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Petri Käpylä (AIP)

Resurrecting the turbulent dynamo: starspots without flux tubes
When Nov 30, 2017 from 02:30 PM to 03:30 PM
What
  • Colloquium
Where SH Lecture Hall
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The solar dynamo has been described for the past two decades mostly in terms of flux transport dynamo models which rely thin magnetic flux tubes that are produced and stored at the base or just below the convection zone. They were thought to rise to the surface, and thus form spots, once reaching a high enough field strength (~100kG). A single-cell meridional flow and a low magnetic diffusivity are prerequisites for the model to reproduce the solar cycle.

 

Recently the main assumptions in the flux transport models have been questioned by new observational and numerical results. At the same time, increasing interest toward distributed dynamos, which produce much weaker (~1kG) diffuse fields throughout the convection zone, has been rekindled. Arguably the most severe remaining argument against distributed dynamos has been that there has been no mechanims to form strong concentrations of magnetic field, i.e. sunspots, from weak diffuse fields. A promising candidate, the Negative Effective Magnetic Pressure Instability (NEMPI) has since been verified in idealised simulations. I will present results from an ongoing effort to enable spot-formation due to NEMPI with high-resolution simulations of turbulent convection and the implications of the results to stellar dynamo theory.