Coincident observations of ionospheric troughs and the equatorial plasmapause
Abstract
Explorer 45 traversed the plasmapause (determined approximately via the saturation of the d.c. electric field experiment) at near-equatorial latitudes on field lines which were crossed by Ariel 4 (~600km altitude) near dusk in May 1972 and on field lines which were crossed by Isis II (~1400km altitude) near midnight in December 1971 and January 1972. Many examples were found in which the field line through the near-equatorial plasmapause was traversed by Explorer 45 within one hour local time and one hour universal time of Ariel and Isis crossings of the same L coordinate. For the coincident passes near dusk, the RF electron density probe on Ariel detected electron density depletions near the plasmapause L coordinates when Ariel was in darkness. When the Ariel passes were in sunlight, however, electron depletions were not discernable near the plasmapause field line. On the selected near-midnight passes of Isis II, electron density depressions were typically detected (via the topside sounder) near the plasmapause L coordinate. The dusk Ariel electron density profiles are observed to reflect O + density variations. Even at the high altitude of Isis near midnight, O + is found to be the dominant ion in the trough region whereas H + is dominant at lower latitudes as is evident from the measured electron density scale heights. In neither local time sector was it possible to single out a distinctive topside ionosphere feature as an indicator of the plasmapause field line as identified near the equator. At both local times the equator-determined plasmapause L coordinate showed a tendency to lay equatorward of the trough minimum.
- Publication:
-
Planetary and Space Science
- Pub Date:
- December 1976
- DOI:
- 10.1016/0032-0633(76)90154-9
- Bibcode:
- 1976P&SS...24.1177G
- Keywords:
-
- Ionospheric Electron Density;
- Night Sky;
- Plasmapause;
- Upper Ionosphere;
- Ariel 4 Satellite;
- Explorer Satellites;
- Graphs (Charts);
- Isis-B;
- Lines Of Force;
- Geophysics