Effects of Density Stratification on Convective Turbulence and Dynamo Action

• Applicant: Dr. Stephan Stellmach
• Subject Area: Geophysics
• Term: from 2010 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 169802547

The magnetic fields of the planets in our solar system are generated by turbulent convective flows in the planetary interiors. In most numerical simulations of this process the convection is modelled in the framework of the Boussinesq approximation. Typically, the density field however varies considerably with radius in planetary dynamo regions. Such background density variations have a large impact on the interior flow dynamics and are completely neglected in Boussinesq models. We plan to study the effects of density stratification on turbulent magnetohydrodynamic convection in an anelastic framework which filters out fast time scales caused by sound waves. Compared to a simple Boussinesq approach, anelastic models allow for additional dynamical effects like fluid expansion and contraction, weakening of the Taylor-Proudman Theorem by local fluid compression, generation of mean flows by a local mechanism independent of boundary effects and magnetic buoyancy instabilities. In contrast to global simulations targeted at reproducing observable features of planetary magnetic fields as closely as possible, our approach is aimed at investigating the details of (magneto)-convective turbulence in small sub-sections of the global domain, thus channelling all available computational resources into the numerical resolution of highly turbulent states. Different from previous studies which have been carried out in the context of solar applications, we will focus on flows which are strongly influenced by rotation. Methodically, we will use a mixed pseudo-spectral, finite-difference code well adapted to massively parallel computers. We believe that the proposed work will provide new results applicable to dynamos in terrestrial planets, gas and ice giants as well as to rapidly rotating stars.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1488: Planetary Magnetism (PlanetMag)