Coordinated airborne and satellite measurements of equatorial plasma depletions

A series of experiments conducted in December 1979 to investigate the structure of plasma depletions in the low latitude, nighttime ionosphere is discussed. Density biteouts of about one order of magnitude in the dominant ion, O(+), are mapped to lower altitudes along magnetic field lines for comparison with 6300-A and 7774-A O I airglow depletions. Owing to the different airglow production mechanisms (dissociative recombination of O2(+) for 6300 A and radiative recombination of O(+) for 7774 A), the 6300-A depletions reflect plasma depletions near the bottomside of the F layer, while those at 7774 A are located near the peak of the layer. The O(+) biteouts map directly into the 7774-A airglow depletions in the same hemisphere and also when traced into the opposite hemisphere, which suggests magnetic flux tube alignment over north-south distances of approximately 2220 km. The 6300-A (bottomside) depletions are found to be wider in longitude than the 7774-A (F-peak) depeletions near the equatorward edge of the Appleton anomaly.