The formation of jets such as dynamic fibrils, mottles, and spicules in the solar chromosphere is one of the most important, but also most poorly understood, phenomena of the Sun's magnetized outer atmosphere. We use extremely high resolution observations from the Swedish 1 m Solar Telescope combined with advanced numerical modeling to show that in active regions these jets are a natural consequence of upwardly propagating slow-mode magnetoacoustic shocks. These shocks form when waves generated by convective flows and global p-mode oscillations in the lower lying photosphere leak upward into the magnetized chromosphere. We find excellent agreement between observed and simulated jet velocities, decelerations, lifetimes, and lengths. Our findings suggest that previous observations of quiet-Sun spicules and mottles may also be interpreted in light of a shockdriven mechanism.

We present unprecedented high resolution Hα observations, obtained with the Swedish 1-m Solar Telescope, that, for the first time, spatially and temporally resolve dynamic fibrils in active regions on the Sun. These jet-like features are similar to mottles or spicules in quiet Sun. We find that most of these fibrils follow almost perfect parabolic paths in their ascent and descent. We measure the properties of the parabolic paths taken by 257 fibrils, and present an overview of the deceleration, maximum velocity, maximum length and duration, as well as their widths and the thickness of a bright ring that often occurs above dynamic fibrils. We find that the observed deceleration of the projected path is typically only a fraction of solar gravity, and incompatible with a ballistic path at solar gravity. We report on significant differences of fibril properties between those occurring above a dense plage region, and those above a less dense plage region where the magnetic field seems more inclined from the vertical. We compare these findings to advanced numerical 2D radiative MHD simulations, and find that fibrils are most likely formed by chromospheric shock waves that occur when convective flows and global oscillations leak into the chromosphere along the field lines of magnetic flux concentrations. Detailed comparison of observed and simulated fibril properties shows striking similarities of the values for deceleration, maximum velocity, maximum length and duration. We compare our results with observations of mottles and find that a similar mechanism is most likely at work in the quiet Sun.

We use state-of-the-art radiation-MHD simulations and 3D non-LTE radiative transfer computations to investigate Hα line formation in the solar chromosphere and apply the results of this investigation to develop the potential of Hα as diagnostic of the chromosphere.We show that one can accurately model Hα line formation assuming statistical equilibrium and complete frequency redistribution provided the computation of the model atmosphere included nonequilibrium ionization of hydrogen, and the Lyman-α and Lyman-β line profiles are described by Doppler profiles.We find that 3D radiative transfer is essential in modeling hydrogen lines due to the low photon destruction probability in Hα. The Hα opacity in the upper chromosphere is mainly sensitive to the mass density and only weakly sensitive to temperature.We find that the Hα line-core intensity is correlated with the average formation height: the larger the average formation height, the lower the intensity. The line-core width is a measure of the gas temperature in the line-forming region. The fibril-like dark structures seen in Hα line-core images computed from our model atmosphere are tracing magnetic field lines. These structures are caused by field-aligned ridges of enhanced chromospheric mass density that raise their average formation height, and therefore makes them appear dark against their deeper-formed surroundings. We compare with observations, and find that the simulated line-core widths are very similar to the observed ones, without the need for additional microturbulence.

An extension of Joint Phase Diverse Speckle image restoration is presented. Multiple realizations of multiple objects having known wavefront relations with each other can now be restored jointly. As the alignment of the imaging setup does not change, near-perfect alignment can be achieved between different objects, thus greatly reducing false signals in the determination of derived quantities, such as magnetograms, Dopplergrams, etc. The method was implemented in C++ as an image restoration server, to which worker clients can connect and disconnect randomly, so that a large number of CPUs can be used to speed up the restorations. We present a number of examples of applications of the restoration method to observations obtained with the Swedish 1-m Solar Telescope on La Palma.

High-resolution images obtained in Hα with the new Swedish Solar Telescope at La Palma, Spain, have been used for studies of fine-scale threads in solar filaments. The widths of the thin threads are ≤0.3 arc sec. The fact that the width of the thinnest threads is comparable to the diffraction limit of the telescope of about 0.14 arc sec, at the wavelength of Hα, suggests that even thinner threads may exist. Assuming that the threads represent thin magnetic strings, we conclude that only a small fraction of these are filled with observable absorbing plasma, at a given time. The absorbing plasma is continuously flowing along the thread structures at velocities 15 ± 10 km s −1 , which suggests that the flows must be field-aligned. In one case where a bundle of thin threads appears to be rooted in the nearby photosphere, we find that the individual threads connects with intergranular, dark lanes in the photosphere. We do not find signs of typical network fields at the 'roots' of the fine threads, as normally evidenced by bright points in associated G-band images. It is suggested that filament threads are rooted in relatively weak magnetic fields.