The Sun's Preferred Longitudes and the Coupling of Magnetic Dynamo Modes

Observations show that solar activity is distributed nonaxisymmetrically, concentrating at "preferred longitudes." This indicates the important role of nonaxisymmetric magnetic fields in the origin of solar activity. We investigate the generation of the nonaxisymmetric fields and their coupling with the axisymmetric solar magnetic field. Our kinematic generation (dynamo) model operating in a sphere includes a model of solar differential rotation, as obtained by inversion of helioseismic data, modeled distributions of the turbulent resistivity, nonaxisymmetric mean helicity, and meridional circulation in the convection zone. We find that (1) the nonaxisymmetric modes are localized near the base of the convection zone, where the formation of active regions starts, and at latitudes around 30 degree ; (2) the coupling of nonaxisymmetric and axisymmetric modes causes the nonaxisymmetric mode to follow the solar cycle; the phase relations between the modes are found; and (3) the rate of rotation of the first nonaxisymmetric mode is close to that determined in interplanetary space.