Response of mesopheric ozone to particle precipitation

In the mesosphere, water vapor photolysis is the major source of odd hydrogen (H, OH and HO₂) under normal conditions. The odd hydrogen produced may then be converted to H₂ by the reaction H + HO₂→ H₂ + O₂. This process is responsible for the calculated decrease in the H₂O mixing ratio and accompanying increase in the H₂ mixing ratio with altitude in the upper mesosphere and lower thermosphere. Charged particle precipitation events are calculated to produce the same effect, particularly in the 70–85 km region, thus temporarily resulting in enhanced conversion of H₂O to H₂ following such an event. Since odd hydrogen is produced predominantly by water vapor photolysis at these altitudes, decreased odd hydrogen concentrations are also anticipated. Odd hydrogen processes dominate ozone destruction in this region, and so an increase in ozone may occur if odd hydrogen concentrations decrease. We have examined the calculated time behavior of these processes in a numerical model using the August 1972 solar proton event as an example, and we present calculations indicating what might be observed in future events.