Electron Rolling‐Pin Distributions Preceding Dipolarization Fronts

Abstract Electron rolling‐pin distribution (RPDs), characterized by triple peaks at pitch angles 0°, 90°, and 180°, have recently been discovered in the terrestrial magnetosphere. Since RPDs' formation is typically attributed to local betatron acceleration, RPDs believed appear primarily inside strong magnetic regions, such as flux pileup regions (FPRs) behind dipolarization fronts (DFs). Different from expectation, this study we present unique observations of made Cluster spacecraft magnetotail, showing that are weak field ahead DFs but absent region them. The presence RPD prior may be atttributed combined effect global Fermi frontward transport driven gradient drift. atypical features important for fully understanding electron acceleration