Research Interests

My research interests lie mainly in Geophysical Fluid Dynamics. I try to combine theoretical approaches, numerical simulations and observations to better understand phenomena that matter for atmospheric circulation, typically on mesoscales, tens to hundreds of kilometers. My main areas of interest are gravity waves, the Upper Troposphere Lower Stratosphere (UTLS) region, cirrus clouds, and atmosphere-ocean interactions on small scales.

Gravity Waves

Satellite image of a gravity wave made visible in a deck of
clouds. Internal gravity waves are waves occuring in the interior of a stratified fluid, the restoring force being due to buoyancy. These waves are typically small-scale features of the flow (10-1000km in the horizontal). A lot can be understood of atmospheric and oceanic dynamics without taking them into account (i.e. using balanced approximations such as the quasi-geostrophic on). Yet, there are aspects of both atmospheric and oceanic circulations which can not be understood without considering gravity waves (e.g. the circulation of the middle atmosphere and in particuar the mesosphere, the energy budget in the ocean). At present, one essential challenge is to understand and quantify the sources of these waves, in order to be able to parameterize them in global models.

The above satellite picture comes from Nasa's Planetary Photojournal. As in this example, gravity waves are sometimes visible thanks to clouds, when water vapor saturates in the regions where air is ascending due to the gravity wave present.

Ocean-Atmosphere interactions

As satellite observations allow a more global and more detailled outlook on oceanic Sea-Surface Temperatures (SST) and surface winds, it has come out that there were striking correlations at small scales (of the order of 100 km) between variations of SST and surface winds. The mechanisms are partially understood, but many issues remain. In particular, the impacts for the free troposphere, the importance of this connection, and the presence of similar correlations at yet shorter scales remain issues of active research.

Other themes

Below are some other themes I have worked or still work on, rather i intermittently for the first, more systematically for the last.

Symmetric and inertial instability

In the study of the geostrophic adjustment of jets, we have underlined the key role of anticyclonic regions for trapping inertia-gravity waves with frequencies lower than the inertial frequency. Inertial instability appears as the unstable counterpart of these subinertial waves when the anticyconic vorticity becomes lower than -f. This instability, its selection of a vertical scale, its nonlinear saturation and its impacts for mixing are not yet fully understood.

Cheese fondue

The proper combination of cheeses to use for a cheese fondue remains a matter of heatedd debates: emmenthal, comte, beaufort, appenzeller, gruyere, abondance are of course all on the list, but are they all necessary? In which proportions? The choice of the wine and the addition of Kirsch are also a subject of numerous experiments, and for which theory is still lacking. Finally, the status of alternative fondues, involving cheeses like goat, roquefort or munster, or using milk instead of white wine (for pregnant and breastfeeding mothers) are further subjets of investigation.