Direction‐finding measurements of auroral kilometric radiation

Direction‐finding measurements with plasma wave experiments on the Hawkeye 1 and Imp 8 satellites are used to locate the source region of auroral kilometric radiation. This radiation has peak intensities between about 100 and 300 kHz and is emitted in intense sporadic bursts lasting for from half an hour to several hours. At peak intensity the total power emitted in this frequency range exceeds 10 9 W. The occurrence of this radiation is known to be closely associated with bright auroral arcs which occur in the local evening auroral regions. Hawkeye 1 provides direction‐finding measurements of kilometric radiation from observations at high latitudes (5–20 R E ) over the northern polar regions, and Imp 8 provides similar observations at large radial distances (23–46 R E ) near the equatorial plane. Results from both satellites place the source of the intense auroral kilometric radiation in the late local evening at about 22.0 hours LT and at a distance of about 0.75 R E from the polar axis of the earth. These direction‐finding measurements, together with earlier results from the Imp 6 satellite, strongly indicate that the intense auroral kilometric radiation is generated by energetic auroral electrons at low altitudes in the evening auroral zone. The observed source location is in good quantitative agreement with the source position expected from simple propagation and ray path considerations.