Department of Computer Science

How important is turbulence in the solar dynamo?

Aalto scientists show that all turbulent effects are decisive.
Comparison of the time-latitude (butterfly) diagrams of mean radial and azimuthal magnetic field from direct numerical simulation (top) and the Mean-field model (bottom)  White lines: zero contours of mean azimuthal magnetic field from the MF model at the same time. Image copyright Jörn Warnecke, MPS.
Comparison of the time-latitude (butterfly) diagrams of the Direct Numerical Simulation (upper row) and mean-field model (lower row). Image copyright: Jörn Warnecke, MPS

The role of turbulent effects for dynamos in the Sun and stars continues to be debated. Mean-field (MF) theory provides a broadly used framework to connect these effects to fundamental magnetohydrodynamics. While inaccessible observationally, turbulent effects can be directly studied using global convective dynamo (GCD) simulations. We measure the turbulent effects in terms of turbulent transport coefficients, based on the MF framework, from an exemplary GCD simulation using the test-field method. These coefficients are then used as an input into an MF model. We find a good agreement between the MF and GCD solutions, which validates our theoretical approach. This agreement requires all turbulent effects to be included, even those which have been regarded as unimportant so far. Our results suggest that simple dynamo models, as are commonly used in the solar and stellar community,  relying on very few, precisely fine-tuned turbulent effects, may not be representative of the full dynamics of dynamos in global convective simulations and astronomical objects.

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Astroinformatics (external link)

Simulations of turbulence and magnetism in astrophysical objects

PML Research Group in Department of Computer Science

Department of Computer Science

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