The development of Satellite Based Augmentation Systems (SBAS) provides the possibility to retrieve ionospheric Total Electron Content (TEC) from the dual frequency L1/L5 observations from a number of geostationary satellites using the same approach as for dual frequency GPS/GLONASS observations. In this work we study L1/L5 signals of Indian GAGAN geostationary satellites observed with geodetic GNSS receivers at several stations at midlatitudes and estimate corresponding geosta- tionary TEC variations. We present geostationary SBAS TEC response to X1.7 solar flare on October 25, 2013 showing good correlation between TEC and EUV flux for the stations at the sunlit hemisphere. We also present SBAS TEC response to geomagnetic field variations during moderate geomagnetic storm on June 1, 2013 showing examples of positive anomalies of order of tens TECU in TEC diurnal variations during main storm phase.