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Abstract

Novel analysis of phase space densities at multiple energies allowsfor differentiation between various acceleration mechanisms atultra-relativistic energies. This method allows us to trace howparticles are being accelerated at different energies and show howlong it takes for acceleration to reach particular energy. This method clearly demonstrates the importance of local acceleration and alsodemonstrates the importance of the outward radial diffusion intransporting electrons to GEO. Acceleration to such high energies occurs only when cold plasma in the trough region is extremelydepleted, down to the values typical for the plasma sheet. We perform event and statistical analysis of these depletions and show that the ultra-relativistic energies are reached for each such depletion thatis accompanied by the intensification of ~2MeV. VERB-2D simulations are then used to explain these observations. There is also a clear difference between the loss mechanisms at MeV and multi-MeV energies due to EMIC waves that can very efficiently scatter ultra-relativistic electrons but leave MeV electrons unaffected. Modeling and observations clearly show that cold plasma has a controlling effect over the ultra-relativistic electrons that are 10^6-10^7 times more energetic. We also present how the new understanding gained from the Van Allen Probes mission can be used to produce the most accurate data assimilative forecast. Under the recently funded EU Horizon 2020 Project Prediction of Adverse effects of Geomagnetic storms and Energetic Radiation (PAGER), we study how ensemble forecasting from the Sun can produce long-term probabilistic forecasts of the radiation environment in the inner magnetosphere.