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

Abstract:

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. In this study 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 75.2° to 64.7° in corrected geomagnetic latitude (MLAT) as functions of the SME and SYM/H magnetic activity indices, the interplanetary magnetic field, and the dynamic pressure of the solar wind (Psw). Analyses were produced at each station for all events, for premidnight and postmidnight subsets, and for three ranges of time after the most recent substorm onset: 0-30 min, 30-60 min, and >60 min. There was a wide range of SME values before and after MPE events, but a 1-2 hr duration, ~200-400 nT rise and fall roughly symmetric about the event time appeared overall and in most subcategories of events. The median of IMF Bz had a 1-2 hr wide, 2-3 nT negative minimum before t = 0 and a gradual rise across t = 0. SYM/H values showed a rather wide distribution and little temporal association with MPEs, but with a lower median at the lowest latitude station. Median time series for Psw, IMF Bx, and IMF By were nearly flat for all events and subsets. Slightly more disturbed conditions postmidnight than premidnight appeared in SME, SYM/H, and IMF Bz plots. These differences, as well as others noted in our recent studies, suggest that different mesoscale processes act to generate the MPEs in these two local time ranges, but that they probably share a common source in the magnetotail.