Source location measurements of terrestrial kilometric radiation obtained from lunar orbit

Abstract

Two‐dimensional source locations of individual terrestrial kilometric radiation (TKR) events have been measured by the Radio Astronomy Explorer‐2 (RAE‐2) spacecraft in lunar orbit. Although the average source location at 250 kHz is above the polar regions near the Earth (r ∼ 2‐3 R E ), approximately 10% of the events occur at > 7 R E from the Earth. Furthermore, there is considerable evidence for multiple sources and source motion over the time scale of tens of minutes. Recent TKR mechanism theories which assume that the emission occurs at or near the local electron plasma or gyrofrequency would predict generation much closer to the Earth's surface. We therefore suggest that alternative emission mechanisms or special propagation conditions are required to explain many TKR events.