Study of the ionospheric anomaly before the Wenchuan earthquake

Abstract

The behavior of the ionosphere before the Wenchuan earthquake is analyzed with the global TEC and ionospheric foF2 observed at Xiamen. It can be found from TEC maps that in the afternoon (16–18LT) on May 9, 2008, 3 days before the earthquake, there is an enhancement of TEC with an amplitude of 10–15 TECU appearing in the east-south direction of Wenchuan, and another enhancement appears at the conjugate region of the Southern Hemisphere with an amplitude of 10 TECU, but no obvious increment or decrement can be seen in other regions on global scale. It can also be found that on May 6 (6 days before the great earthquake), there is a decrement of TEC with small amplitude of 4TECU and larger area with 80° along the longitude in southern China, and there is no synchronous decrement observed at the conjugate region of the Southern Hemisphere. There are also many anomalies observed by ionosondes across China. The result shows that foF2 and TEC abnormally increased, which is different from pervious results that ionospheric parameters decreased prior to earthquakes. Preliminary results suggest that the enhancement on May 9 maybe has a close relationship with the possible enhancement of ionospheric electric fields, and it may be an ionospheric precursor of earthquakes. Whereas the decrement on May 6 may be attributed to the geomagnetic disturbance appearing on May 5.