Solar Magnetic Fields

The solar activity is determined by the magnetic field, which is present in all atmospheric layers of the Sun and connects them with the interplanetary space and thus also to Earth. In the solar atmosphere, the magnetic field is highly structured, from large to small temporal and spatial scales. This leads to the formation of the well-known sunspots, pores, eruptions, flares and solar storms, as well as the generation of high-energetic particles, so-called solar cosmic rays.

The source of solar magnetic fields is a dynamo at the interface between the convection zone and the radiative core. Magnetic fields generated by the dynamo rise through the convection zone and emerge at the visible solar surface in the form of bipolar magnetic regions, finally forming loops whose tops lie in the corona. The locations where the loop intersects the solar surface are visible as either sunspots or faculae. High in the corona, the magnetic field is so weak that the solar wind can pull the field open into interplanetary space. The field is almost radial. 

The magnetic activity of the Sun shows a cyclic variation with a mean period of about 11 years. The 11-year solar cycle strongly supports the idea of a large-scale solar dynamo. The solar cycle has a great effect on the evolution of the global coronal magnetic field. Sunspots, a by-product of the large-scale dynamo, appear, evolve and disperse over several days. The interaction between the emergence of sunspots and the pre-existing coronal magnetic field creates a variety of dynamic solar phenomena.

Researchers at AIP's solar group have a special focus on:

• Deriving magnetic fields from spectroscopic as well as spectropolarimetric (Stokes profiles) observations using inversion codes for, e.g., sunspots, solar flares, or filaments.
• Investigation of the changes in the magnetic field in solar phenomenae and eruptive events.
• Long-term studies of the evolution of the magnetic field on the Sun over decades.