Dynamics of axial torsional libration under the mantle-inner core gravitational interaction
Dynamics of axial torsional libration under the mantle-inner core gravitational interaction
复制标题
DOI：
10.1002/2016jb013515
复制
发表时间：
2017-01-01
影响因子：
3.9
通讯作者：
Chao, B. F.
中科院分区：
文献类型：
--
作者：
Chao, B. F.
本文的主要目的是：（1）用球谐多极质量密度描述地幔-内核引力相互作用的动力学。模拟的MICG系统是由两个同心的刚体（地幔和内核）的近球形，但在其他方面的异构配置，与流体外核之间发挥被动的作用。我们推导出矢量旋转的一般运动方程，但只关注描述MICG轴向扭转天平动的极分量。扭转常数和天平动的自然频率的平方与地幔和内核大地水准面的赤道椭圆率的乘积成正比，（指两种不同的类型）二次和二阶的（如核幔边界以上的大低切变速度区）和（ii）研究了将上述MICG天平动等同于地球自转速率或日长变化（LOD）中观察到的稳定的6年振荡的地球物理含义。特别地，发现MICG扭转常数为（Gamma）/波浪线（z）= C-IC sigma（2）（z），近似为6.5 × 10（19）Nm，而内核的（B-IC - A（IC））近似为1.08 x 10（31）kg m（2），给出了内核的三轴度（B-IC - A（IC））/C-IC约为1.8 x 10（-4），约为全地球值的8倍。它还断言，所需的内核椭圆度不超过类似于140米的大地水准面高度，远小于所需的灵敏度的地震波旅行时间来解决内核的变化。
The aims of this paper are (i) formulating the dynamics of the mantle-inner core gravitational (MICG) interaction in terms of the spherical-harmonic multipoles of mass density. The modeled MICG system is composed of two concentric rigid bodies (mantle and inner core) of near-spherical but otherwise heterogeneous configuration, with a fluid outer core in between playing a passive role. We derive the general equation of motion for the vector rotation but only focus on the polar component that describes the MICG axial torsional libration. The torsion constant and hence the square of the natural frequency of the libration is proportional to the product of the equatorial ellipticities of the mantle and inner-core geoid embodied in their multipoles (of two different types) of degree 2 and order 2 (such as the Large Low-Shear-Velocity Provinces above the core-mantle boundary) and (ii) studying the geophysical implications upon equating the said MICG libration to the steady 6year oscillation that are observed in the Earth's spin rate or the length-of-day variation (LOD). In particular, the MICG torsion constant is found to be (Gamma) over tilde (z) = C-IC sigma(2)(z) approximate to 6.5 x 10(19) N m, while the inner core's (B-IC - A(IC)) approximate to 1.08 x 10(31) kg m(2) gives the inner core triaxiality (B-IC - A(IC))/C-IC approximate to 1.8 x 10(-4),about 8 times the whole-Earth value. It is also asserted that the required inner-core ellipticity amounts to no more than similar to 140m in geoid height, much smaller than the sensitivity required for the seismic wave travel time to resolve the variation of the inner core.