Chorus Acceleration of Relativistic Electrons in Extremely Low L‐Shell During Geomagnetic Storm of August 2018.

Based on data from the Van Allen Probes and ZH‐1 satellites, relativistic electron enhancements in extremely low L‐shell regions (reaching L∼3) were observed during August 2018 major geomagnetic storm (minimum Dst≈−190 nT). Contrary to what occurs in the outer belt, such an intense and deep electron penetration event is rare and more interesting. Strong whistler‐mode (chorus and hiss) waves, with amplitudes 81–126 pT, were also observed in the extremely low L‐shell simultaneously (reaching L∼2.5) where the plasmapause was suppressed. The bounce‐averaged diffusion coefficient calculations support that the chorus waves can play a significantly important role in diffusing and accelerating the 1–3 MeV electrons even in such low L‐shells during storms. This is the first time that the electron acceleration induced by chorus waves in the extremely low L‐shell region is reported. This new finding will help to deeply understand the electron acceleration process in radiation belt physics. Key Points: Relativistic electron enhancement, companied with chorus wave disturbance, appears in the extremely low L‐shell (reaching L∼3) during the stormChorus wave can efficiently accelerate relativistic electrons in low L‐shell regionMomentum diffusion further enhanced the diffusion rate of relativistic electrons, especially in the low equatorial pitch angle [ABSTRACT FROM AUTHOR]