Anomalous Atmospheric Electric Field Just around the Time of Earthquakes: Case and statistical studies

In this paper, we report on the Atmospheric Electric Field (AEF) anomalies immediately before and after earthquakes (within 12 hours) in Japan. We demonstrate the results of a case study for several earthquakes that occurred close to our AEF observation network (within 100-200 km of the epicenter) under relatively fair local weather conditions. We found the common features for different earthquakes at different field sites e.g. 20~90 min period of clear anomalous signatures in wavelet spectrograms within a few hours around the main shock. Clear arrival time differences between AEF stations indicate propagating nature of observed AEF anomaly and enable us to calculate the propagation velocities and its occurrence timing. The observational results are compared with the dispersion relation of Internal Gravity Waves (IGW). Moreover, statistical results of the occurrence rate of the AEF anomalies support above mentioned results. Above-mentioned results may indicate the Lithosphere-Atmosphere Coupling, and we propose the physical mechanism of the observed electric field anomalies considering IGW originating from the epicenter region propagating over the field site and disturbing the local atmospheric electric field.