Extreme Geomagnetic Disturbances (GMDs) Observed in Eastern Arctic
Canada: Occurrence Characteristics and Solar Cycle Dependence
Abstract
Extreme (≥ 20 nT/s) geomagnetic disturbances (GMDs, also denoted as MPEs
- magnetic perturbation events) – impulsive nighttime disturbances with
time scale ~5-10 min, have sufficient amplitude to cause
bursts of geomagnetically induced currents (GICs) that can damage
technical infrastructure. In this study we present occurrence statistics
for extreme GMD events from five stations in the MACCS and AUTUMNX
magnetometer arrays in Arctic Canada at magnetic latitudes ranging from
65° to 75°. We report all large (≥ 6 nT/s) and extreme GMDs from these
stations from 2011 through 2022 to analyze variations of GMD activity
over a full solar cycle and compare them to those found in three earlier
studies. GMD activity between 2011 and 2022 did not closely follow the
sunspot cycle, but instead was lowest during its rising phase and
maximum (2011-2014) and highest during the early declining phase
(2015-2017). Most of these GMDs, especially the most extreme, were
associated with high-speed solar wind streams (Vsw > 600
km/s) and steady solar wind pressure. All extreme GMDs occurred within
80 min after substorm onsets, but few within 5 min. Multistation data
often revealed a poleward progression of GMDs, consistent with a
tailward retreat of the magnetotail reconnection region. These
observations indicate that extreme GIC hazard conditions can occur for a
variety of solar wind drivers and geomagnetic conditions, not only for
fast-coronal mass ejection driven storms.