F layer irregularity observations of the SAR arc event of March 5–6, 1981


  • Jules Aarons


Over several years, various observers have recorded irregularities in the F layer of the ionosphere at latitudes which were identified as the plasmapause region. During the stable auroral red arc of March 5–6, 1981, intense irregularities were recorded using amplitude fluctuations of satellite beacon signals. In the case of this SAR arc optical intensity was well correlated with irregularity intensity. The location of the small scale (∼1 km) irregularities was centered at plasmapause latitudes; scintillation levels tapered off in the same longitude sector at trough latitudes and were of lower than normal intensity and of different nature at auroral latitudes. Reported optical measurements indicated no visible aurora until areas four L shells poleward. Low energy (<12 eV) electron precipitation accompanied by elevated electron temperatures have been reported within the region covered by SAR arcs. High neutral gas temperatures have also been reported. Scintillation of moderate level is not uncommon for the plasmapause region. In March 1981, approximately 60% of the nights had scintillation levels > 6 dB at 137 MHz lasting over one hour. These irregularities, frequently of lower intensity than those accompanying the March 5–6 SAR arc, are probably initiated by low energy precipitation at these latitudes. However the role of convection is not as yet clear in this latitude region.