Interhemispheric Comparisons of Large Nighttime Magnetic Perturbation
Events Relevant to GICs
Abstract
Nearly all studies of impulsive magnetic perturbation events (MPEs) with
large magnetic field variability (dB/dt) that can produce dangerous
geomagnetically-induced currents (GICs) have used data from the northern
hemisphere. Here we present details of four large-amplitude MPE events
(|DBx|> 900 nT and
|dB/dt| > 10 nT/s in at least one
component) observed between 2015 and 2018 in conjugate high latitude
regions (65 - 80° corrected geomagnetic latitude), using magnetometer
data from (1) Pangnirtung and Iqaluit in eastern Arctic Canada and the
magnetically conjugate South Pole Station in Antarctica and (2) the
Greenland West Coast Chain and two magnetically conjugate chains in
Antarctica, AAL-PIP and BAS LPM. From 1 to 3 different isolated MPEs
localized in corrected geomagnetic latitude were observed during 3
pre-midnight events; many were simultaneous within 3 min in both
hemispheres. Their conjugate latitudinal amplitude profiles, however,
matched qualitatively at best. During an extended post-midnight
interval, which we associate with an interval of omega bands, multiple
highly localized MPEs occurred independently in time at each station in
both hemispheres. These nighttime MPEs occurred under a wide range of
geomagnetic conditions, but common to each was a negative IMF Bz that
exhibited at least a modest increase at or near the time of the event. A
comparison of perturbation amplitudes to modeled ionospheric
conductivities in conjugate hemispheres clearly favored a current
generator model over a voltage generator model for 3 of the 4 events;
neither model provided a good fit for the pre-midnight event that
occurred near vernal equinox.