VARIATIONS IN EARTH S ROTATION BOTH POLAR MOTION AND LENGTH-OF-DAY (LOD) KNOWN AS EARTH ORIENTATION PARAMETERS (EOP) ARE CAUSED BY VARIOUS SOURCES OF MASS REDISTRIBUTION AND MOTION INCLUDING INTERACTIONS BETWEEN THE MANTLE AND CORE. DISTINGUISHING AMONG THE VARIOUS SOURCES THAT CONTRIBUTE TO OBSERVED EOP VARIATIONS IS ESSENTIAL FOR UNDERSTANDING ASSOCIATED DYNAMICAL PROCESSES BOTH NEAR THE SURFACE AND IN THE INTERIOR AND IMPLICATIONS TO THE GLOBAL CHANGES. FOR THE AXIAL COMPONENT OF EARTH ROTATION (LOD) AT DECADAL OR LONGER TIMESCALES DYNAMICAL COUPLING BETWEEN THE CORE AND MANTLE IS WIDELY REGARDED AS THE MAIN SOURCE. THIS ASSUMPTION ALLOWS LOD VARIATIONS TO BE INTERPRETED IN TERMS OF PHYSICAL PROPERTIES AND VARIABILITY IN EARTH S DEEP INTERIOR. HOWEVER FOR EOP EQUATORIAL COMPONENTS POLAR MOTION X AND Y THE CORE-MANTLE COUPLING EFFECT IS GENERALLY ASSUMED TO BE NEGLIGIBLE. THESE ASSUMED DIFFERENCES IN THE ROLE OF THE CORE FOR LOD AND POLAR MOTION HAVE INFLUENCED DEVELOPMENT OF MODERN EARTH ROTATION THEORY. WHILE THE ASSUMED DYNAMICAL CORE-MANTLE COUPLING FOR LOD IS INDICATED BY DECADAL AND LONGER VARIATIONS NOT EXPLAINED BY GEOPHYSICAL EXCITATIONS IN THE CLIMATE SYSTEM (ATMOSPHERE OCEAN HYDROSPHERE AND CRYOSPHERE) THE CORE-MANTLE COUPLING EFFECT ON EQUATORIAL COMPONENTS IS NOT WELL UNDERSTOOD AND HAS NOT BEEN INDEPENDENTLY VERIFIED DUE TO LACK OF ADEQUATE OBSERVATIONS OF GLOBAL MASS REDISTRIBUTION AND MOVEMENT IN THE EARTH SYSTEM IN A COHERENT FRAMEWORK. TIME-VARIABLE GRAVITY MEASUREMENTS FROM THE GRAVITY RECOVERY AND CLIMATE EXPERIMENT (GRACE) SATELLITE MISSION HAVE PROVIDED A UNIQUE MEASURE OF LARGE-SCALE MASS TRANSPORT OF DIFFERENT COMPONENTS OF THE EARTH SYSTEM WITH UNPRECEDENTED ACCURACY. GRACE DATA PROVIDE AN INTEGRATED MEASURE OF MASS REDISTRIBUTION IN THE EARTH SYSTEM RANGING FROM SURFACE GEOPHYSICAL FLUIDS TO MANTLE AND CORE. WE PROPOSE TO INTEGRATE GRACE DATA SATELLITE LASER RANGING (SLR) MEASUREMENTS EOP OBSERVATIONS AND ADVANCED CLIMATE MODEL PREDICTIONS TO COMPREHENSIVELY EXAMINE GEOPHYSICAL EXCITATIONS OF EARTH ROTATION. THE GOAL IS TO DISCERN ANY DIFFERENCES IN INTERPRETATION OF OBSERVED-EOP EXCITATIONS WHEN DIFFERENT CORE-MANTLE COUPLING ASSUMPTIONS ARE CONSIDERED. THE MAIN GOAL IS TO PROVIDE IMPROVED UNDERSTANDING OF THE DYNAMICS OF MANTLE-CORE INTERACTIONS AND THEIR CONTRIBUTIONS TO EOP VARIATIONS THROUGH OBSERVATIONAL VALIDATION OF THE DIFFERENT ASSUMPTIONS. THE PROPOSED INVESTIGATION WILL FOCUS ON THE FOLLOWING SUBJECTS. 1) QUANTIFY OBSERVED EOP EXCITATIONS INFERRED FROM THE INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS) C04 08 EOP SOLUTIONS. 2) QUANTIFY ATMOSPHERIC WIND AND OCEAN CURRENT CONTRIBUTIONS (THE MOTION TERM) TO EOP EXCITATIONS USING ADVANCE ATMOSPHERIC AND OCEANIC CIRCULATION MODELS (E.G. NCEP AND ECMWF REANALYSIS AND ECCO). 3) ESTIMATE EOP EXCITATIONS DUE TO MASS REDISTRIBUTION (THE MASS TERM) USING THE EXTENDED RECORD OF GRACE GRAVITY SOLUTIONS AND SLR MEASUREMENTS. 4) VALIDATE CORE-MANTLE COUPLING/DECOUPLING ASSUMPTIONS ADOPTED IN CURRENT EARTH ROTATION THEORIES ON DIFFERENT TIMESCALES THROUGH COMPARISON OF OBSERVED EOP EXCITATIONS WITH ESTIMATED TOTAL GEOPHYSICAL (MASS + MOTION TERMS) EXCITATIONS UNDER DIFFERENT COREMANTLE COUPLING ASSUMPTIONS (FULLY COUPLED FULLY UNCOUPLED OR PARTIALLY COUPLED). 5) PROVIDE IMPROVED OBSERVATIONAL CONSTRAINTS ON ANGULAR MOMENTUM EXCHANGES BETWEEN THE CORE AND MANTLE ON DIFFERENT TIMESCALES. 6) ISOLATE AND QUANTIFY POSSIBLE CORE-INDUCED OSCILLATIONS IN LOW-DEGREE GRAVITATIONAL CHANGES. THE PROJECT TEAM INCLUDES RECOGNIZED EXPERTS IN SPACE GEODESY EARTH ROTATION GRACE APPLICATIONS SOLID EARTH GEOPHYSICS AND CORE DYNAMICS WITH EXTENSIVE RESEARCH EXPERIENCES IN STUDYING GEOPHYSICAL EXCITATIONS OF EARTH ROTATION USING VARIOUS GEOPHYSICAL DATA SOURCES. OUR PAST EXPERIENCE BROAD EXPERTISE AND STRONG PUBLICATION RECORDS PROVIDE A SOLID FOUNDATION FOR THE PROPOSED INVESTIGATION.