Composition changes after the "Halloween" solar proton event: the High Energy Particle Precipitation in the Atmosphere (HEPPA) model versus MIPAS data intercomparison study

Abstract

spheric models to reproduce observed atmospheric perturbations generated by SPEs, particularly with respect to NO y and ozone changes. We have further assessed the meteorological conditions and their implications for the chemical response to the SPE in both the models and observations by comparing temperature and tracer (CH 4 and CO) fields.Simulated SPE-induced ozone losses agree on average within 5 % with the observations. Simulated NO y enhancements around 1 hPa, however, are typically 30 % higher than indicated by the observations which are likely to be related to deficiencies in the used ionization rates, though other error sources related to the models' atmospheric background state and/or transport schemes cannot be excluded. The analysis of the observed and modeled NO y partitioning in the aftermath of the SPE has demonstrated the need to implement additional ion chemistry (HNO 3 formation via ion-ion recombination and water cluster ions) into the chemical schemes. An overestimation of observed H 2 O 2 enhancements by all models hints at an underestimation of the OH/HO 2 ratio in the upper polar stratosphere during the SPE. The analysis of chlorine species perturbations has shown that the encountered Published by Copernicus Publications on behalf of the European Geosciences Union. 9090 B. Funke et al.: HEPPA intercomparison study differences between models and observations, particularly the underestimation of observed ClONO 2 enhancements, are related to a smaller availability of ClO in the polar night region already before the SPE. In general, the intercomparison has demonstrated that differences in the meteorology and/or initial state of the atmosphere in the simulations cause a relevant variability of the model results, even on a short timescale of only a few days.

Solar forcing for CMIP6 (v3.2)

“…Direct measurements of SPE-caused OH and HO 2 enhancements have confirmed these early predictions (e.g., Damiani et al, 2008;Jackman et al, 2011Jackman et al, , 2014). Other observations of increased H 2 O 2 and of chlorine-containing constituents HOCl (an increase; see von Jackman et al, 2008;Damiani et al, 2008Damiani et al, , 2012Funke et al, 2011) and HCl (a decrease; see Winkler et al, 2009;Damiani et al, 2012) support the SPE-caused HO x enhancement theory. Since HO x constituents have relatively short lifetimes (hours), these SPE-enhanced species have only a short-term impact on ozone.…”

“…Precipitating energetic particles ionize the neutral atmosphere leading to the formation of NO (Porter et al, 1976;Rusch et al, 1981;Solomon et al, 1981) as well as some more minor species (Verronen et al, 2008;Funke et al, 2008;Winkler et al, 2009;Verronen et al, 2011a;Funke et al, 2011) due to both dissociation and ionization of the most abundant species, as well as due to complex ion chemistry reaction chains. The formation of NO x and HO x radicals leads to catalytic ozone loss that further triggers changes of the thermal and dynamical structure of the middle atmosphere.…”

Analysis and parameterisation of ionic reactions affecting middle atmospheric HO<sub>x</sub> and NO<sub>y</sub> during solar proton events

“…Seppälä et al, 2004;. Also, the magnitude of the nighttime NO y redistribution by negative ion chemistry is large enough to be detected by satellite-based observations of, for example, HNO 3 (López-Puertas et al, 2005b;Verronen et al, 2011;Funke et al, 2011). However, the daytime ionic NO y redistribution effect is counteracted at the upper altitudes by solar radiation through photochemical reactions, which drive rapid NO y changes.…”

“…However, atmospheric models using the parameterisation based on Solomon et al (1981) significantly underestimate the amount of HNO 3 produced compared to observations (e.g. Jackman et al, 2008;Funke et al, 2011).…”

“…In recent years, changes in other minor species have received substantial attention after a wealth of satellite observations of the winter polar regions became Published by Copernicus Publications on behalf of the European Geosciences Union. (López-Puertas et al, 2005b;von Clarmann et al, 2005;Orsolini et al, 2009;Verronen et al, 2008;Funke et al, 2008;Jackman et al, 2008;Winkler et al, 2009;Verronen et al, 2011;Winkler et al, 2011;Funke et al, 2011;Damiani et al, 2012).…”