Study on Seasonal Variability of Ionospheric TEC Estimated Using Signals of Compass/BeiDou Geostationary Satellites

Recent developments in GNSS systems include the launches of geostationary satellites used in Compass/BeiDou constellations. Those satellites have proven themselves to be a useful and convenient tool for ionospheric studies. In this work, the capability of geostationary GNSS data for studying the equatorial ionosphere is evaluated. To provide experimental data for this research, a GNSS base station located in Singapore (SIN1)is used, with long-term data being collected during October 2013-0ctober 2014. A modified technique for estimating TEC variations using geostationary GNSS data is applied. Wavelet power spectrums using complex Morlet wavelet are calculated for obtained long-term geostationary TEC series to study quasiperiodic variations at the scales of approximately one week to one month. To study inter-daily changes in the occurrence rate of small-scale ionospheric irregularities, ROTI index is calculated from obtained TEC series. Results are discussed in the context of various ionospheric phenomena that cause those seasonal variations.