Prediction and modelling of doubly-charged ions in the Earth's upper atmosphere

Abstract

We discuss the existence of the doubly-charged ions N2++, O2++ and O++ in the Earth's ionosphere through the theoretical computation of density profiles over the altitude range 100-500 km calculated with the TRANSCAR model. Photoproductions and electron impact productions are described in detail. The photochemical equilibrium assumption verified in this context yields density profiles, validated by comparison to the measurements of the satellite Atmosphere Explorer. Those three dications are lost essentially by dissociative recombination and collisions with the neutrals N2, O2 and O. The metastable lifetime of N2++ is 3 s and is estimated at 4 s for O2++. A survey of the sensitivity to geophysical parameters (solar activity, latitude and solar zenith angle) is also shown. Emphasis is cast on the need for rate constants for chemical reactions involving doubly-charged ions. The fit of the model yields an estimated value of 1.06±0.40×10-10 cm3 s-1 for the rate constant of the O+++O reaction. © European Geosciences Union 2005.