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

• Published in: AGU advances 2024-10, Vol.5 (5), p.n/a
• Main Authors: Qiu, Hui‐Xuan, Han, De‐Sheng, Shi, Run, Liu, Jianjun
• Format: Article
• Language: English
• Subjects: auroral arcs; high‐speed jet; Ionosphere; Magnetic fields; Meteorological satellites; Saturn; Sensors; ULF waves; Velocity
• ISSN: 2576-604X; 2576-604X
• DOI: 10.1029/2024AV001197

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. Plain Language Summary Magnetosheath High‐Speed Jets (HSJs) are transient irregularities observed between Earth's magnetopause and bow shock. They can cause various geoeffects like ultra‐low‐frequency (ULF) waves and auroras. However, the specific auroral types driven by HSJs remain elusive. Through coordinated in situ and ground observations, we reveal a novel geoeffect of HSJs—driving multiple discrete auroral arcs near local noon on closed field lines, displaying “inverted‐V” electron acceleration structures. This challenges the conventional understanding that discrete auroras near local noon predominantly occur on open field lines. Also, our study provides valuable insights into the mechanism and favorable conditions of discrete auroras on closed field lines near local noon. Simultaneously, ground magnetic ULF signals indicate a crucial role of HSJ‐induced ULF waves in shaping these “inverted‐V” arcs. Supported by a kinetic simulation, our observations provide evidence for the recently established electron acceleration mechanism of “inverted‐V