It has been well recognized that the radio occultation technique using GPS signal received by LEO satellite can be applied to the measurements of the globe-wide atmospheric parameters above the point tangent to the GPS signal ray path, including atmospheric refractivity, temperature, water vapor, and ionopsheric electron density. A number of international scientific projects associated with GPS radio occultation have been or are now being conducted, including GPS/MET (USA), SAC-C (Argentina), CHAMP (Germany), FORMOSAT-3/COSMIC (Taiwan), GRACE (Germany), EQUARS (Brasil), and so on, in which 6 COSMIC satellites have been successfully launched in the middle of April 2006 and functioned in parking and operation orbits as expected. With nearly uniform distribution of the radio occultation sounding data over the land and ocean of the Earth, the studies of the global meteorological variations, large scale atmospheric wave propagations, ionopsheric responses to the solar and magnetic disturbances, and so on, are promising and beneficial. Moreover, combined with other data obtained by models and adequate instruments, the regional weather forecasting and the investigations of the local ionospheric irregularities may also be possible using GPS occultation data. This special session solicits the papers related to the applications of radio occultation sounding data to the studies of the lower and upper atmospheres, such as weather analysis and prediction, global climate change, gravity wave activity, atmospheric wave propagation, coupling between upper and lower atmospheres, ionospheric irregularities, ionospheric modeling, and so on. In addition, the validation of the radio occultation data, gravity and geodesy, data assimilation, and theoretical studies of radio occultation technique are also welcome.