The enigmatic magnetic fields of the Sun

Physikalisches Kolloquium

The solar magnetic field exhibits remarkable properties - while observations show a very chaotic behavior instantaneously, the long-term behavior shows remarkable coherence over space and time. The sunspots, for example, arrange themselves in preferred latitude bands over the solar surface. This latitude band migrates towards the equator in an eleven year cycle, after which the polarity of the sunspot pairs changes sign, the magnetic cycle hence being 22 years long. Explaining the existence of such coherence has turned out to be extremely challenging, and debate about how this so called dynamo mechanism actually operates in the Sun continues. One of the challenges, preventing analytical treatment of the problem, is the vigorous turbulence that prevails in the solar convection zone. Much, therefore, relies on numerical modelling, but even in this frontier, the more sophisticated simulations one is able to produce, the vigorous turbulence presents new surprises. In this talk I will discuss the challenges related to the numerical modelling of the solar dynamo, and some ideas how to go forward. The solar dynamo being the ultimate driver of all solar magnetic activity, including space weather and climate, finding answers to these questions is an important and urgent topic.

Käpylä, P. J., Mantere, M. J., Brandenburg, A. 2012: Cyclic Magnetic Activity
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Käpylä, M. J., Käpylä, P. J., Olspert, N., Brandenburg, A., Warnecke, J., Karak,
B. B., Pelt, J., 2016: Multiple dynamo modes as a mechanism for long-term solar
activity variations, A&A, 598, A56.

Käpylä, P. J., Käpylä, M. J., Warnecke, J., Brandenburg, A., Olspert, N., 2017:
Convection-driven spherical shell dynamos at varying Prandtl numbers, A&A, 599,

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