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The very outer solar atmosphere (corona) is very hot with temperatures over a million degrees K, while the photosphere is of the order of 5000 K. Embedded in this hot outer corona are cool, =10,000 K, magnetic structures called solar prominences. As seen on the disk, they are long filamentary structures while on the solar limb they look like intricate loops. In this paper, we present the development of our understanding of solar prominences, which have played a central role in the development of solar science. Solar prominences were first observed during the few minute episodes of total eclipses. The introduction of spectroscopy allowed continuous observations, which also led to information on temperatures, temporal variations and dynamics of the associated plasma. The discovery of strong magnetic fields in sunspots provided a breakthrough in our understanding of the physics of the Sun. Weaker magnetic fields formed both the large and small-scale structures of prominences, their time-variable shapes, and explained why they could remain floating high above the solar surface in the less dense corona. Appearing as dark, thin, elongated filaments against a brighter solar disk, they provided further information through their interaction with and dependence on how magnetic fields are distributed on the solar surface, in the chromosphere and corona. Access to X-ray and short-wavelength ultraviolet radiation in prominences from spacecraft revealed large ranges of temperature in thin layers between the 10,000-degree prominence cores and the surrounding million-degree corona. The advent of increasingly more powerful computers has led to advanced modelling of prominence plasma based on radiative transfer and magnetohydrodynamic (MHD) calculations. Theoretical and observational progress has opened up new possible formation mechanisms. The spectacular eruptions of solar prominences have led to a considerable amount of observational and theoretical work on possibly similar events on other stars, which could affect the existence of life on their orbiting planets. [ABSTRACT FROM AUTHOR]

A straight cylindrical, electrically shielded magnetic flux rope is considered as the upper part of a weakly curved magnetic loop whose footpoints are fixed in the photosphere. All parameters of the flux rope depend on one variable—the distance from the axis of its symmetry. As the flux rope rises into the rarefied solar atmosphere, the external pressure keeping the flux rope from lateral expansion drops continuously. At some critical value of it the longitudinal magnetic field of the flux rope vanishes on the magnetic surface where the longitudinal electric current changes its sign in accordance with the requirement for the total current to be shielded. At the same time, the azimuthal current and the force-free parameter near this surface grow indefinitely. Because of this growth, the electron drift velocity near this surface exceeds the ion-sound speed, leading to the excitation of a plasma ion-sound instability as a trigger of flare energy release. The plasma conductivity in the region of plasma turbulence drops by seven orders of magnitude. Rapid magnetic energy dissipation at the anomalous resistivity generates an inductive electric field in the plasma that exceeds considerably the Dreicer limit. This explains the efficient acceleration of particles in the region where the magnetic field weakens rapidly. [ABSTRACT FROM AUTHOR]

Quiescent filaments appear as absorption features on the solar disk when observed in chromospheric lines and at continuum wavelengths in the millimeter (mm) range. Active region (AR) filaments are their small-scale, low-altitude analogues, but they could not be resolved in previous mm observations. This spectral diagnostic can provide insight into the details of the formation and physical properties of their fine threads, which are still not fully understood. Here, we shed light on the thermal structure of an AR filament using high-resolution brightness temperature (Tb) maps taken with ALMA Band 6 complemented by simultaneous IRIS near-UV spectra, Hinode/SOT photospheric magnetograms, and SDO/AIA extreme-UV images. Some of the dark threads visible in the AIA 304 Å passband and in the core of Mg ii resonance lines have dark (Tb

The Sun is the celestial body in the sky with the closest relationship with the Earth. The violent eruptive activities happening on the Sun can greatly impact the human living environment and lead to disastrous consequences. It is well accepted that solar eruptions including the solar flare, prominence eruption and coronal mass ejection are the different manifestations of a single physical process powered by the magnetic free energy gradually stored in the corona prior to eruptions. Therefore, mapping the three-dimensional structure of coronal magnetic field is a prerequisite to understand the initiation mechanism of solar eruptions. Due to the technological and methodological difficulties, routine observations of the coronal magnetic field are still unavailable. Therefore, a number of methods have been developed to reconstruct the coronal magnetic field. This paper mainly reviews the applications of various reconstruction methods to the studies of the solar eruptions in the recent ten years. [ABSTRACT FROM AUTHOR]