HEPPA-I: Composition changes after the “Halloween” solar proton event

The HEPPA-I exercise has focused on the intercomparison of MIPAS/Envisat data obtained in the aftermath of the “Halloween” SPE (26 October – 30 November 2003) with state of the art GCMs and CTMs. The large number of models participating in this exercise allowed for an evaluation of the overall ability of atmospheric models to reproduce observed atmospheric perturbations generated by SPEs, particularly with respect to NOy and ozone changes. This model validation represents a mandatory first step towards an accurate implementation of particle precipitation effects in long-term climate simulations. Further, the quasi-instantaneous perturbation of the atmosphere due to the SPE acts as a natural laboratory for studying stratospheric and mesospheric chemistry. This has allowed to test and to identify deficiencies in the chemical schemes, particularly with respect to nitrogen and chlorine chemistry, being relevant for stratospheric ozone. 


MIPAS/ENVISAT L2 data generated at IMK and IAA have been used. Among the species affected by SPEs we focused on NO, NO2, N2O, N2O5, HNO3, HNO4, H2O2, O3, ClO, HOCl, and ClONO2. Further, the meteorological conditions in both the models and the real atmosphere as observed by MIPAS have been assessed by comparing temperature and tracer fields (CH4 and CO).

Participating models



  • State-of-the art atmospheric models do a very good job in reproducing observed SPE-induced ozone depletion (within 5% on both short- and mid-term scales) and NOy enhancements (except region around 1 hPa).
  • Possible reasons for remaining differences have been identified (see Funke et al., 2011)
  • Differences in meteorology and/or initial state of the atmosphere in the simulations cause important dispersion of the model responses to the SPE.
  • SPE-induced changes of new species (H2O2, HNO4, and CO) have been identified.

Figure 1: The left panel shows MIPAS measurements of SPE-related ozone changes (bold dashed line) in comparison with numerous model simulations. The bold solid line represents the multi-model mean. The right panel is the same for NOy changes.