New Estimation Of Triaxial Three-layered Earth's Principal Inertia Moments And Normal Mode Of Earth Rotation

The study of the Earth rotation mainly focuses on the rate changes in the rotation from west to east around the reference axis(the length of day variation),and the change in the position of the reference axis against the Earth itself and the inertial space(polar motion,precession and nutation).For a long time,the study of the Earth rotation has been mainly carried out based on the assumption of the biaxial symmetric earth model(ie,A(28)B(27)C,where A?B is the equatorial moment of inertia and C is the polar moment of inertia).However,with the improvement of modern observation accuracy and the need of scientific research and application,a large number of theoretical studies have pointed out that the traditional Earth rotation theory has shown some aspects of its shortcomings.The establishment of a high-precision triaxial Earth rotation theory is a challenging subject.In this paper,the high-precision gravitational field model EGM2008 and EIGEN-6C4 are used to determine the principal inertia moments(PIMs)of the whole earth.Meanwhile we use SLR and GRACE model's second order coefficients to determine the time constant principal moment of inertia.Based on the EEMD signal processing method,we also analyze them and observe the periodicity of the change of the PIMs.Until now,the calculation of the PIMs of the triaxial three-layered Earth mainly adopts the scaling method.This method assumes that the corresponding principal inertia axes of the layers coincide each other,but this is not the case.In this paper,a 3D mantle model Gy PSu M is used to calculate the PIMs of the mantle,and a rigorous tensor transformation rule is adopted to calculate the PIMs of different layers.Better estimates of the PIMs of different layers may provide better constrains on relevant physical parameters of the Earth's interior.Guo and Shen(2020)derived a new theory of the triaxial three-layered earth rotation(new theory for short).Appling the new estimated PIMs to their theory with considering various couplings to calculate rotational normal modes,the numerical calculations show that the periods of the Chandler Wobble(CW),Free Core Nutation(FCN),Free Inner Core Nutation(FICN)and Inner Core Wobble(ICW)are respectively 433.00,430.96,942.66 and 2735.84 mean solar days,which are well comparable with the corresponding values accepted at present in geoscience community.Based on the new theory,we studied the influence of inner core tilt and superrotation on the rotational normal mode.The results show that the inner core tilt mainly affects ICW the most,it also has a certain impact on FICN,a slight impact on FCN,and no significant impact on CW.Inner core super-rotation mainly affects ICW,with only minor impact on FICN,and no significant impact on CW and FCN.