The formation of ionosphere-magnetosphere ducts over the seismic zone

A physical mechanism of whistler duct formation due to electric field growt h in the ionosphere above the seismic zone is considered. The ducts are pla sma irregularities, stretched along geomagnetic field, with the transverse spatial scale of the order of 10 km and with the relative plasma density va riation over the background value of the order of 10%. It is shown that suc h structures are formed by the field-aligned currents as a result of the in teraction between the ionospheric electric field and the horizontal irregul arities of the ionospheric conductivity. The conductivity irregularities ar e excited by the instability of acoustic-gravity waves (AGW), developed in the ionosphere when the electric field exceeds a certain critical value. Si nce the ionosphere conductivity disturbances depend on the AGW parameters, the wave amplitude growth results in modulating the conductivity and formin g 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 th e oscillations and in the exponential growth of the disturbances, associate d with the acoustic-gravity wave. (C) 2000 Published by Elsevier Science Lt d. All rights reserved.