Cyril Ron

Earth Orientation Parameters — Combination of Results Obtained by Different Techniques

The recently developed method of ‘combined smoothing’ is shortly introduced and its main philosophy presented. The method is tested with simulated data in order to demonstrate that the method is capable of removing both long-term and stepwise systematic errors in time derivatives of certain Earth Orientation Parameters measured by satellite methods.

Common 22-year cycles of Earth rotation and solar activity

Astronomical Institute, Academy of Sciences of Czech RepublicBoˇcn´i II, 141 31 Prague, Czech Republicemail: vondrak@ig.cas.cz, ron@ig.cas.czAbstract.The 22-year oscillations of the Earth rotation due to several geophysical processesin the core-mantle system, oceans, atmosphere and geomagnetic field are excited mainly by 22-year cycles of the solar activity. These geophysical processes produce their own oscillations ofthe Earth rotation with different periods around 22 years. The direct and indirect influence ofthe solar activity on 22-year cycles of the Earth rotation are separated from the core effects andcorresponding amplitudes are estimated by means of two approaches. The first, direct approachuses extended time series of Wolf’s numbers with22-year cycles, determined by sign alternationof even sunspot cycles. A linear regression between 22-year cycles of UT1 and solar activityis determined and this regression model is used to calculate the UT1 response to the 22-yearcycles of the solar activity. The second, indirect approach uses 22-year oscillation of the mean sealevel, caused by water evaporation due to variations of the total solar irradiance. The influenceof the mean sea level variations on the Earth rotation is calculated by means of an empiricalmodel of global water redistribution. The core-mantle effects on the 22-year UT1 variations aredetermined by excluding the UT1 response to the solar activity and core angular momentumdue to the geomagnetic field variations, according to the solutions from the Special Bureau oftheCore(SBC).Keywords.Sun: activity, sunspots, solar-terrestrial relations, time

Precession-Nutation Estimates from Optical Astrometry 1899.7–1992.0 and Comparison with VLBI Results

Abstract : The most recent solution of Earth Orientation Parameters (EOP) from the observations made by optical astrometry from 1899.7 to 1992.0 at 33 observatories is used to estimate the corrections of the present International Astronomical Union (IAU) model of precession-nutation. Since the resolution of the solution is about 5 days, only the terms with periods of 14 days and longer are considered. The results are compared with Very Long Baseline Interferometry-based corrections of the standard precession-nutation model, and the differences are discussed.

New solution of Earth Orientation Parameters in 20th century

We present a new solution of Earth Orientation Parameters, based on optical astrometry and catalog EOC-4.

The Determination of the Tidal Variations of the Plumb Line and the Nearly Diurnal Free Wobble from the PZT Observations

The optical astrometric observations contain beside the information on the Earth rotation parameters (polar motion, changes of the Earth’s rotation) also the information on other geodynamical events. There are the tidal influence on the Earth’s mantle, the influence of the inner construction of the Earth on the space motion of the rotational axes. We have tried to determine some of the events from the observations made on the PZT at Ondřejov Observatory during the years 1973–1990. We have modified slightly the least-square method for simultaneous estimation of corrections for star places, proper motions and short periodic latitude-longitude variations (Manabe et al., 1977). Also (Hefty, 1989) dealt with the similar problems aiming at the nearly diurnal free wobble by using the group results of the PZT at Ondfřejov.