Ionospheric electron content anomalies detected by a FORMOSAT-3/COSMIC empirical model before and after the Wenchuan Earthquake

An empirical model of ionospheric electron content (IEC), based on FORMOSAT3/COSMIC (F3/C) data, is constructed in order to detect pre-earthquake anomalies. The empirical model provides IEC with four parameters of local time, season, longitude and latitude. For the first time we try to detect anomalies in the F3/C IEC by comparing the model values with observations during the 12 May 2008 Wenchuan Earthquake period. It is found that around the epicentre an IEC enhancement appears on day 3 (9 May) and sequential IEC reductions occur on day 6 to day 1 (6 to 11 May) before the earthquake.