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The Features of Quasi-Periodic ELF-Radiation Outside the Plasmosphere
New information about ELF/VLF emissions is being considered outside the plasmasphere, contained in the data of observations performed on the Van Allen Probe spacecraft. Near the apogee of the trajectory behind the plasmasphere, quasi-periodic sequences of bursts of electromagnetic radiation at frequencies below 2 kHz with deep intensity modulation were observed. Morphologically, the separate burst of radiation is similar to a fragment of QP 2 emissions. The burst sequences under consideration can have different time structures. First, they can be clearly periodic. Second, bursts of different intensities can periodically alternate in them. Third, the sequence of bursts can have a more complex temporal structure. The excitation of radiations that are considered noise by their nature probably occurs during the development of cyclotron instability in detached plasma regions, which exist outside the plasmasphere after magnetic disturbances. Many properties of radiation are explained by the theory of a plasma magnetospheric maser, which admits the existence of a self-oscillating process of radiation generation due to modulation of the anisotropy of the distribution function of energetic electrons. The theory explains the new results of observations of quasi-periodic emissions with a more complex temporal structure in the presence of a periodic external influence on the dynamics of a plasma magnetospheric maser. In all the considered cases, the absence of geomagnetic pulsations with periods comparable to the periods of repetition of spectral forms on the spectrograms of electromagnetic radiation was checked in the data of the spacecraft magnetometer. Model calculations have shown
that an acoustic-gravity wave in the ionosphere at the base of a magnetic field tube with a cloud of detached
plasma can provide the formation of the observed temporal structure of radiation.