The formation of ionosphere–magnetosphere ducts over the seismic zone

A physical mechanism of whistler duct formation due to electric field growth in the ionosphere above the seismic zone is considered. The ducts are plasma irregularities, stretched along geomagnetic field, with the transverse spatial scale of the order of 10 km and with the relative plasma density variation over the background value of the order of 10%. It is shown that such structures are formed by the field-aligned currents as a result of the interaction between the ionospheric electric field and the horizontal irregularities of the ionospheric conductivity. The conductivity irregularities are excited by the instability of acoustic-gravity waves (AGW), developed in the ionosphere when the electric field exceeds a certain critical value. Since the ionosphere conductivity disturbances depend on the AGW parameters, the wave amplitude growth results in modulating the conductivity and forming the additional currents due to the ionospheric electric field. The Joule heat released by these currents amplifies the AGW amplitude and, hence, the magnitude of the conductivity variations, which resulted in a growth of the oscillations and in the exponential growth of the disturbances, associated with the acoustic-gravity wave.