SISTED
SISTED is monitoring simultaneous sudden enhancements in the ionospheric Total Electron Content (TEC) using the drift rate (second difference in time) of the carrier phase ionospheric combination (LI) which can be derived from GNSS signals gathered in real time by permanent receivers distributed world-wide. LI is linearly related to the Slant TEC (STEC) along the satellite-receiver ray path under consideration. The drift rate is used to generate a set of three Impact Parameters (IP). An IP tells (in %) how many satellite-receiver pairs are affected by an abrupt over ionisation (positive drift rate) simultaneously in a certain region. Then, the ray paths between satellites and receivers are categorised into three groups according to the Solar Zenith Angle (SZA) of their Ionospheric Piercing Point (IPP): Sunlit (0°≤SZA<70°), Dawn/Dusk (70°≤SZA<110°), or Night (110°≤SZA<180°). A solar flare is detected if the sunlit IP exceeds 74%.