Global ENA Imaging and In Situ Observations of Substorm Dipolarization on 10 August 2016. Issue 4 (22nd April 2020)

• Record Type: Journal Article
• Authors: Goldstein, J.; Valek, P. W.; McComas, D. J.; Redfern, J.; Spence, H.; Skoug, R. M.; Larsen, B. A.; D. Reeves, G.; Nakamura, R.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 4(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-04-22
• Subjects: substorm dipolarization -- cross‐scale physics -- imaging -- multipoint in situ -- ring current; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2019JA027733
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: This paper presents the first combined use of data from Magnetospheric Multiscale (MMS), Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS), and Van Allen Probes (RBSP) to study the 10 August 2016 magnetic dipolarization. We report the first correlation of MMS tail observations with TWINS energetic neutral atom (ENA) images of the ring current (RC). We analyze 15‐min, 1° TWINS 2 images in 1–50 keV energy bins. To characterize the high‐altitude RC we extract peak ENA flux from L = 2.5 to 5 in the postmidnight sector. We estimate peak low‐altitude ion flux from ENAs near the Earth's limb. For a local perspective, we use spin‐averaged proton fluxes from the RBSP A Helium Oxygen Proton Electron (HOPE) spectrometer. We find that the 1000 UT dipolarization triggered an abrupt and significant increase in low‐altitude ions and a gradual but modest increase in the high‐altitude RC. The relative strength and timing of the low versus high‐altitude flux indicate that the dipolarization isotropized the injected ions and initially filled the loss cone. The substorm injection brought cooler ions in from the magnetotail, reducing the peak energy at both low and high altitudes. The post‐dipolarization low‐altitude flux exhibited a decay rate dispersion favoring longer decay times at lower energies, possibly caused by growth of the low energy RC providing enhanced flux into the loss cone. A variety of finer scale local injection structures were observed in the high‐altitude RC both before and after the dipolarization, and the average system level RC intensity increased after 1000 UT. Key Points: First combined use of MMS, TWINS, and Van Allen Probes to study response to 10 August 2016 magnetic dipolarization during isolated substorm Dipolarization triggered abrupt/gradual increase in low/high‐altitude ions, indicating that injection isotropized ions and filled loss cone Large variety of finer scale local injection structures observed both before and after dipolarization, but average global RC increased