Sketch of the initial configuration. The simulation domain (filled with blue color) is contained in the XOZ plane, where x varies between −L₀ and L₀ and z varies between −4L₀ and 4L₀. The magnetic field, B (red lines), is contained in the XOY plane (filled with gray color). At the height z = 0, the magnetic field only has the component, B_y, and it is slowly rotated above and below z = 0 by an angle which depends on height, keeping its modulus constant. The value of the angle is anti-symmetric with respect to z = 0. The maximum angle obtained at the top and the bottom of the atmosphere is indicated by θ₀. When the field is perpendicular, the direction of B is along the y-axis for all the heights, θ₀ = 0°. For the sheared magnetic field configurations θ₀ = 1°. The gravity, g, points in the negative z direction and is indicated by a green line. The direction of the perturbation, k, is shown by a blue line.