THE SOURCE LOCATION AND BEAMING OF TERRESTRIAL CONTINUUM RADIATION

Plasma wave data from the spacecraft Dynamics Explorer 1 were used to study the source location and beaming of terrestrial continuum radiation. This study shows that the radiation usually is generated near the magnetic equator at radial distances ranging from 2.0 to 4.0 R(E). The radiation is beamed outward in a broad beam directed along the magnetic equator with a beam width of about 100-degrees. The overall frequency of occurrence of continuum radiation was found to be 60% with a sharp increase near the midnight meridian, increasing in the dawnward direction. Several case studies are presented to illustrate various characteristics of continuum radiation. The observed characteristics are then compared with the radio window model of Jones. Several characteristics not predicted by Jones' model are observed. These include large latitudinal asymmetries, an absence of a minimum in the occurrence and intensity at the equator, a tendency for higher frequency bands to come from larger and more diffuse source regions, and the emergence of several distinct beams from a single region. In particular the absence of a minimum in the occurrence and intensity at the equator and the emergence of beams of radiation at sharply distinct angles from one source region constitute evidence against the radio window model. Also, the basic equation for the beaming angle with respect to the magnetic equatorial plane is found to be a poor predictor of the observed beaming angle. The evidence against the radio window model is partially mitigated by the facts that the source of radiation is probably extended in space and frequency and that sometimes radiation from the Sun interferes with the direction finding. Overall, these observations imply that the radio window model does not fully explain the beaming pattern of continuum radiation.