The chemistry of daytime sprite streamers - a model study

The chemical processes in daytime sprite streamers in the altitude range of 30-54 km are investigated by means of a detailed ion-neutral chemistry model (without consideration of transport). The focus lies on nitrogen, hydrogen and oxygen species, and in particular on ozone perturbations. Initial effects of the breakdown electric fields at the tip of sprite streamers include a short-term loss of ozone due to ion-chemical reactions, a production of nitrogen radicals, and a liberation of atomic oxygen. The latter leads to a formation of ozone. In terms of relative ozone change, this effect decreases with altitude. The model results indicate that the subsequent ozone perturbations due to daytime sprites streamers differ considerably from the ones of night-time events. For night-time conditions, reactive nitrogen produced at the streamer heads is rapidly converted into significantly less reactive NO2, and there is basically no ozone depletion. The situation is different for daytime conditions where NOx causes catalytic ozone destruction. As a consequence, there is significant ozone loss in sprite streamers in the daytime atmosphere, in particular at higher altitudes. At an altitude of 54 km, ozone in the streamer column has decreased by about 15% fifteen minutes after the sprite event.