Dipolarization Events With Inductive, Radial Electric Fields Observed by
Van Allen Probes
Abstract
Dipolarization events with inductive, radial electric fields are
examined, using Van Allen Probes data between 2013 and 2018. Two cases
are studied, followed by statistical analyses. These events were
observed between evening and premidnight magnetic local times (MLTs)
under moderate geomagnetic activities. Radial electric field variations,
azimuthal magnetic field variations, and energetic protons were often
observed when horizontal magnetic fields started to decrease in the dip
region. Magnetic field lines were stretched with their motion similar to
the gradient B/curvature drift velocities of energetic protons. Signs of
electric fields changed when horizontal magnetic fields started to
increase in the dipolarization front (DF). Electric field variations
were correlated with magnetic field ones with ~ 90 deg.
phase shift. These observations are mainly interpreted in terms of
energetic proton structures drifting toward the probe locations, while
being accompanied by standing waves.