| 3 | Assessment of the effect of three-dimensional mantle density heterogeneity on Earth rotation in tidal frequencies显示文摘In this paper,we report the assessment of the effect of the three-dimensional(3D)density heterogeneity in the mantle on Earth orientation parameters(EOP)(i.e.,the polar motion,or PM,and the length of day,or LOD) in the tidal frequencies.The 3D mantle density model is estimated based upon a global S-wave velocity tomography model(S16U6L8) and the mineralogical knowledge derived from laboratory experiment.The lateral density variation is referenced against the preliminary reference earth model(PREM).Using this approach the effects of the heterogeneous mantle density variation in all three tidal frequencies(zonal long periods,tesseral diurnal,and sectorial semidiurnal)are estimated in both PM and LOD.When compared with mass or density perturbations originated on the Earth's surface such as the oceanic and barometric changes,the heterogeneous mantle contributes less than 10% of the total variation in PM and LOD in tidal frequencies.However,this is the gap that has not been explained to close the gap of the observation and modeling in PM and LOD.By computing the PM and LOD caused by 3D heterogeneity of the mantle during the period of continuous space geodetic measurement campaigns(e.g.,CONT94) and the contribution from ocean tides as predicted by tide models derived from satellite altimetry observations(e.g.,TOPEX/Poseidon) in the same period,we got the lump-sum values of PM and LOD.The computed total effects and the observed PM and LOD are generally agree with each other.In another word,the difference of the observed PM and LOD and the model only considering ocean tides,at all tidal frequencies(long periods,diurnals,and semidiurnals) contains the contributions of the lateral density heterogeneity of the mantle.Study of the effect of mantle density heterogeneity effect on torque-free Earth rotation may provide useful constraints to construct the reference earth model(REM),which is the next major objective in global geophysics research beyond PREM. | Lanbo Liu Benjamin F.Chao Wenke Sun Weijia Kuang | 2016 | Geodesy and Geodynamics2016，7，6： | 0 |
| 4 | Reassessment of electromagnetic core-mantle coupling and its implications to the Earth’s decadal polar motion显示文摘The observed Earth’s polar motion on decadal time scales has long been conjectured to be excited by the exchange of equatorial angular momentum between the solid mantle and the fluid outer core,via the mechanism of electromagnetic(EM)core-mantle coupling.However,past estimations of the EM coupling torque from surface geomagnetic observations is too weak to account for the observed decadal polar motion.Our recent estimations from numerical geodynamo simulations have shown the opposite.In this paper,we re-examine in detail the EM coupling mechanism and the properties of the magnetic field in the electrically conducting lower mantle(characterized by a thin D '-layer at the base of the mantle).Our simulations find that the toroidal field in the D'-layer from the induction and convection of the toroidal field in the outer core could be potentially much stronger than that from the advection of the poloidal field in the outer core.The former,however,cannot be inferred from geomagnetic observations at the Earth’s surface,and is missing in previous EM torque estimated from geomagnetic observations.Our deduction suggests further that this field could make the actual EM coupling torque sufficiently strong,at approximately 5×1019 Nm,to excite,and hence explain,the decadal polar motion to magnitude of approximately 10 mas. | Weijia Kuang Benjamin F.Chao Jianli Chen | 2019 | Geodesy and Geodynamics2019，10，5： | 0 |
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