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Home > News > Seminar > Seminar 2019

Mardi 5 novembre 2019 à 11h00 en amphi K118

Louis-Alexandre Couston, British Antarctic Survey, Cambridge, UK

Titre/Title : Direct numerical simulations of turbulence for geophysical applications

Contact : Pierre Augier (équipe MEIGE)

Résumé/Abstract : Energy transfers from small-scale turbulence and waves to large-scale flows are ubiquituous in oceans, atmospheres, planetary cores and stars. Therefore, turbulence and waves have a direct effect on the large-scale organization of geo/astrophysical fluids and affect their long-term dynamics. In this talk I will discuss recent direct numerical simulation (DNS) results of two upscale energy transfer mechanisms that emerge from the dynamics of a fluid that is self-organized in a turbulent layer next to a stably-stratified one. The self-organization in a ”two-layer” turbulent-stratified system is common in nature and is representative of e.g. Earth’s troposphere-stratosphere system, the oceans’ surface mixed layer-thermocline system, and stars’ convective-radiative interiors. The first set of DNS results will demonstrate how turbulent motions can generate internal waves,which then force a slowly-reversing large-scale flow, akin to Earth’s Quasi-Biennial Oscillation (QBO). The second set of DNS results will show how the stratified layer regulates the emergence of large-scale vortices (LSV) in the turbulent layer under rapid rotation in the regime known as geostrophic turbulence. I will demonstrate why it is important to resolve both the turbulence and the waves, as otherwise the natural variability of the QBO is lost and LSV cannot form. I will discuss future works and highlight how the results may change the implementation of upscale energy transfers in global earth system models.