Statistical Physics of Large-scale Flow Generation in Geophysical Turbulence
| Quand ? |
Le 02/10/2017, de 11:00 à 12:00 |
|---|---|
| Où ? | Amphi.Schrödinger |
| Participants |
Corentin Herbert |
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The behavior of a turbulent flow strongly depends on whether it lives on a 2D surface or in a 3D volume. Geophysical flows, which are among the most turbulent flows in nature, lie somewhere in between these two cases. In particular, due to the effect of rotation and density stratification, they exhibit spontaneous formation of large-scale coherent structures, just like 2D flows. Understanding these large-scale structures is crucial for atmospheric and oceanic dynamics. In this talk, I will give examples of questions of practical interest for geophysical fluid dynamics, and also show that this phenomenon is interesting from a theoretical point of view: Indeed, it allows for developing statistical theories, which have no equivalent in the classical framework of homogeneous isotropic turbulence. In particular, we shall see that geophysical flows have non-trivial equilibrium states, and that their non-equilibrium behavior can be approached by perturbative methods due to the appearance of a timescale separation regime. Under certain circumstances, this allows us to obtain explicit formulae for quantities such as the mean-flow and the Reynolds tensor, which is very rare in turbulence. Finally, I will discuss the long term dynamics of large-scale geophysical flows and the abrupt transitions they undergo, using tools from large deviation theory.