Detection of phase disturbances of free core nutation of the Earth and their concurrence with geomagnetic jerks

Toshimichi Shirai,Toshio Fukushima,Zinovy Malkin

doi:10.1186/bf03352559

Abstract

Abstract We detected phase disturbances of the Free Core Nutation (FCN) of the Earth directly from the analysis of the Very Long Baseline Interferometer (VLBI) observation of the Earth rotation for the period 1984–2003 by applying the Weighted Wavelet Z-Transform (WWZ) method and the Short-time Periodogram with the Gabor function (SPG) method. During the period, the FCN had two significant phase disturbances in 1992 and 1998. These epochs coincide with the reported occurrence of geomagnetic jerks.

Highlights

The Earth rotation possesses a free nutational mode rotating clockwise with the period about 430 sidereal days as viewed from the inertial frame
Most of recent determinations of the Free Core Nutation (FCN) period are based on the estimation of the indirect effect using Very Long Baseline Interferometer (VLBI) nutation of the Earth rotation (e.g. Shirai and Fukushima, 2001a) or monitoring of the tidal variation of the gravity (e.g. Sato et al, 1994)
The theoretical model suggests that the instability of a layer at the top core and its downward propagation induce a step in the core-mantle torque strong enough to explain the phase disturbances in the CW (Bellanger et al, 2001)

Summary

Introduction

The Earth rotation possesses a free nutational mode rotating clockwise (retrograde) with the period about 430 sidereal days as viewed from the inertial frame. This mode, named as the Free Core Nutation (FCN), appears since the Earth has a rotating and elliptical fluid core (Toomre, 1974). The time variation of the FCN amplitude has been well studied from the direct effect in the VLBI data (e.g. Shirai and Fukushima, 2001b; Dehant et al, 2003). Most of recent determinations of the FCN period are based on the estimation of the indirect effect using VLBI nutation of the Earth rotation Exceptions are Roosbeek et al (1999) and Hinderer

Methods

Discussion

Conclusion