Dresden 2017 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 16: Focus: Fundamental aspects of turbulent convection

DY 16.2: Vortrag

Dienstag, 21. März 2017, 10:00–10:15, ZEU 118

Turbulent convection in planetary interiors — •Ulrich Hansen and Claudia Stein — Institut für Geophysik, Unii Münster, Correnstrasse 24, 48149 MuensterGermany

The dynamics of planetary mantles is largely governed by convection. The Earth's mantle for example, extends from 100 km to about 3000 km depth and consists mostly of silicate rocks. Phenomena like plate tectonics and hot-spot volcanism are intimately coupled to processes within the boundary layers of the convective system. Due to the high viscosity of the material, mantle convection is characterized by a virtually infinite Prandtl number, i.e. mechanical inertia is unimportant for the flow. At the same time the Rayleigh number is high ( Ra > 107) , such that thermal advection dominates by far the transport of heat. Under such conditions numerical experiments reveal typical features of turbulent convection. For constant material properties a large scale flow (l.s.c) typically evolves, stipulated with instabilities of smaller scales. These instabilities develop within the thermal boundary layer of the l.s.c. and their interaction with the large scale wind give rise to chaotic fluctuations. In particular, we observe reversals of the l..s.c. without any external triggering Since the experiments are performed under stress free conditions, also counter-flows can be excluded to trigger the reversals. In planetary interiors non-Boussinesq effects complicate the dynamics, especially the strong dependence of the viscosity on temperature.At large viscosity contrasts a viscous lid self consistently develops, which overlies a region of turbulent convection.