摘要
核幔电磁耦合、地形耦合、引力耦合是影响十年尺度日长变化的主要因素.本文简要阐述了这三大耦合的机制,并收集了前人的一些资料和数据,分别估算了这三种耦合的周期、力矩幅度及可能引起的日长变化幅度.结果表明:核幔电磁耦合周期约为10.3年,力矩约为3.1×10^(17)Nm,引起的日长变化幅度约为0.27 ms;核幔地形耦合的周期约为10年,力矩约为1.7×10^(18)Nm,引起的日长变化幅度约为1.4 ms.引力耦合引起的日长变化是否是十年尺度的仍存在争议,采用不同内核三轴椭球模型,日长变化的周期从亚十年尺度(3.5年、4.6年)到十年尺度(18.4年)变化.由于地核与地幔相对运动状态未知,无法确切估算引力耦合的力矩,但在假定引起耦合引起的日长变化幅度为4 ms的极限情况下,引力耦合的力矩约在10^(18)(十年尺度)~10^(19)Nm(亚十年尺度)的量级,低于前人的计算结果.
Electromagnetic Core-mantle Coupling（ECC）,Topographic Core-mantle Coupling（TCC）and Gravitational Coremantle Coupling（GCC）,these three types of core-mantle coupling are the main factors to influence the decadal fluctuations in the Length of Day（LOD）.In this study,we make a briefly review of the three types of couplings mechanisms,and then we use the data collected in the previous study to estimate the periods and amplitudes of the three types of coupling torques,as well as the amplitudes of variation in the LOD caused by the coupling torques.The results show that the period and the torque amplitude of ECC is about 10.3 year and 3.1×10^17 Nm,respectively,which may cause the variation in the LOD about 0.27 ms.The period and the moment amplitude of TCC is about 10 year and 1.7×10^18Nm,respectively;which lead to the variation in the LOD about 1.4 ms.Because the LOD oscillation period depends on the choice of triaxiality model for the Earth’s inner core,whether the fluctuation caused by the GCCis decadal or sub-decadal is still controversial.Based on different triaxiality model,the LOD varies between sub-decadal（3.5 and 4.6 year）and decadal（18.4）fluctuation.Due to the lack of the detailed information about the motion of the Earth’s core related to the mantle,we are not able to extract the amplitude of GCC.However,based on the assumption the upper limit of fluctuation in the LOD is no more than 4 ms,we find that the order of magnitude of the torque of GCC is about 10^18（corresponding to decadal fluctuation）-10^19 Nm（corresponding to sub-decadal fluctuation）,which is less than the previous study.
作者
叶庆东
贺伟光
毛远凤
YE Qing-dongl;HE Wei-guang;MAO Yuan-feng(The First Monitoring and Application Center,China Earthquake Administration,Tianjin 300180,China;University of Grenoble Alpes,lSTerre,Grenoble 38400,France)
出处
《地球物理学进展》
CSCD
北大核心
2018年第5期1854-1861,共8页
Progress in Geophysics
基金
中国地震局测震台网青年骨干专项(20170629)
国家自然科学基金(41504073)共同资助
关键词
电磁耦合
地形耦合
引力耦合
十年尺度日长变化
electromagnetic coupling
topographic coupling
gravitational coupling
decadal fluctuation in length of day
