SPATIAL RELATIONSHIPS BETWEEN HF RADAR AURORA OPTICAL AURORA AND ELECTRON PRECIPITATION

HF backscatter data were obtained at College, Alaska, during 16 passes of satellite-borne particle-detectors near the College meridian. On the nightside of the Earth the gross position and the occurrence of precipitating auroral electrons and radar aurora were in good agreement, whereas on the dayside, part of the electron precipitation was generally not accompanied by radar aurora. Previous work has shown that the precipitation of auroral electrons into the dayside atmosphere occurs in two distinct zones of latitude. The characteristics of the incoming electron flux in the poleward of the two zones correspond to those required for the production of the observed characteristics of the dayside optical aurora in the auroral oval. The HF radar aurora was found to be closely associated in space with the electron flux in the pole-ward precipitation zone. During a 3-month period when simultaneous optical and HF radar observations were made hourly on the College meridian, 14 instances were found when precise auroral positions could be derived by photometric triangulation. Most of the HF echoes examined originated close to the narrow, discrete auroras used for the triangulation measurements. A study also showed that when no aurora occurred in a given general region, no auroral echoes were received from that region. It is concluded that HF radar aurora are closely associated in time and space with oval aurora, although exact correspondence was not found. Thus, the good agreement between the various data indicates that HF radars can track the aurora in the oval with sufficient reliability that the radar data can be used in the study of the morphology of the auroral oval. © 1969.