The response of ozone to solar proton events during solar cycle 21: The observations

We have analyzed ozone profile data from the solar backscattered ultraviolet instrument on NIMBUS 7 from 1979 to the present and have found clear cases of ozone destruction associated with five solar proton events (SPE's) of this solar cycle: on June 7, 1979, August 21, 1979, October 13–14, 1981, July 13, 1982, and December 8, 1982. During the SPE on July 13, 1982, the largest of this solar cycle, we observed no depletion at all at 45 km but a 15% ozone depletion at 50 km increasing to 28% depletion at 55 km, all at a solar zenith angle of 85°. We find that there is a strong variation of the observed depletion with solar zenith angle, with maximum depletion occurring at the largest zenith angles (near 85°) decreasing with distance from the terminator. The observed depletion in every case was short lived, disappearing within hours of the end of the SPE, suggesting that HO x reactions were responsible for the observed ozone depletion.