Definition of substorm
: a disturbance in the magnetosphere that manifests as increased activity in the aurora (see aurora sense 3) and that is caused by an influx of high-energy particles from the sun (as from a solar flare) Even when the sun is being well behaved, parcels of plasma shoot sporadically toward Earth's dark side, prompting a bright aurora and intensifying radiation belts. These events, called substorms, last only a few hours, but they occur several hundred times a year and are quite capable of disrupting satellites …— Tim Beardsley
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