Heating the outer layers of the magnetically quiet solar atmosphere to more than one million kelvin and accelerating the solar wind requires an energy flux of approximately 100 to 300 watts per square metre, but how this energy is transferred and dissipated there is a puzzle and several alternative solutions have been proposed. Braiding and twisting of magnetic field structures, which is caused by the convective flows at the solar surface, was suggested as an efficient mechanism for atmospheric heating. Convectively driven vortex flows that harbour magnetic fields are observed to be abundant in the photosphere (the visible surface of the Sun). Recently, corresponding swirling motions have been discovered in the chromosphere, the atmospheric layer sandwiched between the photosphere and the corona. Here we report the imprints of these chromospheric swirls in the transition region and low corona, and identify them as observational signatures of rapidly rotating magnetic structures. These ubiquitous structures, which resemble super-tornadoes under solar conditions, reach from the convection zone into the upper solar atmosphere and provide an alternative mechanism for channelling energy from the lower into the upper solar atmosphere.

While the nature of the heating mechanisms in the corona remains elusive their associated cooling is also a poorly known but a far less observationally restrictive subject. In this work, we analyse coordinated observations spanning chromospheric, transition region (TR) and coronal temperatures at very high resolution which reveal essential characteristics of thermally unstable plasmas. Coronal rain is found to be a highly multi-thermal phenomenon with a high degree of co-spatiality in the multi-wavelength emission. EUV darkening and quasi-periodic intensity variations are found to be strongly correlated to coronal rain and especially 'showers'. Progressive cooling of coronal rain is observed, leading to a height dependence of the emission. Furthermore, a fast-slow twostep catastrophic cooling progression is found, which may reflect the transition to optically thick plasma states. The intermittent and clumpy appearance of coronal rain at coronal heights becomes more continuous and persistent at chromospheric heights just before impact, in agreement with previous observations above sunspots. This change of character is mainly due to a funnel effect from the observed expansion of the magnetic field at low heights. Strong density inhomogeneities on spatial scales of 0.2 ′′ − 0.5 ′′ are found, in which TR to chromospheric temperature transition occurs at the lowest detectable scales. The shape of the distribution of coronal rain widths is found to be independent of temperature with peaks close to the resolution limit of each telescope, ranging from 0.2 ′′ to 0.8 ′′ . However we find a sharp increase of clump numbers at the coolest wavelengths and especially at higher resolution, suggesting that the bulk of the rain distribution remains undetected. Rain clumps appear organised in strands. Such structure is not limited to chromospheric temperatures but extends at least to TR temperatures as well, suggesting an important role of thermal instability in the shaping of fundamental loop substructure. At the smallest detected scales

The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere -a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA's scientific potential for studying the Sun for a large range of science cases.

The existence of the Sun’s hot atmosphere and the solar wind acceleration continues to be an outstanding problem in solar-astrophysics. Although magnetohydrodynamic (MHD) modes and dissipation of magnetic energy contribute to heating and the mass cycle of the solar atmosphere, yet direct evidence of such processes often generates debate. Ground-based 1-m Swedish Solar Telescope (SST)/CRISP, Hα 6562.8 Å observations reveal, for the first time, the ubiquitous presence of high frequency (~12–42 mHz) torsional motions in thin spicular-type structures in the chromosphere. We detect numerous oscillating flux tubes on 10 June 2014 between 07:17 UT to 08:08 UT in a quiet-Sun field-of-view of 60” × 60” (1” = 725 km). Stringent numerical model shows that these observations resemble torsional Alfvén waves associated with high frequency drivers which contain a huge amount of energy (~105 W m−2) in the chromosphere. Even after partial reflection from the transition region, a significant amount of energy (~103 W m−2) is transferred onto the overlying corona. We find that oscillating tubes serve as substantial sources of Alfvén wave generation that provide sufficient Poynting flux not only to heat the corona but also to originate the supersonic solar wind.

Recently, it was shown that the complex dynamical behaviour of spicules has to be interpreted as the result of simultaneous action of three kinds of motion: (1) field aligned flows, (2) swaying motions, and (3) torsional motions. We use high-quality observations from the CRisp Imaging SpectroPolarimeter at the Swedish 1-meter Solar Telescope to investigate signs of these different kinetic modes in spicules on the disk. Earlier, rapid blue-shifted excursions (RBEs), short-lived absorption features in the blue wing of chromospheric spectral lines, were identified as the disk counterpart of type II spicules. Here we report the existence of similar absorption features in the red wing of the Ca II 8542 and Hα lines: rapid red-shifted excursions (RREs). RREs are found over the whole solar disk and are located in the same regions as RBEs: in the vicinity of magnetic field concentrations. RREs have similar characteristics as RBEs: they have similar lengths, widths, lifetimes, and average Doppler velocity. The striking similarity of RREs to RBEs implies that RREs are a manifestation of the same physical phenomenon and that spicules harbour motions that can result in a net red-shift when observed on-disk. We find that RREs are less abundant than RBEs: the RRE/RBE detection count ratio is about 0.52 at disk center and 0.74 near the limb. We interpret the higher number of RBEs and the decreased imbalance towards the limb as an indication that field-aligned up-flows have a significant contribution to the net Dopplershift of the structure. Most RREs and RBEs are observed in isolation but we find many examples of parallel and touching RRE/RBE pairs which appear to be part of the same spicule. We interpret the existence of these RRE/RBE pairs and the observation that many RREs and RBEs have varying Dopplershift along their width as signs that torsional motion is an important characteristic of spicules. The fact that most RBEs and RREs are observed in isolation agrees with the idea that transversal swaying motion is another important kinetic mode. We find examples of transitions from RRE to RBE and vice versa. These transitions sometimes appear to propagate along the structure with speeds between 18 and 108 km s −1 and can be interpreted as the sign of a transverse (Alfvénic) wave.

Observations in the 171 Å channel of the Atmospheric Imaging Assembly of the space-borne Solar Dynamics Observatory show tornadoes-like features in the atmosphere of the Sun. These giant tornadoes appear as dark, elongated and apparently rotating structures in front of a brighter background. This phenomenon is thought to be produced by rotating magnetic field structures that extend throughout the atmosphere. We characterize giant tornadoes through a statistical analysis of properties like spatial distribution, lifetimes, and sizes. A total number of 201 giant tornadoes are detected in a period of 25 days, suggesting that on average about 30 events are present across the whole Sun at a time close to solar maximum. Most tornadoes appear in groups and seem to form the legs of prominences, thus serving as plasma sources/sinks. Additional Hα observations with the Swedish 1-m Solar Telescope imply that giant tornadoes rotate as a structure although clearly exhibiting a thread-like structure. We observe tornado groups that grow prior to the eruption of the connected prominence. The rotation of the tornadoes may progressively twist the magnetic structure of the prominence until it becomes unstable and erupts. Finally, we investigate the potential relation of giant tornadoes to other phenomena, which may also be produced by rotating magnetic field structures. A comparison to cyclones, magnetic tornadoes and spicules implies that such events are more abundant and short-lived the smaller they are. This comparison might help to construct a power law for the effective atmospheric heating contribution as function of spatial scale.

Ellerman bombs (EBs) have been widely studied in recent years due to their dynamic, explosive nature and apparent links to the underlying photospheric magnetic field implying that they may be formed by magnetic reconnection in the photosphere. Despite a plethora of researches discussing the morphologies of EBs, there has been a limited investigation of how these events appear at the limb, specifically, whether they manifest as vertical extensions away from the disc. In this article, we make use of high-resolution, high-cadence observations of an Active Region (AR) at the solar limb, collected by the CRisp Imaging SpectroPolarimeter (CRISP) instrument, to identify EBs and infer their physical properties. The upper atmosphere is also probed using the Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). We analyse 22 EB events evident within these data, finding that 20 appear to follow a parabolic path away from the solar surface at an average speed of 9 km s −1 , extending away from their source by 580 km, before retreating back at a similar speed. These results show strong evidence of vertical motions associated with EBs, possibly explaining the dynamical 'flaring' (changing in area and intensity) observed in on-disc events. Two in-depth case studies are also presented which highlight the unique dynamical nature of EBs within the lower solar atmosphere. The viewing angle of these observations allows for a direct linkage between these EBs and other small-scale events in the Hα line wings, including a potential flux emergence scenario. The findings presented here suggest that EBs could have a wider-reaching influence on the solar atmosphere than previously thought, as we reveal a direct linkage between EBs and an emerging small-scale loop, and other near-by small-scale explosive events. However, as previous research found, these extensions do not appear to impact upon the Hα line core, and are not observed by the SDO/AIA EUV filters.

New and advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer sub-structures within coronal loop crosssections, in order to understand the nature of the solar corona. Here, we push this lower limit further to search for the finest coronal loop sub-structures, through taking advantage of the resolving power of the Swedish 1m Solar Telescope (SST) / CRisp Imaging Spectro-Polarimeter (CRISP), together with co-observations from the Solar Dynamics Observatory (SDO) / Atmospheric Image Assembly (AIA). High resolution imaging of the chromospheric Hα 656.28 nm spectral line core and wings can, under certain circumstances, allow one to deduce the topology of the local magnetic environment of the solar atmosphere where its observed. Here, we study post-flare coronal loops, which become filled with evaporated chromosphere that rapidly condenses into chromospheric clumps of plasma (detectable in Hα) known as a coronal rain, to investigate their fine-scale structure. We identify, through analysis of three datasets, large-scale catastrophic cooling in coronal loop-tops and the existence of multi-thermal, multi-stranded sub-structures. Many cool strands even extend fully-intact from loop-top to foot-point. We discover that coronal loop fine-scale strands can appear bunched with as many as 8 parallel strands, within an AIA coronal loop cross-section. The strand number density vs cross-sectional width distribution, as detected by CRISP within AIA-defined coronal loops, most-likely peaks at well below 100 km and currently 69% of the sub-structure strands are statistically unresolved in AIA coronal loops.