Abstract
We investigate sharp changes in magnetic field that can produce
Geomagnetically Induced Currents (GICs) which damage pipelines and power
grids. We use one-minute cadence SuperMAG observations to find the
occurrence distribution of magnetic field “spikes”. Recent studies
have determined recurrence statistics for extreme events and charted the
local time distribution of spikes; however, their relation to solar
activity and conditions in the solar wind is poorly understood. We study
spike occurrence during solar cycles 23 and 24, roughly 1995 to 2020. We
find three local time hotspots in occurrence: the pre-midnight region
associated with substorm onsets, the dawn sector associated with omega
band activity, and the pre-noon sector associated with the
Kelvin-Helmholtz instability occurring at the magnetopause. Magnetic
field perturbations are mainly North-South for substorms and KHI, and
East-West for omega bands. Substorm spikes occur at all phases of the
solar cycle, but maximise in the declining phase. Omega-band and KHI
spikes are confined to solar maximum and the declining phase. Substorm
spikes occur during moderate solar wind driving, omega band spikes
during strong driving, and KHI spikes during quiet conditions but with
high solar wind speed. We show that the shapes of these distributions do
not depend on the magnitude of the spikes, so it appears that our
results can be extrapolated to extreme events.