Superposed Epoch Analysis of Nighttime Magnetic Perturbation Events Observed in Arctic Canada

Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |Delta B| 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 degrees to 75.2 degrees 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 h wide 1-3 nT negative minimum at all stations beginning similar to 30-80 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.

Automated summary

Superposed epoch analyses were conducted on large nighttime magnetic perturbation events observed in Arctic Canada in 2015 and 2017. The study found that only the IMF Bz component showed consistent temporal variations before MPEs, and most of the MPEs did not coincide with large-scale peaks in ionospheric electrojets. More disturbed values of various parameters appeared post-midnight than pre-midnight.