Signatures of Auroral Potential Structure Extending Through the Near‐Equatorial Inner Magnetosphere. Issue 10 (25th May 2022)

• Record Type: Journal Article
• Authors: Imajo, S.; Miyoshi, Y.; Asamura, K.; Shinohara, I.; Nosé, M.; Shiokawa, K.; Kasahara, Y.; Kasaba, Y.; Matsuoka, A.; Kasahara, S.; Yokota, S.; Keika, K.; Hori, T.; Shoji, M.; Nakamura, S.; Teramoto, M.
• Is Part Of: Geophysical research letters. Volume 49:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-05-25
• Subjects: auroral acceleration region -- upflowing ion beam -- inner magnetosphere -- plasma convection; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL098105
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The auroral acceleration region plays an important role in the magnetosphere‐ionosphere coupling system. In this study, signatures of an auroral U‐shaped potential structure were found for the first time in the near‐equatorial inner magnetosphere by the Arase satellite at ∼6.0 RE geocentric distance and 11° magnetic latitude. The observed magnetic and electric field variations corresponded to the equatorward motion of the upward field‐aligned current and converging perpendicular electric field. Examining the three‐dimensional velocity distribution function of H + and O + ions, we demonstrate that upflowing ion beams were significantly deflected in an east‐west direction with a perpendicular velocity up to ∼80 km/s, which is consistent with the ExB drift velocity. A simple particle drift model with the inferred auroral perpendicular potential presents a new kink‐like drift path of ions from the magnetotail, implying that the auroral potential structure has a great impact on particle dynamics in the near‐earth plasma sheet. Plain Language Summary: The auroral arc involves multiple physical processes over a wide altitude range in the upper atmosphere. While the primary energy sources are at high altitudes, the accelerated electrons that are directly responsible for auroral emissions are mainly produced at lower altitudes. In the region where the electrons are accelerated downward, known as the auroral acceleration region, a peculiar electric field structure is formed. We clarified whether this electric field structure exists up to near the energy source region and how it affects the plasma dynamics by an in situ observation by the Arase satellite. We found for the first time that ions accelerated from below the satellite were supplied to the energy source region, and were deflected by the observed auroral electric field structure. Our model calculation shows that the electric field structure can significantly meander the motion of the entire near‐Earth space plasma as it flows toward the Earth. Our result invites a new perspective that the structure of the electric field from low altitudes associated with the auroral arc has a significant impact on the dynamics of near‐Earth space plasmas. Key Points: Signatures of an auroral U‐shaped potential structure were found first in the near‐equatorial inner magnetosphere by the Arase satellite Upflowing ion beams, especially O + ion beams, were significantly deflected from field lines by a converging perpendicular electric field The converging electric field and ion beam potentially affect the particle dynamics in the near‐Earth plasma sheet