Nitric oxide under different constraints imposed on ion-neutral chemistry

Abstract

The variation of nitric oxide density has been studied on the basis of a currently known ion-neutral chemical scheme under various theoretical constraints, viz. an increase of ionization in photochemical equilibrium, an increase of ionization with vertical transport and different eddy diffusion coefficients, an increase of ionization during nighttime and withdrawal of ionization at night. It is seen that in the absence of a horizontal transport, [NO] increases with increasing ionization. Downward vertical transport which increases with increasing ionization, contributes negligibly in determining the steady-state density of NO. The eddy diffusion has very little effect at heights above 90 km. It is also seen that the present chemical scheme is unable to explain [NO] as large as2× 10 11 cm −3 as observed by Zipf et al. (1970) during an enhanced auroral ionization at Fort Churchill indicating thereby that either the measurement is in error or there is a need of a powerful source of NO. The decay of [NO] is very slow at heights below the peak when ionization is switched off after attaining the maximum value due to the enhancement in ionization.