Very low frequency waves stimulated by an electron accelerator in the auroral ionosphere

The sounding rocket POLAR 5 carried a 10 keV electron accelerator and various diagnostic instruments in a mother-daughter configuration. Onboard wave receivers recorded several types of VLF wave phenomena directly associated with the operation of the accelerator, with delays from 5 to 50 ms after the injection of the electrons. These delayed after-effects range from broadband noise, f > 3 kHz, observed above 170 km, through narrow band emissions at 2 and 5.6 kHz which appeared when the rocket crossed a region with precipitation of energetic electrons, to emissions covering frequencies from 3–4 to well above 100 kHz observed within the E-region (150-95 km). The latter was also associated with apparent changes in electron density. The observed emission properties indicate that the region perturbed by the beam and the neutralizing return current to the daughter may be a favoured generation region.