Non-axisymmetric solar magnetic fields
Seminar Room 1, Newton Institute
Solar magnetic activity tends to cluster at ``preferred" longitudes, which indicates the involvement of non-axisymmetric large-scale (mean) magnetic fields in the process of the activity formation. We investigate the generation of non-axisymmetric modes of the mean solar magnetic field and their coupling to the axisymmetric mode.
Our dynamo model incorporates the solar rotation reconstructed by inversion of helioseismic data in the convection zone and simulated distributions of the turbulent resistivity and the mean kinetic helicity. We demonstrate first that the dynamo breaks the axial symmetry by exciting non-axisymmetric modes even when all sources of generation are axisymmetric. Then we couple axisymmetric and non-axisymmetric modes using a non-axisymmetric addition to the mean helicity. Mathematically, it is done in the kinematic approximation without the use of a non-linear quenching.
We find that this coupling of non-axisymmetric and axisymmetric modes (1) reproduces the phase relation between these modes observed in the solar cycle; (2) the non-axisymmetric modes are localized near the base of the convection zone (thus influencing the formation of active regions) and appear near 30 degrees latitude.