Hej,

This is my homepage. I am current a Senior Postdoc & Scientist at the Max-Planck Institute for Solar System Research in Göttingen, Germany. I am there in SOLSTAR and UniSDyn group and collaborate with the Solar and Stellar Coronae group , working on the interplay of dynamos, flux concentrations with coronal structures and activity in the Sun and other stars.

In Summer 2013 finished my PhD Studies at Nordita and the Astronomy Department of Stockholm University under the supervision of Axel Brandenburg.

I am a core-developer of the open source PENCIL CODE, which is hosted by GitHub.

On the following pages, you can find my Curriculum Vitae, an overview of my research topics and a detail a list of publications and talks.

JÖRN WARNECKE

NEWS:

                                                                                                            September 2021

New paper published:

Investigating Global Convective Dynamos with Mean-field Models: Full Spectrum of Turbulent Effects Required

Jörn Warnecke, Matthias Rheinhardt, Mariangela Viviani, Frederick A. Gent, Simo Tuomisto & Maarit J. Käpylä: 2021, ApJL 919 L13, ([ArXiv],[DOI],[ADS],[PDF])

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.

Time–latitude (butterfly) diagrams of mean radial, Br, and azimuthal, Bf, magnetic field from GCD (top) and the MF model (bottom) at fractional radius 0.95. The TTCs are symmetrized, and α is scaled by 1.5, while exponential growth has been compensated for clarity. The color range is cut to make the northern hemisphere more visible. Black lines: zero contours of Bf from the MF model at the same time.