Guangli Wang

The solar acceleration obtained by VLBI observations

Aims. The three-dimensional acceleration vector of the solar system barycenter was estimated from VLBI delay observations. We also provide a first physical explanation for this acceleration vector. Methods. Two methods for the acceleration estimation were developed in the analysis of the global astrometric/geodetic VLBI observations. One is to take the solar acceleration vector as a global parameter that is to be directly estimated. The second method is to obtain the acceleration by fitting the solar velocity variation time series produced from the VLBI data analysis. Results. The results of these two methods are consistent with each other within their uncertainties. The acceleration vector derived from the first method is (7.47 ± 0.46, 0.17 ± 0.57, 3.95 ± 0.47) mm s −1 yr −1 in the Galactic Cartesian coordinate system. Conclusions. The Galactocentric component of the solar acceleration we obtained agrees well with the predicted value from the rotation movement of the Sun and has a high accuracy. The detected strong vertical component perpendicular to the Galactic plane may be important for the research of the Milky Way.

An analysis of the polar motion series from VLBI observations

From the reduction of 2893 globally distributed astrometric and geodetic VLBI sessions from August 1979 to the end of 1998, coordinates of 722 radio sources at J2000.0, coordinates and velocities of 128 stations at J1997.0 and about 20 years Earth Orientation Parameters were estimated. From the analysis of the resultant polar motion series, the following are demonstrated: (i) During the VLBI data span the Markowitz wobble is not exhibited. (ii) The amplitudes of both annual and Chandler wobble show temporal variations, with the former being more obvious than the latter. (iii) Wavelet analysis shows that all the signals in the polar motion series are characterized by temporal variation in amplitudes. If we take any signal as strictly periodic, it is impossible to remove it completely from the polar motion series by least-squares fit because the hypothesis of a constant amplitude conflicts with VLBI measurements. (iv) By applying a filter, the secular polar motion was found to be (2.74 ± 0.01) masla towards (83.9 ± 0.3) ° W longitude, which is smaller in rate and more westward in direction compared with those determined from optical observations or the combination of optical and space geodetic observations.