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Keywords
Fluid mechanics, Atmospheres, Exoplanets, Simulations
Profile and skills required
Skills and interest in fluid mechanics, atmospheric modelling, and numerical simulations. Computer skills in a language used in scientific computing (Python, Julia, C++, Fortran, etc.).
Project description
The atmospheric thermal tide in the periodic perturbation resulting from the heating of the atmosphere by the incident stellar flux, which varies between the day and night sides. This perturbation takes the form of oscillations of the fields describing the state of the atmosphere (temperature, pressure, density, winds, etc.) in the vicinity of state of equilibrium. It is accompanied with a global mass redistribution, which induces a tidal torque and, consequently, changes in the planet’s rotation on large time scales. Atmospheric thermal tides can act on rotation in the opposite way to gravitational tides, making them capable of keeping a planet out of synchronous rotation, as demonstrated in the case of Venus (Correia & Laskar 2001).
With a few rare exceptions (Leconte et al. 2015, Auclair-Desrotour et al. 2019, Wu et al. 2023), the effects of thermal tides on the rotation of planets has so far been studied mainly using classical tidal theory (e.g. Lindzen & Chapman 1969), which provides closed-form solutions, but at the cost of numerous simplifications. These limitations mean that we also need to carry out numerical studies that approach the phenomenon in all its complexity.
In this thesis, we will seek to characterise the atmospheric thermal tide and constrain the associated torque using the general circulation model (GCM) of the Laboratoire de Météorologie Dynamique (LMD), which solves the 3D primitive equations of atmospheric dynamics using the finite volume method. The starting point will be Earth-like planets, with the parameter space to be explored more widely in a second phase.
The thesis could focus on studying the sensitivity of the atmospheric thermal tide to various key parameters, such as surface pressure, stellar irradiation, atmospheric mixture, and the topography of the solid surface. It will be possible to examine the differences or similarities between obliquity and eccentricity thermal tides, whose effect on rotation remains unconstrained, and semidiurnal tides, which have already been the subject of several studies. One could also characterise the tidal response of specific extrasolar planets, such as the rocky planets of the TRAPPIST-1 system, and thus give a ruling on the existence of possible asynchronous states maintained by the thermal tide.
This subject deals with a general problem that opens the door a broad diversity of possible research lines. It is based on recent advances obtained for the Earth using the analytical approach (Farhat et al. 2024, in press), and could lead to new reference prescriptions for introducing atmospheric thermal tides into models of planetary evolution.
Topics
Theoretical astrophysics, Fluid mechanics, Atmospheres, Terrestrial planets, Numerical methods.
Purpose and context
The aim of the work is to obtain constraints on the various effects of atmospheric thermal tides, which have an impact on the evolution of planetary systems, the rotation of planets, and their climate. The main quantities to be quantified are the tidal torque exerted by the star on the planet, the dissipated energy, and the associated heating.
Several missions, including the James Webb Space Telescope (JWST), provide access to numerous observations of rocky planets close to Earth in terms of size, mass, and surface conditions. These observations allow for better characterising the nature of these bodies and potentially inferring signatures of tidal effects.
In addition, barometric measurements from meteorological stations provide an abundance of observational constraints for Earth’s thermal tides that can be used to validate model predictions.
Methods
Numerical methods, numerical simulations.
Expected results
Constraints on the tidal torque, dissipated energy, and heating for rocky planets of various features. Analysis of the associated tidal perturbation.
Clarification of framework
PhD thesis carried out at IMCCE (Paris), main supervision by P. Auclair-Desrotour, and co-supervision by J. Laskar and G. Boué. Regular meetings, at a frequency to be defined with the student (weekly for example).
Scientific material conditions (specific safety conditions) and financial conditions of the research project
No specific safety conditions. Funding for equipment and missions from the Astronomy and Dynamical Systems (ASD) team at IMCCE.
Objectives for promoting the doctoral student’s research work: dissemination, publication and confidentiality, intellectual property rights, etc.
Dissemination of research results in peer-reviewed journals, scientific conferences and seminars. On-line publication of the tools developed (analysis codes for numerical solutions) possible and desirable.
Planned collaborations
Collaboration with M. Farhat (IMCCE) on the theory of thermal tides, and with B. Charnay (LESIA), G. Avice (IPGP) and G. Le Hir (IPGP) on the modelling of planetary atmospheres.
International
No foreign partnerships.
References
- Lindzen R., Chapman S., 1969, Space Science Reviews, 10, 1 ;
- Correia A. C. M., Laskar J., 2001, Nature, 411, 6839 ;
- Covey C., Dai A., Marsh D., Lindzen R., 2011, Journal of the Atmospheric Sciences, 68, 3 ;
- Covey C., Dai A., Lindzen R., Marsh D., 2014, Journal of the Atmospheric Sciences, 71, 6 ;
- Schindelegger M., Ray R., 2014, Monthly Weather Review, 142, 12 ;
- Leconte J., Wu H., Menou K., Murray N., 2015, Science, 347, 6222 ;
- Auclair-Desrotour P., Leconte J., Mergny C., 2019, Astronomy & Astrophysics, 624, A17 ;
- Wu H., Murray N., Menou K., Lee C., Leconte J., 2023, Science Advances, 9, 27 ;
- Farhat M., Auclair-Desrotour P., Boué G. Deitrick R., Laskar J., 2024, Astronomy & Astrophysics, arXiv:2309.11946.