On the amplitude of low-frequency signals in the nighttime ionosphere over thunderstorm discharges

It is shown that the origin of anomalous amplitudes of ULF/ELF signals in the topside ionosphere over thunderstorm discharges could be caused by the existence of regions of highly-ionized plasma in the lower ionosphere. The alternating current of the lightning electromagnetic pulse can generate in the region of highly-ionized plasma formed in the lower ionosphere due to the influence of thunderstorm discharges magneto-hydrodynamic waves propagating into the topside ionosphere. On the basis of the suggested model, the estimates of amplitude and duration of the Alfven mode propagating into the topside ionosphere are obtained, which agree with the measurements in rocket experiments over thunderstorms.