Substormar

Substormar, or substorms in English, are transient disturbances of Earth's magnetosphere associated with energy release from the magnetotail, leading to intensification and expansion of auroral displays and energetic particle injections near Earth. They occur on timescales of tens of minutes and can be repeated every few hours during active solar wind driving. They are observed as auroral brightenings, poleward expansions of aurora, and magnetic field perturbations at the surface.

Substorms proceed through growth, expansion, and recovery phases. During the growth phase the tail-mounted magnetic field stores energy as tail stretch; expansion phase features rapid magnetic field reconfiguration and bright auroras; recovery phase returns to quiet conditions. The onset is often marked by a sharp southward turning of the magnetotail field or by ground magnetic disturbances.

The leading explanations include the Near-Earth Neutral Line (NENL) model, where reconnection near 20-30 Earth radii forms a dipolar field and ejects plasmoids; and the current disruption model, where near-Earth current disruption causes rapid field dipolarization. Observations rely on ground-based magnetometers, all-sky cameras, radar, and in-situ satellite measurements (e.g., THEMIS). Substorms contribute to energizing the inner magnetosphere and auroral activity, with implications for space weather forecasting.