Over the last two decades the uninterrupted, high resolution observations of the Sun, from the excellent range of telescopes aboard many spacecraft complemented with observations from sophisticated ground-based telescopes have opened up a new world producing significantly more complete information on the physical conditions of the solar atmosphere than before. The interface between the lower solar atmosphere where energy is generated by subsurface convection and the corona comprises the chromosphere, which is dominated by jet-like, dynamic structures, called mottles when found in quiet regions, fibrils when found in active regions and spicules when observed at the solar limb. Recently, space observations with Hinode have led to the suggestion that there should exist two different types of spicules called Type I and Type II which have different properties. Groundbased observations in the Ca ii H and K filtergrams reveal the existence of long, thin emission features called straws in observations close to the limb, and a class of short-lived events called rapid blue-shifted excursions characterized by large Doppler shifts that appear only in the blue wing of the Ca ii infrared line. It has been suggested that the key to understanding how the solar plasma is accelerated and heated may well be found in the studies of these jet-like, dynamic events. However, while these structures are observed and studied for more than 130 years in the visible, but also in the UV and EUV emission lines and continua, there are still many questions to be answered. Thus, despite their importance and a multitude of observations performed and theoretical models proposed, questions regarding their origin, how they are formed, their physical parameters, their association with the underlying photospheric magnetic field, how they appear in the different spectral lines, and the interrelationship between structures observed in 2 Please give a shorter version with: \authorrunning and \titlerunning prior to \maketitle quiet and active regions on the disk and at the limb, as well as their role in global processes has not yet received definitive answers. In addition, how they affect the coronal heating and solar wind need to be further explored. In this review we present observations and physical properties of small-scale jet-like chromospheric events observed in active and quiet regions, on the disk and at the limb and discuss their interrelationship.

Coronal bright points (CBPs) are a fundamental class of solar activity. They represent a set of low-corona small-scale loops with enhanced emission in the extreme-ultraviolet and X-ray spectrum that connect magnetic flux concentrations of opposite polarities. CBPs are one of the main building blocks of the solar atmosphere outside active regions uniformly populating the solar atmosphere including active region latitudes and coronal holes. Their plasma properties classify them as downscaled active regions. Most importantly, their simple structure and short lifetimes of less than 20 h that allow to follow their full lifetime evolution present a unique opportunity to investigate outstanding questions in solar physics including coronal heating. The present Living Review is the first review of this essential class of solar phenomena and aims to give an overview of the current knowledge about the CBP general, plasma and magnetic properties. Several transient dynamic phenomena associated with CBPs are also briefly introduced. The observationally derived energetics and the theoretical modelling that aims at explaining the CBP formation and eruptive behaviour are reviewed.

Abstract. High spectral, spatial and temporal resolution UV observations of the quiet Sun transition region show a highly structured and dynamical environment where transient supersonic flows are commonly observed. Strongly non-Gaussian line profiles are the spectral signatures of these flows and are known in the literature as explosive events. In this paper we present a high spatial resolution (≈1 ) spectroheliogram of a 273 × 291 area of the quiet Sun acquired with SUMER/SOHO in the O  spectral line at λ103.193 nm. The extremely high quality of these observations allows us to identify tens of explosive events from which we estimate an average size of 1800 km and a birthrate of 2500 s −1 over the entire Sun. Estimates of the kinetic and enthalpy fluxes associated with these events show that explosive events are not important as far as solar coronal heating is concerned. The relationship with the underlying photospheric magnetic field is also studied, revealing that explosive events generally occur in regions with weak (and, very likely, mixed polarity) magnetic flux. By studying the structure of upward and downward flows exceeding those associated to average quiet Sun profiles, we find a clear correlation between the "excess" flows and the magnetic network. However, although explosive events are always associated with flow patterns often covering areas larger than the explosive event itself, the contrary is not true. In particular, almost all flows associated with the stronger concentrations of photospheric magnetic flux do not show non-Gaussian line profiles. In some cases, non-Gaussian line profiles are associated with supersonic flows in small magnetic loops. The case of a small loop showing a supersonic siphon-like flow of ≈130 km s −1 is studied in detail. This is, to our knowledge, the first detection of a supersonic siphon-like flow in a quiet Sun loop. In other cases, the flow patterns associated with explosive events may suggest a relation with UV spicules.

Abstract. This paper presents the formation, evolution and decay of a coronal bright point via a spectroscopic analysis of its transition region counterpart and the evolution of the underlying magnetic bipole during 3 days of almost continuous observations. The data were obtained with various instruments on-board SoHO, including the SUMER spectrograph in the transition region line S  933.40 Å, CDS in the He  584.33, O  629.73 and Mg  368.06 Å lines, plus MDI and EIT. The existence of the coronal feature is strongly correlated with the evolution of the underlying bipolar region. The lifetime of the bright point from the moment when it was first visible in the EIT images until its complete disappearance was ∼18 hrs. Furthermore, the bright point only became visible at coronal temperatures when the two converging opposite magnetic polarities were ∼7000 km apart. As far as the temporal coverage of the data permits, we found that the bright point disappeared at coronal temperatures after a full cancellation of one of the magnetic polarities. The spectroscopic analysis reveals the presence of small-scale (∼6 ) transient brightenings within the bright point with a periodicity of ∼6 min. The Doppler shift in the bright point was found to be in the range of −10 to 10 km s −1 although it is dominated by a red-shifted emission which is associated with regions characterized by stronger "quiet" Sun photospheric magnetic flux. Small-scale brightenings within the bright point show velocity variations in the range 3-6 km s −1 . In general the bright point has a radiance ∼4 times higher than that of the network. No relation was found between the bright point and the UV explosive event phenomena.

Context. Eruptions from coronal bright points (CBPs) are investigated in a two part study. Aims. The present study aims to explore in full detail the morphological and dynamical evolution of these eruptions in the context of the full lifetime evolution of CBPs. A follow-up study employs data-driven modelling based on a relaxation code to reproduce the time evolution of the magnetic field of these eruptive CBPs, and provide an insight on the possible causes for destabilisation and eruption. Methods. Observations of the full lifetime of CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory in four passbands, He ii 304 Å, Fe ix/x 171 Å, Fe xii 193 Å, and Fe xviii 94 Å are investigated for the occurrence of plasma ejections, micro-flaring, mini-filament eruptions and mini coronal mass ejections (mini-CMEs). Data from the Helioseismic Magnetic Imager are analysed to study the longitudinal photospheric magnetic field evolution associated with the CBPs and related eruptions.Results. First and foremost, our study shows that the majority (76%) of quiet Sun CBPs (31 out of 42 CBPs) produce at least one eruption during their lifetime. From 21 eruptions in 11 CBPs, 18 occur in average ∼17 hrs after the CBP formation for an average lifetime of the CBPs in AIA 193 Å of ∼21 hrs. This time delay in the eruption occurrence coincides in each BP with the convergence and cancellation phase of the CBP bipole evolution during which the CBPs become smaller until they fully disappear. The remaining three happen 4 -6 hrs after the CBP formation. In sixteen out of 21 eruptions the magnetic convergence and cancellation involve the CBP main bipoles, while in three eruptions one of the BP magnetic fragments and a pre-existing fragment of opposite polarity converge and cancel. In one BP with two eruptions cancellation was not observed. The CBP eruptions involve in most cases the expulsion of chromospheric material either as elongated filamentary structure (mini-filament, MF) or a volume of cool material (cool plasma cloud, CPC), together with the CBP or higher overlying hot loops. Coronal waves were identified during three eruptions. A micro-flaring is observed beneath all erupting MFs/CPCs. It remains uncertain whether the destabilised MF causes the micro-flaring or the destabilisation and eruption of the MF is triggered by reconnection beneath the filament. In most eruptions, the cool erupting plasma obscures partially or fully the micro-flare until the erupting material moves away from the CBP. From 21 eruptions 11 are found to produce mini-CMEs. The dimming regions associated with the CMEs are found to be occupied by both the 'dark' cool plasma and areas of weakened coronal emission caused by the depleted plasma density. Conclusions. The present study demonstrates that the evolution of small-scale loop structures in the quiet Sun determined by their magnetic footpoint motions and/or ambient field topology, evolve into eruptive phase that triggers the ejection of cool and hot plasma in the c...