Earth's rotations and core-mantle coupling

基于一个真实的地球密度和弹性结构模型，对两个核相对于地幔的轴向和赤道旋转与第四纪冰川旋回进行了评价。该流变模型由可压缩的麦克斯韦粘弹性地幔、无粘的外核和不可压缩的麦克斯韦粘弹性内核组成。在外核边界没有摩擦力矩的模型中，预测的外核和内核轴向旋转的最大幅度分别为102 ° yr^<-1>和101 ° yr^<-1>，尽管预测对下地幔粘度敏感。这些数值明显大于由观测到的磁向西移值（0.02 ° yr^）推断的外核流速<-1>。然而，在赤道旋转的两个核心预测脉动条款与一个周期为1225年。如果我们考虑到最近的地球发电机模型在核心流上产生了真实的特征， 关于我们 轴向旋转的结果可能需要边界处的某种耦合机制。因此，我评估的差异旋转，考虑到时间依赖的电磁（EM）耦合在核幔边界（CMB）和内核边界（ICB）。对于一个现实的径向磁场在CMB估计从一个向下延续的表面磁场，轴向和赤道旋转耦合通过在边界处的摩擦力矩。根据地球章动、岁差和日长变化的研究结果，对地幔底层电导率为10^8 S的电导率模型进行了差分旋转评价。赤道自转的长期部分对描述电磁转矩的这些参数不太敏感，并且与没有摩擦转矩的参数类似。两个核的长期轴向自转的最大幅度最大为0.02° yr^<-1>。然而，这些模型，产生两个核心的赤道旋转和脉冲状的条款在整个地球和外部和内部核心的轴向旋转的脉动项。虽然通过摩擦力矩的耦合可能导致脉冲状项的激发，但脉动项的激发可能是描述两个核心的赤道旋转的欧拉方程中固有的。这些项的周期对CMB处的径向磁场的大小和电导率结构都很敏感。一个尖锐的孤立的光谱峰是没有预测的模型与薄的导电层（200米）在地幔的底部。对于一个模型的导电层厚度为100公里，然而，尖锐的频谱峰值预测在10225年和10225年的脉动和脉冲状条款，分别，虽然这些取决于在CMB的径向磁场的强度。研究结果表明，地球发电机可能受到气候变化的影响，通过长期和混乱的轴向和赤道差分旋转的两个核心。少

The axial and equatorial rotations of both cores relative to the mantle associated with the Quaternary glacial cycles were evaluated based on a realistic earth model in density and elastic structures. The rheological model is composed of compressible Maxwell viscoelastic mantle, inviscid outer core and incompressible Maxwell viscoelastic inner core. In models with no frictional torques at the boundaries of the outer core, the maximum magnitude of the predicted axial rotations of the outer and inner cores amounts to 〜2° yr^<-1> and 〜1° yr^<-1>, respectively, although the predictions are sensitive to the lower mantle viscosity. These values are significantly larger than the flow velocity of the outer core inferred from the observed magnetic westward drift of 〜0.2° yr^<-1>. Pulsation terms with a period of 〜225 years are, however, predicted in the equatorial rotations for both cores. If we consider that the recent geodynamo modelling produces realistic features on the core flow, then the … More results for axial rotations may require some coupling mechanism at the boundaries. I therefore evaluated the differential rotations by taking into account a time-dependent electromagnetic(EM) coupling at the core-mantle boundary(CMB) and inner core boundary(ICB). For a realistic radial magnetic field at the CMB estimated from a downward continuation of surface magnetic field, the axial and equatorial rotations couple through the fricctional torques at the boundaries. The differential rotations were evaluated for conductivity models with the conductance of 10^8 S of the bottom layer of the mantle inferred from the studies of nutation and precession of the Earth and variations of length of day(LOD). The secular parts of equatorial rotations are less sensitive to these parameters describing the EM torque, and similar to those with no frictional torques. The maximum magnitude of the secular axial rotations of both cores is 〜0.02° yr^<-1> at most. These models, however, produce both pulsation terms in the equatorial rotations of both cores and pulse-like terms in the axial rotations of the whole Earth and outer and inner cores. While the coupling through the frictional torque probably causes the excitation of the pulse-like terms, the excitation of pulsation terms may be inherent in the Euler's equations describing the equatorial rotations of both cores. The periods of these terms are sensitive to both the magnitude of the radial magnetic field at the CMB and the conductivity structure. A sharp isolated spectral peak is not predicted for a model with a thin conductive layer (〜200 m) at the bottom of the mantle. For a model with a conductive layer of 100 km thickness, however, sharp spectral peaks are predicted at the periods of 〜225 and 〜25 years for pulsation and pulse-like terms, respectively, although these depend on the strength of the radial magnetic field at the CMB. The results obtained in this study may suggest that the geodynamo may be affected by climate changes through both the secular and chaotic axial and equatorial differential rotations of both cores. Less