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

. The behaviour of the toroidal and meridional components of the solar large-scale magnetic field and linear Alfv´en and Rossby waves during solar activity cycles and bi-annual time periods are theoretically investigated in this work. The shear of the toroidal and meridional components of velocity is taken into account. We consider the case of periodical velocity shear with bi-annual oscillation period, hereinafter the Velocity Shear Quasi Bi-annual Oscillations (VSQBO). The large-scale magnetic field toroidal and meridional components are obtained as harmonic functions of the time and the oscillation phase difference between them is equal to π/ 2. The sign reversal of the magnetic field toroidal and meridional components is studied. The numerical simulations show that in the case of significant VSQBO amplitude values 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 magnetic canopy of the solar chromosphere Roberts (1996)). The excitement of the linear Rossby and Alfv´en 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 Alfv´en and Rossby waves and they propagate as localized in time powerful pulses. Properties of these pulses are governed by the direction of waves phase velocity and the initial phase of VSQBO, and such behavior of waves well explains mechanisms of the solar flare excitement and activity.