In order to check the relationship between ground-based electromagnetic anomaly and ionospheric effect before the famous Wenchuan M_S 8.0 earthquake, three physical models have been established to simulate the communication process of electromagnetic energy from the Wenchuan hypocenter to the Earth’s surface, via the atmosphere to the ionosphere to cause ionospheric variations.

The geomagnetic and solar effect on Es is studied. The negative correlation between Es and geomagnetic activity at mid-latitude is related to the decreased meteor rate during storm period. The increased Es occurrence in high latitude relates to the changing electric field. The positive correlation between Es and solar activity at high latitude is due to the enhanced IMF in solar maximum. The negative correlation in mid and low latitudes relates to the decreased meteor rate during solar activity.

We use satellite data to analyze precursory anomalies of the western China Ms 7.1 Yushu earthquake by analyzing the signal-to-noise ratio (SNR) and using the full-wave model to illustrate a possible mechanism for how the anomalies occurred. The results show that very low-frequency (VLF) radio wave SNR in the ionosphere decreased before the Yushu earthquake. The full-wave simulation results confirm that electron density variation in the lower ionosphere will affect VLF radio signal SNR.

Underground nuclear explosion (UNE) can produce ionospheric disturbances through a lithosphere–atmosphere–ionosphere coupling mechanism, which is very similar with earthquakes. By using the total electron content observations and Swarm ionospheric current data, we have investigated the geomagnetic conjugate ionospheric disturbances. We proposed that the electric field generated during the UNE test can be an important mechanism for ionospheric disturbance.