magnetotail

The magnetotail is the elongated extension of Earth’s magnetosphere on the night side, formed by the solar wind’s pressure stretching the planet’s dipolar magnetic field into a tail-like structure. It represents the region where the magnetic field lines are drawn out into space, away from the dayside magnetosphere, creating a long, dynamic cavity in the solar wind’s wake.

Structurally, the magnetotail consists of two magnetic lobes with opposite field directions, separated by a thinner current sheet known as the plasma sheet. The lobes are relatively low in dense plasma, while the plasma sheet contains hotter, denser plasma and carries the cross-tail current that threads the tail. The tail extends from near Earth to far into space, with a near-Earth portion and a distant tail that can reach many tens to hundreds of Earth radii.

Dynamic processes in the magnetotail store and release energy from the solar wind. Magnetic reconnection in the tail converts magnetic energy to particle energy, driving magnetospheric substorms, earthward injections of energetic particles, and auroral intensifications. The reconnection can produce plasmoids or magnetic flux ropes that travel tailward, and can cause earthward flows that lead to dipolarization of the inner magnetosphere.

Observationally, the magnetotail is studied by spacecraft that measure magnetic fields and plasma, as well as by ground-based auroral observations. It plays a central role in space weather, influencing the radiation belts, geomagnetic activity, and auroras, and it responds to changing solar wind conditions, expanding during southward interplanetary magnetic field and contracting under different solar wind pressures.