Global-scale interactions between the solid Earth and its fluid envelopes at the seasonal time scale

Changes in the mass distribution inside the surface fluid envelopes in resp onse to climate changes affect the Earth by changing its gravitational fiel d, its rotation and the position of its centre of mass. At subdecadal time scales, temporal changes of these global Earth parameters are now currently determined by space geodesy. Here we focus on annual variations which carr y the largest energy. We combine space geodesy-derived annual variations of the centre of mass position, rotation pole position and dynamical flatteni ng, allowing us to map annual variations of the long-wavelength geoid. Annu al amplitude maxima amounting to 5 mm are located over continental regions of the Northern Hemisphere. These variations result from seasonal transfers of air and water mass among atmosphere, oceans, continents and ice sheets as evidenced by a comparison with the annually varying geoid deduced from h ydrometeorological loading data (atmospheric surface pressure, snow and soi l moisture load, ocean mass load). (C) 1999 Elsevier Science B.V. All right s reserved.