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Postdoc on Penetrative convection: experiments on a rotating table, LPENSL & LGL-TPE, Lyon (France)

Du 1 septembre 2021 au 31 août 2023

Starting date : 01/09/2021
Duration : 2 years
Site actualite
Laboratoire de Physique, ENS de Lyon / CNRS
Laboratoire de Géologie de Lyon, U. Claude Bernard Lyon 
Contacts :
podier@ens-lyon.fr
thierry.alboussiere@ens-lyon.fr
stephane.labrosse@ens-lyon.fr

The LIO Laboratory of Excellence (LabEx) proposes a 2-year post-doctoral position on "Penetrative convection: experiments on a rotating table". Research fields : Fluid dynamics - Geophysics - Convection

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Recruitment 2021 LIO postdoctoral position « Penetrative convection: experiments on a rotating table »

JOB DESCRIPTION

[Link to the original job offer] 

The LIO Laboratory of Excellence (LabEx) proposes a 2-year post-doctoral position.

Starting date: September the 1st, 2021

The net salary (+social benefits) will depend on experience. A €3,000 annual package for travels and equipment will be allotted.

Research field(s)

Fluid dynamics - Geophysics - Convection

Supervisor and contact

Name: Philippe Odier
Laboratory: Laboratoire de Physique, ENS de Lyon, 46 allée d’Italie, 69007 Lyon Phone number: (+33) 6 37 20 61 52
Email: 
podier@ens-lyon.fr

Name: Thierry Alboussière
Laboratory: Laboratoire de Géologie de Lyon, U. Claude Bernard Lyon 1, Bâtiment Géode, 2 rue Raphael Dubois, 69622 Villeurbanne
Phone number: (+33) 6 28 06 37 71
Email: 
thierry.alboussiere@ens-lyon.fr

Name: Stéphane Labrosse
Laboratory: Laboratoire de Géologie, ENS de Lyon, 46 allée d’Italie, 69007 Lyon Phone number: (+33) 6 20 28 20 66
Email: 
stephane.labrosse@ens-lyon.frpage1image35225792 page1image35239616 

WORKING ENVIRONMENT

Job location and description

One part of the work will take place (especially at the beginning) at the Laboratoire de Géolo- gie de Lyon, on the University Campus of Lyon I. The experimental setup will be assembled and tested in the fluid laboratory, and reference experiments, without rotation, will be run. Other parts of the work will take place at the Laboratoire de Physique of Ecole Normale Su- périeure de Lyon, where a rotating platform will be available for the measurements in a rotat- ing frame.

More details on the job description are available in the scientific project attached.

Team

Philippe Odier belongs to the team “Waves, Flows and Fluctuation” of the Laboratoire de Phy- sique. His research subjects involve internal waves, stratified mixing, as well as aerodynamics of cycling. He is currently supervising one post-doc.

Sylvain Joubaud, belonging to the same team, will also take part in the project and he is cur- rently supervising one Ph-D student.

Thierry Alboussière (DR CNRS), from the Laboratoire de Géologie de Lyon, is involved in fluid mechanics, phase change and dynamo processes associated with planetary interiors. He is the co-supervisor of one PhD-student.

Stéphane Labrosse, also part of the Laboratoire de Géologie, is working on the dynamics of planetary interiors and their long term evolution. He is currently supervising two Phd students.

Allocated resources (technical facilites, computing...)

The project will use the rotating platform PERPET, located at the Laboratoire de Physique, as well as the computing resources of the “Pôle Scientifique de Modélisation Numérique” for data analysis, allowing fast computing for CPU consuming data processing such as PIV anal- ysis.

Recent publications of the team

[1] S. Boury, P. Odier, and T. Peacock. Axisymmetric internal wave transmission and resonant interference in nonlinear strat- ifications. J. Fluid Mech., 886:A8, 2020.

[2] S. Boury, R. S. Pickart, P. Odier, P. Lin, M. Li, E. C. Fine, H. L. Simmons, J. A. MacKinnon, and T. Peacock. Whither the Chukchi Slope Current? Journal of Physical Oceanography, 50(6):1717–1732, 2020.

[3] P. Husseini, D. Varma, T. Dauxois, S. Joubaud, P. Odier, and M. Mathur. Experimental study on superharmonic wave generation by resonant interaction between internal wave modes. Phys. Rev. Fluids, 5(7), 2020.

[4] E. Horne, F. Beckebanze, D. Micard, P. Odier, L. R. M. Maas, and S. Joubaud. Particle transport induced by internal wave beam streaming in lateral boundary layers. J. Fluid Mech., 870:848–869, 2019.

[5] T. Dauxois, S. Joubaud, P. Odier, and A. Venaille. Instabilities of Internal Gravity Wave Beams. In Davis, SH and Moin, P, editor, Ann. Rev. of Fluid Mech., volume 50 of Annual Review of Fluid Mechanics, pages 131–156. 2018.

[6] Agrusta, R., Morison, A., Labrosse, S., Deguen, R., Alboussière, T., Tackley, P. J., and Dubuffet, F. Mantle convection interacting with magma oceans. Geophys. J. Int., 220:1878–1892, 2019.

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[7] Bouffard, M., Choblet, G., Labrosse, S., and Wicht, J. Chemical convection and stratification in the Earth's outer core. Frontiers in Earth Science, 7:99, 2019.

[8] Morison, A., Labrosse, S., Deguen, R., and Alboussière, T. Timescale of overturn in a magma ocean cumulate. Earth Planet. Sci. Lett., 516:25 – 36, 2019.

[9] Deguen, R., Alboussière, T., and Labrosse, S. Double-diffusive translation of Earth's inner core. Geophys. J. Int., 214:88- 107, 2018.

[10] Labrosse, S., Morison, A., Deguen, R., and Alboussière, T. Rayleigh-Bénard convection in a creeping solid with a phase change at either or both horizontal boundaries. J. Fluid Mech., 846:5–36, 2018.

[11] F. Plunian and T. Alboussière, Axisymmetric dynamo action is possible with anisotropic conductivity, Physical Review Research 2, 013321 (2020)

[12] T. Alboussière, K. Drif and F. Plunian, Dynamo action in sliding plates of anisotropic electrical conductivity, Physical Review E, 101, 033107 (2020)

[13] J. Curbelo, L. Duarte, T. Alboussière, F. Dubuffet, S. Labrosse and Y. Ricard, Numerical solutions of compressible con- vection with an infinite Prandtl number: comparison of the anelastic and anelastic liquid models with the exact equations, Journal of Fluid Mechanics, 873, pp. 646–687 (2019)

[14] R. Menaut, Y. Corre, L. Huguet, T. Le Reun, T. Alboussière, M. Bergman, R. Deguen, S. Labrosse and M. Moulin, Ex- perimental study of convection in the compressible regime, Phys. Rev. Fluids, 4: 3, 033502 (2019)

[15] L. Huguet, H. Amit and T. Alboussière, Geomagnetic Dipole Changes and Upwelling/Downwelling at the Top of the Earth’s Core, Frontiers in Earth Science, 6:170, (2018)

Description of LabEx LIO

In 2011, The Lyon Institute of Origins LabEx was selected following the first “Laboratory of Excellence” call for projects, part of the “Investissement d’Avenir” program for forward-look- ing research. It is one of 12 LabExes supported by the University of Lyon community of uni- versities and establishments (COMUE). LIO brings together more than 200 elite researchers recruited throughout the word and forming 18 research teams from four laboratories in the Rhône-Alps region, all leaders in their fields, under the auspices of the University Claude Ber- nard Lyon 1 (UCBL), the Ecole Normale Supérieure de Lyon, and the CNRS. LIO’s goal is to explore questions about our origins, operating in a broad field of study that ranges from particle physics to geophysics, and includes cosmology, astrophysics, planetology and life.

SELECTION PROCESS

Qualifications / Skills / Education & Research requirements

The ideal candidate must hold a PhD in Physics or Geophysics and have skills in experimental measurements for fluid dynamics, data analysis, physical modelling of geophysical phenom- ena. Skills in numerical modeling of fluid dynamics will also be considered as a welcome ad- dition.

Application deadline : January 31st, 2021 Requested documents for application

Applicants must email a CV, a statement of interest, a letter of recommendation and con- tact details for 2-3 references to thierry.alboussiere@ens-lyon.fr before January 31st, 2021.

Candidates on the short list will be informed by mid February. They will be interviewed in the second half of February.

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Penetrative convection: experiments on a rotating table

112 Thierry Alboussière , Stéphane Labrosse , Philippe Odier

The concept of penetrative convection has been identified to play a role in various astrophysical and geo- physical contexts. On Earth, a typical example of penetrative convection consists in the interaction between the convective troposphere and the stably stratified upper atmosphere. Another occurrence of penetrative convection is related to the dynamics of the interior of the Earth. The core is known to be in a convective state, vigorous enough to sustain the Earth's magnetic field by dynamo action. However, there could be a stably stratified layer at the top of the core that may have been there since the origin of the Earth. Seismology does not bring a definite answer, with a few researchers claiming that seismic velocities are slightly slower than expected in a well-mixed core in the top 100~km or less of the core. Others argue that crystallization of the inner core or exsolution within the core should bring light elements to the top of the core. It has also been argued that the secular cooling of the Earth should allow light elements of the lower mantle to be incorporated in the top of the core. Finally, current estimates of the thermal conductivity of the core would lead to an excessive heat flux out of the core for a fully convective core.

Experimental studies can help answer key questions relative to penetrative convection. In the last example above, it is important to determine what kind of motion can exist in a potentially stable layer. This top layer, and its dynamics, are linked to the magnetic observations. The picture from the observations is rather blurred and restricted to large scales, but can be used to discriminate between flow models. The experimental task is made more difficult due to the large effect of Coriolis forces in the core. Compared to the ocean or atmosphere, Coriolis forces are much stronger because the typical velocities -- 10-4 m/s -- are much smaller. The config- uration creates a rich environment in terms of physical processes: convection, gravity waves due to the stable stratification and inertial waves from rotation. Our mixed group of geophysicists and physicists is particularly expert in these phenomena.

Some experimental results can be found in the literature, but very few have been carried out in a rotating frame. In the phys- ics laboratory, we have a rotating table (2 m diameter, 60 rpm maximum) which can host an experimental setup devoted to penetrative convection. We have actually already been running preliminary experiments, showing that measurements are pos- sible and will bring interesting results. The setup will use the peculiar property of liquid water between 0°C and 4°C where it has a negative thermal expansion coefficient. Maintaining the bottom of a water tank at 0°C and the top at 25°C generates a lower convective region (between 0°C and 4°C) while the upper part is stably stratified. The measurements consist in simultane- ous velocimetry (PIV) and temperature (LIF) measurements on various plane laser sheets. Moving continuously the measure- ment planes will allow us to extract a 3D picture of the flow. The post-doctoral researcher will participate in the setup and testing of the experimental rig. She or he will perform measure- ments and extract velocity and temperature fields and use the results in the geophysical context, bringing expertise in the in- terpretation of geomagnetic data concerning the top of the Earth's core. She or he will have a PhD in fluid mechanics, po- tentially gravity or inertial waves, and experience, or a keen in- terest, in the dynamics of the Earth. She or he will interact with members of the physics laboratory and members of the geology laboratory.

1 : Laboratoire de Géologie de Lyon
2 : Laboratoire de Physique – ENS de Lyon

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IllustrationSchlieren image of convection in water, cooled from below at 0°C, in a 15 rpm rotating frame of reference. Elongated convective cells (bottom) interact with a nearly motionless fluid layer (top).