We obtained average global distributions of standard deviations of mesoscale variations of atmospheric radio refraction at the altitudes 5 - 35 km from the data of radio occultation experiments during the low-orbit GPS satellite CHAMP mission from year 2001 to 2009. Filtering of vertical profiles of atmospheric radio refraction allows us to determine the standard deviations of variations having vertical scales less than 8 km. Time-latitudinal distributions of zonal-mean standard deviations exhibit significant inter-annual variations at different heights. Seasonal changes of standard deviations of atmospheric radio refraction were investigated. Quasi-biennial oscillations have been detected at low latitudes. The cause of mesoscale standard deviations of atmospheric radio refraction may be acoustic-gravity waves, turbulent and convective motions in the atmosphere.