Subdiurnal variations in the Earth's rotation from continuous Very Long Baseline Interferometry campaigns

Abstract

Subdiurnal periodic effects in the Earth's rotation as seen by Very Long Baseline Interferometry (VLBI) are investigated on the basis of continuous VLBI observing campaigns (CONT) observed by the International VLBI Service for Geodesy and Astrometry (IVS). In 2008, the latest campaign (CONT08) was observed adding another valuable data set of 15 consecutive days to the series of CONT sessions. Among other things, CONT08 as well as CONT02 and CONT05 had been scheduled with the aim of observing short‐period variations of the Earth orientation parameters. In this publication, we describe an analysis, which is based on hourly estimates of polar motion and UT1‐TAI and a subsequent spectral analysis. The generation of the time series is performed with a modified analysis approach. We add the normal equations of each individual 24 hour session to one big equation system for the whole campaign where observations of adjacent sessions contribute to parameters at session borders simultaneously. Over the years, the experience in operating and analyzing the CONT sessions has improved and the procedures have been adapted for improvement of the results. However, at the same time, the observing network has suffered considerable changes. Thus, a comparative overview over the three CONT campaigns is given in this paper. The intermittent detection of periodicities as reported by Haas and Wünsch (2006) applies in this analysis for CONT02 as well. For CONT05 and CONT08 minute signals at periods of around 6 hours are contained in the amplitude spectra. The origin of these signals is still questionable.