A 3-dimensional, fully nonlinear numerical geodynamo model is used to study the core-mantle coupling arising from a non-hydrostatic pressure field acting on an aspherical core-mantle boundary (CMB) based on a seismological model. The simulation results demonstrate that the topographic coupling torque is close to being proportional to the square of the amplitude of the CMB topography. We conclude that the contribution of the topographic coupling to the total torque that is responsible for the axial angular momentum transfer on decadal timescales (for the decadal length-of-day variation) is significant only if the amplitude of the CMB topography is considerably larger than 3 km inferred from seismological evidence. ¿ 2001 American Geophysical Union