Rotational Normal Modes And Polar Motion Excitation Under Triaxial Three-Layered Earth Rotation

Earth rotation is the key branch and inter-discipline of geodesy,geophysics and astronomy,which are intimately related with meteorology,oceanography,space environment and human survival.Especially,with the development of space geodetic techniques,the observations of Earth rotation were brought into high precision times.Space geodetic techniques not only bring the ultra-high precision Earth orientation parameters to provide the basis for Earth rotation parameters forecasts,satellite orbit determinations,navigation and aeronautical applications,but also improve the observational resolution of Earth rotation variations to provide the evidence for interpreting these variations.Modern observations of principal moments of inertia of the Earth indicate that the Earth is not a rotational symmetric body,but a triaxial layered spheroids with three different principal moments,which demands a new triaxial Earth rotation theory to better interpret the observations.At present,the triaxial Earth rotation theories include triaxial rigid Earth rotation theory,triaxial elastic Earth rotation theory and triaxial two-layered Earth rotation theory.Modern seismological observations indicate that,the solid Earth is composed of the crust and mantle,the fluid outer core and the elastic inner core,with the constructed PREM Earth model and 1066A/B Earth model.Hence,it is necessary to build a triaxial three-layered Earth rotation theory on the basis of the current Earth model and observations of principal moments of inertia of the Earth.Based on current rotational symmetric three-layered Earth rotation theory,by triaxializing inertia tensor of moments,viscoelectromagnetic coupling torques near core mantle boundary(CMB)and inner core boundary(ICB),pressure and gravitational coupling torque acting on the elastic inner core,a new triaxial three-layered Earth rotation theory is built.The new theory provides four rotational normal modes solutions of periods and quality factors: Chandler wobble(CW),free core nutation(FCN),free inner core nutation(FICN),inner core wobble(ICW),including the former results as special case.Besides,the following topics about rotational normal modes are investigated: the effect of triaxiality on rotational normal modes,the disspative properties of rotational normal modes,the effect of different core mantle couplings on rotational normal modes,and so on.Although there are lots of studies on polar motion excitation,including elastic Earth rotation and two-layered Earth rotation,no one have attempted to do research on polar motion excitation of three-layered Earth rotation.Based on rotational symmetric three-layered Earth rotation theory and triaxial three-layered Earth rotation theory,the polar motion excitation models for rotational symmetric three-layered Earth rotation and triaxial three-layered Earth rotation are constructed.Combining with the effective angular momentum data of GFZ,the atmospheric,oceanic,hydrological and sea-level excitation of polar motion of three-layered Earth rotation are calculated,which matches well with the geodetic excitation calculated from polar motion data of International Earth Rotation and Reference Systems Service(IERS).