Direct measurements of auroral kilometric radiation in a limited source

The enhancement of auroral kilometric radiation near its lowest frequency has been detected in the polar edge of the auroral zone in the POLRAD experiment with the INTERBALL-2 satellite. The difference between the local electron cyclotron frequency and the lowest frequency of enhanced radiation is $8$–$20$ kHz, indicating the closeness to the source of auroral kilometric radiation. According to the detailed analysis of low-frequency auroral kilometric radiation, its amplitude is larger than the “background”; values by a factor of $20$–$70$ and has amplitude modulation with characteristic periods of $40$–$60$ s. The increase in the intensity at low frequencies is attributed to the intersection of the source region by the satellite and the detection of waveguide modes in it.