Full Range Energetic Particle Precipitation Impacting the Middle Atmosphere (FREPPIMA)

Energetic electrons and protons, trapped in the Earth?s magnetic field, can collide with gases in the upper atmosphere (> 50 km). The collisions initiate a number of chemical reactions leading to the production of NOx and HOx gasses, which in turn can reduce the ozone concentration. Ozone is important in the energy budget at these altitudes. Hence changing the concentration of ozone at 50 km might also impact temperature and winds which links to our weather system. A good estimate of the particle energy input and its altitude distribution is therefore crucial for determining its effects on the atmosphere, as well as its potential impact on the regional surface temperature. This project's objectives were twofold in nature: - improve the estimate of the full range of energetic electron precipitation (EEP) - apply the estimate for both modelling and observational studies. In the first part we have applied a new technique to determine fluxes of energetic electron precipitation (EEP) (>30 keV) in the atmosphere on more than 20 years of measurements from the NOAA/POES and EUMETSAT/MetOp satellites. The corrected EEP fluxes are then combined with EEP fluxes of auroral energies (<30 keV) measured by the same satellites to create a full range energetic electron spectrum. The corrected data set is applied in several studies. We have demonstrated that the current recommendation used in the Coupled Model Intercomparison Project phase 6 (CMIP 6) for climate models typically underestimate the electron flux into the atmosphere by an order of size. This implies that the impact of EEP on the ozone concentration will also be underestimated. To accommodate this challenge, we have modified the chemistry climate model WACCM (version 6) to be able to also use the full range energetic electron spectrum. This is utilized in the international working group "Medium Energy Electrons Model-Measurement intercomparison". Here the full range energetic electron spectrum is compared to other electron flux estimates, and the associated chemical impact are evaluated in several atmospheric chemistry-climate models. In summary, FREPPIMA has contributed to a significant step forward to an improved parameterization of the full energy range of EEP to be implemented in chemistry-climate models. It has been successful, dedicated support for collaboration between the Space Physics community and the Climate research community and has built a fundament for new future collaborations.

The FREPPIMA project has been a dedicated support for collaboration between the Space Physics community and the Climate research community. It has developed techniques which gives new estimates of the energetic electron precipitation (EEP) (> 30 keV) into the atmosphere and modified the input files of the latest version of the WACCM (v.6) to incorporate this input. Applying the new EEP estimates to both observations and model studies has been crucial to get deeper insight in the overarching goal: What are the effects of energetic particle precipitation on the atmospheric system? Answering this question is also the goal for one of the three research groups at the Birkeland Centre for Space Science (BCSS) where FREPPIMA has been an important contribution. Through overseas stays and international working groups close collaboration with the stakeholders in the atmosphere and climate modelling community has been established.

Precipitating electrons and protons deposit their energy at various altitudes throughout the atmosphere depending on their initial energy. It has long been recognized that they are an important source of NOX and HOX gasses which can reduce the ozone concentration through catalytic cycles. Ozone plays a key role in the middle atmospheric energy budget. A good estimate of the particle energy input and its altitude distribution is crucial for determining the role of energetic particle precipitation in affecting the temperature and dynamics in the middle atmosphere, as well as its potential impact on the regional surface temperature. The proton energy input associated with rare solar proton events and its impact on NOX and HOX has been widely explored. The effects of the frequent energetic electrons events are, however, still undetermined and often poorly represented in current atmospheric models: - The precipitation of electrons with medium to high energies (30 keV-1 MeV) is missing/largely underestimated. - The precipitation of electrons with low energies (1-30 keV) are parameterized by geomagnetic indices. - The lower and higher electron energy parameterizations are decoupled from each other creating an unrealistic energy deposition height profile. We will apply a new physics based technique to determine the loss cone fluxes from energetic electron measurements from the NOAA/POES and EUMETSAT/MetOp. We will concatenate low and high energy electron measurement and investigate long term trend in the energy spectra and its relationship to solar wind parameters and geomagnetic indices. The result will prepare the ground for a parameterization of the full energy range of precipitating electrons to be implemented in the atmosphere climate model WACCM. The progress and evaluation of results will be closely linked to the project: "Solar effects on natural climate variability in the North Atlantic and Arctic (SOLENA)", supported the NFR Climate call 2015.