Ground truth validation of the CMIP energetic particle precipitation forcing

The forcing component of energetic particle precipitation (EPP) is recently added into the IPCC's official Coupled Model Intercomparison Project (CMIP) climate modelling. According to these simulations, the impact of inclusion of the medium energy electrons to the ozone variability was estimated to be 12-24% in the mesosphere and 5-7% in the stratosphere. However, to obtain a continuous particle forcing required for these multi-decadal simulations, the precipitating particle flux spectrum was parameterised by the magnetic Ap index to match statistically to the POES satellite's MEPED particle detector data. This rather simple approach has several uncertainties, but the most critical one is that the existing satellite-borne particle detectors, including the MEPED instrument, struggle to separate the loss cone populations from trapped particles, leading to biases in EPP forcing especially in the relativistic energies.In this presentation, we evaluate various EPP forcing models proposed for the future CMIP climate models against the EISCAT VHF data. This can be regarded as a ground-thruth approach for the mesospheric ionisation essential for the atmospheric consequences of the EPP.