6300 Å night airglow and the geomagnetic control of the equatorial anomaly

Abstract

The intertropical red arc in the night airglow studied from a low latitude station (Mt. Abu, India) shows that in the years of high solar activity and on the magnetically quiet nights the arc is well developed and can be detected up to midnight or even in the early morning hours. In the beginning of the night and on many nights the arc appears overhead at 12° to 15° geomagnetic latitude. As the night progresses the movement of the arc towards the magnetic equator can be traced by azimuthal 6300 Å scanning. The intensity of the arc and its equatorward velocity vary from night to night. On the magnetically disturbed nights the arc is poorly developed, fades before midnight and its southward velocity is less. In the years of low sunspot activity also the arc is weak. These observations are consistent with those of the F-region Appelton equatorial anomaly at night time which presumably shows that the bulk of 6300 Å is due to the dissociative recombination of electrons with oxygen (and nitrogen) ions.