The Gauss coefficients of the geomagnetic field since 1903 are used as a time-dependent boundary condition for the poloidal field in the Earth's mantle. The coefficients are Fourier transformed, and the induction equation for the mantle field is solved in Fourier space. The phase advance of the poloidal field at the base of the mantle, and of the ensuing “poloidal” electromagnetic couple, is investigated as a function of the conductivity profile.