Large scale 6300Å, 5577Å, 3914Å dayside auroral morphology

• Published in: Geophysical research letters Vol. 7; no. 4; pp. 239 - 242
• Main Authors: Murphree, J. S., Cogger, L. L., Anger, C. D., Ismail, S., Shepherd, G. G.
• Format: Journal Article
• Language: English
• Published: Blackwell Publishing Ltd 01.04.1980
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/GL007i004p00239

Simultaneous observations at 6300Å, 5577Å, and 3914Å by the ISIS‐2 satellite are used to examine the morphology of auroras in the noon sector. While a minimum in intensity is generally observed in the 5577Å and 3914Å emissions from approximately 10 to 12 MLT, the 6300Å emissions may be most intense there. The latitudinal extent of 6300Å emissions is much greater than that of 5577Å and 3914Å and discrete features are generally not apparent in the 6300Å emission. Peak levels of 6300Å emission may occur at noon, prenoon, or afternoon and thus 6300Å emission is not confined to the "gap" or minimum in the day side discrete aurora seen at 5577Å and 3914Å. Substantial 6300Å emission occurs on closed field lines which is evidently due to boundary layer plasma. No optical signature of direct entry particles is identified. It is apparent that large differences in morphology and intensity exist between wavelengths in dayside auroras due to different source regions for the precipitating particles. For example, Cogger et al. (1977) have pointed out that the gap in dayside emissions (observed at 5577Å) is really a wavelength dependent feature in that 6300Å measurements indicate a maximum at noon rather than a gap (Shepherd and Thirkettle, 1973; Shepherd et al., 1976). Whalen and Pike (1973) have also shown that an enhanced band of 6300Å emission occurs across the dayside and when discrete midday auroras occur they locate within this band. Heikkila et al. (1972) have used 4278Å and 6300Å data from aircraft flights and satellite particle measurements to characterize the nature of the particle precipitation and the resulting aurora on the dayside. However, with ground based or direct satellite observations only a single meridian can be observed in a short period of time. In this paper, the "instantaneous" relationship between 6300Å, 5577Å and 3914Å emissions in the entire noon sector is studied to provide new information of the two dimensional morphology of these emissions. The data were taken by the Auroral Scanning Photometer (ASP) and the Red Line Photometer (RLP) on ISIS‐2 during the northern hemisphere winter solstice period in December 1974.