Speaker: Maarit Korpi-Lagg (Aalto University)

Title: Recent results on modelling solar-stellar dynamics and dynamo and comparisons with observations

Abstract: Solar and stellar dynamos and differential rotation are both driven by the complicated interplay between convection, rotation and stratification. Differential rotation, on the other hand, is one of the basic ingredients of large-scale dynamo action in stars. All these ingredients influence each other through non-linear interactions, making the direct modelling of the problem, that is solving the full MHD equations, extremely complicated and resource-demanding. In the solar case we have reliable rotation profile at our use thanks to helioseismology against which the modelling results can be calibrated. In addition, we have long-term and high-resolution data of the solar magnetic field at the surface, enabling us to match models and observations even further. It is now evident that magnetic features, such as the famous butterfly diagram, can be obtained with rotation profiles that are not in agreement with helioseismology. Resolving this discrepancy boils down to be able to model and/or parameterise the vigorous turbulence correctly in the convection zone, dubbed “cracking the convection conundrum”.
Does the situation improve or worsen when you include data from other stars and try to constrain the models further, not just fitting models to one single observation point matching the Sun? Such attempts are complicated by the fact that we do not yet know the rotation profiles of others stars from asteroseismology to a high precision. Nevertheless, simple theoretical considerations can be used as a guideline. Data from the magnetic cycles and activity, on the other hand, is rather abundant and nowadays exceeds timescale of decades. Using the latter it appears that the model predictions are in a very good agreement with active rapid rotator data in terms of the cycles, but not consistent with data from inactive solar-like stars. Hence, the solar-stellar comparisons seem to strengthen the discrepancy between observations and models.
Currently we are entering the era of pre-exascale GPU computing. Such resources move global DNS models into a regime where also a small-scale dynamo instability is excited. This instability has recently been proposed to remedy the dynamics into the direction where helioseismic rotation profiles can be obtained. On the other hand, our simulations show that the dynamo cycles become even more irregular and features such as the butterfly diagram can vanish. In this talk I review the above-described current status of solar and stellar dynamics and dynamo modelling in more detail.

• Date:
  June 12, 2025, 2:30 p.m. – 3:30 p.m.
  
  
• Location:

  AIP; Kirch building, Conference room

  
  
• Contact:
  Julián Alvarado-Gómez
  julian.alvarado-gomez@aip.de