Side‐band mutual interactions in the magnetosphere

Man-made whistler-mode waves (WM) in the magnetosphere can interact with other WM waves at nearby frequencies. This interaction must involve nonlinear processes because linear mechanisms cannot explain energy exchange between waves at different frequencies. Using the Siple VLF transmitter, an experiment was performed to determine the critical frequency separation within which wave-wave interaction (WWI) occurs. Using frequency-shift-keying (FSK) modulation techniques, several constant-frequency waves (side bands) were generated simultaneously. Preliminary results show that the energetic electrons in the magnetosphere can interact only with side bands generated by signals with short modulation periods, indicating that electrons have a finite 'memory time' during interaction with the waves. Using the value of this memory time, the length of the electron interaction region is estimated to lie between 2000 and 4000 km. It is also found that side bands with less than 50-Hz spacing mutually interact. Suppression and energy coupling among the side bands are often observed. The experiments in general reveal the 50Hz is the order of magnitude of the critical frequency range within which side bands interact. Mutual interaction between two side bands is explained by the overlap of the ranges of the parallel velocity (V/sub double-prime/) of electrons which the side bandsmore » can organize. The electrons in the overlap can exchange energy with both side bands and thus are responsible for the interaction. By estimating the size of the perturbed V/sub double-prime/ range the wave intensity is estimated to be of the order of 2.5--10 m..gamma.., in good agreement with satellite measurements.« less