Plasma Waves and Particles during Multi-dip Storms Invoked by Turbulent Solar Wind

The temporal variations of the disturbance storm time index show the occurrence of multi-dip storms during 2015 April. Specifically, a double-dip storm was observed during April 9–12 and a six-dip storm occurred during April 13–21. This work analyzes the data from the electric field and wave (EFW) instrument, relativistic electron proton telescope (REPT), and electric and magnetic field instrument suite (EMFISIS) on board radiation belt storm probe A (RBSP-A) during the selected multi-dip storms. The ultra low-frequency (ULF) as well as very low-frequency (VLF) electromagnetic oscillations were observed by EFW and EMFISIS simultaneously with the REPT observed fluctuating fluxes of relativistic electrons in the slot and outer Van Allen belt. The timescales, for relativistic electrons flux increase in slot and depletion, refilling of the outer Van Allen belt, were much faster than the temporal variations expected from the radial diffusion driven by drift resonance between ULF waves and relativistic electrons. Therefore, the contribution of VLF interaction with the relativistic electrons is important for understanding rapid flux variations on times of few hours during the considered multi-dip geomagnetic storms. The findings of this study may be helpful for understanding the relativistic electrons dynamics and transport in the Earth's magnetosphere during multi-dip geomagnetic storms.