中文摘要：

行星地球是一个旋转的扁椭球体,其动力学扁率（即J2）变化主要由地球系统物质流动和各圈层相互作用引起.目前国际上地球动力学扁率测定主要用卫星激光测距（SLR）资料得到,然而SLR地面观测台站少,南北半球分布不均,且不是连续观测,以及受动力学模型和常数等影响.尽管新一代重力卫星（GRACE）观测大大提高了地球重力场球谐系数低阶项一两个数量级,但对二阶项C20不敏感.本文利用全球连续GPS观测得到的地表负荷位移估计地球动力学扁率J2,并联合GPS与海底气压（OBP）以及OBP和GRACE资料分别估计地球动力学扁率J2,比较和分析地球动力学扁率多尺度变化特征及其机理.结果发现GPS单独估计结果振幅偏小,GPS＋OBP,GPS＋OBP＋GRACE和GRACE估计J2周年变化与SLR结果非常接近.而J2半周年变化,GRACE估计相对较差,主要由于GRACE资料处理没有很好扣除约161天的S2潮汐影响.另外,GPS＋OBP和GPS＋OBP＋GRACE估计J2季节内和年季变化与SLR结果较一致,而GRACE和GPS单独估计结果与SLR结果偏差较大.并进一步利用地球物理模型资料研究对J2变化的贡献,结果表明,地球动力学扁率J2季节性、季节内和年季变化主要由大气、海洋和陆地水地表流体质量重新分布和迁移激发.

英文摘要：

Planet Earth is a rotating flat ellipsoid and its dynamics oblateness（i.e.J2） changes were mainly driven by the redistribution of Earth＇s fluid mass and interaction of various spheres in the Earth system.Currently,the dynamics oblateness was determined from the satellite laser ranging（SLR） data.However,it was subject to the sparse SLR stations,uneven distribution in the Northern and Southern Hemispheres and non-continuous observation as well as dynamic models and constants in SLR data processing.Although the new generation of satellite gravity mission GRACE（gravity recovery and climate experiment） measurement has largely improved the lower-order coefficient estimates with one or two orders of magnitude,but the C20 is not sensitive.In this paper,the high precise dynamics oblateness J2 is derived from global continuous GPS loading displacements and GPS＋OBP（ocean bottom pressure） as well as GPS＋OBP＋GRACE,respectively,which are analyzed and compared at multi-scales variations as well as their implications.It has shown that the annual variations of J2 have a good agreement between GPS＋OBP,GPS＋OBP＋GRACE,SLR and GRACE,while GPS alone has a smaller amplitude.For semi-annual variations,GRACE estimate is relatively worse due to the effect of about 161-day S2 tide.Also the GPS＋OBP and GPS＋OBP＋GRACE have a good correlation with SLR in intraseasonal and interannual J2 variations,while GPS or GRACE alone is worse.Furthermore,the excitations of multi-scale J2 variations are investigated and analyzed using geophysical models data.Results show that the variations of J2 at seasonal,intraseasonal and interannual scales are mainly driven by the transfer and redistribution of Earth＇s surface atmosphere,ocean and land water mass.