Turbulence in the Core

Abstract

Flows in natural systems are usually turbulent. The core of the Earth makes no exception. However, turbulence in the core departs from classical hydrodynamic turbulence because of the presence of a strong magnetic field and rotation. In this chapter, we work out how these two ingredients alter the organization of turbulence, and build plausible scenarios for turbulence in planetary cores. We recall basics of classical turbulence and review various tools that are used to study turbulence. Turbulence involves a wide range of spatial and temporal scales. Forces that dominate at a given scale become unimportant at other scales. We carefully analyse the ordering of forces in the Earth’s core at all scales. We introduce tau-ell regime diagrams, which represent how timescales tau and length scales ell are related to the various relevant physical phenomena. Using these diagrams, we investigate step by step the different turbulent regimes that can take place. Our analysis emphasizes the role of rotation in limiting magnetic dissipation.