Consideration of ocean tides in an OGCM and impacts on subseasonal to decadal polar motion excitation

Ocean induced changes of Earth's rotation are attributed either to tides or to variations of the general circulation. Analogously, numerical world ocean models can still be divided into Ocean General Circulation and tidal models, although a neglect of nonlinear interactions in favor of a linear superimposition of both components of motion is questionable. By means of a simultaneous simulation of the ocean's circulation and tides we estimate the importance of two oceanic effects with respect to excitation of polar motion: nonlinearities between circulation and long-period tides and the circulation induced potential due to loading and self-attraction of a baroclinic ocean. Comparing the linear superimposition of separate model simulations with the simultaneous calculation of circulation and tides it turns out that these second-order effects contribute about 8% to ocean induced changes in Earth's orientation.