Abstract
The 1859 Carrington event is the most intense geomagnetic storm in
recorded history, and the literature provides numerous explanations for
what drove the negative $H$ perturbation on the Earth. There is debate
on what dominated the event. Our analysis shows a combination of causes
of similar orders of magnitude. Previous analyses generally rely upon on
the observed $H$ perturbation at Colaba, India; historic newspaper
reports; and empirical models. We expand the analysis using two Space
Weather Modeling Framework simulations to examine what drove the event.
We compute contributions from currents and geospace regions to the
northward $B$ field on Earth’s surface, $B_N$. We examine
magnetospheric currents parallel and perpendicular to the local $B$
field, ionospheric currents, and gap region field–aligned currents
(FACs). We also evaluate contributions from the magnetosheath,
near–Earth, and neutral sheet regions. A combination of currents and
geospace regions significantly contribute to $B_N$ on the Earth’s
surface, changing as the storm evolves. At storm onset, magnetospheric
currents and gap–region FACs dominate in the equatorial region. At
auroral latitudes, gap–region FACs and ionospheric currents are the
largest contributors. At storm peak, azimuthal magnetospheric currents
and gap–region FACs dominate at equatorial latitudes. Gap–region FACs
and ionospheric currents dominate in the auroral zone, down to
mid-latitudes. Both the magnetosheath and FACs contribute at storm peak,
but are less significant than that from the near–Earth ring current.
During recovery, the near–Earth ring current is the largest contributor
at equatorial latitudes. Ionospheric currents and gap–region FACs
dominate in the auroral zone.