Simultaneous measurements of stratospheric NO and NO2 and their comparison with model predictions

Measurements of stratospheric NO and NO2 from the last four flights of the Oxford radiometer are compared with predictions by a diurnal photochemical model. The rapid sunrise and sunset changes predicted by the model and detected on previous flights are confirmed. The observations suggest agreement with model predictions of the night time decay of NO2 associated with N2O5 production but do not fully verify them. For three of the flights this is due to insufficient measurement precision and short flight duration, and in the other flight it is due to disruption of the diurnal cycle by viewing parts of the stratosphere of different composition. The 1982 flight showed both NO and NO2 to be greatly reduced between 30 and 35 km. We attribute this to the eruption of the El Chichon volcano. Possible mechanisms for this reduction are discussed.