Nighttime magnetic perturbation events observed in Arctic Canada:
Investigating their associations with localized field-aligned currents
and with substorms
Abstract
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.