Helioseismic Modelling of the Magnetic Solar Cycle

The Sun has a variable magnetic field. The most peculiar manifestation of this variability is the 11-year sunspot cycle. Besides the number of sunspots, the frequencies of the seismic waves that propagate through the solar interior are changing.

In the left panel, we show the effect of a magnetic field model that is located at about 70 000 km below the solar surface and extends over 28 000 km. If the magnetic field strength changes from 40kG to 50kG the frequency shifts strongly resemble the values observed on the Sun (right panel). This might indicate that there are magnetic field configurations inside the Sun, which are similar to that in this model.

Using a wave mechanical approach the effect of the solar internal magnetic field on seismic waves in the Sun and stars was modelled. Six models of the interior magnetic field inside were calculated, which all change the frequencies of the oscillation. Depending on the location and the structure of the field the frequencies are differently affected. By comparing these theoretical results with observed frequency shifts we found that a strong magnetic field at the base of the solar convection zone at approximately 200 Mm depth cannot be responsible for the observed frequency shift.

 

Publication: Kiefer, R., Roth, M., 2018, Astrophysical Journal 854, 74