A corotating interaction region (CIR) is a recurring plasma structure in the

heliosphere The heliosphere is the magnetosphere, astrosphere, and outermost atmospheric layer of the Sun. It takes the shape of a vast, tailed bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding ...

formed when fast

solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

streams interact with slower solar wind ahead of them. This interaction creates a compressed region that appears to rotate with the Sun's rotation; accordingly it is named "corotating". CIRs develop when high-speed solar wind, typically originating from

coronal hole Coronal holes are regions of the Sun's corona that emit low levels of ultraviolet and X-ray radiation compared to their surroundings. They are composed of relatively cool and tenuous plasma (physics), plasma permeated by magnetic fields that are o ...

s, catches up to slower wind streams. The resulting compression creates distinct boundaries: a forward pressure wave at the leading edge and a reverse pressure wave at the trailing edge. At greater distances from the Sun, these pressure waves can develop into shock waves. The three-dimensional structure of CIRs is influenced by the Sun's magnetic field configuration. Because the Sun's magnetic equator is often tilted and warped relative to its rotational equator, CIRs typically show significant north–south tilts that differ between hemispheres. The forward waves tend to move toward the solar equatorial plane as distance increases, while reverse waves propagate toward higher latitudes. CIRs play several important roles in

space weather Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the varying conditions within the Solar System and its heliosphere. This includes the effects of the solar wind, especially on the Earth's magnetosphere, ion ...

and heliophysics: they can trigger

geomagnetic storm A geomagnetic storm, also known as a magnetic storm, is a temporary disturbance of the Earth's magnetosphere that is driven by interactions between the magnetosphere and large-scale transient Plasma (physics), plasma and magnetic field structur ...

s when they reach Earth, influence the distribution of energetic particles in the heliosphere, contribute to the modulation of

cosmic rays Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar ...

, particularly during periods of low solar activity, and cause compression of the

interplanetary magnetic field The interplanetary magnetic field (IMF), also commonly referred to as the heliospheric magnetic field (HMF), is the component of the solar magnetic field that is dragged out from the solar corona by the solar wind flow to fill the Solar System ...

References

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