EMISSION TRIGGERING IN THE MAGNETOSPHERE BY CONTROLLED INTERRUPTION OF COHERENT VLF SIGNALS

Man-made VLF whistler mode (WM) waves are employed in controlled experiments on wave growth and triggering within the magnetosphere. In one such experiment, VLF pulses of 1-s duration are interrupted by a 10-ms gap. The data indicate that the growth rate and saturation level of the postgap section of a pulse are independent of the phase shift introduced in the gap. Moreover, it is often observed that rising frequency emissions are triggered during the 10-ms gap. The gap-induced emissions may then interact with the postgap signals. Suppressions and entrainments between those signals are often observed. An explanation of the phenomenon of gap-induced emissions is presented. An earlier observation that falling emissions always start with a small rise in frequency is confirmed.