Investigation of stronger diurnal ERP signals in summer derived from the VLBI CONT08 campaign

A series of very successful Continuous Very Long Baseline Interferometry Campaigns(CONT) have been carried out at irregular intervals since 1994.One of the goals is to support high-resolution earth rotation studies.The most recent CONT08 campaign was conducted with a network of 11 observatories at an increased recording rate of 512 Mbit per second over a fortnightly time span,from which stronger diurnal variations of the Earth Rotation Parameters(ERP) have been detected.We compared the high-frequency ERP from VLBI and GPS observations during CONT02,CONT05 and CONT08 with the atmospheric angular momentum functions derived from the National Centers for Environmental Prediction/National Center for Atmospheric(NCEP/NCAR) during these periods.We attribute the detected diurnal discrepancies between the theoretical models and the CONT08 observations to atmospheric excitations.