Schematic depiction of the application of Stokes’ theorem. The white and gray zones represent the convection zone and the radiative zone, respectively. The blue contour 𝒞 shows the path of integration around the area 𝒮 in the northern hemisphere. And the contour 𝒞 is clockwise and consists of the solar surface (a, surface), a radial segment in the equatorial plane (b, equator), a circular arc slightly below the bottom of the convection zone (c, base), a part along the axis of rotation (d, axis).