Identifying the magnetotail source region leading to preonset poleward boundary intensifications. Issue 7 (24th July 2013)

• Record Type: Journal Article
• Authors: Nishimura, Y.; Lyons, L. R.; Xing, X.; Angelopoulos, V.; Donovan, E. F.; Mende, S. B.; Bonnell, J. W.; Auster, U.
• Is Part Of: Journal of geophysical research. Volume 118:Issue 7(2013:Jul.)
• Page Start: 4335
• Page End: 4340
• Publication Date: 2013-07-24
• Subjects: poleward boundary intensifications -- auroral streamers -- THEMIS ASI -- ARTEMIS -- distant neutral line -- near‐Earth neutral line; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/jgra.50407
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: [1] Substorm auroral onset is often preceded by plasma sheet flow bursts, poleward boundary intensifications (PBIs), and subsequent auroral streamers, suggesting that enhanced transient flows in the plasma sheet propagating toward the near‐Earth plasma sheet play an important role in leading to substorm onset. This study aims at determining the magnetotail source region of preonset PBIs and plasma sheet flows by using the ARTEMIS spacecraft coordinated with the THEMIS all‐sky imager array. ARTEMIS has an advantage of measuring flows between the nominal near‐Earth neutral line (NENL) and distant neutral line (DNL) locations, and thus, the flow direction allows identifying which source region is dominant. We found three preonset conjunction events, and all cases show earthward flow bursts ~10–30 min before substorm onset when PBIs and streamers are detected in the conjugate ionosphere. This time lag is sufficiently long to bring plasma from the ARTEMIS location toward the near‐Earth plasma sheet before onset. The earthward flow direction indicates that preonset enhanced flow channels leading to precursor PBIs originate from further downtail of ARTEMIS, possibly from DNL rather than from NENL. The flow direction changes to tailward after the substorm onset, suggesting that NENL is not related to preonset flow and auroral activity but becomes active during the expansion phase. Key Points: We determined the source region of pre‐onset PBIs using the ARTEMIS‐ASI pair. All cases show earthward flows ~10‐30 min before substorm onset during PBIs. The earthward flow direction indicates pre‐onset flows originating from DNL.