Journal Article

Single‐Hemisphere Oxygen Outflow From Earth's Subauroral Zone

Liu, J.‐J., Liu, Z.‐Y., Zhou, X.‐Z., Zong, Q.‐G., Hu, Z.‐J., Fu, S.‐Y., Yue, C.

2024

Overview

Besides the cusp, polar cap, and auroral oval, the nightside subauroral zone has also recently been reported as a source region of the ionospheric oxygen outflows. However, the detailed mass and energy sources of these ions remain open questions. Here, we address this issue from the perspective of the response of conjugate hemispheres. Investigation of Van Allen Probes data demonstrates a notable preference of oxygen outflows from the nightside subauroral zone from the sunlit hemisphere. This characteristic eliminates the possibility of nightside auroral precipitation playing a significant role, as it is more prominent in darkness. Instead, it highlights sunlight‐induced ionization as the mass source and enhanced plasma waves from the magnetotail as the energy source. The results presented here further support the nightside subauroral zone as an independent source of magnetospheric oxygen ions. Plain Language Summary Single‐charged oxygen ions, believed to ultimately originate from the ionosphere, are the main carriers of the ring current during severe space weather, including super geomagnetic storms and substorms. Therefore, comprehending where and how they come from is crucial for understanding the magnetosphere and space weather. Recent studies have reported the nightside subauroral zone as a source region, besides the usually cited cusp, polar cap, and auroral oval. However, the detailed mechanisms for the subauroral oxygen outflows remain open questions. In this study, we address this issue by studying how opposite hemispheres react simultaneously in subauroral oxygen outflow events observed by the Van Allen Probes. Data analysis reveals that these outflows tend to occur in the local summer hemisphere, where the nightside subauroral ionosphere receives more sunlight compared to the opposite hemisphere. This feature rules out nightside auroral precipitation playing a significant role, as it is more noticeable in the dark. Instead, it points to sunlight‐induced ionization as the source of mass and enhanced plasma waves from the magnetotail as the source of energy. Our findings reinforce the idea that the nightside subauroral zone is an important source of ionospheric oxygen outflows. Key Points The Van Allen Probes have observed oxygen outflows from the nightside subauroral ionosphere in a single hemisphere Statistics reveal a preference for the outflows in sunlit hemisphere, distinguishing them from auroral outflows more prominent in darkness This preference highlights sunlight‐induced ionization and waves from the magnetotail as the source of mass and energy

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Auroral oval / Current carriers / Cusps / Darkness / Data analysis / Energy resources / Energy sources / Geomagnetic storms / Hemispheres / Ionization / Ionosphere / ionospheric outlfows / Ions / Magnetic storms / Magnetospheres / Magnetotails / mass source of magnetosphere / north‐south asymmetry / Outflow / Oxygen / Oxygen ions / oxygen outflows / Plasma waves / Polar caps / Polar cusps / Precipitation / Probes / Questions / Ring currents / seasonal variations / Space weather / Storms / subauroral region / Sunlight