The reconstruction of the magnetic field longitudinal structure was performed in different coordinate systems; rotating rigidly, and like the photosphere. A longitudinal structure, exceptionally regular in both hemispheres and symmetric, has been found without any a priori assumption about the rotation of the Sun. This structure is originated in the tachocline zone under the convective envelope. A comparison between the rotational rate of the large scale magnetic field and helioseismological findings of as a function of latitude and radius Ω was performed and it was concluded that the rotation rate at the base of the convective envelope at a latitude of about 55° coincides with the rotation rate where the longitudinal structure is generated.