Conditions of Observation of Whistler Emissions in Space

The peculiarities of whistler wave fields spontaneously radiated by electron beams artificially injected into the Earth's ionosphere are discussed. The conditions of registration of the whistler wave packets by a remote on board VLF receiver have been analyzed ; they depend on mutual disposition of the electron gun and the VLF receiver as well as on the pitch angle of the injected electrons. It is shown that the internal frequency width of the whistler signal, connected with the ray representation of a wave field, depends on the distance between the emitting region of the beam and the receiver and determines the lowest bandwidth of the VLF receiver in use. It is found that near the double pole singularity at the Gendrin's velocity the energy loss of a single electron increases by a factor of the order of ratio of the background electron plasma frequency to the electron gyrofrequency. The estimations for the coherence length of the beam and the ratio of coherent to incoherent level of radiated whistler amplitude are also presented. The theoretical analysis of the whistler wave field near the beam front has revealed crucial differences between the registration pattern of high-frequency and whistler frequency emissions in active experiments similar to ARAKS [l] and APEX [2-3]