![]() These processes occur over tens of minutes to several hours. These phenomena are the most energetic plasma processes observed in the solar system: each occurrence expels an estimated 10 14–10 16 g of mass and 10 30–10 33 ergs of energy as kinetic energy of bulk plasma motion (CMEs and EPs) and photon energy (flares). Most flares are much less energetic and are observed in limited wavelength bands such as X-rays, extreme ultraviolet (EUV), and hydrogen alpha (H α, λ = 6562.8 Å) where the background is relatively dark (e.g., Fig. Exceptionally powerful flares are visible in white light against the bright solar disk, but such events are rare. Figure 1 shows the morphology of a solar flare (solid arrow) observed in X-rays. Solar flares, detectable in electromagnetic radiation ranging from radiowaves to γ-rays, appear as localized quasi-stationary brightening in the low corona. Their speeds can reach several hundred to a few thousand kilometers per second in tens of minutes. CMEs and EPs appear as large plasma structures of the order of the solar radius, 1 R ⊙ = 6.96 × 10 5 km, accelerating and expanding away from the Sun. ![]() To the keen observer, however, it is neither constant nor placid, sporadically exhibiting “eruptions” that are observed as coronal mass ejections (CMEs), eruptive prominences (EPs), or solar flares depending on the method of observation. To the casual observer, the Sun is constant and placid. Most of this mass is in the form of plasma. Its mass, M ⊙ = 1.99 × 10 33 g, constitutes approximately 99.8% of the total mass of the system. The Sun is the most dominant object in the solar system. The present paper reviews the latest advances in observational and theoretical understanding of CMEs with the emphasis on quantitative comparisons of theory and observation. The key physics in CME dynamics is the Lorentz hoop force acting on toroidal “flux ropes,” scalable from tokamaks and similar laboratory plasma structures. Thus, a new theoretical framework with testable predictions is emerging to model eruptions and the coupling of CME ejecta to geomagnetic disturbances. 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. 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. Until recently, the physical mechanisms responsible for eruptions were major unanswered questions in solar and by extension stellar physics. 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. The scientific and practical importance of CMEs has led to numerous satellite missions observing the Sun and SW. If they reach the Earth, their magnetic fields can drive strong disturbances in the ionosphere, causing deleterious effects on terrestrial technological systems. CMEs are the central component of solar eruptions and are detected as coherent magnetized plasma structures expanding in the solar wind (SW). ![]() ![]() Solar eruptions, observed as flares and coronal mass ejections (CMEs), are the most energetic visible plasma phenomena in the solar system. ![]()
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