F-layer and 6300-A measurements in the day sector of the auroral oval

Abstract

A circum-oval flight by the AFCRL flying ionospheric laboratory over the Arctic Ocean from Keflavik, Iceland, to Fairbanks, Alaska, passed completely around the auroral oval under conditions of darkness. Airborne all-sky cameras, a photometer, and a vertical incidence ionospheric sounder permitted the tracing out of the latitudinal and longitudinal (local time) extent of discrete auroral forms, auroral emissions, and ionospheric features. In the geomagnetic day sector, between 0820 and 1730 corrected geomagnetic (CG) local times, a continuous band of enhanced 6300-A emission (‘red band’) was found to be coincident with an F-layer irregularity zone (FLIZ). The red band was 2° to 5° wide and occurred between 75.0° and 80.0° corrected geomagnetic latitude. Although discrete auroras were absent at times, when they occurred, they lay within the red band. Past observations had indicated a close correspondence at noon between the red band and discrete aurora, but on this day no discrete aurora was observed in the noon sector. The red band and the FLIZ may have extended from the day sector into the night sector, but, unfortunately, the aircraft was not favorably located to determine the continuity. In the geomagnetic day sector the red band and the FLIZ are most probably produced by low-energy electrons that have precipitated through the polar cusp. Therefore, by tracing out the latitudinal and longitudinal (local time) extent of the red band and the FLIZ, we have mapped, over the extent of our observations, the zone of the ionospheric response to these low-energy electrons. This zone coincided with the dayside auroral oval.