D.: The response of ozone to solar proton events during solar cycle 21: A theoretical interpretation

Substantial ozone decreases at the stratopause and in the mesosphere have now been observed by instruments on the NIMBUS 7 solar backscattered ultraviolet (SBUV) and Solar Mesosphere Explorer (SME) satellites during solar proton events (SPE's) of solar cycle 21. Since the ozone depletion was only observed uring the SPE's, we believe that increased production of short-lived HO,, species by protons is responsible for the depletion. We find that one-dimensional time-dependent model calculations are close to agreement with the two satellite instrument measurements in the upper stratosphere and lower mesosphere only when the observed ozone decrease as a function of altitude is used in our model calculations. Most of the ozone depletion between 2 and 0.5 mbar (•45 and 55 km) was caused not by direct particle effects, but by the large ozone decreases at higher altitudes allowing increased penetration of ultraviolet to lower than normal altitudes. Our calculations are qualitatively in agreement with the SBUV measurements but tend to underestimate the ozone depletion for pressure levels between 1 and 0.3 mbar ( ~ 50 and 60 km). The calculated ozone depletions at 0.5 and 0.3 mbar ( ~ 55 and 60 km) agree fairly well with the observations of SME. The strong solar zenith angle (SZA) dependent depletion that was observed is predicted by the model. Larger SZA's generally reflected larger ozone depletions. How-ever, for SZA's greater than 84 ø during the July 13, 1982, SPE an ozone decrease less than the ozone decrease at 84 ø SZA and 1 mbar ( ~ 50 km) was predicted by theory and observed in SBUV data. Similar behavior was observed in three other SPE's. As far as we know, this ozone response is the first reported evidence for the much discussed self-healing effect