Seasonal variations in radial components of VLBI stations

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Abstract
We consider seasonal variations of baselength from global VLBI data adjustment. Spectral analysis of the baselength time series showed that annual and semiannual signals are significant. Estimates of the signal amplitudes and phases as well as relative rates are represented for 35 independent baselines. This allows us to determine the seasonal variations in radial components of 14 individual VLBI sites. The typical estimate is 4–7 mm for annual and 1–3 mm for semiannual harmonic. Possible reasons of the effect are discussed. This must be included into the routine procedure of observational VLBI adjustment to avoid possible bias of other parameter estimates.