Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5-10 min duration can induce geomagnetically-induced currents (GICs) that can harm technological systems. Here we present superposed epoch analyses of large nighttime MPEs (|dB/dt| ≥ 6 nT/s) observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of the interplanetary magnetic field (IMF), solar wind dynamic pressure, density, and velocity, and the SML, SMU, and SYM/H geomagnetic activity indices. Analyses were produced for premidnight and postmidnight events and for three ranges of time after the most recent substorm onset: A) 0-30 min, B) 30-60 min, and C) >60 min. Of the solar wind and IMF parameters studied, only the IMF Bz component showed any consistent temporal variations prior to MPEs: a 1-2 hour wide 1-3 nT negative minimum at all stations beginning ~30 to 80 min before premidnight MPEs, and minima that were less consistent but often deeper before postmidnight MPEs. Median, 25th, and 75th percentile SuperMAG auroral indices SML (SMU) showed drops (rises) before pre- and post-midnight type A MPEs, but most of the MPEs in categories B and C did not coincide with large-scale peaks in ionospheric electrojets. Median SYM/H indices were flat near -30 nT for premidnight events and showed no consistent temporal association with any MPE events. More disturbed values of IMF Bz, Psw, Nsw, SML, SMU, and SYM/H appeared postmidnight than premidnight.

The rapid changes of magnetic fields associated with nighttime magnetic perturbations with amplitudes |ΔB| of hundreds of nT and 5-10 min periods can induce bursts of geomagnetically-induced currents that can harm technological systems. Recent studies of these events in eastern Arctic Canada, based on data from four ground magnetometer arrays and augmented by observations from auroral imagers and high-altitude spacecraft in the nightside magnetosphere, showed them to be highly localized, with largest |dB/dt| values within a ~275 km half-maximum radius that was associated with a region of shear between upward and downward field-aligned currents, and usually but not always associated with substorms. In this study we look in more detail at the field-aligned currents associated with these events using AMPERE data, and compare the context and characteristics of events not associated with substorms (occurring from 60 min to over two days after the most recent substorm onset) to those occurring within 30 min of onset. Preliminary results of this comparison, based on events with |dB/dt|≥ 6 nT/s observed during 2015 and 2017 at Repulse Bay (75.2° CGMLAT), showed that the SYM/H distributions for both categories of events were similar, with 85% between -40 and 10 nT, and the SME values during non-substorm events coincided with the lower half of the range of SME values for events during substorms (200 – 700 nT). Dipolarizations of ≥ 20 nT amplitude at GOES 13 occurred within 45 minutes prior to 73% of the substorm events but only 29% of the non-substorm events. These observations suggest that predictions of GICs cannot focus solely on the occurrence of intense substorms.

We investigate the timing and relative influence of VLF in the chorus frequency range observed by the DEMETER spacecraft and ULF wave activity from ground stations on daily changes in electron flux (0.23 to over 2.9 MeV) observed by the HEO-3 spacecraft. At each L shell, we use multiple regression to investigate the effects of each wave type and each daily lag independent of the others. We find that reduction and enhancement of electrons occur at different time scales. Chorus power spectral density and ULF wave power are associated with immediate electron decreases on the same day but with flux enhancement 1-2 days later. ULF is nearly always more influential than chorus on both increases and decreases of flux, although chorus is often a significant factor. There was virtually no difference in correlations of ULF Pc3, Pc4, or Pc5 with electron flux. A synergistic interaction between chorus and ULF waves means that enhancement is most effective when both waves are present, pointing to a two-step process where local acceleration by chorus waves first energizes electrons which are then brought to even higher energies by inward radial diffusion due to ULF waves. However, decreases in flux due to these waves act additively. Chorus and ULF waves combined are most effective at describing changes in electron flux at >1.5 MeV. At lower L (2-3), correlations between ULF and VLF (likely hiss) with electron flux were low. The most successful models, over L=4-6, explained up to 47.1% of the variation in the data.

Nearly all studies of impulsive magnetic perturbation events (MPEs) that can produce dangerous geomagnetically induced currents (GICs) have used data from the northern hemisphere. In this study we investigated MPE occurrences during the first 6 months of 2016 at four magnetically conjugate high latitude station pairs using data from the Greenland West Coast magnetometer chain and from Antarctic stations in the conjugate AAL-PIP magnetometer chain. Events for statistical analysis and four case studies were selected from Greenland/AAL-PIP data by detecting the presence of >6 nT/s derivatives of any component of the magnetic field at any of the station pairs. For case studies, these chains were supplemented by data from the BAS-LPM chain in Antarctica as well as Pangnirtung and South Pole in order to extend longitudinal coverage to the west. Amplitude comparisons between hemispheres showed a) a seasonal dependence (larger in the winter hemisphere), and b) a dependence on the sign of the By component of the interplanetary magnetic field (IMF): MPEs were larger in the north (south) when IMF By was > 0 (< 0). A majority of events occurred nearly simultaneously (to within ± 3 min) independent of the sign of By as long as |By| ≤ 2 |Bz|. As has been found in earlier studies, IMF Bz was < 0 prior to most events. When IMF data from Geotail, Themis-B, and/or Themis C in the near-Earth solar wind were used to supplement the time-shifted OMNI IMF data, the consistency of these IMF orientations was improved.