Magnetotail Dipolarizations and Ion Flux Variations During the Main Phase of Magnetic Storms. Issue 5 (12th May 2021)

• Record Type: Journal Article
• Authors: Runov, A.; Angelopoulos, V.; Henderson, M. G.; Gabrielse, C.; Artemyev, A.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 5(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-12
• Subjects: dipolarization -- injections -- magnetotail -- ring current; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA028470
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Near‐Earth tail dipolarizations are usually associated with fast plasma flows and an increase in energetic particle fluxes. Yet, the role of these dipolarizations in energetic ion flux transport toward the inner magnetosphere and in ring current (including partial ring current) development during the main phase of a geomagnetic storm is not fully understood. We investigated observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes A, D, and E with apogees at X ≈ −13 R E and Los Alamos National Laboratory (LANL) geosynchronous spacecraft in the midnight magnetic local time (MLT) sector (21.5–1.5 h MLT) during the main phases of storms with integrated D st exceeding 600 nT*hr from the 2010 to 2016 THEMIS tail seasons. We selected 10 storms during which at least one of the THEMIS probes was in the midnight sector during a storm's main phase and identified 39 dipolarization events with a B z increase exceeding 10 nT within 500 s during these storms' main phases. In 21 of the 39 events, an increase in the magnetic field elevation angle Θ estimated from LANL magnetospheric plasma analyzer (MPA) data was detected at geosynchronous orbit (GEO) within ±15‐min‐long time window around dipolarization onset detected by THEMIS. In only 10 of those 21 events, however, did ion fluxes at energies from 50 to 500 keV increase in three or more consecutive energy bins at LANL. Comparisons of ion spectra collected by THEMIS and LANL in these 10 events revealed a similar increase in fluxes at energies E > 20 keV. Our results indicate that a dipolarization that occupies a large portion of the nightside magnetosphere from GEO to ∼12 R E is a necessary but not sufficient condition for energetic ion flux enhancements at GEO. As suggested in previous studies, an increase in the azimuthal electric field (i.e., enhanced earthward magnetic flux transport) is most likely required for an ∼100 keV ion flux increase at GEO. Key Points: Time History of Events and Macroscale Interactions during Substorms (THEMIS) detected 39 magnetotail dipolarizations in the 21.5–1.5 magnetic local time (MLT) sector during selected storms' main phases beyond synchronous orbit In 21 of those events, dipolarizations were detected at synchronous orbit by Los Alamos National Laboratory (LANL) in the same MLT sector However, in only 10 of those events did LANL see robust >50 keV ion enhancements in at least three consecutive energy bins at synchronous orbit