Dissertations / Theses on the topic 'Calotte polaire'
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Partouty, S. "Interprétation des séries temporelles altimétriques sur la calotte polaire Antarctique." Phd thesis, Université Paul Sabatier - Toulouse III, 2009. http://tel.archives-ouvertes.fr/tel-01018319.
Full textParouty, Soazig. "Interprétation des séries temporelles altimétriques sur la calotte polaire Antartique." Toulouse 3, 2009. http://thesesups.ups-tlse.fr/900/.
Full textThis work aims at improving our understanding of the altimetric time series acquired over the Antarctic Ice Sheet. Dual frequency data (S Band - 3. 2GHz and Ku Band - 13. 6GHz) from thealtimeter onboard the ENVISAT satellite are used, during a five year time period from january2003 until december 2007. These data cover around 80% of the surface of the Antarctic continent,up to 82°S. Having data in two different frequencies is valuable when it comes to better estimatethe altimeter sensitivity regarding snow surface property changes. Over the Antarctic ice sheet, snow surface changes with respect to space and time, beingaffected by meteorological conditions close to the surface, and especially winds. The altimetricwave penetrates more or less deeply beneath the surface, depending on snow surface and subsurfaceproperties. As a result, when the wave comes back to the satellite, the recorded signal, namedwaveform, is more or less distorted. The accuracy of the ice sheet topographic changes computedthanks to satellite altimetric techniques depends on our knowledge of the processes inducing thisdistortion. The purpose of the present work is to better understand the effect of changing windconditions on altimetric data. Winds in Antarctica are indeed famous for their strength and theirimpact on the snow surface state. First, spatial and temporal variability of the altimetric data on the one hand, and of wind speedreanalysis fields (from ERA-Interim, NCEP/NCAR and NCEP/DOE projects) on the other handare studied. We estimate spatial and temporal typical length scales for all datasets. As a result, weare able to smooth the data, so that all datasets have the same spatial and temporal caractericticlength scales. Furthermore, we note that our time series are well described by an annual signal. This annual cycle shows that whereas wind speed would always be maximum in austral winter,altimetric seasonal cycles have very different behaviors depending on the location. .
Merino, Nacho. "Interactions calotte polaire/océan : vers la mise en place d'une modélisation couplée." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAU051/document.
Full textThe next generation of climate models will include an ice-sheet model in order to improve the ice sheet mass balance projections by accounting for the ice dynamics and ice-oceans interactions. On the one hand, the Southern Ocean (SO) is indeed driving the acceleration of the Antarctic outlet glaciers via an increase in the basal melting of the ice shelves. On the other hand, the increasing ice discharge from Antarctic Ice Sheet (AIS) contributes to the current sea level rise and is likely to become the largest cryospheric contributor to sea level rise by the end of the current century. In addition, the related freshening may have significant implications on future sea-ice cover and on bottom water formation. However, it is not clear yet how the ocean and ice-sheet components of future coupled systems will account for the ice-ocean interactions, which are both causes and consequences of the AIS mass imbalance. Here in this work, different aspects of the standalone ocean and ice-sheet components have been investigated. A first step of this thesis has been focused in the representation of the glacial freshwater fluxes in current ocean models. Based on recent glaciological estimates, the ice shelf basal melting fluxes have been spatially distributed in an ORCA025 grid, and the calving rates have been applied into an improved version of the NEMO-ICB iceberg model. This preliminary study has been used to produce a monthly iceberg meltwater climatology, to be used to force current ocean models. This work shows the importance of representing the iceberg meltwater fluxes when modeling sea ice, which can be inexpensively achieve by using our climatology. The improvements in the representation of the glacial freshwater fluxes have been considered in the study of the ocean model response to the Antarctic mass imbalance. This study considers a realistic perturbation in the glacial freshwater forcing as close as possible as it will be represented in future ice-sheet/ocean models. According to our results, up to 50% of the recent Antarctic sea ice volume changes might be caused by the observed decadal AIS mass imbalance rate. Glacial freshwater forcing appears to be crucial to correctly represent the ice-ocean interactions and projecting sea ice cover of future coupled systems. However, the estimation of the glacial freshwater input in future climate models will be strongly dependent upon the capacity of ice-sheet models to reproduce the grounding line migrations of marine ice sheet glaciers. Current ice-sheet models present large uncertainties related to different parametrizations. In the context of the future climate models, we have studied the sensitivity of ocean-driven grounding line retreats to the application of two different friction laws and two different englacial stress approximations. The model responses almost indistinctively to either the SSA or the SSA* englacial stress approximations. However, differences in the contribution of the glacier to the sea level rise can be up to 50% depending on the friction law considered. The more physically constrained Schoof friction law is significantly more reactive to the ocean perturbations than Weertman law and should be considered in future coupled systems. This work underlines that uncertainties related to the ice sheet model estimates of grounding line migrations may not only contribute to uncertainties in sea level projections, but also the sea ice cover through the ice-ocean interaction in future ocean models.This conclusion suggests the need for improving the representation of both the ice shelf basal melting and the glacier interaction with the bedrock, in order to improve the climate projections of future climate models, in which the spatial and seasonal distribution of the glacial freshwater fluxes may play an important role in setting the sea ice cover
Lacroix, Pascal. "Apport de l'altimétrie radar spatiale à l'étude de la neige de la calotte polaire Antarctique." Phd thesis, Université Paul Sabatier - Toulouse III, 2007. http://tel.archives-ouvertes.fr/tel-00216105.
Full textDepuis 2002 et le lancement de ENVISAT, on dispose d'un altimètre radar qui couvre 80 \% de la calotte polaire Antarctique, dont la particularité est d'acquérir des signaux à deux fréquences différentes (bande S à 3.2 GHz et bande Ku à 13.6 GHz). Ces deux ondes pénètrent dans le manteau neigeux sur plusieurs mètres et ont des sensibilités aux propriétés de la neige différentes. Ainsi, l'idée de cette thèse est d'utiliser cette double information pour retrouver les propriétés du manteau neigeux.
On se propose de résoudre cette problématique par une analyse et une modélisation des signaux altimétriques bi-fréquences sur la calotte polaire, puis par leur inversion. On se penche tout d'abord sur quelques études de cas pour estimer la sensibilité des signaux aux différentes propriétés de la neige: i/ On montre tout d'abord que le signal altimétrique est sensible à la rugosité de la surface à différentes échelles, puis ii/ que le signal altimétrique est sujet à des variations saisonnières causées par la densification de la neige en surface, et enfin iii/ que les ondes radars sont réfléchies par des strates en profondeur.
Un modèle de l'interaction de l'onde avec le manteau neigeux est réalisé simultanément aux deux fréquences, afin de permettre une comparaison de ces signaux entre eux. Les résultats du modèle sont utilisés pour expliquer les variations saisonnières précédemment observées. Finalement, les paramètres du manteau neigeux sont estimés à l'échelle de la calotte polaire antarctique. Les tailles de grains retrouvées présentent un grossissement vers l'intérieur du continent. La densité montre des variations saisonnières de plusieurs g.cm3 notamment sur les côtes antarctiques. Certaines régions présentent un état de surface de la neige particulièrement lisse (Dronning Maud Land, par exemple).
La donnée in situ de l'état de surface de la neige étant quasi inexistante sur les calottes polaires, on développe finalement un protocole de mesure de la rugosité de la neige, qui est testé sur un glacier du Spitzberg.
Bonan, Bertrand. "Assimilation de données pour l'initialisation et l'estimation de paramètres d'un modèle d'évolution de calotte polaire." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00930097.
Full textMassé, Marion. "Nature et origine des dépôts de sulfates dans les régions équatoriales et polaires de Mars : comparaison morphologique et minéralogique entre Aram Chaos et la calotte polaire Nord." Phd thesis, Université de Nantes, 2010. http://tel.archives-ouvertes.fr/tel-00762257.
Full textFlament, Thomas. "Variations de hauteur de la calotte antarctique par altimétrie radar par satellite : amincissement dynamique, vidanges de lacs sous-glaciaires et autres curiosités." Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2592/.
Full textThe Antarctic Ice Sheet is a vast and remote hostile land. It is nonetheless an important part of the planetary climate system. Space-borne instruments are among the best tools to study the evolution of the ice sheet. In this work, we use data from one of these space sensors: the Envisat radar altimeter. This instrument provided us repeated measurements of the ice sheet surface elevation every 35 days during 8 years. From this dataset, we investigated volume change of the ice sheet between 2002 and 2010. This period is relatively short compared to the typical duration of ice sheet response (thousands of years after an ice age) but the data show some evolution, either extreme precipitation events or accelerated flow and associated thinning. The high space and time resolution also allowed us to observe rapid and local events such as subglacial lake drainages. These were only recently discovered in Antarctica and altimetry is one of the best suited tools to study them. The reflection and backscatter of the radar wave by the snowpack is still a complex problem that has to be further investigated. The own behavior of the snowpack must be better understood. We present the state of the art of the understanding of the radar/snowpack interaction. We conclude with an outlook on future techniques that will enhance our understanding of the ice sheet process and ice sheet evolution: new altimeters, longer time series, multi-sensor studies and additional in situ calibration
Krug, Jean. "Intéractions calottes polaires/océan : modélisation des processus de vêlage au front des glaciers émissaires." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU033/document.
Full textPolar ice-sheets discharge and subsequent sea level rise is a major concern. Warming climate affects the behaviour of tidewater outlets glaciers and increases their ice discharge. As they drain the ice flow toward the ocean, it is pivotal to incorporate their dynamics when modelling the ice-sheet response to global warming. However, tidewater glacier dynamics is still complicated to understand, as they are believed to involve many feedbacks. The one between calving margin dynamics and glacier general dynamics is fundamental. This PhD thesis focuses on modelling the calving front of outlet glaciers, in order to enhance the representation of physical processes occurring at their margin. To do so, we build up a new framework for calving based on damage mechanics and fracture mechanics. This allows us to represent the slow degradation of the ice rheological properties from a virgin state to the appearance of a crevasse field, as well as the rapid fracture propagation associated with calving events. Our model is then constrained within a 2D flow-line representation of Helheim Glacier, Greenland. We find some parameters sets for which the glacier behaviour is coherent with its past evolution. Sensitivity tests are carried out and they reveal the significance of each model parameter. This new calving law is then employed to study the impact of submarine frontal melting and ice mélange (heterogeneous mixture of sea-ice and icebergs) on glacier dynamics. These two forcings are usually suspected to be responsible for the seasonal variations of the calving margin. Our results show that both forcings impact the front dynamics. The melting, however, only slightly changes the front position, when the ice mélange can force the glacier front to displace up to a few kilometers. Additionally, if the melting at the front is not sufficient to affect the inter-annual mass balance, this is not obvious when forced by ice mélange. At last, our model highlights a feature which is specific to floating glaciers: for the strongest forcings, the glacier equilibrium may be modified, as well as its pluri-annual mass balance.STAR
Gillet-Chaulet, Fabien. "Modélisation de l'écoulement de la glace polaire anisotrope et premières applications au forage de Dôme C." Université Joseph Fourier (Grenoble), 2006. http://www.theses.fr/2006GRE10255.
Full textThe ice crystal is one of the most anisotropic natural materials. Observations of polar ice show that the crystals are orientated along very marked privileged directions and that the fabric of the ice polycristal is the result of the strain history that the polycristal has undergone. The macroscopic polycristal behaviour depends on the fabric and can be strongly anisotropic. It has been shown that anisotropy can introduce the occurrence of stratigraphy disturbances and influences strongly the flow of the ice sheet. The aim of this work is to build an ice flow model for anisotropic ice and the evolution of its fabric. To this end, we model the ice monocrystal as a transversely isotropic continuous medium around its c-axis and we compare it with a slip-planes grain model. The ice fabric is described in a continuous way by the second order orientation tensor and a closure approximation for the fourth ordre orientation tensor. By homogenization, assuming uniform stresses or strain-rates, we obtain analytical solutions for the polycrystal behaviour and the evolution of its fabric. From these solutions, we derive a linear orthotropic flow law for the ice polycrystal and an equation for the evolution of the second order orientation tensor. These equations are able to reproduce the results of the self-consistent model using a discrete fabric description, with an important improvement as regards the computing time and the number of variables necessary to describe the fabric. These equations are then implemented in a finite element code, used for simulating the flow of an ice sheet with strain-induced evolving anisotropy. By performing synthetic tests, we show the influence of anisotropy on the ice flow. Finally, through our model results, we propose an interpretation of the Dome-C ice-core fabric data
Lacour, Adrien. "Les nuages du Groenland observés par CALIPSO." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066460/document.
Full textOver 80% of Greenland is covered by ice. Melting of this ice contributes to the sea level rise. By modulating the radiation reaching the surface, clouds can accelerate or slow down the melting. Through this thesis, we use CALIPSO satellite measurements (GOCCP product) to document clouds over Greenland, including their vertical structure, and understand their role in surface melting.We compare these observations with radar and lidar measurement taken from the Summit ground station in the middle of Greenland. The comparison shows that GOCCP does not include optically thin ice clouds (τ < 0.3). Extending this analysis over all Greenland shows that cloudiness follows different cloud annual cycles in North and South regions, and that Summit is one of the cloudiest regions of the Greenland especially for the liquid cloud cover.To understand the atmospheric conditions favorable to cloud formation, we follow two weather regime classification approaches. We do not find a clear relationship between cloud variability and atmospheric circulation. These results show the complexity of the interactions between clouds and synoptic circulation and highlight the need to accumulate more data over long time periods.Finally, we evaluate cloud representation over Greenland in simulated lidar profiles over output from CMIP5 climate models. We identify several biases that lead to models being unable to simulate surface melting. Models underestimate the surface temperature and the cloud cover. Also when clouds are simulated they are either too opaque or too thin to affect surface melting
Gagliardini, Olivier. "Simulation numérique d'un écoulement bidimensionnel de glace polaire présentant une anisotropie induite évolutive." Phd thesis, Grenoble 1, 1999. http://tel.archives-ouvertes.fr/tel-00701282.
Full textGagliardini, Olivier. "Simulation numérique d'un écoulement bidimensionnel de glace polaire présentant une anisotropie induite évolutive." Phd thesis, Université Joseph Fourier (Grenoble ; 1971-2015), 1999. http://www.theses.fr/1999GRE10008.
Full textLacour, Adrien. "Les nuages du Groenland observés par CALIPSO." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066460.
Full textOver 80% of Greenland is covered by ice. Melting of this ice contributes to the sea level rise. By modulating the radiation reaching the surface, clouds can accelerate or slow down the melting. Through this thesis, we use CALIPSO satellite measurements (GOCCP product) to document clouds over Greenland, including their vertical structure, and understand their role in surface melting.We compare these observations with radar and lidar measurement taken from the Summit ground station in the middle of Greenland. The comparison shows that GOCCP does not include optically thin ice clouds (τ < 0.3). Extending this analysis over all Greenland shows that cloudiness follows different cloud annual cycles in North and South regions, and that Summit is one of the cloudiest regions of the Greenland especially for the liquid cloud cover.To understand the atmospheric conditions favorable to cloud formation, we follow two weather regime classification approaches. We do not find a clear relationship between cloud variability and atmospheric circulation. These results show the complexity of the interactions between clouds and synoptic circulation and highlight the need to accumulate more data over long time periods.Finally, we evaluate cloud representation over Greenland in simulated lidar profiles over output from CMIP5 climate models. We identify several biases that lead to models being unable to simulate surface melting. Models underestimate the surface temperature and the cloud cover. Also when clouds are simulated they are either too opaque or too thin to affect surface melting
Surdyk, Sylviane. "Etudes des signatures spectrales micro-ondes obtenues par télédétection sur la calotte polaire antarctique : comparaison avec des données de terrain et modélisation de l'émissivité de la neige." Phd thesis, Grenoble INPG, 1993. http://tel.archives-ouvertes.fr/tel-00765202.
Full textMondet, Jean. "Etude des paramètres de surface de la calotte polaire antarctique, dans les domaines spectraux du visible et du proche infrarouge, à partir des données de l'instrument de télédétection POLDER." Phd thesis, Grenoble 1, 1999. http://tel.archives-ouvertes.fr/tel-00766029.
Full textQuiquet, Aurelien. "Reconstruction de la calotte polaire du Groenland au cours du dernier cycle glaciaire-interglaciaire à partir de l'association de la modélisation numérique 3D et des enregistrements des carottages glaciaires profonds." Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00704253.
Full textQuiquet, Aurélien. "Reconstruction de la calotte polaire du Groenland au cours du dernier cycle glaciaire-interglaciaire à partir de l'association de la modélisation numérique 3D et des enregistrements des carottages glaciaires profonds." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENU006/document.
Full textThe Greenland ice sheet represents a potential sea level rise contribution of 7.3 meters. When drastic changes are recently observed, multi-centennal futur projections are urgently needed. 3D numerical modelling is one of the tools to realize these projections. This work intensively incorporates the use of Greenland deep ice core drillings, which represent an important amount of information of past states of the ice sheet. The validity of the reconstructions are thus assured by constant back and forth between observations and simulations. Robustness of these reconstructions and of future projections are largely questionned through wide sensitivity experiments. The ice sheet model calibration is performed during the last deglaciation considering the numerous constraints during this period. Given that, scenarios of ice sheet states during the whole last climatic cycle, in particular during the last interglacial, the Eemian, potential analogue for a future climate
Teste, Alexandra. "Aurores et échappements de particules au-dessus des calottes polaires terrestres : observations à haute altitude par la mission Cluster." Paris 6, 2007. https://tel.archives-ouvertes.fr/tel-00803178.
Full textSix, Delphine. "Analyse statistique des distributions spatiales et temporelles des séries de bilans de masse des glaciers alpins et des calottes polaires de l'hémisphère nord." Grenoble 1, 2000. http://www.theses.fr/2000GRE10255.
Full textPimienta, Pierre. "Etude du comportement mécanique des glaces polycristallines aux faibles contraintes : applications aux glaces des calottes polaires." Grenoble 1, 1987. http://www.theses.fr/1987GRE10169.
Full textAdodo, Fifi Ibrahime. "Altimétrie et radiométrie en Antarctique." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30135/document.
Full textIn the context of global climate changes, the Antarctic ice sheet contribution to sea-level rise is one of the main uncertainty sources. The extent and extreme meteorological conditions of this continent render remote sensing a useful tool for long term monitoring. Altimetry and radiometry observations in the microwave range reveal variations of the volume of the ice sheet and surface properties of the snowpack. Radar altimeters, provide repeated observations of the surface topography elevation, which allow the quantification of volume variations of the ice sheet. However, the penetration of radar waves in dry and cold snowpack adversely affects the estimated surface elevation. Approaches to minimize the penetration error are all based on a relationship with the backscattering coefficient. Understanding the annual and interannual variations of the backscattering coefficient is thus a key issue in order to improve the estimation accuracy of the surface elevation and to refine the ice-sheet volume trend. This thesis aims at studying the backscattering coefficients acquired by radar altimeters, which until now have received little attention. Radar altimeters on board ENVISAT (S and Ku bands) and SARAL/AltiKa (Ka band) have different sensitivities to the snowpack properties. The annual and interannual variations of the backscattering coefficient at the three bands is investigated. Sensitivity tests are carried out with an electromagnetic model to determine the prevailing snowpack properties that drive the signal. The seasonal signal is sensitive to surface density and roughness at S band, to snow temperature at Ka band and to either snow surface density and roughness or temperature depending on the location on the continent at Ku band. The seasonal signal of the backscattering coefficient is then compared with that of the brightness temperature measured by radiometers on SARAL and SSM/I. The results show a significant influence of surface roughness on brightness temperatures at Ka band, which has often been neglected in brightness temperature modeling studies. This thesis provides a better understanding of the seasonal dynamics of the near surface properties of the Antarctic ice sheet. It also provides new clues to build a more robust corrections of the penetration errors in the future. It highlights the importance of multi-frequency altimetry missions and the potential of the S band to study the seasonal variability in surface roughness. In summary, surface roughness is an important property which should be taken into account for a better modeling of backscattering coefficient and brightness temperature
Castelnau, Olivier. "Modélisation du comportement mécanique de la glace polycristalline par une approche auto-cohérente : application au développement de textures dans les glaces des calottes polaires." Phd thesis, Université Joseph Fourier (Grenoble), 1996. http://tel.archives-ouvertes.fr/tel-00748169.
Full textKaitheri, Athul. "Caractérisation des variations de masse en Antarctique en réponse aux fluctuations climatiques à partir des données de gravimétrie spatiale et d'altimétrie radar." Thesis, Université Côte d'Azur, 2021. http://www.theses.fr/2021COAZ4100.
Full textQuantifying the mass balance of the Antarctic Ice Sheet (AIS), and the resulting sea level rise, requires an understanding of inter-annual variability and associated causal mechanisms. This has become more complex and challenging in the backdrop of global climate change. Very few studies have been exploring the influence of climate anomalies on the AIS and only a vague estimate of its impact is available. Usually changes to the ice sheet are quantified using observations from space-borne altimetry and gravimetry missions. In this study, we use data from Envisat (2002 to 2010) and Gravity Recovery and Climate Experiment (GRACE) (2002 to 2016) missions to estimate monthly elevation changes and mass changes, respectively. Similar estimates of the changes are made using weather variables (surface mass balance (SMB) and temperature) from a regional climate model (RACMO2.3p2) as inputs to a firn compaction (FC) model. Using the firn compaction model we were able to model the transformation of snow into glacial ice and hence estimate changes in the elevation of the ice sheet using climate parameters.Elevation changes estimated from different techniques are in good agreement with each other across the AIS especially in West Antarctica, Antarctic Peninsula, and along the coasts of East Antarctica. Inter-annual height change patterns are then extracted using for the first time an empirical mode decomposition followed by a reconstruction of modes. These signal on applying least square method revealed a sub-4-year periodic signal in the all the three distinct height change patterns. This was indicative of the influence of the El Niño Southern Oscillation (ENSO), a climate anomaly that alters, among other parameters, moisture transport, sea surface temperature, precipitation, in and around the AIS at similar frequency by alternating between warm and cold conditions. But there existed altering periodic behavior among inter annual height change patterns in the Antarctic Pacific (AP) sector which was found possibly by the influence of multiple climate drivers, like the Amundsen Sea Low (ASL) and the Southern Annular Mode (SAM). A combined analysis of the three distinct estimates using a PCA (principal component analysis) along the coast revealed similar findings. Height change anomaly also appears to traverse eastwards from Coats Land to Pine Island Glacier (PIG) regions passing through Dronning Maud Land (DML) and Wilkes Land (WL) in 6 to 8 years. This is indicative of climate anomaly traversal due to the Antarctic Circumpolar Wave (ACW) which propagates anomalies through the Southern Ocean in 8 to 10 years. Altogether, inter-annual variability in the SMB of the AIS is found to be modulated by multiple competing climate anomalies
Teste, Alexandra. "AURORES ET ECHAPPEMENTS DE PARTICULES AU-DESSUS DES CALOTTES POLAIRES TERRESTRES Observations à haute altitude par la mission Cluster." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2007. http://tel.archives-ouvertes.fr/tel-00803178.
Full textArnaud, Laurent. "Modélisation de la transformation de la neige en glace à la surface des calottes polaires : étude du transport des gaz dans ces milieux poreux." Phd thesis, Université Joseph Fourier (Grenoble), 1997. http://tel.archives-ouvertes.fr/tel-00709566.
Full textRémy, Frédérique. "Etude des calottes polaires par altimétrie satellitaire." Toulouse 3, 1989. http://www.theses.fr/1989TOU30223.
Full textSeroussi, Hélène. "Modélisation des calottes polaires par des formulations multi-modèles." Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00697005.
Full textTestut, Laurent. "Apport de la topographie à l'étude des calottes polaires." Toulouse 3, 2000. http://www.theses.fr/2000TOU30170.
Full textBulthuis, Kevin. "Towards robust prediction of the dynamics of the Antarctic ice sheet: Uncertainty quantification of sea-level rise projections and grounding-line retreat with essential ice-sheet models." Doctoral thesis, Universite Libre de Bruxelles, 2020. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/301049.
Full textLes progrès récents effectués dans la modélisation de la dynamique de la calotte polaire de l'Antarctique ont donné lieu à un changement de paradigme vis-à-vis de la perception de la calotte polaire de l'Antarctique face au changement climatique. Une meilleure compréhension de la dynamique de la calotte polaire de l'Antarctique suggère désormais que la réponse de la calotte polaire de l'Antarctique au changement climatique sera déterminée par des mécanismes d'instabilité dans les régions marines. Tandis qu'un nouvel engouement se porte sur une meilleure compréhension de la réponse de la calotte polaire de l'Antarctique au changement climatique, un intérêt particulier se porte simultanément vers le besoin de quantifier les incertitudes sur l'évolution de la calotte polaire de l'Antarctique ainsi que de clarifier le rôle joué par les incertitudes sur le comportement de la calotte polaire de l'Antarctique en réponse au changement climatique. D'un point de vue numérique, les modèles glaciologiques dits essentiels ont récemment été développés afin de fournir des modèles numériques efficaces en temps de calcul dans le but de réaliser des simulations à grande échelle et sur le long terme de la dynamique des calottes polaires ainsi que dans l'optique de coupler le comportement des calottes polaires avec des modèles globaux du sytème terrestre. L'efficacité en temps de calcul de ces modèles glaciologiques essentiels, tels que le modèle f.ETISh (fast Elementary Thermomechanical Ice Sheet) développé à l'Université Libre de Bruxelles, repose sur une modélisation des mécanismes et des rétroactions essentiels gouvernant la thermodynamique des calottes polaires au travers de modèles d'ordre réduit et de paramétrisations. Vu l'efficacité en temps de calcul des modèles glaciologiques essentiels, l'utilisation de ces modèles en complément des méthodes du domaine de la quantification des incertitudes offrent de nombreuses opportunités afin de mener des analyses plus complètes de l'impact des incertitudes dans les modèles glaciologiques ainsi que de développer de nouvelles méthodes du domaine de la quantification des incertitudes dans le cadre de la modélisation glaciologique. Les contributions de cette thèse sont doubles. D'une part, nous contribuons à une nouvelle estimation et une nouvelle compréhension de l'impact des incertitudes sur la réponse de la calotte polaire de l'Antarctique dans les prochains siècles. D'autre part, nous contribuons au développement de nouvelles méthodes pour la quantification des incertitudes sur les caractéristiques géométriques de la réponse spatiale de modèles physiques numériques avec, comme motivation en glaciologie, un intérêt particulier vers la prédiction sous incertitudes du retrait de la région de la calotte polaire de l'Antarctique en contact avec le lit rocheux. Dans le cadre de la première contribution, nous réalisons de nouvelles projections probabilistes de la réponse de la calotte polaire de l'Antarctique au changement climatique au cours des prochains siècles à l'aide du modèle numérique f.ETISh. Nous appliquons des méthodes du domaine de la quantification des incertitudes au modèle numérique f.ETISh afin d'étudier l'impact de différentes sources d'incertitude sur la réponse continentale de la calotte polaire de l'Antarctique. Les sources d'incertitude étudiées sont relatives au forçage atmosphérique, au glissement basal, à la paramétrisation du flux à la ligne d'ancrage, au vêlage, à la fonte sous les barrières de glace, à la rhéologie des barrières de glace et à la relaxation du lit rocheux. Nous réalisons de nouvelles projections probabilistes de la contribution de la calotte polaire de l'Antarctique à l'augmentation future du niveau des mers; nous réalisons une analyse de sensibilité afin de déterminer les sources d'incertitude les plus influentes; et nous réalisons de nouvelles projections probabilistes du retrait de la région de la calotte polaire de l'Antarctique en contact avec le lit rocheux.Dans le cadre de la seconde contribution, nous étudions la quantification des incertitudes sur les caractéristiques géométriques de la réponse spatiale de modèles physiques numériques dans le cadre de la théorie des ensembles aléatoires. Dans le cadre de la théorie des ensembles aléatoires, nous développons le concept de régions de confiance qui contiennent ou bien sont inclus dans un ensemble d'excursion de la réponse spatiale du modèle numérique avec un niveau donné de probabilité. Afin d'estimer ces régions de confiance, nous proposons de formuler l'estimation de ces régions de confiance dans une famille d'ensembles paramétrés comme un problème d'estimation de quantiles d'une variable aléatoire et nous proposons une nouvelle méthode de type multifidélité pour estimer ces quantiles. Finalement, nous démontrons l'efficacité de cette nouvelle méthode dans le cadre d'une application relative au retrait de la région de la calotte polaire de l'Antarctique en contact avec le lit rocheux. En plus de ces deux contributions principales, nous contribuons à deux travaux de recherche additionnels. D'une part, nous contribuons à un travail de recherche relatif au calcul des indices de Sobol en analyse de sensibilité dans le cadre de petits ensembles de données à l'aide d'une nouvelle méthode d'apprentissage probabiliste sur des variétés géométriques. D'autre part, nous fournissons une comparaison multimodèle de différentes projections de la contribution de la calotte polaire de l'Antarctique à l'augmentation du niveau des mers.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
Lestringant, Renaud. "Etude numérique et mathématique des transitions abruptes "fort frottement - faible frottement" : application aux transitions "calottes polaires - ice shelf"." Phd thesis, Université Joseph Fourier (Grenoble), 1994. http://tel.archives-ouvertes.fr/tel-00759940.
Full textLEDROIT, MICHELE. "Observation satellitaire des calottes polaires par radar a visee laterale." Toulouse 3, 1992. http://www.theses.fr/1992TOU30350.
Full textBouhier, Nicolas. "Etude de l'impact des icebergs Antarctiques sur l'Océan Austral." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0143/document.
Full textThe Antarctic polar ice cap constrains a freshwater flaux into the Austral Ocean through two equally important pathways : a localized and immediate injection through the melting of ice-shelves bases, and a delayed offshore injection through the calving and subsequent melt of icebergs. Some studies reckon that melting icebergs have the capacity to alter the hydrological and biogeo-chemical characteristics of the water column. The numerical models trying to evaluate this impact have shown contrasting results. Yet, they might suffer from a poor representation of the icebergs, namely due to our limited knowledge on both the spatial and size distributions of the icebergs, or even the processes involved in their mass loss. A new method using satellite altimetry measurements has lead to the creation of a database mapping Antarctic icebergs distribution with an unprecedented spatial and temporal coverage. Our joint analysis between these data and sea ice concentration fields highlights a possible transport of the freshwater injected by an iceberg and its impacts on sea ice.We also analyze the links between icebergs of different sizes : the large ones can be seen as ice buffers that diffuse across the whole ocean when breaking into small fragments of various sizes. We finally study the evolution of two giant icebergs, suggest the first parametrization of the fragmentation process and analyze the subsequent size distribution of the fragments. These results can be valuable to account in a more realistic way the fresh water flux constrained by icebergs in models
Beghin, Pauline. "Interactions entre les calottes polaires et la circulation atmosphérique pendant les âges glaciaires." Thesis, Versailles-St Quentin en Yvelines, 2015. http://www.theses.fr/2015VERS003V/document.
Full textThe last glacial period is characterized by the presence of two large ice sheets covering Canada and North Eurasia. These ice sheets are a key element of the climatic system by interacting with all the components of the Earth system. The aim of this thesis is to determine by which mechanisms changes in atmospheric circulation may have induced a teleconnexionbetween the Northern hemisphere paleo-ice sheets. The use of a simplified coupled climate-ice sheet model allowed to test separately the influence of the ice-sheet topography and albedo on temperature and precipitation fields throughout the last glacial cycle and to highlight the role of atmospheric circulation within the synergy of past boreal ice sheets.To investigate in more details the underlying mechanisms, the use of a general circulation model was necessary.I therefore carried out an inter-comparisonof the PMIP3 models to examine the GCM responsesto glacial conditions. This work allowed to determinethe role of glacial conditions on the shift of the NorthAtlantic jet stream position and to establish a relationshipbetween this shift and the amount of precipitationover southern Europe. The last part of this thesisis devoted to the respective role of each ice sheeton atmospheric circulation changes observed underglacial conditions. To achieve this, I performed idealizedexperiments with the atmospheric circulationmodel LMDZ. The results highlight the key influenceof the North American ice sheet on the Eurasian icesheet surface mass balance
Beghin, Pauline. "Interactions entre les calottes polaires et la circulation atmosphérique pendant les âges glaciaires." Electronic Thesis or Diss., Versailles-St Quentin en Yvelines, 2015. http://www.theses.fr/2015VERS003V.
Full textThe last glacial period is characterized by the presence of two large ice sheets covering Canada and North Eurasia. These ice sheets are a key element of the climatic system by interacting with all the components of the Earth system. The aim of this thesis is to determine by which mechanisms changes in atmospheric circulation may have induced a teleconnexionbetween the Northern hemisphere paleo-ice sheets. The use of a simplified coupled climate-ice sheet model allowed to test separately the influence of the ice-sheet topography and albedo on temperature and precipitation fields throughout the last glacial cycle and to highlight the role of atmospheric circulation within the synergy of past boreal ice sheets.To investigate in more details the underlying mechanisms, the use of a general circulation model was necessary.I therefore carried out an inter-comparisonof the PMIP3 models to examine the GCM responsesto glacial conditions. This work allowed to determinethe role of glacial conditions on the shift of the NorthAtlantic jet stream position and to establish a relationshipbetween this shift and the amount of precipitationover southern Europe. The last part of this thesisis devoted to the respective role of each ice sheeton atmospheric circulation changes observed underglacial conditions. To achieve this, I performed idealizedexperiments with the atmospheric circulationmodel LMDZ. The results highlight the key influenceof the North American ice sheet on the Eurasian icesheet surface mass balance
Pimienta, Pierre. "Etude du comportement mécanique des glaces polycristallines aux faibles contraintes application aux glaces des calottes polaires /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37608920d.
Full textChemison, Alizée. "Impacts d'une déstabilisation des calottes polaires sur le climat et les maladies vectorielles au XXIème siècle." Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASJ007.
Full textMosquitoes, major vectors of diseases, are sensitive to rainfall which is necessary for their immature aquatic stages, and to temperature which affects their development and life cycle dynamics. Climate change can therefore impact the transmission of vector-borne diseases such as malaria, the world's major parasitic disease causing over 600,000 deaths per year, and Rift Valley Fever (RVF), a zoonotic disease decimating herds, causing health risks and catastrophic economic losses in Africa.The Intergovernmental Panel on Climate Change (IPCC) report provides climate scenarios for the 21st century with different standard greenhouse gas emission scenarios, named Representative Concentration Pathway (RCP). By 2080, the risk of malaria transmission is estimated to decrease in the Sahel region and to increase in the East African Plateau as a result of rising temperatures under the RCP8.5 scenario. Although paleoclimate studies show that melting ice sheet can induce abrupt climate change, state of the art IPCC future projections do not consider such a potential rapid destabilisation of polar ice sheets. However, the West Antarctic and Greenland ice sheet are vulnerable to climate change and even a partial melting would cause major climatic changes, even in tropical regions. No study has yet quantified the impact of an abrupt melting of the ice sheets on the distribution of malaria and RVF. This work is based on future climate numerical simulations using the coupled global climate model IPSL-CM5A-LR with RCP8.5 as radiative forcing. Simulations of freshwater release, corresponding to the accelerated and partial melting of the polar ice sheets, were carried out with different melting assumptions:- for Greenland, a freshwater flux equivalent to a global sea level rise of 0.5m, 1m, 1.5m and 3m is released into the North Atlantic;- for Antarctica, a quantity of freshwater equivalent to a global sea level rise of 3m is released off its western part.These continuous water inputs are prescribed from 2020 to 2070.This study showed that the oceanic and atmospheric impacts of a partial melting of Greenland are stronger on the global climate, and particularly on monsoons, than those associated with the melting of West Antarctica, probably due to the effect of the circumpolar current. Subsequently, only scenarios considering a partial melting of Greenland were used to study their impacts on malaria. Simulated and/or observed temperature and precipitation were used to drive mathematical models of malaria transmission risk. Five mathematical malaria models were used. An accelerated melting of Greenland leads to a southward shift of the American and African monsoons. Malaria risk increases in southern Africa, decreases in the Sahel and increases moderately on the East African Plateau.For the study of RVF, the Liverpool Rift Valley Fever (LVRF) model was validated at country scale by comparing simulations driven by observed daily temperatures and rainfall from climate reanalyses with different health data sets. Then, a potential correlation between simulated RVF transmission risk and the main regional climate variability modes (ENSO and DMI) is shown over the Rift African region. The model correctly reproduces RVF epidemics in Kenya, Somalia and Zambia, and to a lesser extent in Senegal and Mauritania. RVF risk increases over the epidemic areas in East Africa during the El Niño phenomenon
Morlighem, Mathieu. "Détermination de propriétés des glaciers polaires par modélisation numérique et télédétection." Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00697004.
Full textMangeney, Anne. "Modélisation de l'écoulement de la glace dans les calottes polaires : prise en compte d'une loi de comportement anisotrope." Phd thesis, Université Pierre et Marie Curie - Paris VI, 1996. http://tel.archives-ouvertes.fr/tel-00781625.
Full textLegresy, Benoit. "Teledetection des calottes polaires par altimetrie satellitaire : application a la climatologie et au bilan de masse de l'antarctique." Toulouse 3, 1998. http://www.theses.fr/1998TOU30054.
Full textMangeney, Anne. "Modelisation de l'ecoulement de la glace dans les calottes polaires : prise en compte d'une loi de comportement anisotrope." Paris 6, 1996. https://tel.archives-ouvertes.fr/tel-00781625.
Full textMontagnat, Rentier Maurine. "Contribution à l'étude du comportement viscoplastique des glaces des calottes polaires : modes de déformation et simulation du développement des textures." Université Joseph Fourier (Grenoble), 2001. http://www.theses.fr/2001GRE10206.
Full textDriesschaert, Emmanuelle. "Climate change over the next millennia using LOVECLIM, a new Earth system model including the polar ice sheets." Université catholique de Louvain, 2005. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-10172005-185914/.
Full textAlvarez-Solas, Jorge. "Changements abrupts et variabilité rapide dans différents contextes climatiques : une étude basée sur une stratégie de plusieurs modèles." Paris 6, 2010. http://www.theses.fr/2010PA066357.
Full textIce core data as well as marine and continental records reveal the existence of pronounced millennial time-scale variability in the Quaternary climate system. Such rapid climate variability appears to be stronger in glacial periods than during interglacials, but there is not yet a full consensus about its origin. Firstly, the Dansgaard-Oeschger events are characterized by abrupt transitions occurring in a few decades, and by a period of a few thousand years. Two types of explanation have been suggested concerning its triggering mechanism: periodic external forcing and internal oscillations in the climate system, for which ocean circulation is a likely candidate. On the other hand, six periods of extreme cooling in the Northern Hemisphere were marked by an enhanced discharge of icebergs into the North Atlantic Ocean, increasing the deposition of ice-rafted debris (known as Heinrich events). Increased sliding at the base of ice sheets as a result of basal warming has been proposed to explain the iceberg pulses, but recent observations suggest that iceberg discharge is related to a strong coupling between ice sheets, ice shelves and ocean conditions. In this work, I tried to bring new insights about the mechanisms responsible for the millennial glacial variability, more consistent with the present knowledge of the different Earth's components. This work is based on the use of a hierarchy of climate and ice-sheet models of different complexities. We used a conceptual numerical model to simulate the effect of ocean temperature on ice-shelf width, as well as the impact of the resulting changes in ice-shelf geometry on ice-stream velocities. Our results demonstrate that ocean temperature oscillations affect the basal melting of the ice shelf and will generate periodic pulses of iceberg discharge in an ice sheet with a fringing shelf. Using a state-of-the-art tri-dimensionnal ice-sheet model we also explore the conditions leading to internal oscillations of geometrically idealised ice sheets. We describe in detail the thermomechanical feedback responsible of the so-called ``binge-purge'' oscillations and we analyse the effects of ocean circulation changes on ice shelves and the dynamic implications resulting from a break-up of these ice shelves. Our studies are then focalised on the Heinrich event 1, showing a new mechanism based on the effects of a subsurface warming on the ice shelves stability. We demonstrate that such ice-shelf break-up and the subsequent ice-stream acceleration should be considered as a likely candidate to generate the icebergs surge implicated in Heinrich event 1. Leaving glacial period we finally focus on the present-day anthropically perturbed interglacial. We analyse with a fully coupled climate ice sheet model whether the shift into a warmer climate in the future could favor the occurrence of a new millennial-scale climate variability
Lombard, Alix. "Les variations actuelles du niveau de la mer : Observations et causes." Phd thesis, Université Paul Sabatier - Toulouse III, 2005. http://tel.archives-ouvertes.fr/tel-00079969.
Full textDiverses observations disponibles depuis peu nous ont permis de quantifier les contributions des divers facteurs climatiques à la hausse observée du niveau de la mer : expansion thermique de la mer due au réchauffement des océans, fonte des glaciers de montagne et des calottes polaires, apport d'eau des réservoirs continentaux. Le bilan de ces nouvelles observations nous permet d'expliquer en partie la hausse observée du niveau de la mer. En particulier, nous montrons que l'expansion thermique des océans n'explique que 25% de la hausse séculaire du niveau de la mer enregistrée par les marégraphes depuis 50 ans, tandis qu'elle contribue à la hauteur de 50% à la montée du niveau marin au cours de la dernière décennie. Parallèlement, des études récentes estiment que la fonte des glaciers de montagne et des calottes polaires pourraient contribuer pour environ 1 mm/an à l'élévation du niveau de la mer au cours de la dernière décennie.
De plus, la forte variabilité régionale des vitesses d'évolution du niveau de la mer révélée par les observations altimétriques de Topex/Poseidon résulte en grande partie de l'expansion thermique. Nous mettons également en lumière l'importante variabilité spatio-temporelle décennale de l'expansion thermique des océans au cours des 50 dernières années, qui semble dominée par les fluctuations naturelles du climat. De plus nous posons pour la première fois la question du lien qui existe entre les fluctuations décennales de l'expansion thermique des océans et la contribution climatique des eaux continentales au niveau de la mer. Enfin, une analyse préliminaire des observations gravimétriques de la mission spatiale GRACE sur les océans nous permet d'évaluer les variations saisonnières du niveau moyen de la mer liées aux variations du bilan de masse d'eau des océans.
Gillet-Chaulet, Fabien. "MODELISATION DE L'ECOULEMENT DE LA GLACE POLAIRE ANISOTROPE ET PREMIERES APPLICATIONS AU FORAGE DE DOME C." Phd thesis, 2006. http://tel.archives-ouvertes.fr/tel-00125476.
Full textL'objectif de cette étude est de construire un modèle d'écoulement pour la glace polaire anisotrope et l'évolution de sa fabrique.
Dans ce but, nous modélisons le monocristal de glace comme un matériau continu orthotrope de révolution autour de son axe c et nous le comparons à un modèle de grain à plans de glissement. La fabrique est décrite de manière continue par le tenseur d'orientation d'ordre 2 et une fonction de fermeture pour le tenseur d'orientation d'ordre 4. Par homogénéisation, en supposant des contraintes ou des vitesses de déformation uniformes, nous obtenons des solutions analytiques pour le comportement du polycristal de glace et l'évolution de sa fabrique. A partir de ces solutions, nous adoptons une loi de comportement orthotrope linéaire pour le polycristal et une équation d'évolution pour le tenseur d'orientation du second ordre. Ces équations permettent de bien reproduire les résultats du modèle auto-cohérent utilisant une description discrète de la fabrique, avec un gain important au niveau du temps de calcul et du nombre de variables nécessaires pour décrire la fabrique.
Ces équations sont implantées ensuite dans un code aux éléments finis utilisé pour simuler l'écoulement d'une calotte polaire présentant une anisotropie induite évolutive. Par des tests synthétiques, nous montrons l'influence de l'anisotropie sur l'écoulement de la calotte. Enfin, nous présentons une analyse des données de fabrique du forage de Dôme C à la lumière de notre modèle.
GAGLIARDINI, Olivier. "Simulation numérique de l'écoulement bidimensionnel de glace polaire présentant une anisotropie induite évolutive." Phd thesis, 1999. http://tel.archives-ouvertes.fr/tel-00004273.
Full textSix, Delphine. "Analyse statistique des distributions des séries de bilans de masse des glaciers alpins et des calottes polaires de l'hémisphère nord." Phd thesis, 2000. http://tel.archives-ouvertes.fr/tel-00701276.
Full textMontagnat, Maurine. "Contribution à l'étude du comportement viscoplastique des glaces des calottes polaires : modes de déformation et simulation du développement des textures." Phd thesis, 2001. http://tel.archives-ouvertes.fr/tel-00010695.
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