Competition between the source and loss processes of radiation belt source, seed, and relativistic electrons induced by a magnetic cloud event

Abstract

The radiation belt energetic electrons that are trapped by the geomagnetic field are one kind of space plasma and magnetic fluid. We quantitatively study the competition process between source and loss processes of radiation belt “source” (a few to tens of keV), “seed” (hundreds of keV), and “relativistic” (>1 MeV) electrons when a typical magnetic cloud (MC) event impinged on the magnetosphere on 19–20 July 2016. A very weak geomagnetic storm with SymHmin = −32 nT was driven by this magnetic cloud event. With the MC-driven shock arrival, the relativistic electrons experienced a “one-kick” energization at lower L-shells while having a moderate dropout at higher L-shells. The dropout became pronounced during the weak storm main phase. However, the seed electrons had a slight depletion after the shock and recovered to the pre-event level in the main phase, while the source electrons continued increasing during the entire event. Further analysis demonstrates that the loss processes (magnetopause shadowing and ultralow-frequency waves-driven outward transport) were competing with the source processes (shock-induced energization, substorm ejections, and wave–particle interactions), which are strongly sensitive to electron energy and L-shells. It is found that L*= ∼ 4 and μ = 102–102.5 MeV/G could be typical values at which the source and loss processes arrived at dynamic equilibrium. Our study first provides the “balance lines” in both energy channels and L* of the radiation belt source, seed, and relativistic electrons in response to magnetic cloud events. The quantitative results could be a key factor when investigating MC–magnetosphere coupling.