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Abstract

In recent years, medium energy electrons (MEE) (>30keV) precipitating from the radiation belt has been a topic of increased attention. Studies have revealed large uncertainties in respect to quantify the MEE ionization rates throughout the mesosphere. We report on results from the High Energy Particle Precipitation in the Atmosphere (HEPPA) III intercomparison experiment which is a collective effort to address this point. HEPPA III intercompares eight different estimates MEE which are all based on the Medium Energy Proton and Electron Detector (MEPED) on board the NOAA/POES and EUMETSAT/MetOp spacecraft series. However, different data handling, ionization rate calculations, and background atmospheres result in a wide range of mesospheric electron ionization rates. Although the eight data sets agree well in terms of the temporal variability, they differ by about an order of magnitude in ionization rate strength both during geomagnetic quiet and disturbed periods. The mesospheric NO densities simulated with the Whole Atmospheric Community Climate Model driven by highest and lowest ionization rates differ by more than a factor of eight. Moreover, to understand the importance of accurate of MEE precipitation, we raise the question: How strong MEE fluxes are needed to modulate the atmospheric dynamics? A model study using WACCM demonstrate that even the weakest of the eight MEE ionization rates can directly modulate the mesospheric temperature, zonal wind and the residual circulation affecting NOx transport. We discuss to which degree the impact of the MEE precipitation depends on the dynamical preconditions in the atmosphere itself.