Definition of substorm
: a disturbance in the magnetosphere that manifests as increased activity in the aurora (see aurora 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
Recent Examples of substorm from the Web
Ninety seconds after the satellites sensed the substorm starting, ground observatories witnessed a Northern Lights display suddenly brighten and dance.
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