Mathieu Ossendrijver

Mathieu Ossendrijver

Astrophysical dynamos

Until 1 Dec. 2005 this research was conducted at the Kiepenheuer Institute for Solar Physics (Freiburg, Germany)

Topics of interest: theory and numerics of dynamo action in the Sun, stars and Earth. Below you can see a glimpse of recent 3D simulations of solar magnetoconvection. I'm also interested in the reversals of the geodynamo, statistical aspects of dynamo theory, and mean-field methods.

Publications

Refereed papers, invited reviews

Thesis

Other publications

Other items

  • Dynamotheorie, M. Ossendrijver, Lecture notes, Freiburg University (WS 1997/1998)

Magnetoconvection and dynamo coefficients

Snapshot of the flow (u). The vertical velocity is indicated by the coloring (red: upward, blue: downward), the direction of the flow by the arrows.

Simultaneous snapshot of the magnetic field (B). The strength of the magnetic field is indicated by the coloring (blue: low, red: high), and its orientation by the arrows. The white curve denotes the zero level of the vertical velocity.

3D simulation of solar magnetoconvection

The large-scale magnetic field of the Sun is produced by dynamo action in the convection zone. In order to understand the dynamo process, knowledge of the dynamo coefficients is crucial. By means of 3D magnetohydrodynamic (MHD) simulations, these are calculated from the electromotive force, uxb, where u and b are the disturbances of the velocity and the magnetic field, respectively. The simulation domain shown here represents a section of the solar convection zone, sandwiched between a thin cooling layer on top and a stably stratified layer underneath. From below the box is supplied with a constant heat flux; at the top the temperature is held fixed. The axis of rotation points downward, as is the case on the south pole of the Sun. Initially, the magnetic field is vertical and homogeneous.

Turbulent diffusion and magnetic pumping in 3D magnetoconvection

Three snapshots of the magnetic field (B). The strength of the magnetic field is indicated by the coloring (green: low, red: high), and its orientation by the arrows. The white curve denotes the zero level of the vertical velocity. It separates isolated upwelling regions from downflowing lanes. Initially, a weak magnetic field with a horizontal orientation and a Gaussian dependence on depth is introduced into the middle of the convectively unstable layer. Subsequently, this layer is modified by advection.

On average, this results in a spreading of the magnetic field equivalent to turbulent diffusion as well as a net downward advection that can be attributed to magnetic pumping.

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