(a) Schematic drawing of the axisymmetric magnetic flux tube, the surface of which is defined by the poloidal x and toroidal ϕ axes. The winding thin lines represent the magnetic field lines, which illustrate the nonlinear propagation of Alfvén waves. (B) Schematic drawing of the magnetic field configuration in the vicinity of the stellar surface. The parameters defining the flux tube geometry in this study, such as f_ph and H_m, are indicated.