Plasmaspheric High‐Frequency Whistlers as a Candidate Cause of Shock Aurora at Earth

Auroral brightening driven by interplanetary shocks on Earth's closed magnetic field lines is commonly attributed to the 0.1–10 keV electron precipitations by electron cyclotron harmonic waves and whistler‐mode chorus waves in the low‐density region. In contrast, we propose here a new candidate driver, high‐frequency whistlers in the high‐density plasmasphere. Theoretical calculations predict the comparable abilities of whistler‐mode waves with sufficiently high frequencies inside the plasmasphere and chorus waves outside to produce auroral electron precipitations. Such expected waves are further verified to exist following an interplanetary shock. The shock perpendicularly accelerated source electrons inside the plasmasphere and then produced strong high‐frequency whistler‐mode waves. These waves appeared as a hybrid of chorus and hiss in the frequency‐time spectrogram and probably resulted from a combination of linear and nonlinear instabilities. Our findings demonstrate that interplanetary shocks can promptly promote energy transfer toward the ionosphere from the inner high‐density magnetosphere.