A 12-hour case study of auroral phenomena in the midnight sector:Flayer and 6300-Å measurements

Abstract

A constant local midnight flight by the Air Force Geophysics Laboratory airborne ionospheric observatory over the North American continent from Goose Bay, Labrador, to Fairbanks, Alaska, stayed under the midnight sector of the auroral oval for 9 hours. Airborne all-sky cameras, a photometer, and a vertical incidence ionospheric sounder permitted the continuous monitoring, over two periods of auroral disturbance, of the latitudinal extent of discrete auroral forms, auroral emissions, and ionospheric features. These airborne observations were supplemented by auroral photographs from a Defense Meteorological Satellite Program satellite and by particle flux measurements from the Isis 2 satellite. From this data base a band of enhanced red (6300 Å) emission (red band) is identified. This red band extends over 2°–10° in latitude, is oval aligned, and contains within it auroras, both discrete and continuous, as observed from both satellite and aircraft. Thus it differs from the dayside red band, seen in previous measurements, which contains the discrete midday auroras but not the continuous aurora. In the night sector the red band was observed to contract in width near the substorm onset, to expand in width during the substorm expansive phase, to contract during the substorm recovery, and to continue contracting even after recovery was complete. An F layer irregularity zone (FLIZ) is associated with the red band, and in the night sector the red band and the FLIZ are most probably produced by low-energy electrons which have originated in the plasma sheet. Therefore meridional variations of the red band may reflect changes in the configuration of the plasma sheet.