The morphology of n and no in auroral substorms

The effects of a typical auroral electron precipitation substorm sequence on odd nitrogen species in the thermosphere have been investigated. The analysis makes use of the time dependent model of the aurora developed by Roble and Rees (1977), which couples the thermal properties to the ionospheric chemistry and transport self-consistently and includes diffusive transport of NO, N(²D) and N(⁴S). A substantial increase in the E-region density of NO or of N(⁴S) is predicted, with the result depending on the production ratio of N(²D) to N(⁴S) in the aurorally dominant source mechanism, electron impact dissociation of N₂. A production ratio that favors N(²D) by a factor of one half or larger leads to enhancement of NO, while a ratio of $\text{1}\text{4}\text{N}\text{(}{}^2\text{D}\text{)+}\text{3}\text{4}\text{N}\text{(}{}^4\text{S}\text{)}$ results in a buildup of N(⁴S). The cyclical behaviour of the substorm, i.e. alternate intervals of electron precipitation and quiet periods, accentuates the scavenging effect of the initially dominant odd nitrogen species upon the less abundant one.