Surfing Acceleration of Radiation Belt Relativistic Electrons Induced by the Propagation of Interplanetary Shock

Interplanetary shocks (IPS) can initiate prompt acceleration of relativistic electrons in the Earth's radiation belt, which is related to the generation and propagation of impulsive electric field (IEF). We investigate the effect of IEF on accelerating radiation belt electrons in the 6 September 2017 IPS event. A “surfing” effect of electrons with respect to the electric field, referring to electrons that drift together with the tailward‐propagating IEF in the duskside, is investigated in this study. Our results show that the maximum increase of electron differential flux is at 3.4 MeV by a factor of 2.2, corresponding to a drift velocity of 531 km/s, which is more consistent with the IPS propagating speed of 621 km/s rather than the fast‐mode speed of 1,074 km/s. We suggest that the effect of IPS propagation is important for radiation belt dynamics, and we highlight the potential importance of the parameter of IPS propagation speed. Plain Language Summary Acceleration and injection of the relativistic electrons are frequently occurred when interplanetary shocks impinge on the Earth’s magnetosphere. The impulsive electric field is the direct driver and its propagation may strongly affect the efficiency of the acceleration. In this study, we use the Van Allen Probes observation to investigate the interplanetary shock‐induced acceleration of the relativistic electrons occurred on 6 September 2017. It is found that the drift velocity of electrons in the energy ranges that experience a maximum increase in differential flux is better correlated with the propagation speed of the interplanetary shock rather than the fast‐mode speed in the inner magnetosphere. A new mechanism of the effect of interplanetary shocks’ propagation on radiation belt dynamics is proposed, and the potential importance of the propagation speed of the interplanetary shock on electron acceleration is highlighted. Key Points The effect of the propagation of the shock‐induced electric field on accelerating radiation belt electrons is investigated The drift velocity of electron experiencing maximum flux increase is consistent with the interplanetary shock’s propagation speed A new mechanism of how interplanetary shocks' propagation influence the radiation belt dynamics is proposed in this study