Simultaneous observations of discrete and diffuse auroras by the Isis 2 satellite and airborne instruments

All-sky camera and photometric data were obtained by airborne instrumentation as a function of latitude and time during the course of an auroral substorm. During the substorm recovery phase the Isis 2 satellite passed within 60 km of the aircraft zenith. The discrete and diffuse auroral regions were identified from the airborne all-sky camera data. Satellite and photometric observations of the corresponding incoming particles led to the following conclusions: (1) The diffuse and the discrete auroras seen in the all-sky camera data correspond to the two different particle precipitation regions observed from satellites and referred to as CPS and BPS, respectively (Winningham et al., 1975). (2) The diffuse auroral region is associated with high-energy stably trapped energetic electrons, and the discrete aurora is poleward of the stable electron trapping boundary. (3) The latitudinal distribution of characteristic particle energies does not change in a relative sense during the poleward expansion, but expands 'accordionlike.' (4) The height-integrated intensity ratio of the red (6300 A) to green (5577 A) emissions of atomic oxygen is a good indicator of the characteristic energy of the incoming particle spectrum. (AIP)