Ionospheric electron density anomaly prior to the December 26, 2006 M7.0 Pingtung earthquake doublet observed by FORMOSAT-3/COSMIC

Six microsatellites termed Formosa Satellite 3 and Constellation Observing System for Meteorology, Ionosphere, and Climate (FORMOSAT-3/COSMIC or F3/C in short) are employed to study the 3-D structure of the ionospheric electron density during two M7.0 offshore earthquakes occurred near Pingtung, the most south county of Taiwan, on December 26, 2006. Results show that around the epicenters the F2-peak height descends and the ionospheric electron density between 300 and 350 km altitude significantly decreases within 5 days prior to the earthquakes.