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MEIGE team

Head: HURTHER David

The MEIGE team, Modeling, Experiments and Instrumentation for Geophysics and the Environment, brings together all of LEGI’s research activities related to flows in natural environments: ocean, atmosphere, coastline. The research conducted within the team focuses on describing, understanding and modeling the dynamics of these environments at small scales. This approach combines physical modeling approaches in the laboratory, in-situ measurement campaigns and theoretical and numerical modeling approaches. A major effort is also being made to develop measurement and analysis tools within the team, for example with the image analysis software (UVMAT), an acoustic profiler for measuring speed and concentration. sediment (ACVP) or Laser Induced Fluorescence (LIF) temperature measurement. These tools are essential for observing and understanding small-scale processes in laboratory experiments and possibly during in-situ measurement campaigns.

The research activities of the team can be grouped according to the following three themes:

- Boundary Layer processes and turbulence in geophysics

-  Gravity waves : internal waves and waves in the nearshore

-  Environnemental engineering

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Researchers in the team use many experimental facilities. At the European level, the team is involved in the Hydralab+ and EuHIT projects (ACCESS and JRAs COMPLEX and FREE programs http://hydralab.cnrs.fr/) and at regional level, the team co-operates with IRSTEA Lyon and LMFA (Lyon), the ECOUFLU meetings on the physical processes related to free surface flows .

The numerical modeling activity is based on local, regional (GRICAD) and national resources (GENCI : IDRIS, CINES, TGCC). Numerical models developed/used by the team are presented here

The MEIGE team mainly develop researches on physical processes in geophysical flows with applications to:

- Ocean

The exact determination of the temperature and salinity distribution in
the ocean and their time evolution is essential
for the determination of the ocean dynamics on all spatial and temporal
scales, as it is for the climate dynamics.
Thermo-haline fronts are usually associated to strong and unstable
currents or meso-scale eddies, are due to the formation of mixed layers
by air-sea exchanges or the vertical exchanges of water masses.
Generation of inertio-gravity waves, due to tidal motion or
spontaneously by the eddy dynamics, leading to vertical mixing, play an
important role.

- Coastal zone

The physic of coastal zone is focused on the understanding of the multi-scale processes at work from the sand grain scale (few hundreds of microns) to geomorphological scales (few hundreds of meters). These processes are mostly linked with sediment transport arising from waves and currents.

The coastline, of a few hundreds of meters wide, is mainly submitted to the waves forcing (or surface gravity waves) from the shoaling to the swash zones including the surf zone. This last zone is marked by the intense energy dissipation induced by wave breaking and the shallow water conditions induce a confinment of the turbulent and sedimentary processes in the water column and in the near bed region (ripples, sheet-flow, …), respectively. These shallow water flows forced by the wave breaking are also characterised by a mean circulation with vertical vorticity organised at the surf zone scale (of order hundreds of meters) that interacts with the bathymetry (crescentic bars, crosshore bar, …).

- Atmosphere

Fluid dynamical processes are at the heart of the dynamics of the Earth atmosphere, from the motions at large scales of the anticyclones that govern our day to day wheather forecast to the motion at small scales of our living envrionment. Global temperature changes, devasting tropical cyclones, and the effects of pollution induced by the increasing population density have brought with them an increasing demand on geophysical fluid dynamics modelers.

On the small scales, this modeling implies knowledge of the mixing of pollutants in stratified fluids, such as may occur in the relatively cold air drafts descending from mountains in populated areas. Questions have to be answered. What is the condition of the air we live in and respire?

Midlattitude cyclones and anticyclones depend on the instability of fronts, but how do their occurrence change with climate. Cyclones are large propagating vortices. What are their dynamics, in which direction do they move in the atmosphere of our rotating Earth?

Planetary atmospheres such as jupiter show a particular zonal ciruclation. Where does it come from, and could we see it on our own planet?

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