Magnetosheath High-Speed Jet Drives Multiple Auroral Arcs Near Local Noon

Abstract

Magnetosheath High-Speed Jets (HSJs) are transient disturbances characterized by increased dynamic pressure. They can cause various geoeffects, including ultra-low-frequency (ULF) waves and auroras. Theoretically, when ULF waves propagate into the ionosphere as Alfvén waves, they can accelerate electrons and generate discrete auroras. However, what types of aurora can be driven by HSJs and what are the underlying mechanisms remain unknown. Using coordinated magnetosheath in situ and ground observations, here, we showed that when a HSJ was identified in the magnetosheath, multiple auroral arcs parallel to the auroral oval were observed near local noon. The electron energy spectrogram of these arcs exhibited “inverted-V” structures, indicating the existence of quasi-static parallel electric fields. Concurrently, long-period ULF signals were detected on the ground, suggesting the arrival of Alfvén waves. These observations are represented by a kinetic simulation using realistic observational inputs, showing consistency with the theory regarding the generation of the “inverted-V” structure by long-period Alfvén waves. This study builds a previously unestablished connection among HSJ, ULF wave, and aurora, and provides a mechanism for generation of discrete auroral arcs near local noon, which may reveal the underlying mechanism behind a specific auroral activity commonly observed near local noon as shown in the paper.