: Salle Conf. IV – E244
By: Laurent Bopp (LMD-ENS) & Julien Rochette (IDDRI)
Title: Bouleversement des écosystèmes marins par le changement climatique : quels outils pour la protection de la haute mer ?

Laboratoire de Météorologie Dynamique

Date: March 25, 2020
Time: 11h
Location: Froidevaux – E314
By: Karin van der Wiel (KNMI)
Title: TBA

Laboratoire de Géologie

Date: March 31, 2020
Time: 11h
Location: Froidevaux – E314
By: Laurence Bodelot (École Polytechnique)
Title: TBA

Laboratoire de Météorologie Dynamique

Date: April 1, 2020
Time: 11h
Location: Froidevaux – E314
By: Lia Siegelman (UBO/Caltech)
Title: TBA

Laboratoire de Géologie

Date: April 21, 2020
Time: 11h
Location: Froidevaux – E314
By: Julia Le Noe (BOKU)
Title: TBA

Laboratoire de Météorologie Dynamique

Date: April 22, 2020
Time: 11h
Location: Froidevaux – E314
By: Witold Bagniewski (ENS)
Title: TBA

Laboratoire de Géologie

Date: April 28, 2020
Time: 11h
Location: Froidevaux – E314
By: James Biemiller (UT Austin)
Title: TBA

Laboratoire de Météorologie Dynamique

Date: April 29, 2020
Time: 11h
Location: Froidevaux – E314
By: Maud Devès (Université de Paris – IPGP/IHSS)
Title: The IPCC and the bottom-up strategy
Abstract: This seminar will present the results of a series of public discussions, led by the Association française de prévention des catastrophes naturelles (AFPCN), on the possible need to adapt the modalities of international expertise on climate change to better support the bottom-up strategy adopted under the Paris Agreement. As the AFPCN is more generally dedicated to the issue of disaster risk reduction, a parallel will be drawn with the organization of international expertise on disaster risk reduction.

Département de Géosciences

Date: May 12, 2020
Time: 11h
Location: Froidevaux – E314
By: Frédéric Hélein (Université de Paris)
Title: Science ouverte

Laboratoire de Météorologie Dynamique

Date: May 13, 2020
Time: 11h
Location: Froidevaux – E314
By: Damien Heron (Université de la Réunion)
Title: TBA

Laboratoire de Géologie

Date: May 19, 2020
Time: 11h
Location: Froidevaux – E314
By: Emma Gregory (IPGP)
Title: TBA

Laboratoire de Météorologie Dynamique

Date: May 20, 2020
Time: 11h
Location: Froidevaux – E314
By: Claudine Wenhaji-Ndomeni (ENS)
Title: TBA

Laboratoire de Géologie

Date: May 26, 2020
Time: 11h
Location: Froidevaux – E314
By: Jorge Jara (ENS)
Title: TBA

Département de Géosciences

Date: June 2, 2020
Time: 11h
Location: Froidevaux – E314
By: Mathias Girel & Boris Barbour (Comité intégrité scientifique de l’ENS)
Title: Intégrité scientifique : contextes local et global

Laboratoire de Géologie

Date: June 9, 2020
Time: 11h
Location: Froidevaux – E314
By: Steve Miller (Univ. de Neuchâtel)
Title: TBA

Laboratoire de Géologie

Date: June 23, 2020
Time: 11h
Location: Froidevaux – E314
By: Sergio Vinciguerra (Univ. of Leicester)
Title: TBA

Past seminars

Laboratoire de Météorologie Dynamique

Date: February 26, 2020
Time: 14h – UNUSUAL SCHEDULE
Location: Froidevaux – E314
By: Sylvia Sullivan (KIT – IMK)
Title: From environmental moisture to precipitation intensity in tropical convective systems
Abstract: In the tropics, the majority of high-intensity precipitation comes from the organization of multiple convective cells into convective systems (CS). Environmental moisture can affect these precipitation intensities in a multiplicity of ways. For example, while precipitation onset occurs beyond a threshold in column water vapor content, lower tropospheric drying can also enhance instability and ascent rate. We investigate these moisture-precipitation relationships for tropical CS semi-observationally with satellite data and high-resolution reanalysis values. In particular, the long duration of these datasets allows us to establish robust shifts in the precipitation intensity distribution with the El Niño Southern Oscillation and to explain them on the basis of a vertical momentum budget. Given the role of free tropospheric relative humidity in this budget, we proceed to examine how the relations of precipitation intensity, saturation deficit, and instability differ with spatiotemporal scale and in idealized simulations versus observations. Organized convective activity can affect not just local but also remote precipitation intensities, and we give an outlook on the utility of causal algorithms here.

Soutenance – HDR

Date: February 26, 2020
Time: 10h
Location: Froidevaux – E314
By: Matthias Delescluse (LG-ENS)
Title: Apports de l’imagerie sismique marine pour l’étude de l’activité passée et présente des failles
Abstract: L’imagerie sismique marine permet de caractériser la géométrie des structures géologiques et nous renseigne au premier ordre sur la nature des roches de subsurface. Les différentes techniques d’imagerie permettent ainsi de cartographier les structures et de mieux comprendre leur formation résultant de déformations intégrées au cours des temps géologiques. En Mer de Chine du sud, une analyse conjointe de données de sismiques réfraction et réflexion longue flûte, couvrant toute l’épaisseur crustale, permet de détailler une chronologie relative des phases extensives lors du rifting et confirme l’importance des contacts pré-existants dans la localisation de la déformation finie. En revanche, même si la distribution et le style de la sismicité sont dans certaines régions également influencés par l’héritage structural (e.g. l’Océan indien), il est plus délicat de tirer des enseignements de la complexité structurale sur l’activité à plus court terme des failles. Les zones de subduction en sont l’illustration la plus flagrante: les structures de la plaque plongeante et de l’avant arc sont abondamment discutées et reconnues comme influençant le comportement sismogénique de l’interface, au même niveau cependant que d’autres paramètres comme les fluides, le régime thermique ou la sédimentation. On résumera ici les apports de l’imagerie sismique moderne permettant notamment de suivre en continu la réflectivité de l’interface de subduction jusqu’à la zone de transition asismique. On discutera les nouvelles possibilités d’étude du comportement des zones de subduction qui en découlent au travers d’exemples en Alaska et d’un projet de campagne au Chili centré sur l’imagerie des variations latérales (le long de la fosse) de la géométrie et des propriétés de l’interface.
Jury: Nicolas Coltice (École normale supérieure) – Correspondant HDR / Tim Minshull (University of Southampton) – Rapporteur / Stéphane Mazzotti (Université de Montpellier) – Rapporteur / Frauke Klingelhoefer (Ifremer Brest) – Rapportrice / Carole Petit (Université de Nice) – Examinatrice / Dieter Franke (BGR Hannover) – Examinateur / Javier Escartin (CNRS-ENS) – Examinateur

Laboratoire de Géologie

Date: February 25, 2020
Time: 11h
Location: Froidevaux – E314
By: Laurent Métivier (IGN)
Title: Reference frames, glacial isostatic adjustment and climate changes

Soutenance – Thèse

Date: February 21, 2020
Time: 14h
Location: Froidevaux – E314
By: Ludivine Conte (ENS / CEA)
Title: Emissions océaniques de gaz d’intérêt pour la chimie atmosphérique – Modélisation des dynamiques océaniques du CO, de l’isoprène et du DMS
Abstract: L’activité phytoplanctonique est à l’origine de la production dans l’océan de composés volatils, qui, une fois émis dans l’atmosphère, ont un impact sur sa capacité oxydante, la formation d’aérosols et la régulation du climat. Les émissions océaniques de la plupart de ces composés sont néanmoins mal connues en raison d’un faible nombre d’observations in situ et d’un manque de connaissance dans les processus océaniques en jeu. Dans un premier temps, je me suis intéressée aux cycles océaniques du monoxyde de carbone (CO) et de l’isoprène (C5H8). Afin de ré-évaluer leurs émissions vers l’atmosphère, les processus de production et de consommation de ces gaz dans la colonne d’eau ont été intégrés au modèle 3-D de circulation océanique et de biogéochimie marine NEMO-PISCES. En parallèle, des compilations de concentrations océaniques mesurées in situ et de résultats de laboratoire ont été réalisées à partir de la littérature afin de mieux contraindre ces processus océaniques. Dans un second temps, je me suis intéressée aux réponses des émissions océaniques de CO, isoprène et sulfure de diméthyle (DMS) au changement climatique. Ce travail devrait permettre à terme d’intégrer ces cycles dans un modèle du système terre, couplant biogéochimie marine et chimie atmosphérique, afin de mieux quantifier le rôle potentiel de ces interactions sur l’évolution de la chimie atmosphérique et du climat.
Jury: Inga Hense (University of Hamburg) – Rapporteuse / Véronique Garçon (LEGOS, Toulouse) – Rapporteuse / Agnès Borbon (LaMP, Clermont-Ferrand) – Examinatrice / Matthieu Roy-Barman (UVSQ) – Examinateur / Laurent Bopp (LMD, ENS) – Directeur / Sophie Szopa (LSCE, CEA Saclay) – Co-directrice

Laboratoire de Géologie

Date: February 18, 2020
Time: 11h
Location: Froidevaux – E314
By: Émilie Klein (ENS)
Title: From ice shelf to subduction zone, hunting down transient signals using GPS

Laboratoire de Géologie

Date: February 11, 2020
Time: 11h
Location: Froidevaux – E314
By: Veronique Leonardi (HydroSciences Montpellier)
Title: Karstogenèse : Processus, Facteurs et Modélisation – Exemple d’un aquifère méditerranéen (Lez, France)
Astract: La complexité et l’hétérogénéité des aquifères karstiques rendent difficile une exploitation optimisée de leur ressource souterraine; les drains karstiques qui comprennent l’eau souterraine mobilisable en grande quantité, étant difficilement localisables. Aucun modèle et aucune méthodologie actuellement ne permet d’identifier précisément ces zones de drainage préférentielles, pouvant aider à l’implantation de forage d’exploitation de cette ressource en eau. Une meilleure connaissance de la mise en place au cours du temps de ces drains permettrait cependant d’identifier les zones propices à leur existence. De nombreuses études ont été ainsi réalisées afin de comprendre comment ces drains se développent permettant de supposer leurs zones d’expansion dans l’espace. Ces études reposent soit sur des approches qualitatives avec des mesures et observations de terrain (Blanc, 1995a; Mocochain et al., 2006; Combes et al., 2008; Durand et al., 2009; Leonardi et al., 2011; Jouves et al., 2017; Harmand et al., 2017), soit sur des approches quantitatives avec des modèles numériques théoriques de la karstogenèse basés sur des lois physico-chimiques (Palmer, 1991; Dreybrodt et al., 2005; Kaufmann, 2009, Dreybrodt and Gabrovšek, 2018; Alliouche et al., 2019). Cependant, du fait de la complexité de ces modèles physico-chimiques, très peu de modèles de karstogenèse n’ont pu être appliqué à des aquifères karstiques à l’échelle régionale, permettant de valider dans l’espace les hypothèses de karstification issues des observations de terrain.
Cette étude a pour objectif d’identifier et caractériser les principales phases de karstification qui ont affecté l’aquifère du Lez (Nord Montpellier, France), ceci à partir d’observations in situ, de données bibliographiques et d’analyses de données structurales et hydrodynamiques. A partir de celles-ci, une modélisation de ce réservoir karstique a été réalisé à partir d’un modèle génétique de type probabilistique (GOdiag, développé par G. Massonnat (Massonnat, 2012, 2014; Massonnat and Morandini, 2012) : ce modèle génétique a permis de tester différents scénarios et d’identifier les phases de karstification qui ont eu un impact majeur sur la morphologie karstique souterraine actuelle, et ainsi de caractériser les structures et processus qui sont à l’origine de cette morphologie.

Soutenance – Thèse

Date: February 6, 2020
Time: 14h
Location: Froidevaux – E314
By: Angélique Benoit (ENS / CEA)
Title: Vers un suivi continu des faibles déplacements de surface par interférométrie radar : étude du comportement asismique le long de la faille Nord Anatolienne
Abstract: The North Anatolian fault, which cuts across the northern part of Turkey from west to east over more than 1000 km, is one of the largest active faults on earth. During the 20th century, almost the entire length of this fault ruptured during the westward propagation of more than a dozen major earthquakes (M7+). If this fault is known for its active seismicity, it exhibits on the other hand an aseismic behavior, especially in its central segment, where it slips continuously at a rate of about 2.5 cm/yr. However, the study of recent geodetic data and creepmeters suggests that aseismic slip is episodic rather than steady in time, where slip on the fault is thought to occur within days to month-long slip episodes (slow slip events), hence calling for a new assessment of the physics of fault slip along this segment.
Thanks to synthetic aperture radar interferometry, we analyze the spatial and temporal variations of interseismic deformation occurring along the central segment of the North Anatolian fault, a 300 km-long section covering the segments that rup- tured during the last M7.3 earthquake in 1944. To do so, we detect and characterize each slow slip event detected along this segment.
First, we develop tools to mitigate sources of noise in InSAR, such as those associated to atmospheric effects and to phase unwrapping. We generate 333 interferograms from SAR data of the ascending track covering the study area, acquired by the Sentinel-1 satellites during the period from 2014 to 2018. We compare the performances of three atmospheric models, HRES, ERA-Interim and ERA-5, and demonstrate that the best atmospheric corrections are performed with ERA-5 model, a reanalysis of meteorological data delivered by ECMWF. Then, we develop an innovative algorithm called CorPhU, which allows us to automatically correct unwrapping errors by considering the phase closure of triplets of interferograms. Thanks to our fast implementation, all these errors are corrected automatically within our entire interferometric network. In addition, we process three ascending tracks acquired by the ALOS satellite during the period from 2007 to 2011, covering the same area, and correct interferograms from ionospheric delays with a split-range spectrum method.
We then use a Small Baseline approach to perform a time series analysis of the interferograms corrected for each of the tracks. All mean line-of-sight (LOS) deformation velocity maps agree with a dextral movement across the fault and show both temporal and lateral variations of the velocity gradient in the fault zone. Aseismic slip mostly concentrates along a 100 km-long section, located near the city of Ismetpasa, and slip velocity decreases over time, from 2 cm/yr between 2007 and 2011, to less than 1 cm/yr from 2014 to 2018.
We then characterize fault slip modes along this section by visual inspection, searching for possible aseismic slip events in the time series. We identify, at least, three slow slip events from Sentinel-1 data. We then characterize these events in terms of lateral extension, duration and amount of displacement. We finally open the discussion on the study of slow slip events relate to the associated seismic hazard.
Jury: Juliet BIGGS (University of Bristol) / Rowena LOHMAN (Cornell University) / Rodolphe CATTIN (Université de Montpellier) / Gabriel DUCRET (IFPEN) / Christophe VIGNY (ENS) / Béatrice PINEL-PUYSSÉGUR (CEA) / Romain JOLIVET (ENS)

Laboratoire de Météorologie Dynamique

Date: February 5, 2020
Time: 11h
Location: Froidevaux – E314
By: Julien Boé (CERFACS)
Title: Uncertainties in future summer climate change in Europe: global climate models versus regional climate models
Abstract:
We assess the differences of future climate changes over Europe in summer as projected by state-of-the-art regional climate models (RCM, from the EURO-Coordinated Regional Downscaling Experiment) and by their forcing global climate models (GCM, from the Coupled Model Intercomparison Project Phase 5) and study the associated physical mechanisms. We show that important discrepancies at large-scales exist between global and regional projections. The RCMs project at the end of the 21st century over a large area of Europe a summer warming 1.5-2 K smaller, and a smaller decrease in precipitation.
The RCMs generally simulate a much smaller increase in shortwave radiation at surface, which directly impacts surface temperature. In addition to differences in cloud cover changes, the absence of time-varying anthropogenic aerosols in most regional simulations plays a major role in the differences of solar radiation changes. We confirm this result with twin regional simulations with and without time-varying anthropogenic aerosols. Additionally, the RCMs simulate larger increases in evapotranspiration over the Mediterranean sea and larger increases / smaller decreases over land, which contribute to smaller changes in relative humidity, with likely impacts on clouds and precipitation changes. Potential causes of these differences in evapotranspiration changes are discussed. Finally, new results from CMIP6 are put in perspective.

CERES

Date: February 4, 2020
Time: 14h
Location: Amphithéâtre Galois – Bâtiment Rataud, 45 rue d’Ulm
By: Jean-Baptiste Fressoz (EHESS) & Cédric Philibert (AIE)
Title: La transition énergétique est-elle vraiment possible ? Approches historiques, technologiques et économiques

Département de Géosciences

Date: February 4, 2020
Time: 11h
Location: Froidevaux – E314
By: Corinne Le Quéré (Haut Conseil pour le Climat / University of East Anglia)
Title: Le budget global de carbone et son évolution dans les décennies à venir
Abstract:
Cette présentation se fera en trois parties. La première mettra l’emphase sur les connaissances scientifiques. Elle couvrira nos connaissances actuelles des émissions de CO2 globales et de leur répartition dans l’environnement. Elle portera sur les limites de notre capacité à expliquer dans les détails l’évolution du CO2 atmosphérique observée, ainsi que le rôle de l’océan et de la biosphère terrestre dans la modulation de ce signal. La deuxième partie portera un regard sur les dernières tendances en émissions de CO2. Elle montrera les progrès faits par les 18 pays où les émissions ont diminuées significativement lors de la décennie 2005-2015 (dont la France), et les facteurs principaux qui ont soutenu ces diminutions. Finalement la présentation fera un survol des recommandations émises par le Haut conseil pour le climat et des réponses nationales et internationales attendues pour stabiliser le climat conformément avec les objectifs de l’Accord de Paris, pour conclure avec quelques mots sur le rôle que la communauté scientifique peut jouer en appui à la transition vers la neutralité carbone.

Laboratoire de Météorologie Dynamique

Date: January 30, 2020 – THURSDAY
Time: 11h
Location: Froidevaux – E314
By: Gisela Charó (Lab. de Fluidodinámica, Fac. de Ingeniería, Univ. de Buenos Aires)
Title: The heritage of Poincaré and the algebraic topology of the Lorenz model’s random attractor
Abstract:
Poincaré first described the way in which a dynamical system’s properties depend upon its topology. In this work, we study the temporal evolution of the topological structure of the branched manifold associated with the Lorenz model’s random attractor (LORA), when driven by multiplicative noise. While the attractor associated with the classical, deterministic Lorenz (1963) model is “strange” but fixed in time, LORA is a pullback attractor that changes in time in a rather spectacular fashion.
LORA’s topological structure can be studied by using homology groups Hn. These groups are a key tool of algebraic topology that characterizes the number of n-dimensional holes of a branched manifold: the connected components (0- dimensional holes), the cycles (1-dimensional holes), the cavities (2- dimensional holes), and so on. Our work shows that LORA is a 2-dimensional branched manifold whose number of 1-dimensional holes changes over time, i.e., its homology group H1 is distinct from the fixed one of Lorenz’s “butterfly” and cycles are created or destroyed by the noise

Laboratoire de Géologie

Date: January 28, 2020
Time: 11h
Location: Froidevaux – E314
By: Suzanne Atkins (ENS)
Title: Attempts to access mantle history using geodynamics, plate reconstructions and machine learning
Abstract: 
The Earth’s crust and mantle move together. We can follow this movement through time using the geological record to create plate tectonic reconstructions. This history of the surface gives us a starting point from which to make inferences about the state of the mantle.  These inferences are often based on geodynamic modelling. However, going from simple inferences to more robust inversions is severely hampered by the uncertainties in plate reconstruction models, missing equations of state for the mantle and limited computational resources.  We can improve these inferences by considering the statistics of mantle convection and using tools such as neural networks.  The statistical consideration of the mantle can also be used to improve plate tectonic reconstructions, thereby improving the data available to study the history of the mantle.

Laboratoire de Météorologie Dynamique

Date: January 22, 2020
Time: 11h
Location: Froidevaux – E314
By: David Flack (ENS)
Title: Can CMIP 6 models represent the dynamics of the Stalactite Cyclone (NAWDEX IOP 6)
Abstract: For confidence to be achieved in future projections of extra-tropical cyclones we need to be sure that climate models can represent them in the current climate. However, this representation should be considered through the dynamical and diabatic processes operating within cyclones rather than just the statistics. Using CMIP6 and higher resolution configurations of the IPSL and CNRM climate models run in “weather-forecast” mode in depth case studies of a rapidly-deepening cyclone sampled during the NAWDEX (North Atlantic Waveguide and Downstream impact EXperiment) field campaign is considered. Differences between the simulations and the analysis is associated with the representation of initial cyclogenesis. The quasi-geostrophic omega equation is then used to separate the contributions between dynamical and diabatic processes in the development of the cyclones. The results show that for both cyclones and all simulations the strongest deepening stage is first dominated by diabatic processes and then dynamical processes. Contrary to expectations, there is no obvious stronger contribution of diabatic processes with increased resolution, instead the dynamic processes increase with importance. The climate models are also compared against observations made during the NAWDEX campaign, and indicate that the models produce too much supercooled liquid. These cases show that further work into the representation of cyclones in climate models, focusing on baroclinic interaction and latent heating is required to improve confidence in the projections for the behaviour of extra-tropical cyclones in the future.

Soutenance – Thèse

Date: December 3, 2019
Time: 14h
Location: Salle des Actes – 45 rue d’Ulm – 1er étage escalier A
By: Samson Marty (ENS)
Title: Rayonnement haute-fréquence et précurseurs des séismes en laboratoire
Abstract: Au cours de cette thèse, nous avons reproduit expérimentalement des séismes à l’échelle centimétrique dans des conditions de pression proches de la réalité. Les expériences réalisées nous ont permis d’explorer deux grandes thématiques : (i) l’origine du rayonnement haute-fréquence pendant la rupture dynamique et (ii) les signaux précurseurs pendant la phase de nucléation de la rupture dynamique.
Nos résultats montrent que le rayonnement haute-fréquence est concomitant à la propagation du front de rupture et que deux paramètres induisent une augmentation du rayonnement haute-fréquence : l’état de contrainte initial et la vitesse de rupture. Les analyses microstructurales des échantillons de roches suggèrent que la production d’endommagement cosismique ou de particules de gouge contribue au rayonnement haute fréquence.
L’étude des signaux précurseurs (i.e., précurseurs acoustiques) montre que la nucléation est un processus en très large majorité asismique. Ce très faible couplage pourrait expliquer le peu d’observations de séismes précurseurs à l’échelle des failles crustales. L’analyse temporelle des émissions acoustiques suggère que leur dynamique est principalement contrôlée par l’accélération du glissement pendant la phase de nucléation. La microtopographie et la microstructure des échantillons de roches montrent que le couplage est directement relié à la rugosité du plan de faille. Une augmentation des conditions de pression favorise l’occurrence de processus de déformation plastique ou de fusion partielle au cours de la rupture sismique, ce qui diminue la rugosité et donc le couplage.
Jury: Elisa Tinti (SapienzaUniv.) : Rapportrice / Michel Bouchon (ISTerre) : Rapporteur / Aitaro Kato (ERI – Tokyo Univ.) : Examinateur / Clément Narteau (IPGP) : Examinateur / Alexandre SCHUBNEL (ENS) : Directeur / Harsha  S. Bhat (ENS) : CoDirecteur / Eiichi Fukuyama (Kyoto Univ.) : Invité

Laboratoire de Géologie

Date: January 21, 2020
Time: 10h
Location: Froidevaux – E314
By: Lavinia Tunini (ENS / OGS-CSR)
Title: Crustal deformation in stable continental regions – The case of central-western Europe

Laboratoire de Météorologie Dynamique

Date: January 15, 2020
Time: 11h
Location: Froidevaux – E314
By: Davide Faranda (LSCE)
Title: Perils of using Recurrent Neural Network to learn the Dynamics of Geophysical Flows
Abstract: Recent advances in statistical learning have opened the possibility to forecast the behavior of chaotic systems using recurrent neural network. In this letter we investigate the applicability of this framework to geophysical flows, known to be intermittent and turbulent. We show that both turbulence and intermittency introduce severe limitations on the applicability of recurrent neural network both for short term forecasts as well as for the reconstruction of the underlying attractor. We suggest that possible strategies to overcome such limitations should be based on separating the smooth large scale dynamics, from the intemittent/turbulent features.
Authors: D. Faranda, A. Hamid, G. Carella, C.G. Ngoungue Langue, F.M.E. Pons, M. Vrac, S. Thao, M. Rabarivola, V. Gautard, P. Yiou

Laboratoire de Géologie

Date: January 14, 2020
Time: 11h
Location: Froidevaux – E314
By: Frantisek Gallovic (Charles University)
Title: Earthquake Dynamic Rupture Modeling Constrained by Seismic Observations

CERES

Date: January 7, 2020
Time: 14h
Location: Amphithéâtre Galois – Bâtiment Rataud, 45 rue d’Ulm
By: Nathalie De Noblet (LSCE) & Josyane Ronchail (LOCEAN)
Title: Services climatiques : comment les climatologues cherchent à répondre aux demandes sociétales

Département de Géosciences

Date: January 7, 2020
Time: 11h
Location: Froidevaux – E314
By: Cathy Quantin-Nataf (Université Lyon 1)
Title: Early Mars investigations in the perspectives of ExoMars and Mars2020 missions

Soutenance – Thèse

Date: December 19, 2019
Time: 14h
Location: Froidevaux – E314
By: Cédric Bailly (ENS/IFPEN)
Title: Caractérisation géologique et géophysique multi-échelle des carbonates lacustres de l’île de Samos (Miocène supérieur, Grèce) - Liens entre faciès, diagenèse et propriétés élastiques
Abstract: Cette thèse propose une caractérisation géologique et géophysique multi-échelle des carbonates lacustres et palustres d’âge Miocène Supérieur affleurant à Samos (Grèce). Sur le terrain, un couplage entre descriptions naturalistes, mesures acoustiques à l’affleurement et réalisation de profils de sismique réfraction a permis de déterminer les caractéristiques sédimentologiques et les propriétés élastiques de ces carbonates, d’une échelle métrique à décamétrique. Au laboratoire, en parallèle des mesures de vitesse des ondes, porosité et densité sur échantillons, une description pétrographique fine des microstructures carbonatées a été réalisée afin de lier faciès, diagenèse et propriétés élastiques. De plus, sur la base des données de vitesse et de densité, des sismiques synthétiques 1D à haute résolution ont été générées et confrontées aux descriptions naturalistes. Les résultats obtenus montrent que la genèse de réflecteurs synthétiques est contrôlée par des contrastes faciologiques et/ou diagénétiques. Enfin, le changement d’échelle des propriétés élastiques des carbonates est abordé à l’aide de l’utilisation d’un modèle de milieux effectifs. Ce modèle a permis de relier les mesures de vitesse acquises aux fréquences ultrasoniques, soniques et sismiques à différentes échelles d’hétérogénéités. En effet, les résultats obtenus montrent que selon l’échelle d’investigation, les facteurs de contrôle dominants sur les propriétés élastiques des carbonates changent. Cette thèse propose ainsi une approche peu répandue, couplant observations naturalistes, mesures acoustiques et modélisation à différentes échelles. Elle permet d’apporter de nouvelles clés de compréhension et de caractérisation des carbonates continentaux, transposables à la subsurface.
Jury: Rudy SWENNEN (Katholieke Universiteit Leuven) : Rapporteur / François FOURNIER (CEREGE – Aix-Marseille Université) : Rapporteur / Emmanuelle VENNIN (Université de Bourgogne) : Examinateur / Yves GUÉGUEN (École normale supérieure) : Examinateur / Michel DIETRICH (CNRS, ISTerre) : Examinateur / Pierre-Yves COLIN (Université de Bourgogne) : Invité / Youri HAMON (IFP Énergies Nouvelles) : Co-Directeur / Jérôme FORTIN (École normale supérieure) : Directeur

Laboratoire de Météorologie Dynamique

Date: December 18, 2019
Time: 14h
Location: Froidevaux – E314
By: Bernard Legras (ENS)
Title: Campagne Stratoclim 2017 et le confinement de l’air pollué dans l’anticyclone de la mousson d’Asie

Laboratoire de Météorologie Dynamique

Date: December 12, 2019 – THURSDAY
Time: 14h
Location: Froidevaux – E314
By: Matteo Zampieri (JRC)
Title: How to measure resilience of productive systems: an ecological theory applied to climate science
Abstract: The original ecological meaning of the term resilience refers to the largest pressure that a system can cope with before changing its internal structure and losing its functioning capacity (Holling 1973). Afterwards, the concept of resilience has been introduced in other fields such as engineering and social sciences and modified to the point that resilience became an elusive concept, difficult to determine quantitatively. I’m proposing a measure theory for resilience derived directly from its original definition applied to production systems such as crops and natural vegetation. I will present several applications such as the estimations of the relationship between diversity and production resilience, of the effects of the Atlantic Multidecadal Oscillation on the resilience of global maize production, of the effects of climate change on the resilience of wheat production in the Mediterranean, of the relationships between vegetation resilience and green water resources resilience and of the effects of climate change on green water resources resilience.

Soutenance – Thèse

Date: December 3, 2019
Time: 14h
Location: Froidevaux – E314
By: Jérôme Aubry (ENS)
Title: Séismes au laboratoire : friction, plasticité et bilan énergétique
Abstract: Au sein de la lithosphère, la transition entre déformations fragile et plastique des roches s’effectue dans le régime semi-cassant. Comprendre le comportement des failles naturelles dans le régime semi-cassant est fondamental puisque d’importants séismes nucléent à la base de la zone sismogénique, à des conditions de pression et température proches de celles de la transition fragile-plastique. Pendant un séisme, l’énergie élastique accumulée lors de la période intersismique est dissipée au sein de l’interface de glissement par des processus frictionnels et de fracture, le reste étant relâché sous forme d’ondes sismiques. Ce budget énergétique est influencé par la déformation des surfaces de failles pendant des glissements lents à rapides, et plus particulièrement par des processus de chauffage, invisibles aux yeux de la sismologie. Afin d’étudier la déformation semi-cassante des roches et le budget énergétique des séismes, nous avons effectué des expériences de reproduction de séismes au laboratoire, en conditions triaxiales, à l’aide de failles expérimentales de différentes lithologies. Nous avons étudié l’influence de la pression, de la vitesse de déformation, de la température et de la rugosité sur la stabilité des failles le long de la transition fragile-plastique et exploré la dynamique des séismes au laboratoire en mesurant la quantité de chaleur produite sur une faille durant un cycle sismique. Deux conclusions principales émanent de ces travaux. D’abord, les séismes au laboratoire peuvent se déclencher au sein de roches déformées plastiquement dans le régime semi-cassant. Les glissements observés sont majoritairement contrôlés par la rugosité de la faille. Pour finir, lors d’un cycle sismique, les failles opèrent une transition depuis un stade avec de multiples aspérités radiant peu d’énergie, à un stade où elles évoluent comme une aspérité unique, radiant un maximum d’énergie.
Jury: Marie Violay (Ecole Polytechnique Fédérale de Lausanne, Suisse) : Rapporteure / Stefan Nielsen (Durham University, Royaume-Uni) : Rapporteur / Wenlu Zhu (Maryland University, Etats-Unis) : Examinatrice / Jérôme Fortin (École Normale Supérieure Paris, France) : Examinateur / Javier Escartín (Institut de Physique du Globe de Paris, France) : Co-directeur de thèse / Alexandre Schubnel (École Normale Supérieure Paris, France) : Directeur de thèse

Département de Géosciences

Date: December 3, 2019
Time: 11h
Location: Froidevaux – E314
By: Éric Buffetaut (Géosciences-ENS)
Title: À la recherche de l’Autruche géante asiatique

Soutenance – Thèse

Date: December 3, 2019
Time: 9h30
Location: Salle W – 45 rue d’Ulm
By: Henda GUERMAZI (ENS / ENIS)
Title: Télédétection des aérosols sulfatés d’origine volcanique dans l’Infrarouge Thermique
Abstract: The main objective of this thesis is to develop new satellite observations of volcanic sulphate aerosols in the thermal infrared. We found, as first results, that it is important to consider the radiative interference between sulphate aerosols and SO2 in order to optimize satellite retrievals of the two species. For a simulated volcanic eruption, the mutual effect of SO2 and sulphate aerosols on the TIR outgoing radiation is evident after three to five days from the eruption. Significant overestimations may be introduced in SO2 retrievals if the presence of sulphate aerosols is not taken into account. The high spectral resolution of IASI instrument allows the observation of these two effluents as independent quantities with limited uncertainties. Based on these results, we developed a new retrieval algorithm using IASI observations, called AEROIASI-Sulphates, to measure vertically-resolved sulphates aerosols extinctions and mass concentration profiles. The algorithm is applied to a moderate eruption of Mount Etna volcano. AEROIASI-Sulphates correctly identifies the volcanic sulphate aerosols plume morphology both horizontally and vertically after comparisons with SO2 plume observations and simulations. For an initial sulphur mass of 1.5 kT, 60% of the injected sulphur mass is converted to particulate matter after 24 h from the beginning of the eruption. A shortwave and direct radiative forcing of -0.8 W/m2 is exerted at the regional scale in the western Mediterranean area. This is the first time that sulphate aerosols are quantitatively observed from space-based instruments in the nadir geometry, which is of great importance to monitor and quantify volcanic emissions, their evolution and impacts at the regional scale.
Jury: Hervé Herbin (LOA, U-Lille) : rapporteur / Abdelaziz Kallel (CRNS, Tunisie, Sfax) : rapporteur / Fabio D’Andrea (LMD, ENS) : examinateur / Cathy Clerbaux (LATMOS, Sorbonnes Université) : examinatrice / Juan Cuesta (LISA, U-PEC) : examinateur / Bernard Legras (LMD, ENS) : directeur de thèse / Farhat Rekhiss (ENIS, Tunisie, Sfax) : directeur de thèse / Pasquale Sellitto (LISA, U-PEC) : co-directeur de thèse

CERES

Date: November 26, 2019
Time: 14h
Location: Froidevaux – E314
By: Anaïs Orsi (LSCE) & Anne Choquet (Université de Brest)
Title: Fonte de l’Arctique : comment le changement climatique rebat les cartes géopolitiques

Laboratoire de Géologie

Date: November 26, 2019
Time: 11h
Location: Froidevaux – E314
By: Bertrand Guenet (ENS)
Title: Priming effect: from laboratory experiments to global impact

Climaction

Date: November 20, 2019
Time: 11h
Location: Froidevaux – E314
By: Laurent Bopp, Nicolas Rochetin, Bernard Legras (LMD-ENS)
Title: Quelques clés pour répondre aux arguments climatosceptiques
Abstract: Dans une optique d’autoformation, les chercheurs du LMD exposent les résultats récents de leurs communautés et donnent à tous des clés pour répondre à quelques arguments climatosceptiques : « L’augmentation du CO2 dans l’atmosphère n’est pas anthropique mais liée au dégazage de l’océan » ; « L’atmosphère est déjà saturée en CO2 » ; « Ce sont les variations de l’insolation solaire qui causent les variations de températures »…

Laboratoire de Géologie

Date: November 19, 2019
Time: 11h
Location: Froidevaux – E314
By: Michelle Almakari (Mines ParisTech)
Title: Fault Reactivation by Fluid Injection: Insights from Numerical Modeling

Laboratoire de Géologie

Date: November 15, 2019 – FRIDAY
Time: 14h30
Location: Salle Serre
By: Chris Rollins (Leeds University)
Title: How geodesy can help characterize earthquake hazard

CERES

Date: November 12, 2019
Time: 14h
Location: Amphithéâtre Galois – Bâtiment Rataud, 45 rue d’Ulm
By: Aglaé Jézéquel (LMD-ENS) & Sandrine Revet (CERI Sciences-po)
Title: À qui attribue-t-on les catastrophes « naturelles » ? Perspectives croisées entre la climatologie et l’anthropologie

Laboratoire de Géologie

Date: November 12, 2019
Time: 11h
Location: Froidevaux – E314
By: Lucile Bruhat (ENS)
Title: Emergence of complexity from simple physics: how physics-based modeling highlights key features of earthquake processes

Laboratoire de Météorologie Dynamique

Date: November 6, 2019
Time: 11h
Location: Froidevaux – E314
By: Takahito Kataoka (JAMSTEC/YES)
Title: Wind-Mixed layer-SST Feedbacks in a tropical air-sea coupled system: Application to the Atlantic
Abstract: The ocean-atmosphere feedback associated with the thermodynamic coupling among wind speed, evaporation, and sea surface temperature (SST), called the wind-evaporation-SST (WES) feedback, contributes to the cross-equatorial SST gradient over the tropical oceans. By conducting an eigenanalyses of simple linear air-sea coupled models, it is shown that two additional feedback processes are present when the variable oceanic mixed layer depth (MLD) is considered. The horizontal structures of the leading modes are similar to the WES mode, which shows a meridional dipole in the SST anomalies straddling the equator with cross-equatorial wind anomalies that represent the weakening/strengthening of the trade winds over the warm/cool SST anomalies. The coupling of the variable MLD with winds and SST more than doubles the growth rate of the WES mode and enhances the equatorward propagation of the coupled disturbances.
The identified feedbacks operate as follows. The weaker winds associated with warm SST anomalies shoal the mixed layer through suppressed turbulent mixing, which causes the mixed layer to be more sensitive to the climatological shortwave radiation and amplifies the initial positive SST anomalies. Likewise, deepening of the mixed layer due to stronger winds acts to maintain the negative SST anomaly on the other side of the dipole. The MLD anomalies can also be generated by the buoyancy flux anomaly related to the wind-induced latent heat flux anomaly.
The anti-phase relationship between the SST and MLD anomalies seen in the simple model bears some resemblance to that which is observed in the observations and a state-of-the-art coupled model (MIROC6) during the Atlantic meridional mode.
Also, results from an ongoing work on yet another coupled feedback involving freshwater flux, which utilize a theoretical model and sensitivity experiments of fully coupled model, will be mentioned if time allows.

Département de Géosciences

Date: November 5, 2019
Time: 11h
Location: Froidevaux – E314
By: Thierry Huyghes-Beaufond (Société du Grand Paris)
Title: Le Grand Paris Express – Un projet pour le XXIème siècle

Soutenance – Thèse

Date: October 31, 2019
Time: 14h00
Location: Froidevaux – E314
By: Thomas Chartier (ENS)
Title: Modélisation de l’activité sismique des failles pour le calcul probabiliste du risque sismique
Abstract: Les taux de sismicité sont un élément clé du calcul probabiliste de l’aléa et du risque sismique. Une méthodologie innovante est développée pour modéliser les taux de ruptures complexes dans un système de failles (SHERIFS). La flexibilité de la méthodologie permet de la partager et de l’appliquer sur des systèmes de failles différents et de s’en servir comme outil de discussion des hypothèses concernant la sismicité sur les failles. Les taux de sismicité dans la partie Ouest du Rift de Corinthe en Grèce et dans la région de Marmara en Turquie sont modélisés en explorant l’incertitude épistémique sur le scenario de rupture maximale, la distribution en magnitude et fréquence ou encore les conditions de glissement sur la faille. A Marmara, les hypothèses sont pondérées dans un arbre logique en comparant les taux modélisés aux taux calculés à partir des données et des résultats d’un modèle physique basé sur les équations “rate and state”. Pour chaque hypothèse de l’arbre logique, le risque sismique à Istanbul, en termes de probabilité d’effondrement d’un immeuble, est calculé pour deux bâtiments de même type construits respectivement suivant le code de construction de 1975 et celui de 1998. Le risque sismique est six fois plus important pour le bâtiment le plus ancien. Parmi les incertitudes explorées, la source d’incertitude plus importante est liée à la distribution en magnitude et fréquence. L’utilisation des données et du modèle physique permet de réduire l’incertitude sur le risque par un facteur 1.6. Une nouvelle méthodologie de désagrégation du risque permet de montrer que le risque à Istanbul est contrôlé en partie par les séismes de magnitude supérieure à 7 sur la Faille Nord Anatolienne et en partie par les séismes de magnitude modérée (4.5 à 6) dans la sismicité de fond, sur des failles non connues, et à une distance du bâtiment inférieure à 10 km.
Jury: Kuo-Fong Ma (National Central University) : Rapporteur / Stéphane Mazzotti (Université Montpellier 2) : Rapporteur / Alice-Agnes Gabriel (Munich University) : Examinateur / Nicolas Chamot-Rooke (École Normale Supérieure) : Examinateur / Hélène Lyon-Caen (École Normale Supérieure) : Directrice de thèse / Oona Scotti (Institut de Radioprotection et de Sûreté Nucléaire) : Co-Encadrante de thèse / Aurélien Boiselet (Axa) : Invité

Laboratoire de Géologie

Date: October 29, 2019
Time: 11h
Location: Froidevaux – E314
By: Milena Marjanovic (IPGP)
Title: Imaging of crustal structure using waveform inversion techniques at the East Pacific Rise (EPR) 9º50’N: implications for crustal accretion and hydrothermal circulation
Abstract: The East Pacific Rise (EPR) 9ºN is one of the magmatically most dynamic ocean spreading centers along which ~6 km thick oceanic crust has been forming. In addition, the EPR 9ºN is a portion of the mid-ocean ridge system characterized by prolific hydrothermal activity. To image and characterize the properties of the crust and processes involved, we collected high-quality multichannel seismic data (2-D and 3-D) to which I applied advanced waveform-inversion techniques. During the talk, I will first present results of 2-D full-waveform inversion (FWI) on an axis centered seismic line to investigate hydrothermal circulation and propose a fine-scale permeability model for the upper crust. In the second part of the talk, I will focus on the results of elastic 3-D full-waveform inversion to address the physical properties of the upper crustal structure in 3-D and propose a possible mechanism for the upper crust accretion.

Soutenance – Thèse

Date: October 23, 2019
Time: 14h30
Location: Froidevaux – E314
By: Nikolaos Roukounakis (ENS / University of Patras)
Title: Application of a high-resolution weather model in the area of the western Gulf of Corinth for the tropospheric correction of interferometric synthetic aperture radar (InSAR) observations
Abstract: Space geodesy techniques (SAR interferometry and GNSS) have recently emerged as an important tool for mapping regional surface deformations due to tectonic movements. A limiting factor to this technique is the effect of the troposphere, as horizontal and vertical surface velocities are of the order of a few mm yr-1, and high accuracy (to mm level) is essential. The troposphere introduces a path delay in the microwave signal, which, in the case of GNSS Precise Point Positioning (PPP), can nowadays be successfully removed with the use of specialized mapping functions. Moreover, tropospheric stratification and short wavelength spatial turbulences produce an additive noise to the low amplitude ground deformations calculated by the (multitemporal) InSAR methodology. InSAR atmospheric phase delay corrections are much more challenging, as opposed to GNSS PPP, due to the single pass geometry and the gridded nature of the acquired data. Several methods have been proposed, including Global Navigation Satellite System (GNSS) zenithal delay estimations, satellite multispectral imagery analysis, and empirical phase/topography estimations. These methods have their limitations, as they rely either on local data assimilation, which is rarely available, or on empirical estimations which are difficult in situations where deformation and topography are correlated. Thus, the precise knowledge of the tropospheric parameters along the propagation medium is extremely useful for the estimation and minimization of atmospheric phase delay, so that the remaining signal represents the deformation mostly due to tectonic or other geophysical processes.
In this context, the current PhD Thesis aims to investigate the extent to which a high-resolution weather model, such as WRF, can produce detailed tropospheric delay maps of the required accuracy, by coupling its output (in terms of Zenith Total Delay or ZTD) with the vertical delay component in GNSS measurements. The model initially is operated with varying parameterization in order to demonstrate the best possible configuration for our study, with GNSS measurements providing a benchmark of real atmospheric conditions. In the next phase, the two datasets (predicted and observed) are compared and statistically evaluated for a period of one year, in order to investigate the extent to which meteorological parameters that affect ZTD, can be simulated accurately by the model under different weather conditions. Finally, a novel methodology is tested, in which ZTD maps produced from WRF and validated with GNSS measurements in the first phase of the experiment are used as a correction method to eliminate the tropospheric effect from selected InSAR interferograms. Results show that a high-resolution weather model which is fine-tuned at the local scale can provide a valuable tool for the tropospheric correction of InSAR remote sensing data.
Jury: Konstantinos KATSAMPALOS (Aristotle University of Thessaloniki): Reporter / Laurent MOREL (CNAM, Le Mans, France): Reporter / Cécile DOUBRE (Ecole et Observatoire des Sciences de la Terre, Strasbourg, France): Examiner / François LOTT (CNRS, Paris, France): Examiner / Stéphane JACQUEMOUD (Université Denis Diderot – Paris VII): Examiner / Athanassios ARGIRIOU (University of Patras, Greece): Co-director of thesis / Pierre BRIOLE (CNRS, ENS, Paris, France): Co-director of thesis

CERES

Date: October 22, 2019
Time: 14h
Location: Jussieu – salle Pacifique 56/66, 3ème étage
By: Valentin Bellassen (INRA) & Aude Valade (Centre de Recerca Ecologica Catalogne)
Title: Le CO2 qui cache la forêt : la biomasse forestière est-elle une énergie renouvelable ?

Laboratoire de Géologie

Date: October 22, 2019
Time: 11h
Location: Froidevaux – E314
By: Manon Bickert (IPGP)
Title: Strain localization in oceanic detachment faults: the extreme case of a magma-starved slow spreading ridge

Laboratoire de Météorologie Dynamique

Date: October 16, 2019
Time: 11h
Location: Froidevaux – E314
By: Benjamin Fildier (ENS)
Title: Modeling uncertainties on the acceleration of the global hydrologic cycle

Laboratoire de Géologie

Date: October 15, 2019
Time: All day
Location: Froidevaux – E314
By: Laboratoire de Géologie de l’ENS, l’ISTeP et la SFMC
Title: Journée scientifique Metamorphism, equilibrium versus kinetics autour de Dave Pattison

Laboratoire de Météorologie Dynamique

Date: October 9, 2019
Time: 11h
Location: Froidevaux – E314
By: Simon Cabanes (Sapienza Università di Roma)
Title: Describe and estimate energy transfers in the turbulent atmosphere of the gas giants

CERES

Date: October 8, 2019
Time: 14h
Location: Amphithéâtre Galois – Bâtiment Rataud, 45 rue d’Ulm
By: Vivian Depoues (I4CE), Catherine Lelong (RTE) & Pierre Goutierre (RTE)
Title: Infrastructures et réseaux face au changement climatique : adaptation spontanée ou planifiée ?

Laboratoire de Géologie

Date: October 8, 2019
Time: 11h
Location: Froidevaux – E314
By: Guilhem Mollon (INSA / ENS)
Title: Approches discrètes pour la modélisation du frottement

Laboratoire de Géologie

Date: October 7, 2019 – MONDAY
Time: 11h
Location: Froidevaux – E314
By: Antonio Avallone (INGV)
Title: Near-source high-rate GPS, strong motion and InSAR observations to image the 2015 Lefkada (Greece) Earthquake rupture history

Département de Géosciences

Date: October 1, 2019
Time: 11h
Location: Froidevaux – E314
By: Chris Bowler (IBENS-ENS)
Title: Tara Oceans: Eco-Systems Biology at Planetary Scale
Abstract: The ocean is the largest ecosystem on Earth and yet we know very little about it. This is particularly true for the plankton that drift within, even though they form the base of marine food webs and are key players in Earth’s biogeochemical cycles. Ocean plankton are at least as important for the Earth system as the forests on land, but most of them are invisible to the naked eye and thus are largely uncharacterized. To increase our understanding of this underexplored world, a multidisciplinary consortium, Tara Oceans, was formed around the 36m research schooner Tara, which sampled plankton at more than 210 sites and multiple depth layers in all the major oceanic regions during expeditions from 2009-2013 (Karsenti et al. Plos Biol., 2011). This talk will summarize the first foundational resources from the project, which collectively represent the largest DNA sequencing effort for the oceans (see Science special issue May 22, 2015 and Nature 28 April, 2016), and their initial analyses, illustrating several aspects of the Tara Oceans’ eco-systems biology approach to address microbial contributions to macro-ecological processes. The project provides unique resources for several scientific disciplines that are foundational for mapping ocean biodiversity of a wide range of organisms that are rarely studied together, exploring their interactions, and integrating biology into our physico-chemical understanding of the ocean. These resources, and the scientific innovations emerging to understand them, are critical towards developing baseline ecological context and predictive power needed to track the impact of climate change on the oceans.

Laboratoire de Géologie

Date: September 24, 2019
Time: 11h
Location: Froidevaux – E314
By: Yo Fukushima (Tohoku University)
Title: Extremely early recurrence of intraplate fault rupture following the Tohoku-Oki earthquake

Soutenance – HDR

Date: September 18, 2019
Time: 14h
Location: Froidevaux – E314
By: Caroline Muller (LMD-ENS)
Title: Fundamental study of small-scale processes in the atmosphere and in the ocean
Jury: Chantal Staquet, Bjorn Stevens, Frank Roux, Helene Chepfer, Christopher Holloway and Philippe Drobinski

CERES

Date: September 17, 2019
Time: 14h
Location: Froidevaux – E314
By: Dipesh Chakrabarty (The University of Chicago)
Title: The Planet: An Emergent Humanist Category
Discutant: Pierre Charbonnier (EHESS)
Abstract: Earth system science (ESS), the science that among other things explains planetary warming and cooling, gives humans a very long, multilayered, and heterotemporal past by placing them currently at the conjuncture of three (and now variously interdependent) histories whose events are defined by very different timescales: the history of the planet, the history of life on the planet, and the history of the globe made by the logics of empires, capital, and technology. One can therefore read Earth system scientists as historians writing within an emergent regime of historicity. We could call it the planetary or Anthropocenic regime of historicity to distinguish it from the global regime of historicity that has enabled many humanist and social-science historians to deal with the theme of climate change and the idea of the Anthropocene. In the latter regime, however, historians try to relate the Anthropocene to histories of modern empires and colonies, the expansion of Europe and the development of navigation and other communication technologies, modernity and capitalist globalization, and the global and connected histories of science and technology.

Laboratoire de Géologie

Date: September 17, 2019
Time: 11h
Location: Froidevaux – E314
By: Jun Muto (Tohoku University)
Title: Persistent deep afterslip driven by nonlinear transient mantle flow and recovery of coastal subsidence after the 2011 Tohoku earthquake
Abstract: Globally, the largest earthquakes occur on subduction zones, and their associated tsunamis are one of the greatest potential hazards faced by nearby coastal communities. Such great (Mw>8) and giant (Mw>9) earthquakes cause subsequent post-seismic deformation in the wide area depending on viscous structures of crustal and mantle rocks and the frictional properties of the plate interface. In particular, progress of afterslip occurring at the down-dip of the main rupture region where coseismic stress changes are large significantly affects the post-seismic uplift of the cosesimically subsided coastal regions. However, for giant megathrust events, viscoelastic flow and deep afterslip are mechanically coupled to each other, relaxing stress changes induced by both coseismic and post-seismic slip. Here, we show the role of afterslip and viscoelastic relaxation, and their interplay in the aftermath of the 2011 Mw 9.0 Tohoku earthquake. We conduct a two-dimensional analysis of the post-seismic deformation with coeval slip on the subduction interface governed by rate-strengthening friction and distributed deformation away from the fault governed by a power-law rheology with transient creep. The power-law rheology with stress-driven afterslip well explains the observed post-seismic deformation field and its time series in the period 2011 to 2016. Moreover, the geodetic data indicate a persistent deep afterslip directly down-dip of the main rupture region that greatly affects the ongoing post-seismic coastal uplift. Mechanical coupling between viscoelastic relaxation and afterslip notably modifies both the afterslip distribution and the surface deformation. Thus, we find that it is important to consider the interplay of these two deformation mechanisms to more fully understand the geodynamics of the Japan trench during the early stage of the seismic cycle. Finally, we also point out that such mechanical coupling are critical to estimate the future recovery of the coseismically subsided coastal area.

Laboratoire de Géologie

Date: September 10, 2019
Time: 11h
Location: Froidevaux – E314
By: Samuel Angiboust (IPGP)
Title: Knockin’on Mantle’s Door – Field and Modeling Insights onto Tectonic Processes at the Base of the Seismogenic Zone

Laboratoire de Géologie

Date: July 30, 2019
Time: 11h
Location: Froidevaux – E314
By: Ma Kuo-Fong (NCU Taiwan / E-DREaM Center, NCU Taiwan / IES, Academia Sinica)
Title: Kinematics and dynamic modeling of current and past earthquakes: implication to multiple fault segments rupture and seismic hazard analysis in Taiwan

Laboratoire de Géologie

Date: July 12, 2019
Time: 11h
Location: Salle Serre
By: Valère Lambert (Caltech)
Title: Energy budget of earthquakes: Connecting remote observations with local physical behavior

Laboratoire de Géologie

Date: July 9, 2019
Time: 11h
Location: Froidevaux – E314
By: Jean-Paul Callot (Université de Pau et des Pays de l’Adour)
Title: Les pathologies salifères ou « ne zappez pas, tout est possible », exemples de Turquie et de la nappe de Digne

Laboratoire de Géologie

Date: July 3-4, 2019
Time: 11h
Location: Froidevaux – E314
By: Lead by Blandine Gardonio (Géologie ENS) & David Marsan (ISTerre)
Title: Workshop « Repeating Earthquakes Workshop In Paris »

Laboratoire de Géologie

Date: June 25, 2019
Time: 11h
Location: Froidevaux – E314
By: Sylvie Demouchy (Montpellier)
Title: Olivine & Hydrogen & Rheology of Earth upper mantle

Laboratoire de Météorologie Dynamique

Date: June 20, 2019
Time: 14h
Location: Froidevaux – E314
By: Kevin DellaSanta (NYU)
Title: Zonally Symmetric Variability in the Tropics: A Tropical Annular Mode?

Laboratoire de Géologie

Date: June 20, 2019
Time: 10h30
Location: Froidevaux – E314
By: Denis ANGERS (Agriculture Canada et Université Laval)
Title: Sols, carbone et agriculture : perspective canadienne, mais pas que !

Laboratoire de Géologie

Date: June 18, 2019
Time: 11h
Location: Froidevaux – E314
By: Pierre Romanet (Univ. of Tokyo)
Title: Towards a better understanding of fault interactions and fault geometry on the seismic cycle

Laboratoire de Géologie

Date: June 14, 2019
Time: 11h
Location: Froidevaux – E314
By: Giovanni Occhipinti (IPGP)
Title: From Sumatra 2004 to Chile 2015 (through the revolutionary observations of Tohoku-Oki 2011): what we learn about Earthquake & Tsunami detection by ionospheric sounding

Laboratoire de Météorologie Dynamique

Date: June 12, 2019
Time: 11h
Location: Froidevaux – E314
By: Miriam Derrico (LSCE)
Title: Increase of Southern European cold spell intensity under climate change?

Laboratoire de Météorologie Dynamique

Date: June 11, 2019
Time: 9h
Location: Froidevaux – E314
By: Lead by Marie Farge (LMD-ENS)
Title: « International Workshop on Wavelets & CFD »

Département de Géosciences

Date: June 7, 2019
Time: 11h
Location: Froidevaux – E314
By: Samuel Abiven (U. Zurich)
Title: Une approche holistique du cycle du carbone dans les écosystèmes terrestres

Laboratoire de Géologie

Date: June 4, 2019
Time: 11h
Location: Froidevaux – E314
By: Sascha Brune (GFZ)
Title: Continental rift dynamics: Numerical simulation and plate tectonic model analysis

Laboratoire de Géologie

Date: May 29, 2019
Time: 14h
Location: Froidevaux – E314
By: Ralf Giering (FastOpt)
Title: Automatic Differentiation and its applications in carbon cycle data assimilation, inversion, and uncertainty estimation

Laboratoire de Géologie

Date: May 28, 2019
Time: 11h
Location: Froidevaux – E314
By: Laetitia Le Pourhiet (ISTEP)
Title: Propagation de la rupture continentale en 3D: revisiter de vieux concepts avec de nouveaux outils

Laboratoire de Météorologie Dynamique

Date: May 27, 2019
Time: 15h
Location: Froidevaux – E314
By: Keigo Matsuda (JAMSTEC)
Title: Turbulent clustering influence of polydisperse droplets on radar cloud observation

Laboratoire de Météorologie Dynamique

Date: May 24, 2019
Time: 11h
Location: Froidevaux – E314
By: Louis Couston (British Antarctic Survey)
Title: Emergence of large-scale flows in turbulent, stratified geophysical fluids with and without rotation

Laboratoire de Géologie

Date: May 23, 2019
Time: 14h
Location: Salle Serre
By: Timm John (Freie Universitat Berlin)
Title: The variation of petrophysical properties during eclogitization of lower continental crust and their influence on geophysical imaging

Laboratoire de Géologie

Date: May 23, 2019
Time: 11h
Location: Froidevaux – E314
By: Sonia Tikoo (Rutgers)
Title: Lunar Magnetism

Département de Géosciences

Date: May 22, 2019
Time: 16h
Location: Froidevaux – E314
By: Ping Chang (Texas A&M University)
Title: A Case Study of Connection between Hurricanes and Ocean Heat Content – Hurricane Harvey

Département de Géosciences

Date: May 21, 2019
Time: 11h
Location: Froidevaux – E314
By: S. Le Garrec (CEA), L. Bopp (ENS), E. Pili (CEA)
Title: Réunion plénière du Laboratoire de Recherche Conventionné Yves Rocard – Présentation du Département Analyse, Surveillance, Environnement, du Département de Géosciences et du LRC Yves Rocard

Laboratoire de Météorologie Dynamique

Date: May 20, 2019
Time: 11h
Location: Froidevaux – E314
By: Eric Mortenson (University of Victoria, Canada / CSIRO, Australia)
Title: A biogeochemical model study of the recent decline in Arctic sea ice, and implications for air-sea exchange of carbon

Laboratoire de Météorologie Dynamique

Date: May 17, 2019
Time: 11h
Location: Froidevaux – E314
By: Ping Chang (Texas A&M University)
Title: Oceanic Fronts/Eddies, Atmospheric Rivers and Extreme Rainfall

Laboratoire de Géologie

Date: May 15, 2019
Time: 14h
Location: Salle Serre
By: Emily Brodsky (UC Santa Cruz)
Title: Experiments on Naturalistic Granular Flows

Laboratoire de Géologie

Date: May 14, 2019
Time: 11h
Location: Froidevaux – E314
By: Masako Tominaga (WHOI)
Title: Multiscale Magnetometry Frontiers: Establishing a magnetic monitoring scheme of in situ metasomatism in mantle peridotite

Laboratoire de Météorologie Dynamique

Date: May 9, 2019
Time: 11h
Location: Froidevaux – E314
By: Alessandra Giannini (LMD-ENS)
Title: Past, present and future of climate change in the Sahel

Laboratoire de Géologie

Date: May 7, 2019
Time: 11h
Location: Froidevaux – E314
By: James Hollingsworth (ISTerre)
Title: Illuminating active fault zones through correlation of optical satellite imagery

Laboratoire de Géologie

Date: April 30, 2019
Time: 11h
Location: Froidevaux – E314
By: Matthieu Galvez (ETH)
Title: Interactions eau-roche dans le cycle du carbone : du processus microscopique à la dynamique globale

Laboratoire de Géologie

Date: April 23, 2019
Time: 11h
Location: Froidevaux – E314
By: Anne Davaille (FAST/Paris Sud)
Title:  Morphology and dynamics of mid-ocean ridges: from laboratory experiments to the Earth and Venus

Laboratoire de Géologie

Date: April 16, 2019
Time: 11h
Location: Froidevaux – E314
By: Cécile Prigent (Univ. of Delaware)
Title:  Hydratation, déformation et sismicité du manteau le long des failles transformantes océaniques

Département de Géosciences

Date: April 9, 2019
Time: 11h
Location: Froidevaux – E314
By: Florence Habets (Géologie ENS)
Title: La modélisation hydrogéologique pour le suivi et la prévision des ressources en eau souterraine

Laboratoire de Météorologie Dynamique

Date: April 5, 2019
Time: 14h
Location: Froidevaux – E314
By: Pearse BUCHANAN (University of Liverpool)
Title: Dynamic biological functioning important for simulating and stabilizing ocean biogeochemistry

Laboratoire de Géologie

Date: April 5, 2019
Time: 10h
Location: Froidevaux – E314
By: Adriano GUALANDI (JPL)
Title: Geodetic imaging of tectonic deformation: implications for earthquakes predictability

Laboratoire de Géologie

Date: April 2, 2019
Time: 11h
Location: Froidevaux – E314
By: Pascal Lacroix (ISTerre)
Title: Earthquake-triggered-landslides:  the contribution of slow-moving landslide studies

Laboratoire de Géologie

Date: March 27, 2019
Time: 11h
Location: Froidevaux – E314
By: Javier Escartin (IPGP)
Title: Submarine observations of coseismic rupture

Laboratoire de Météorologie Dynamique

Date: March 26, 2019
Time: 10h
Location: Froidevaux – E314
By: Lead by A. Jezequel (LMD-ENS)
Title: Workshop « Compounds events » : Extreme Value Theory for Open Set Classification – GPD and GEV Classifiers by Edoardo Vignotto (Université de Genève) & Assessing the impact caused by compound events, with a focus on the future changes in the compound flooding hazard by Emanuele Bevacqua (Université de Reading)

Laboratoire de Géologie

Date: March 22, 2019
Time: 11h
Location: Froidevaux – E314
By: Jean-Philippe Avouac (Caltech)
Title: Forecasting Earthquakes

Département de Géosciences

Date: March 21, 2019
Time: 14h
Location: Conf 4
By: Alexander Van Geen (Lamont-Doherty Earth Observatory)
Title: Considering geochemistry, hydrology, and human behavior to address the well-water arsenic problem in Bangladesh

Laboratoire de Géologie

Date: March 19, 2019
Time: 11h
Location: Froidevaux – E314
By: Pierre Maffre (GET)
Title: Climate and carbon cycle at geological timescale: mountain building, erosion and weathering

Laboratoire de Météorologie Dynamique

Date: March 12, 2019
Time: 14h
Location: Froidevaux – E314
By: A. Jezequel (LMD)
Title: Extreme event attribution: how and why?
Abstract:

Extreme events are an expression of natural climate variability. Since anthropogenic emissions affect global climate, it is natural to wonder whether recent observed extreme events are a manifestation of anthropogenic climate change. This seminar will be in two parts. First, I will present the existing scientific tools to study the influence of anthropogenic climate change on observed extreme events. I will focus on methods disentangling the influence of climate change on the dynamics leading to European heatwaves. Second, I will assess whether and how this scientific information — and more generally, the science of extreme event attribution (EEA) — could be useful for society.

Laboratoire de Géologie

Date: March 12, 2019
Time: 11h
Location: Froidevaux – E314
By: Rémy Bossu (CEA / Euro-Med Seismological Centre)
Title: How can Seismology Benefit from Citizen Seismology?

Laboratoire de Géologie

Date: March 5, 2019
Time: 11h
Location: Froidevaux – E314
By: Thomas Ferrand (ERI)
Title: Experimental confirmation of a spineloid transitional olivine polymorph using ultrafine-grained aggregates of Mg2GeO4

Laboratoire de Géologie

Date: February 26, 2019
Time: 11h
Location: Froidevaux – E314
By: Rémy Bonnet (CERFACS)
Title: Variations du cycle hydrologique continental en France des années 1850 à aujourd’hui

Département de Géosciences

Date: February 19, 2019
Time: 11h
Location: Froidevaux – E314
By: Philippe Huneman (IHPST)
Title: Pourquoi est-il déraisonnable de croire aux théories du complot et pourquoi et pourquoi est-il déraisonnable d’abuser du mot complotisme

Date: September 25, 2018
Time: 13h
Location: E314
By: O. Pauluis (NYU)
Title: Atmospheric thermodynamics : The atmosphere as a heat engine
Abstract:

TBA

Date: October 1, 2018
Time: 14h30
Location: E314
By: O. Pauluis (NYU)
Title: Isentropic analysis for tropical cyclones
Abstract:

TBA

Date: October 10, 2018
Time: 11h
Location: E314
By: Hiro Masunaga (Nagoya University, Japan)
Title: A Mechanism for the Maintenance of Sharp Tropical Margins
Abstract:

The deep tropics characterized by moist air and deep convection are separated from the dry, quiescent subtropics often by a sharp horizontal gradient of moisture only loosely tied to SST or other geographical constraints. Mapes et al. (GRL, 2018) showed that this margin of the moist tropics is a true PDF minimum (a regime separatrix), along a column water vapor (CWV) contour around 48 mm in instantaneous data. Quasi-meridional statistical composites of observations across the poleward-most excursion of this sinuous contour retain the sharpness of the margin while increasing signal to noise ratio. Observations primarily from a suite of the A-Train satellites show the meridional structure of thermodynamic state and budget terms across the margin of the moist tropics. Composites are computed around the PDF-minimum CWV value of 48 mm as well as a range of other thresholds from 35 mm to 60 mm for comparison.

Major findings are summarized as follows. (1) CWV increases equatorward from the subtropics for all CWV thresholds but eventually converges to ~48 mm deep into the tropical side. Precipitation abruptly intensifies on the tropical side of the margin but declines equatorward to ~3 mm/d regardless of the CWV thresholds. (2) The diabatic forcing to the atmosphere (radiative heating plus surface heat flux) changes its sign across the CWV=48 mm border, being positive on the tropical side and negative on the subtropics. This contrast is owing to the meridional gradient of radiative heating, principally the longwave effect of high clouds. (3) Vertical mode decomposition applied to vertical moisture advection implies that the second -mode moistening is sharply enhanced on the subtropical side of the margin, suggesting that an efficient “congestus moistening” process may be at work as inflowing lower-tropospheric air masses approach the margin. This second-mode moistening changes abruptly to weaker first-mode advective moistening (with a modest fraction of the drying due to the abrupt jump of precipitation) once the air mass enters the tropics. These observed features are interpreted in terms of a simple theory from the moisture and heat budget perspectives.

Date: October 18, 2018
Time: 14h
Location: L369
By: Colin Grudzien, NERSC, Bergen, Norway
Title: A dynamical systems framework for ensemble based filtering: a problem partially solved
Abstract:

Séminaire SAMA (Groupe Statistiques pour l’Analyse, la Modélisation et l’Assimilation).
In physical applications, dynamical models and observational data play dual roles in prediction and uncertainty quantification, each representing sources of incomplete and inaccurate information. In data rich problems, first-principle physical laws constrain the degrees of freedom of massive data sets, utilizing our prior insights to complex processes. Respectively, in data sparse problems, dynamical models fill spatial and temporal gaps in observational networks. The dynamical chaos characteristic of these process models is, however, among the primary sources of forecast uncertainty in complex physical systems. Observations are thus required to update predictions where there is sensitivity to initial conditions and uncertainty in model parameters. Broadly referred to as data assimilation, or stochastic filtering, the techniques used to combine these disparate sources of information include methods from Bayesian inference, dynamical systems and optimal control. While the butterfly effect renders the forecasting problem inherently volatile, chaotic dynamics also put strong constraints on the evolution of errors. It is well understood in the weather prediction community that the growth of forecast uncertainty is confined to a much lower dimensional subspace corresponding to the directions of rapidly growing perturbations. The Assimilation in the Unstable Subspace (AUS) methodology of Trevisan et al. has offered understanding of the mechanisms governing the evolution of uncertainty in ensemble forecasting, exploiting this dimensional reduction prescribed by the dynamics. With my collaborators, I am studying the mathematical foundations of ensemble based filtering in the perspective of smooth and random dynamical systems.

Date: November 15, 2018
Time: 15h
Location: L378
By: Jun-Ichi Yano (Meteo France, Toulouse)
Title: Tropical Atmospheric Madden-Julian Oscillation: Strongly-Nonlinear Free Solitary Rossby Wave?
Abstract:

The Madden-Julian oscillation (MJO), a planetary-scale eastward propagating coherent structure with periods of 30–60 days, is a prominent manifestation of intraseasonal variability in the tropical atmosphere. It is widely presumed that small-scale moist cumulus convection is a critical part of its dynamics. However, the recent results from high-resolution modeling as well as data analysis suggest that the MJO may be understood by dry dynamics to a leading-order approximation. Simple, further theoretical considerations presented herein suggest that if it is to be understood by dry dynamics, the MJO is most likely a strongly nonlinear solitary Rossby wave. Under a global quasi-geostrophic equivalent-barotropic formulation, modon theory provides such analytic solutions. Stability and the longevity of the modon solutions are investigated with a global shallow water model. The preferred modon solutions with the greatest longevities compare overall well with the observed MJO in scale and phase velocity within the factors.

Date: December 5, 2018
Time: 14h
Location: E314
By: Guillermo Scheffler, Centro de Investigaciones del Mar y la Atmosfera, Buenos Aires
Title: Optimization of stochastic parameters using nested ensemble Kalman filters
Abstract:

Séminaire SAMA (Groupe Statistiques pour l’Analyse, la Modélisation et l’Assimilation).
Stochastic parameterizations have been successfully used to represent the uncertainty associated with unresolved scale processes for ensemble forecasting and data assimilation systems. In order to accurately describe the uncertainty associated to the dynamical model and data assimilation system, stochastic parameters have to be optimized. Such parameters are related to the stochastic perturbations amplitude and their spatial covariance structure. A novel technique based on hierarchical ensemble Kalman filters is introduced, aiming to infer these type of parameters. The technique is proposed to be applied offline as part of an a priori optimization of the data assimilation system and could in principle be extended to the estimation of other hyperparameters of a data assimilation system.

Date: December 12, 2018
Time: 11h
Location: Salle serre
By: G. Bellon (University of Auckland)
Title: Oscillation de Madden-Julian dans les modèles de climat :encore et toujours problématique
Abstract:
Abstract: La plupart des modèles de climat ont toujours des difficultés à simuler des évènements réalistes de l’Oscillation de Madden-Julian(OMJ). Deux hypothèses ont été avancées pour expliquer cette déficience généralisée des modèles. La première avance que les modèles ne simule pas correctement le profil dechauffage diabatique dû au dégagement de chaleur latente, à l’effet radiatif et au mélange vertical dans les nuages ou ensembles de nuages, et que cette erreur des modèles influe sur la réponse dynamique de l’atmosphère tropicale qui permet le développement et la propagation de la perturbation convective de l’OMJ. La seconde hypothèse considère que les modèles quasi-hydrostatique sont incapables desimuler l’organisation spatiale de la convection profonde nécessaire à l’initiation d’un évènement del’OMJ. Cette incapacité serait due à l’absence de représentation des processus sous-maille et inter-maille qui sont essentiels cette organisation. Ce séminaire présentera quelques travaux qui s’attachent à évaluer le mérite de ces deux hypothèses: une évaluation des profils de chauffage diabatique simulés par les modèles et une exploration théorique de ce qu’on peut attendre de l’organisation spatiale de la convection.

Date: December 14, 2018
Time: 14h
Location: Salle serre
By: R. Brecht (Memorial University of Newfoundland)
Title: A variational discretization of the rotating shallow water equations on the sphere
Abstract:

We develop a variational integrator for the shallow-water equations on a rotating sphere. The variational integrator is built around a discretization of the continuous Euler–Poincaré reduction framework for Eulerian hydrodynamics. We describe the discretization of the continuous Euler–Poincaré equations on arbitrary simplicial meshes. Standard numerical tests are carried out to verify the accuracy and the excellent conservational properties of the discrete variational integrator.

Date: December 18, 2018
Time: 14h
Location: E314
By: Tom Beucler (MIT)
Title: Interaction between water vapor, radiation and convection in the Tropics
Abstract:

The interaction between convection and large-scale dynamics is a primary source of uncertainty in numerical simulations of the atmosphere, impeding our understanding of the climate. In large-scale atmospheric models, this uncertainty can be attributed to improperly-simulated interactions between atmospheric heating and water vapor across scales. Water vapor has a central role in the atmosphere: it is the most abundant greenhouse gas in the atmosphere, the main absorber of solar radiation in the troposphere. Water vapor is also intimately connected to atmospheric convection which lifts it, leading it to condense into clouds. Once formed, these clouds have even larger radiative effects. *However, we still lack a robust conceptual framework connecting water vapor and clouds to convection and radiation.

Using fluid dynamics, thermodynamics and spectral analysis tools, we investigate the interaction between water vapor, radiation and convection in observations of the tropical atmosphere and in high-resolution models of radiative-convective equilibrium. Radiative-convective equilibrium is the simplest model of the tropical atmosphere, in which convective heating balances radiative cooling in the absence of horizontal energy transport. We introduce a framework relating the evolution of the length scale at which convection organizes to the spatial spectra of radiative cooling, surface enthalpy fluxes, and horizontal energy transport. The cloud longwave radiative effect is most important, stretching humid and dry regions to scales of several thousand kilometers in the Tropics. These findings suggest that resolving the coherence between high, ice-cloud radiation and water vapor across the 1-10,000 km scale range is key to modeling tropical dynamics, and may considerably reduce our biases in modeling large-scale tropical precipitation patterns that are relevant for human activity.

Date: January 10, 2018
Time: TBA
Location: TBA
By: J. McWilliams (UCLA)
Title: TBA
Abstract:

TBA

Date: January 22, 2018
Time: 2pm
Location: E314
By: F. Ragone (Università degli Studi di Milano-Bicocca)
Title: Studying extreme climatic events with rare event algorithms applied to numerical climate models
Abstract:

A reliable quantification of the risk associated with extreme climatic events is crucial for policymakers, civil protection agencies and insurance companies. Studying extremes on a robust statistical basis with complex numerical climate models is however computationally challenging, since extreme events are rare, and thus very long simulations are needed to sample a significant number of them. I will discuss how the problem of sampling extremes in climate models can be tackled using rare event algorithms. Rare event algorithms are numerical tools developed in the past decades in mathematics and statistical physics, dedicated to the reduction of the computational effort required to sample rare events in dynamical systems. Typically they are designed as genetic algorithms, in which a set of cloning rules are applied to an ensemble simulation in order to focus the computational effort on the trajectories leading to the events of interest. I will present a rare event algorithm developed in the context of large deviation theory, and I will show how it can be used to sample very efficiently extreme European heat waves in simulations with the climate model Plasim. This allows to characterise the statistics of heat waves with return times up to millions of years, with computational costs three orders of magnitude smaller than with direct sampling. This allows to sample a large number of trajectories leading to very rare events, which can be used to study their characteristic dynamics, and also to observe ultra rare events that would have never been observed in a normal simulation. I will then discuss how these techniques can be applied to study a wide range of different processes with complex climate models.

Date: January 29 2019)
Time: 2pm
Location: E314
By: Hye-Yeong Chun (Yonsei University, South Korea)
Title: Small-Scale Convective Gravity Waves: Contribution to the Large-Scale Circulations in the Middle Atmosphere
Abstract:

Vertically propagating gravity waves (GWs) transfer their momentum and energy to the large-scale flow in the middle atmosphere, where they are dissipated through the wave breaking, critical-level filtering, and radiative damping processes. The current resolution of general circulation models (GCMs), even for high-resolution ones with horizontal grid spacing of ~0.25o, do not fully resolve GWs, and thus their effects have to be parameterized in GCMs. Among the various sources of GWs, convection can generate high-frequency GWs, which have a broad phase speed spectrum and can propagate to high altitudes without seasonal restrictions. In this seminar, observational characteristics of convective GWs (CGWs), parameterization of CGWs for use in GCMs, and impacts of CGWs in the large-scale circulations in the middle atmosphere are presented. The observational evident of CGWs will be shown, based on satellites, super-pressure balloons, meteor radar, and high-resolution radiosonde measurements. Regarding the CGW parameterization, the basis of GW parameterization and the development history of CGWs will be provided. The impacts of the parameterized CGWs in the middle atmosphere circulations are given, based on recent works from my research group: (i) the quasi-biennial oscillation (QBO), (ii) polar-night jet in the southern hemisphere (SH) wintertime, and (iii) Madden-Julian oscillation (MJO). In the tropical stratosphere, CGWs can significantly contribute to the momentum budget of the QBO. The positive momentum forcing by parameterized CGWs is comparable to that by Kelvin wave during the easterly-to-westerly transition, while the negative momentum forcing by parameterized CGWs during the westerly-to-easterly transition is significantly larger than any other equatorial planetary waves (Kang et al. 2018, JAS). Regarding the polar-night jet, Choi and Chun (2013, JAS) demonstrated that excessive jet and cold-pole biases in the SH stratosphere during the wintertime, which have been a long-lasting problem in GCMs, can be alleviated significantly by including a CGW parameterization into a GCM. Recently, Kalish et al. (2018, JGR) showed that cloud-top momentum flux of CGWs evolve following the MJO phases, and the propagation speed of convective cloud associated with the MJO is similar to the dominant eastward-propagating speed of CGWs in the cloud top. Some important issues on the CGW parameterization will be discussed at the end of the seminar.