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Understanding the altitude distribution of particle precipitation forcingis vital for the assessment of its atmospheric and climate impacts. However,the proportion of electron and proton forcing around the mesopause regionduring solar proton events is not always clear due to uncertainties insatellite-based flux observations.Here we use electron concentration observations of the European IncoherentScatter Scientific Association (EISCAT) incoherent scatter radarslocated at Tromsø (69.58° N, 19.23° E) toinvestigate the contribution of proton and electron precipitation to thechanges taking place during two solar proton events. The EISCAT measurementsare compared to the results from the  Sodankylä Ion and Neutral ChemistryModel (SIC). The proton ionization rates are calculated by two differentmethods – a simple energy deposition calculation and the AtmosphericIonization Model Osnabrück (AIMOS v1.2), the latter providing also theelectron ionization rates.Our results show that in general the combination of AIMOS and SIC is able to reproduce the observedelectron concentration within ± 50% when both electron and proton forcing isincluded. Electron contribution is dominant above 90 km, and can contributesignificantly also in the upper mesosphere especially during low or moderateproton forcing. In the case of strong proton forcing, the AIMOS electronionization rates seem to suffer from proton contamination of satellite-basedflux data. This leads to overestimation of modelled electron concentrationsby up to 90% between 75–90 km and up to 100–150% at 70–75 km.Above 90 km, the model bias varies significantly betweenthe events. Although we cannot completely rule out EISCAT data issues, thedifference is most likely a result of the spatio-temporal fine structure ofelectron precipitation during individual events that cannot be fully capturedby sparse in situ flux (point) measurements, nor by the statistical AIMOSmodel which is based upon these observations

Contribution of proton and electron precipitation to the observed electron concentration in October–November 2003 and September 2005