Production of Odd Hydrogen in the Mesosphere1 During the January 2005 Solar Proton Event2

Using measurements from the MLS/Aura and GOMOS/Envisat instru-7 ments together with a 1-D ion and neutral chemistry model we study the8 changes in odd hydrogen and ozone in the mesosphere during the January9 2005 solar proton event. The unique observational data allow us for the first10 time to directly test the HOx production theory which involves complex ion11 chemistry. MLS measurements from the northern polar region show increases12 of OH concentrations by over 100 % around the stratopause, and by up to13 one order of magnitude in the middle mesosphere after the onset of the SPE.14 GOMOS measurements indicate decreases in O3 concentration throughout15 the lower and middle mesosphere, by up to 90%. The model predictions are16 in reasonable agreement with the observations. We point out that models17 using the so-called PHOx/Q parameterization to include the effects of ion chem-18 istry could underestimate the HOx production and the resulting ozone de-19 pletion.2