The Magnetic Field Sign Reversal and Evolution of Rossby and Alfven Waves Induced by Velocity Shear Oscillations on the Sun

Abstract

The behaviour of the toroidal and meridional components of the solar large-scale magnetic field and linear Alfven and Rossby waves during solar activity cycles and bi-annual time periods are theoretically investigated in this work. We consider the case of periodical velocity shear with bi-annual oscillation period . The large-scale magnetic field toroidal and meridional components are obtained as harmonic functions of the time. The sign reversal of these magnetic field components is studied. The numerical simulations show that, due to the velocity shear oscillations, the toroidal or meridional component of the large-scale magnetic field reverses its sign three times in one of the hemispheres (northern or southern) of the Sun, during the solar activity cycle 23. According to our results the appearance of velocity shear oscillations leads to the modulation of the magnetic field 22-year period oscillations by the bi-annual ones. The presented model is applicable for investigation of the magnetic field evolution at the base of convection zone as well as for understanding the magnetic field properties in the upper solar atmosphere. The excitement of the linear Rossby and Alfven waves in the shear layer at the base of the convection zone is also considered. The periodical impulsive growth is characteristic to the energy density of Alfven and Rossby waves and they propagate as localized in time powerful pulses. Such behavior of waves well explains mechanisms of the solar flare excitement and activity.