Solar Wind, Heliosphere & Space Weather: Physical Mechanisms

The heliosphere includes the supersonic solar wind close to the Sun, the termination shock where that wind slows, the heliosheath beyond it, and the heliopause marking the boundary where solar plasma pressure balances the surrounding interstellar medium. Near Earth, the solar wind interacts with the magnetosphere rather than striking the atmosphere uniformly.

The corona is hot enough that some plasma escapes the Sun's gravity and accelerates outward along open magnetic field lines. As the Sun rotates, its magnetic field is carried outward by the flowing plasma into a spiral structure. Disturbances such as high-speed streams and CMEs compress or reconnect with planetary magnetic fields.

Spacecraft measure solar-wind speed, density, temperature, and magnetic field directly. Auroras, geomagnetic storms, radio disruptions, satellite drag, and induced currents in power systems correlate with changes in solar-wind conditions and eruptive solar activity. Voyager spacecraft have crossed major heliospheric boundaries.

The corona is hot enough that plasma cannot remain gravitationally bound everywhere, producing an expanding wind. Solar rotation bends magnetic-field geometry into a spiral. When high-speed streams overtake slower wind, interaction regions form; CMEs add transient shocks and strong magnetic structures that can disturb Earth's magnetosphere.