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PhD in modelisation of the ice-sheet dynamic

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Français - Anglais

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General information

Reference : UMR5001-BERBOE-007
Workplace : ST MARTIN D HERES
Date of publication : Monday, May 18, 2020
Scientific Responsible name : Fabien GILLET-CHAULET
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2020
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

The sea level rise observed in recent decades is caused by current global warming. The main contributions are the thermal expansion of the oceans, the melting of the world's glaciers and the Greenland and Antarctic ice caps. More specifically, the ice sheets, which have generally been in equilibrium for several millennia, are contributing more rapidly and more strongly to the rise in sea levels than was anticipated only 20 years ago. This major change in the dynamics of the ice sheets remains the main source of uncertainty on future sea level evolution, particularly because the processes controlling the flow of the glaciers remain poorly understood and not well constrained in numerical models.
In recent years, a new era of space-based observation of ice caps has begun, making it possible today to go beyond existing limitations and, in particular, to examine in greater detail the seasonal dynamic changes that are particularly marked for Greenland glaciers.
Model projections are sensitive to the initial state used. To reduce the uncertainties in the projections, many models, including Elmer/Ice, include variational data assimilation (DA) methods and thus derive poorly constrained parameters (usually basal friction) from surface velocity observations. Capturing actual changes (i.e. not initializing the model over a single initial time/state) requires the development of transient assimilation methods where observations are assimilated at the appropriate time. Thus a Kalman filter has recently been coupled to Elmer/Ice and the first applications on synthetic cases show encouraging results (Gillet-Chaulet 2020).
Taking advantage of the opportunity offered by these new satellites and these new numerical developments, this thesis would aim to set up and evaluate realistic ensemble simulation and data assimilation methods in order to reproduce the observed evolution of some greenlandic glaciers over the last decades.

More specifically, the first objectives of this thesis will therefore be to :

- Set up operational configurations for some greenlandic glaciers, define the grid and the initial thermodynamic state. The results will be compared to the reference configurations developed for Elmer/Ice-sheet, and we will evaluate the uncertainty due to the physics under-resolved in the large-scale simulations.

- Develop ensemble data assimilation methods to assimilate observations of surface velocity and geometric changes. The development of model initialization strategies that correctly reproduce the dynamic mass losses of ice caps observed over the last decades requires the development of transient assimilation frameworks capable of taking into account the increasing availability of dense time series, especially from space observations.

- Develop automatic post-processing tools to measure and visualize the performance of the whole model. These tools will compute different measurements to assess the model accuracy and reliability of the whole. This step is necessary to better integrate the observations into the model, prepare and evaluate the benefits of assimilation.

Rigorous evaluation of the model results will allow a better assessment of the performance of the current model parameterizations and the main source of uncertainties in the mass balance estimates.

The selected student should have a Master's degree with an initial training related to numerical modelling and/or data assimilation, preferably with applications related to geophysics.

During his/her thesis, he/she will have to apply his/her knowledge of numerical methods for the advanced use and development of a numerical model of ice flow.

He/she will have a sufficient level of English to follow the literature and present his/her work in international conferences and scientific publications.

Work Context

The Institute for Environmental Geosciences (IGE) is a French public research laboratory under the supervision of CNRS/INSU, IRD, the University of Grenoble Alpes (UGA) and Grenoble-INP.
It brings together about 250 people, including 150 permanent members (researcher, faculty, engineer) and about a hundred contractual agents (doctoral students, post-doctoral researchers, engineers and technicians). The laboratory also welcomes several dozen trainees and scientific visitors every year. The laboratory is located on three sites of the Grenoble University Campus (GLACIOLOGY, OSUG-B and Bergès sites).
The IGE is one of the main laboratories of the Observatoire des Sciences de l'Univers de Grenoble (OSUG) which is a federative structure of the INSU.

The thesis student will carry out his mission within the CryoDyn team of the IGE and will be placed under the responsibility of Fabien GILLET-CHAULET and Jérémie MOUGINOT. The proposed contract is part of the ANR SOSIce young researcher led by Jérémie MOUGINOT, but will also be supported by several other projects carried out by the team (ANRs MAGIC, EIS, EU PROTECT project).
Technical supervision will be provided on a daily basis by F. Gillet-Chaulet for glacial modelling and data assimilation and by J. Mouginot for processing and analysis of remote sensing data.

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