Seasonal polar motion excitation from numerical models of atmosphere, ocean, and continental hydrosphere

Effective angular momentum functions from atmosphere, oceans, and terrestrial water storage are obtained from European Centre for Medium-Range Weather Forecasts atmospheric data and corresponding simulations with the Ocean Model for Circulation and Tides and the Land Surface and Discharge Model (LSDM). Mass exchanges among the subsystems are realized by means of freshwater fluxes, causing the total ocean mass to vary predominantly annually. Variations in total ocean mass affect the oceanic excitations of the annual wobble by almost 1 milliarc second (mas) for both prograde and retrograde components, whereas the motion term contributions of terrestrial water flow derived from LSDM are found to be 3 orders of magnitude smaller. Since differences to geodetic excitations are not substantially reduced and regional decompositions demonstrate the large spatial variability of contributions to seasonal polar motion excitation that compensate each other when integrated globally, it is concluded that the closure of the seasonal excitation budget is still inhibited by remaining model errors in all subsystems.