Ionospheric generation mechanism of geomagnetic pulsations observed on the Earth's surface before earthquake

Abstract

New generation mechanism of ULF geomagnetic oscillations observed on the Earth's surface in seismic zones is presented. This mechanism is based on the formation of periodic structure of ionospheric conductivity due to acoustic-gravity wave instability stimulated by DC electric field enhancement in the ionosphere. Interaction of the background electromagnetic ULF waves with such structure leads to an excitation of polarization currents and generation of narrow band gyrotropic waves at the 0.1– 10 Hz frequency range in the ionosphere. The magnetic field of these waves can be observed on the ground. Since the growth of seismic activity is often accompanied by DC electric field enhancement on the ground and in the ionosphere, the suggested mechanism can be considered as a possible source of the seismogenic geomagnetic pulsations generated before and during earthquakes.