Postdoc position (H/F): Modelling land–atmosphere interactions in the context of surface heterogeneities


Modelling the interactions between the atmosphere and a horizontally heterogeneous land surface is a key challenge for present day weather and climate models. These heterogeneities are ubiquitous over continental areas, part of them occurring at the sub-grid scale of these models. They significantly impact the surface fluxes of energy, matter, and momentum, critical from the atmospheric boundary layer to the whole climate system. Various strategies to account for them within weather and climate models have been developed and include the “parameter-aggregation” and “flux-aggregation”/“mosaic” approaches (see de Vrese et al. 2016 and references therein for more discussion on these approaches). In general, their implementation within models assumes a horizontally uniform atmosphere above the surface layer. However, many observational and modelling studies suggest that such an assumption is erroneous, as the surface heterogeneities extend vertically in the atmosphere, generally far above the surface layer, at least under certain conditions. Only a few studies have assessed the impact of not representing more explicitly (or more adequately) such effects on the boundary layer and the associated feedbacks it may have on the land-atmosphere coupling. Molod et al. (2003, 2004) developed a vertically-extended mosaic approach, tested it in a global atmospheric model and found large impacts on the simulated climate. More recently, de Vrese et al. (2016) proposed a similar framework but including the potential effect of mesoscale circulations generated by the surface heterogeneities.

The objective of the present postdoctoral fellowship is to (1) further develop such approaches, in the context of the ARPEGE-Climat atmospheric model (Roehrig et al. 2020) coupled to the ISBA land surface model (Decharme et al. 2019), both models being developed at the Centre National de Recherches Météorologiques (CNRM), and (2) thereby assess the impact of surface heterogeneities on the land-atmosphere coupling and the simulated climate.

Decharme, B., Delire, C., Minvielle, M., Colin, J., Vergnes, J.-P., Alias, A., Saint-Martin, D., Séférian, R., Sénési, S., and Voldoire, A. (2019). Recent Changes in the ISBA-CTRIP Land Surface System for Use in the CNRM-CM6 Climate Model and in Global Off-Line Hydrological Applications. Journal of Advances in Modeling Earth Systems, 11(5), 1207–1252.
Molod, A., Salmun, H., and Waugh, D. W. (2003). A new look at modeling surface heterogeneity: Extending its influence in the vertical. Journal of Hydrometeorology, 4(5), 810–825.
Molod, A., Salmun, H., & Waugh, D. W. (2004). The Impact on a GCM Climate of an Extended Mosaic Technique for the Land–Atmosphere Coupling, Journal of Climate, 17(20), 3877–3891.
de Vrese, P., Schulz, J.-P., and Hagemann, S. (2016). On the representation of heterogeneity in land-surface–atmosphere coupling. Boundary-Layer Meteorology, 160(1), 157–183.
Roehrig, R., Beau, I., Saint-Martin, D., Alias, A., Decharme, B., Guérémy, J.-F., Voldoire, A., Abdel-Lathif, A. Y., Bazile, E., Belamari, S., Blein, S., Bouniol, D., Bouteloup, Y., Cattiaux, J., Chauvin, F., Chevallier, M., Colin, J., Douville, H., Marquet, P., Michou, M., Nabat, P., Oudar, T., Peyrillé, P., Piriou, J.-M., Salas y Mélia, D., Séférian, R., and Sénési, S. (2020). The CNRM Global Atmosphere Model ARPEGE-Climat 6.3: Description and Evaluation. Journal of Advances in Modeling Earth Systems, 12(7), e2020MS002075.


The ARPEGE-Climat/ISBA climate model makes use of the mosaic approach to represent the land-atmosphere coupling. The successful applicant will thus develop a novel approach to extend the mosaic framework to include the atmosphere boundary layer (and possibly more), implement it in the ARPEGE-Climat/ISBA model, and examine its impact on the simulated climate.

He/she will also interact with other scientists involved in the MOSAI project, either in CNRM or outside, to take benefit of other activities within the project to validate or evaluate his/her developments (e.g., large-eddy simulations with a heterogenous land surface, intense observing periods conducted at the project sites).

Scientific communication, both during international conferences and within peer-reviewed journals is also expected.


Eligible applicants should have a Ph.D. in atmospheric sciences obtained before the starting date of the contract. Expertise in modelling atmospheric processes (especially turbulence) or land-atmosphere interactions will be much appreciated.

Skills in Unix environment and programming languages (e.g., Fortran, Python) are also expected.

A good command of English is also critical, as it is expected from the successful applicant to present his/her results at international conferences and publish them in peer-rewieved journals.

The applicants should demonstrate their ability to conduct research in a rather autonomous manner, with respect to both scientific and technical aspects.

Work Context

The CNRM is a joint laboratory of Météo-France and the Centre National de la Recherche Scientifique (CNRS), which has recognized expertise in modelling the various components of the climate system, for both weather forecast and climate prediction applications. The CNRM also continuously develops expertise in the observations and understanding of physical processes occurring within the different components of the climate system, or at their interface. The successful applicant will be contracted by the CNRS and will be working at the CNRM, in Toulouse, within the climate group. He/she will work in close collaboration with the ARPEGE-Climat and ISBA development teams.

The present fellowship is funded by the 4-year MOSAI project, which started in April 2021. The project aims at obtaining an accurate assessment of the land-atmosphere exchanges at all scales, crucial to better understand the global climate engine and its modelling. Three main scientific questions motivate the MOSAI project: (1) Are the simulations of the land-atmosphere exchanges fairly evaluated with local observations? (2) Can we propose new methodologies for the observation-model comparison? (3) Could the land-atmosphere coupling be improved in models? The combination of new observations collected at three permanent instrumented sites and a wide suite of models from large-eddy simulations to climate models are used to address these questions.

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