Abstract
Interplanetary coronal mass ejections (ICMEs) are large-scale heliospheric transients that originate from the Sun. When an ICME is sufficiently faster than the preceding solar wind, a shock wave develops ahead of the ICME. The turbulent region between the shock and the ICME is called the sheath region. ICMEs and their sheaths and shocks are all interesting structures from the fundamental plasma physics viewpoint. They are also key drivers of space weather disturbances in the heliosphere and planetary environments. ICME-driven shock waves can accelerate charged particles to high energies. Sheaths and ICMEs drive practically all intense geospace storms at the Earth, and they can also affect dramatically the planetary radiation environments and atmospheres. This review focuses on the current understanding of observational signatures and properties of ICMEs and the associated sheath regions based on five decades of studies. In addition, we discuss modelling of ICMEs and many fundamental outstanding questions on their origin, evolution and effects, largely due to the limitations of single spacecraft observations of these macro-scale structures. We also present current understanding of space weather consequences of these large-scale solar wind structures, including effects at the other Solar System planets and exoplanets. We specially emphasize the different origin, properties and consequences of the sheaths and ICMEs.
Highlights
The existence of interplanetary plasma clouds was suggested already before the space era and before discovery of CMEs
This review focuses on the current understanding of observational signatures and properties of Interplanetary coronal mass ejections (ICMEs) and the associated sheath regions based on five decades of studies
In this article we give a review of ICMEs and their sheath regions, mostly based on observations, and we discuss their role in driving space weather disturbances
Summary
Keywords Coronal mass ejections · Solar wind · Space weather · Interplanetary shocks · Magnetic clouds. The first ICME observations emerged in the 1970s suggesting loop- or bubble-like structures behind interplanetary shocks (e.g., Hirshberg et al 1970; Gosling et al 1973; Palmer et al 1978). At the orbit of the Earth, the passage of an ICME past the observing spacecraft takes approximately one day, corresponding to a spatial structure of nearly one-third of the astronomical unit (AU). Signatures of ICMEs vary greatly, but on average, they are distinguished from the ambient solar wind by specific plasma, compositional and magnetic field signatures (e.g., Zurbuchen and Richardson 2006; Wimmer-Schweingruber et al 2006). As we will discuss later in this review, ICMEs with these specific signatures can be described in terms of a magnetic flux rope, i.e., a flux tube with helical magnetic field lines winding about the axis
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