Summary
Unmodelled sub-daily periodic signals can propagate into time series of daily geodetic coordinates and tropospheric estimates at various different frequencies. Geophysical interpretations of geodetic products, particularly at seasonal timescales, can therefore be affected by poorly modelled signals in the geodetic analysis. In this study, we use two solid Earth tide models (IERS2003 and IERS1992) and analyses of global GPS data to demonstrate how this process occurs. Aliased annual and semi-annual signals are evident in the vertical component of the GPS time series, with the amplitudes increasing as a function of latitude up to approximately 2.0 and 0.4 mm, respectively. Tropospheric zenith delay estimates show differences at the 2mmlevel, with a dominant diurnal frequency. These results have significant implications in regard to the geophysical interpretation of GPS time series computed using the outdated IERS1992 model and, more generally, for any mis- or unmodelled periodic signals that affect geodetic sites.