Acceleration to ultra-relativistic energies by a VERB-3D code coupled to a data- assimilative plasmasphere code VERB-CS

Measurements from the Van Allen Probes mission show sporadic and diffi cult-to- predict behavior at ultra-relativistic energies. Recent observational studies demonstrated that cold plasma has a controlling effect over the ultra-relativistic electrons that are million times more energetic. However, the global modeling of the dynamics of relativistic and ultra-relativistic electrons has been missing. In this study, we present the modeling of 3D radiation belts with a variable density, demonstrating that density has a controlling effect over acceleration to these high energies. The density is obtained by using the VERB-CS code with data assimilation. In this study, we also present an analysis of observations showing what are the unique conditions in the solar wind and in the magnetosphere required for the density depletions and for the acceleration of particles to ultra-relativistic energies.