Satellite‐Borne Observations of Ozone Impact by the November 2001 Solar Proton Event

The November 2001 Solar Proton Event (SPE) is one of the strongest events in the era of satellite observations. However, no observational case study of this exceptional event's impact on atmospheric chemistry has been reported. In this paper, we use satellite‐based observations from Optical Spectrograph and Infrared Imaging Systems (OSIRIS) to quantify the SPE impact on middle atmospheric O3 in the southern hemisphere during summertime conditions. The results show a relatively modest, yet detectable, O3 depletion in the upper stratosphere and lower mesosphere. Compared to the observations, the Whole Atmosphere Community Climate Model (WACCM‐D) simulates somewhat lower O3 levels before the event but captures well the relative ozone depletion. The largest depletion is seen on November 6th, after the Geostationary Operational Environment Satellite observed the peak proton fluxes. On this day, the O3 depletion was observed and simulated from the pole to 55°S geographic latitude. The daily polar cap (poleward of 60°S geographic latitude) averaged O3 profiles show a maximum depletion of 16.6 ± 2.2% at 1 hPa and 18.8 ± 3.3% at 1.5 hPa altitude, by OSIRIS and WACCM‐D, respectively. After the SPE, an enhancement in NOx is simulated by the results of the model within altitudes of the observation, which is well correlated with the observed and modeled O3 depletion. Challenges related to the detection of SPE impact on O3 in the summer hemisphere are discussed. We find that a careful analysis of simulation results can be essential when isolating the SPE impact from background variation.