Harmonic variations in the Earth Rotation determined using VLBI

The Earth rotation has harmonic variations caused by external torques exerted directly and directly with the Sun, the Moon, and the planets. Atmospheric and ocean circulation and variations in continental water storage cause additional excitation in the Earth rotation. While excitation due to external torques can be predicted very precisely, excitation due to air and water mass redistribution is not predictable. Layered non-rigid Earth response to the excitation differently than an absolutely rigid body. For instance a boiled egg rotates differently than a raw egg. Comparing observed variations in the Earth rotation with the excitation we can make inference about properties of the Earth's inferior that described by a number of parameter called compliances or basic Earth parameters.

As the first step of studying the response of the Earth to forcings, we have developed a procedure of estimating the spectrum of the Earth rotation by analysis of the time series of VLBI group delays since 1984.0 through present. I estimate close to 1000 constituents in a single least square analysis of 13 million VLBI group delays without resorting to intermediate time series. The frequencies of the estimated constituents are selected to cover

For close tidal and nutation constituents with frequency separation less than 1/Δt constraints are imposed on the ratio of complex amplitude estimates to be close to the radio of theoretical complex amplitudes.

Since the Free core nutation is the unpredictable process, we have to repeat the estimation procedure every 2–4 months. In a time domain this is equivalent to a trigonometric extrapolation of the free core nutation and updating the time series every 2–4 months.

Numerical tables of the results of analysis of VLBI observations.

The tables below contain the estimates of the expansion of the vector of small perturbations of the Earth rotation with respect to the empirical nutation series MHB and empirical precession expression Capitaine_2003 taken as the reference into Fourier series from processing all suitable geodetic VLBI observations. The components of the vector of the small perturbations correspond to Euler angles. The expansion includes so-called nutations and sub-diurnal variations in the Earth orientation parameters. This project is supported by NASA Earth Surface & Interior program, grant This NNX17AE02G.

Back to Astrogeo Center home page.
This web page was prepared by Leonid Petrov ()
Last update: 2018.09.04_06:23:40