A disturbance of the Earth's magnetic field caused by a coronal mass ejection, able to induce destructive currents in large power grids.
A geomagnetic storm results from a solar coronal mass ejection that induces parasitic direct currents in long conductors, extra-high-voltage transformers foremost. The reference event, named after Carrington, dates to 1859, and a 1989 episode collapsed the Hydro-Québec grid in under two minutes. For insurance the peril is singular because it has no geographic elsewhere, striking the exposed hemisphere as one, and its severity depends less on the number of transformers destroyed than on the time to replace them.
On 23 July 2012 a Carrington-class storm crossed the Earth's orbit, the Earth avoiding it only by standing about nine days from the trajectory.
orage géomagnétique, événement de Carrington, tempête solaire, solar storm