Conversion of mesospheric HCl into active chlorine during the solar proton event in July 2000 in the northern polar region

Abstract

For the large solar proton event of July 2000, the Halogen Occultation Experiment instrument observed a short‐term decrease of mesospheric HCl in the northern polar region. Atmospheric chemistry and ion chemistry simulations show that HCl is converted into active chlorine species (ClO, Cl, and HOCl). Two main processes drive the transformation of HCl into active chlorine: reactions of negative chlorine species directly increase the concentrations of uncharged active chlorine compounds at the expense of HCl and the production of reactive O(1D) through N(2D) + O2 → O(3P, 1D) + NO has a considerable impact on the neutral chlorine chemistry.