Diurnal and semidiurnal atmospheric tides observed by co-located GPS and VLBI measurements

The tropospheric zenith total delay (ZTD) derived from very long baseline interferometry (VLBI) is an important parameter of the atmosphere, reflecting various atmosphere-related processes and variations. In this paper, ZTD time series of the IVS rapid combined tropospheric product (2002-2006) with a 1-h resolution are used for the first time to investigate the diurnal and semidiurnal oscillations. Significant diurnal and semidiurnal variations of ZTD are found at all VLBI stations. The amplitude of the diurnal cycle S(1) is 0.6-1.2 mm at most of the VLBI stations, and the amplitude of the semidiurnal cycle S(2) is 0.2-1.9 mm, which nearly accord with the surface pressure tides S(1)/S(2) and co-located GPS estimated S(1)/S(2). The results indicate that the S(1) and S(2) behaviors are mainly dominated by the hydrostatic component, namely pressure tides. In general, the semidiurnal S(2) amplitudes are slightly larger than the diurnal S(1). While S, shows no clear dependency on site altitude, S(2) has a regular distribution with VLBI site altitude. The results are in accordance with predictions of the classic tidal theory [Chapman, S., Lindzen, R.S., 1970. Atmospheric Tides, Gordon and Breach, New York]. (c) 2008 Elsevier Ltd. All rights reserved.