NO+ and O+ in the high latitude F‐region

From an analysis of ionic reactions, we deduce that NO+ should be an important constituent of the high latitude F‐region. Owing to the rapid increase of the reaction O+ + N2 → NO+ + N with ion velocity and temperature, high latitude electric fields and consequent drifts act to deplete O+ in favor of NO+. As a consequence of this and the reduced rate of NO+ dissociative recombination arising from high electron temperatures, it seems that NO+ can, at times, replace O+ as the major F2‐region ion in the vicinity of the auroral ovals. The same processes should also be effective in creating nighttime electron density troughs composed primarily of NO+ in regions equatorward of the auroral ovals where large electric fields are often present.