An analysis of the spatial distribution of dayside cleft optical emissions

Abstract

An analysis of measurements of the 4278‐Å, 5200‐Å, 5577‐Å, and 6300‐Å emissions obtained from a rocket launch through the postnoon dayside cleft into the polar cap ionosphere is reported. The 4278‐Å and 5577‐Å emissions show a clearly defined decrease in intensity at the poleward edge of the dayside particle precipitation, while the 5200‐Å emission extends well into the polar cap with only a slight decrease in intensity. The 6300‐Å emission displays a behavior intermediate between these extremes. The optical data are analysed by using a dynamical model of dayside cleft auroral processes incorporating transport by ion and neutral winds. It is concluded that neutral winds are responsible for modifying the spatial distribution of the 5200‐Å and 6300‐Å emission, while the ion drift component is negligible. In addition, it is found that (1) 80% of the 4278‐Å emission intensity is due to resonance fluorescence in the sunlit cleft ionosphere, (2) the reaction O2(c¹Σu−) + O → O2 + O(¹S) is consistent with the 5577‐Å data if the yield of O(¹S) from the dissociative recombination of O2+ is about 2%, and (3) the rate of the reaction N2+ + O → NO+ + N is apparently higher in the ionosphere than indicated by the laboratory measurements.