The charge structure of thunderstorms revealed by the ground electric field monitoring network deployed in Tainan, Taiwan

The generation and variation of the atmospheric electric field (hereafter E-field), which exists under all meteorological conditions and drives the charge flow around the Earth globally, and many natural phenomena such as lightning, thunderstorms, and even earthquakes have been observed accompanied by surface E-field disturbances; therefore, E-field observations are also used in disaster warnings. Since 2021, a ground E-field network consisting of three stations using in-house electric field mills has been deployed in the Tainan area, covering two known seismic faults, to monitor the characteristics of the e-field variation caused by diurnal cycle, thunderstorms, and earthquake precursor.

The results indicated that the small-area E-field variation did not follow the Carnegie curve because local effects (aerosols, weather conditions, and environment) masked the variations of the global electrical circuit. In addition, the analysis of the disturbed E-field showed that more than 90% of the single-cell thunderstorms observed in the surface E-field could be classified as mature and dissipating stages. Each disturbance lasted approximately 34 minutes and was accompanied by an average of 1.4 times E-field phase reversals. Among them, the negative reversal of the surface electric field caused by the negative charge layer was relatively strong and frequent. Eventually, triangulation was used to reconstruct the charge structure of four distinctive single-cell thunderstorm events and restore the surface E-field responses during the passage of clouds. The correlation coefficients between the simulation and the observation were higher than 85%, and the trajectory and speed of the thunderclouds is also successfully reproduced by the recorded e-field data. Furthermore, some preliminary conclusions about earthquake precursors were drawn by analyzing the surface E-field.