DE-1 AND VIKING OBSERVATIONS ASSOCIATED WITH ELECTRON CONICAL DISTRIBUTIONS

Data from the electron detectors on board the Swedish Viking satellite launched during a period of low solar activity and from the DE 1 satellite launched during active solar conditions have been examined for the occurrence and location of electron conical distributions and several conclusions can be drawn. First, we note that most of the best examples of electron conics observed by the V-3 experiment onboard Viking occurred in the afternoon sector in the range of magnetic local time 14 hours < MLT < 18 hours, at midaltitudes in the range 10,000 km < h < 13,500 km, with few occurring in the nightside auroral region, a region poorly sampled at altitudes greater than 5000 km. For the Viking data there is an association of electron conics with upper hybrid waves. DE 1 observations made by the high-altitude plasma instrument (HAPI) indicate that electron conics were observed in the midmorning sector and the late evening sector, and as has been reported earlier, the correlation with upper hybrid waves was good. The HAPI did not sample the afternoon sector. The electron conics observed on both satellites occurred in the presence of at least a modest (several kilovolts) potential difference beneath the satellite with a maximum energy that was usually, but not always, equal to or greater than the maximum energy of the electron conics; Two independent sets of observations by DE 1 suggest two distinct production mechanisms for electron conics. Examination of DE 1 electric field measurements from the plasma wave instrument during the observation of electron conics show simultaneous parallel oscillations in the frequency range 0.2 Hz < f < 0.5 Hz during one and perhaps two of four events examined, and upper hybrid waves were observed on all four events. In addition, recent observations of ''90-deg'' electron conics associated with auroral kilometric radiation source regions suggest a perpendicular heating mechanism produced by wave-particle interaction. Such distributions may be observed as electron conics at higher altitudes. These results suggest more than one possible source mechanism may be responsible for electron conics.