Understanding the solar dynamo
Abstract
The solar magnetic field continues to be an outstanding challenge of astrophysics. At the solar surface the magnetic field assumes a complex, hierarchical structure consisting of widely different spatial and temporal scales. Systematic features such as the solar cycle and the butterfly diagram point to the existence of a deep-rooted large-scale magnetic field, subject to variability on widely different timescales. At the other end of the spatial scale are magnetic elements and mixed-polarity magnetic fields. In order to explain these phenomena, dynamo theory provides all the necessary ingredients including the α effect, field amplification by differential rotation and other mechanisms, magnetic pumping, turbulent diffusion, magnetic buoyancy, flux storage, stochastic variations and nonlinear dynamics. Due to advances in helioseismology, observations of stellar magnetic fields and computer capabilities, significant progress has been made in our understanding of these and other aspects such as the role of the tachocline and magnetic helicity conservation. However, remaining uncertainties about the nature of the deep-seated magnetic field and the α effect have thus far prevented the formulation of a coherent model for the solar dynamo. A preliminary evaluation of current dynamo models favors a buoyancy-driven or distributed scenario. It is proposed that progress in understanding the solar dynamo is best achieved through a combination of approaches including high-resolution numerical simulations and global mean-field modeling.
- Publication:
-
35th COSPAR Scientific Assembly
- Pub Date:
- 2004
- Bibcode:
- 2004cosp...35.3775O