corotating

Corotating is an adjective describing motion or observations that occur in or relative to a frame rotating with the same angular velocity as a reference body or pattern. The term comes from corotate (to rotate together) and is used across astronomy, space physics, and planetary science to indicate alignment in rotation or angular speed rather than simply spatial proximity.

In solar and space physics, corotation often appears in the study of the solar wind and magnetospheres. Corotating Interaction Regions (CIRs) form when faster solar wind streams overtake slower ones and, guided by the Sun’s rotation, create long-lived, rotating structures that sweep past planets. In a planet’s magnetosphere, the plasma tends to co-rotate with the planet due to magnetic coupling with the ionosphere; this corotation is strongest near the planet and can weaken at greater distances, a behavior known as corotation breakdown.

In planetary rings and satellites, corotation is relevant to resonances. Corotation resonances occur when ring particles experience gravitational forcing at a pattern speed tied to a satellite’s orbit, giving rise to distinctive ring structures, waves, or gaps that co-move with the perturbing body’s orbital motion.

In reference-frame analysis, a corotating frame is a coordinate system rotating with a specified angular velocity, often the orbit or rotation rate of a primary body. Analyzing phenomena in this frame can reveal stationary patterns that are time-dependent in an inertial frame.

Notes: corotation is related to, but distinct from, tidal locking, which describes a body whose rotation period matches its orbital period around a partner. See also corotation resonance and corotating frame.