Swiss Virtual Institute for Solar Science
Dynamo
Dynamo Processes and Internal Structure
Various tools have recently been developed that allow us to explore the physical conditions in the Sun's interior, of fundamental importance for the understanding of stellar structure and evolution, as well as for the understanding of the processes by which macroscopic magnetic fields in the universe (in stars, planets, and galaxies) are being generated. Swiss astronomers have made major contributions to these developments.
The currently most powerful tool to explore the interior structure of a star is that of helioseismology. The Sun, like almost all other stars, exhibits global oscillations due to resonant sound waves that propagate through the Sun's interior. By observational determination of the modal structure of these oscillations and the precise frequencies of the multitude of resonant modes it is possible to determine the properties of the interior, in a similar way as seismic sound waves are used to determine the interior structure of the Earth. PMOD/WRC in Davos has been a major player in this field during the past two decades, most recently with its VIRGO instrument on the SOHO satellite, which records the oscillation signatures in the fluctuations of the Sun's irradiance.
Scientists at the Geneva Observatory have applied the results from helioseismology to the Sun's internal rotational structure together with observations of the Sun's low lithium abundance to successfully model both the rotation profile and the surface abundance of lithium in solar-type stars of various ages, and shown how the rotational profile is coupled to the generation of magnetic fields in the star.
Cosmic magnetic fields are believed to be universally generated by dynamo processes, in the Earth, planets, stars, and galaxies. Practically all stellar activity, including the Sun's 11-year activity cycle, is the product of dynamo processes. The Sun is unique by being a nearby astrophysical dynamo on which the fundamental physics can be studied in great detail. The observational signatures of the solar dynamo express themselves on all scales in the magnetic field pattern, from the smallest, subresolution scales, to the global scales. Both the physical nature of the magnetic fields on the smallest scales as well as the solar-cycle evolution of the global magnetic pattern and its modal structure have been central research topics where ETH Zurich have made major contributions over the past decades.