Abstract
Solar eruptions, observed as flares and coronal mass ejections (CMEs), are the most energetic visible plasma phenomena in the solar system. CMEs are the central component of solar eruptions and are detected as coherent magnetized plasma structures expanding in the solar wind (SW). If they reach the Earth, their magnetic fields can drive strong disturbances in the ionosphere, causing deleterious effects on terrestrial technological systems. The scientific and practical importance of CMEs has led to numerous satellite missions observing the Sun and SW. This has culminated in the ability to continuously observe CMEs expanding from the Sun to 1 AU, where the magnetic fields and plasma parameters of the evolved structures (“ejecta”) can be measured in situ. Until recently, the physical mechanisms responsible for eruptions were major unanswered questions in solar and by extension stellar physics. New observations of CME dynamics and associated eruptive phenomena are now providing more stringent constraints on models, and quantitative theory-data comparisons are helping to establish the correct mechanism of solar eruptions, particularly the driving force of CMEs and the evolution of their magnetic fields in three dimensions. Recent work has demonstrated that theoretical results can simultaneously replicate the observed CME position-time data, temporal profiles of associated solar flare soft X-ray emissions, and the magnetic field and plasma parameters of CME ejecta measured at 1 AU. Thus, a new theoretical framework with testable predictions is emerging to model eruptions and the coupling of CME ejecta to geomagnetic disturbances. The key physics in CME dynamics is the Lorentz hoop force acting on toroidal “flux ropes,” scalable from tokamaks and similar laboratory plasma structures. The present paper reviews the latest advances in observational and theoretical understanding of CMEs with the emphasis on quantitative comparisons of theory and observation.
Highlights
The Sun is the most dominant object in the solar system
Recent work has demonstrated that theoretical results can simultaneously replicate the observed coronal mass ejections (CMEs) position-time data, temporal profiles of associated solar flare soft X-ray emissions, and the magnetic field and plasma parameters of CME ejecta measured at 1 AU
The focus has been on the physics of CMEs—their magnetic configuration, acceleration mechanism and forces, and their physical relationships with the major manifestations of eruption: eruptive prominences (EPs), flare emissions, and interplanetary magnetic cloud” (MC)
Summary
The Sun is the most dominant object in the solar system. Its mass, M 1⁄4 1:99 Â 1033 g, constitutes approximately 99.8% of the total mass of the system. At the Helios 2 spacecraft near 1 AU, it was inferred to be $0.5 AU in radial extent along the Sun-Earth line, and the measured magnetic field in the loop reached Bmax $ 20 nT, with the field vector B smoothly rotating from the southward to the northward orientation over 36 h This observation led the way in clarifying the three-dimensional (3-D) spatial structure of such geoeffective (storm-causing) unipolar IMF periods, which are distinguishable from the rapidly fluctuating background IMF of $5 nT. The association was statistical because coronagraphs had limited fields of view (FOVs) and could not observe CMEs propagating toward the space-borne magnetometers and particle detectors placed at the L1 Lagrange point on the SunEarth line, approximately 10À2 AU from the Earth toward the Sun. With the launch of the Solar Terrestrial Relations.
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