Intensity variation of ELF hiss and chorus during isolated substorms

Abstract

Electromagnetic ELF emissions (100‐1000 Hz) observed on the polar‐orbiting OGO‐6 satellite within three hours of the dawn‐dusk meridian consistently exhibit a predictable response to isolated substorm activity. Near dawn the emissions intensify during the substorm and then subside following the magnetic activity; the waves are most intense at L \>4, exhibit considerable structure and have been primarily identified as chorus. At dusk the response is entirely different; the wave intensity falls to background levels during substorm activity but subsequently intensifies usually reaching levels well in excess of that before the disturbance. The emissions near dusk extend to low L, are relatively featureless, and have been identified as plasmaspheric hiss. These features are interpreted in terms of changes in the drift orbits of outerzone electrons which cyclotron resonate with ELF waves.