Diffuse and Discrete Optical Emissions at the Poleward Border of the Morning Auroral Oval

摘要

A meridian scanning photometer was used to supplement all sky camera observations of high latitude morning auroras. A 5 to 10 deg wide area of diffuse light is recorded at the poleward edge of the morning to noon auroral oval. Discrete auroras known as high latitude morning auroras are embedded in the veil. Discrete as well as diffuse emissions are observed on practically every clear morning, both limited by a well defined border oriented along the geomagnetic meridian between 03 and 07 corrected geomagnetic time. The ratio I 6300A/I 5577A is greater in the diffuse background than in the discrete forms. The intensity of the diffuse emission has its maximum near 75 deg, coinciding with the oval. The intensity at this latitude generally increases 1 to 2 hr before the occurrence of the high latitude veil.