Impact of Interplanetary Coronal Mass Ejections and High Speed Streams on the dynamic variations of the electron population in the outer Van Allen belt

The outer Van Allen radiation belt stands out for its intense variability, due to the complex mechanisms that take place due to the Sun – Earth coupling. One fundamentally important effect is the acceleration of seed electrons to relativistic and ultra – relativistic energies, through different mechanisms, namely radial diffusion and local acceleration.

In our work, we examine 46 events from the Van Allen Probes era (2012 – 2018), which we categorize according to the interplanetary driver of the geomagnetic disturbance. In particular, we study 16 events caused by Interplanetary Coronal Mass Ejections (ICMEs) and 30 events caused by High Speed Streams (HSS), following Stream Interaction Regions (SIRs), for which we calculate the electron Phase Space Density (PSD) for distinct values of the first adiabatic invariant (μ = 100, 1000, 5000 MeV/G) corresponding to seed, relativistic and ultra – relativistic electrons in the outer radiation belt. Furthermore, we perform a Superposed Epoch Analysis (SEA) of the geomagnetic disturbance events, which lead to either enhancements or depletions of the electron PSD, taking into consideration the parameters of solar wind activity, the state of the magnetosphere and the values of the second adiabatic invariant (K = 0.03, 0.09, 0.15 G^1/2R_E). We discuss the effects of the drivers on the variability of the outer radiation belt and how the different electron populations are affected, by comparing the time and radial profiles of the PSD. Our results lead to a clear difference between the two drivers, as far as it concerns the acceleration mechanisms.