Generation of VHF radio emissions by electric discharges in the lower atmosphere over a seismic region

Observational data of the seismic related VHF radio emissions at 41 and 53 MHz obtained at the four stations of Create Island are presented. The epicenter of EQs is located at the distance more than 300 km behind the horizon. It was shown that VHF radiation is generated at the altitudes 1–10 km in the atmosphere over the epicenter of EQs. The theory of generation of electromagnetic radiation by random electric discharges was developed. These discharges are excited by DC electric field enhanced up to the breakdown value in the atmosphere. The field is connected with the electric current flowing in the atmosphere–ionosphere circuit, whose source is generated by convective transport of charged aerosols, which are injected in the atmosphere by soil gases during the enhancement of seismicity. Calculations of the spectrum of electromagnetic radiation are derived, and the theoretical results are confirmed by observation data.

Research highlights
► VHF radiation is generated at the altitudes 1–10 km in the atmosphere during several days before the EQs.
► DC electric field can reach the breakdown value in the lower atmosphere over seismic region.
► The electric discharges are formed by breakdown electric field at the altitudes up to 10 km in the atmosphere.
► The electric discharges are the source of VHF radiation in the diapason (10–100) MHz.