Abstract
We have studied the short‐term effect of the October–November 2003 series of solar proton events on the middle atmosphere. Using the proton flux measurements from the GOES–11 satellite as input, we modeled the effect of the precipitating particles between 26 October and 6 November with a one–dimensional ion and neutral chemistry model. Then we compared the results with ground‐based radio propagation measurements, as well as with NO2 and ozone profiles made by the GOMOS satellite instrument. The very low frequency signal experiences up to −7 dB absorption during the largest solar proton event, subsequently varying with time of day during the recovery phase. The model and radio propagation observations show very good agreement, suggesting that the model is capturing the impact of solar protons on the ionosphere. The model results show order‐of‐magnitude changes in odd hydrogen and odd nitrogen concentrations, as well as ozone depletion varying from 20% at 40 km altitude to more than 95% at 78 km. The magnitude and altitude distribution of ozone depletion is found to depend not only on the flux and energy of the protons but also on the diurnal cycle of atomic oxygen and ozone‐depleting constituents so that the largest depletions of ozone are seen during sunrise and sunset. The after‐event recovery of ozone is altitude‐dependent because of the differences in the recovery of odd hydrogen and odd nitrogen and also because of a relatively faster ozone production at higher altitudes. The modeled and measured NO2 profiles agree well at altitudes 35–60 km, particularly during times of large concentrations observed after the solar proton event onset. A comparison of the time series of ozone depletion shows a good agreement between the model and observations.