Global ENA Imaging and In Situ Observations of Substorm Dipolarization on 10 August 2016

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.

Average Ring Current Response to Solar Wind Drivers: Statistical Analysis of 61 Days of ENA Images

“…This case study illustrates that the global RC is sensitive to even weak/moderate SW driving, as also noted by Goldstein et al. (2020).…”

“…The peak flux increased by factors ranging from 2.0 (at 12 keV) to 3.3 (at 1 keV), with an energy-averaged (1-30 keV) increase factor of 2.4. This case study illustrates that the global RC is sensitive to even weak/moderate SW driving, as also noted by Goldstein et al (2020).…”

“…For each image, we extracted ENA flux versus L and MLT using minimum-L sampling (Goldstein et al, 2012(Goldstein et al, , 2020, as follows. We defined a 10 × 25 sample matrix spanning L = [2.5, 7] in steps of ΔL = 0.5, and spanning MLT = [00:00, 24:00] in steps of ΔMLT = 01:00.…”

What Drove the GICs >10 A During the 17 March 2013 Event at Mäntsälä? A Novel Framework for Distinguishing the Magnetospheric Sources

“…First, these substorm‐associated pulsations are present in BH and GIC heatmaps (Figures 3a and 3b) when the local westward (substorm) currents are enhanced (Figure 6f). These BBFs produce small‐scale wedgelets that combine to form a large‐scale SCW (Palin et al., 2016) while also enhancing the RC (Figure 7b–7d) (Goldstein et al., 2020; Sciola et al., 2023). The flows that penetrate the inner magnetosphere create a compression, which has been observed to create oscillations of 1–2 min periodicity on the ground (Kepko et al., 2001; Lysak et al., 2015), like Pi2 pulsations in Figures 3a and 3b.…”