Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 2. Multiple‐Instrument Observations

Abstract

The rapid changes of magnetic fields associated with nighttime magnetic perturbations with amplitudes |ΔB| of hundreds of nanoteslas and 5‐ to 10‐min periods can induce bursts of geomagnetically induced currents that can harm technological systems. This paper presents three cases of intervals of intense and complex nighttime magnetic perturbations in eastern Arctic Canada in 2015, augmented by observations from auroral imagers and high‐altitude spacecraft in the nightside magnetosphere. Each case occurred within 1 hr after substorm onsets. None occurred during the main phase of a geomagnetic storm, and only the first during the early recovery phase (of a moderate storm). The cases were similar in that two or three intervals occurred in this region over a span of ~1 hr; these showed a spatial progression, in that successive intervals occurred later at more western and northern stations. During several intervals, individual peak Bx impulses occurred nearly simultaneously (within 1–2 min) at several stations, while during others the impulses occurred later at more western and northern stations, and during one interval they occurred later at southern stations. During both of the cases for which auroral images were available, a westward traveling surge and a poleward auroral expansion and/or poleward boundary intensification occurred, and during two events auroral streamers coincided in time and location with magnetic perturbations. These observations appear to be consistent with several earlier studies connecting nighttime magnetic perturbation events to localized auroral structures and to dipolarizing flux bundles and bursty bulk flows in the magnetotail.

Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation Events Relevant to GICs

“…It is possible that the negative spike at 00:21 UT observed at PG5 was caused by a westward traveling surge that moved westward and poleward to appear successively later at more poleward stations: at 00:26 UT at STF, at 00:33 UT at Pangnirtung, and between 00:35 and 00:39 at PG3, PG2, GDH, and UMQ. This would be qualitatively consistent with the progressive appearance of MPEs at more westward and poleward stations found in three recent case studies of MPEs by Engebretson, Steinmetz, et al (2019) using a two‐dimensional array of stations in Arctic Canada.…”

“…The criterion for identifying a substorm onset to be included in the SuperMAG substorm lists (Newell & Gjerloev, 2011a, 2011b) is a drop in SML (the SuperMAG version of the AL index) that was sharp (45 nT in 3 min) and sustained (−100 nT average for 25 min starting 5 min after onset). In contrast to these step function‐like criteria, the large nighttime MPEs studied by Engebretson, Pilipenko, et al (2019) and Engebretson, Steinmetz, et al (2019) and in this paper are unipolar or bipolar pulses of hundreds of nT and ~5–10 min durations.…”

“…However, MPEs are still likely to be causally related to active conditions in the magnetotail such as bursty bulk flows (BBFs) and/or dipolarizing flux bundles (DFBs) (Angelopoulos et al, 1992; Engebretson, Steinmetz, et al, 2019; Gabrielse et al, 2014; Kauristie et al, 2000; Liu et al, 2014; Lyons et al, 2012; Sergeev et al, 1999; Zesta et al, 2000, 2006) that are expected to impact high‐latitude regions in both the Northern and Southern Hemispheres.…”

“…Although the technological risk from GICs is greater during magnetic storms, when the auroral oval expands to subauroral latitudes, impulsive MPEs with duration ~5 to 15 min have also been found to more often occur during nonstorm times (Viljanen et al, 2006) and at up to at least 78° corrected geomagnetic latitude (MLAT) (Engebretson, Pilipenko, et al, 2019). A recent case study of three large‐amplitude MPEs observed using an extensive two‐dimensional set of ground magnetometer arrays in Arctic Canada, western Greenland, and Antarctica (Engebretson, Steinmetz, et al, 2019) showed that these events appeared roughly simultaneously at near–magnetically conjugate locations (at the northern and southern ends of the same magnetic field lines) in each hemisphere. In this study we present multistation data from a large two‐dimensional set of ground‐based magnetometers in the Northern Hemisphere and magnetometers at magnetically conjugate locations in Antarctica, both covering a range in MLAT from ~65° to over 80°.…”

Nighttime Magnetic Perturbation Events Observed in Arctic Canada: 1. Survey and Statistical Analysis

“…In addition to dayside TCVs, intense magnetic perturbation events—large, isolated pulses with similar periods—often appear in ground‐based magnetometer records during nighttime. Case studies of these intense nighttime events, augmented by observations from auroral imagers and high‐altitude spacecraft in the nightside magnetosphere, can be found in a companion paper (Engebretson et al, , hereafter called Paper 2).…”