Evolution of small-scale magnetic elements in the vicinity of granular-size swirl convective motions

Advances in solar instrumentation have led to a widespread usage of time series to study the dynamics of solar features, specially at small spatial scales and at very fast cadences. Physical processes at such scales are determinant as building blocks for many others occurring from the lower to the upper layers of the solar atmosphere and beyond, ultimately for understanding the bigger picture of solar activity. Ground-based (SST) and space-borne (Hinode) high-resolution solar data are analyzed in a quiet Sun region displaying negative polarity small-scale magnetic concentrations and a cluster of bright points observed in G-band and Ca II H images. The studied region is characterized by the presence of two small-scale convective vortex-type plasma motions, one of which appears to be affecting the dynamics of both, magnetic features and bright points in its vicinity and therefore the main target of our investigations. We followed the evolution of bright points, intensity variations at different atmospheric heights and magnetic evolution for a set of interesting selected regions. A description of the evolution of the photospheric plasma motions in the region nearby the convective vortex is shown, as well as some plausible cases for convective collapse detected in Stokes profiles.Comment: 9 figure

Granular-Scale Elementary Flux Emergence Episodes in a Solar Active Region

We analyze data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in Ca II H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading. In time series of magnetograms a diverging bipolar configuration is observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing elementary flux emergence in the solar atmosphere, i.e small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising loops (once they reached chromospheric heights) with pre-existing magnetic fields as well as to reconnection/cancellation events in U-loop segments of emerging serpentine fields. We study the temporal evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet sun regions and serpentine flux emergence signatures in active regions. Incorporating the novel features of granular-scale flux emergence presented in this study we advance the scenario for serpentine flux emergence.Comment: 24 pages, 9 figures. Accepted for publication in Solar Physic

Photospheric plasma and magnetic field dynamics during the formation of solar AR 11190

The Sun features on its surface typical flow patterns called the granulation, mesogranulation, and supergranulation. These patterns arise due to convective flows transporting energy from the interior of the Sun to its surface. In this paper we will shed light on the interaction between the convective flows in large-scale cells as well as the large-scale magnetic fields in active regions, and investigate in detail the statistical distribution of flow velocities during the evolution and formation of National Oceanic and Atmospheric Administration (NOAA) active region 11190. To do so, we employed local correlation tracking methods on data obtained by the Solar Dynamics Observatory (SDO) spacecraft in the continuum as well as on processed line-of-sight (LOS) magnetograms. We find that the flow fields in an active region can be modelled by a two-component distribution. One component is very stable, follows a Rayleigh distribution, and can be assigned to the background flows, whilst the other component is variable in strength and velocity range and can be attributed to the flux emergence visible both in the continuum maps as well as magnetograms. Generally, the plasma flows, as seen by the distribution of the magnitude of the velocity, follow a Rayleigh distribution even through the time of formation of active regions. However, at certain moments of large-scale fast flux emergence, a second component featuring higher velocities is formed in the velocity magnitudes distribution. The plasma flows are generally highly correlated to the motion of magnetic elements and vice versa except during the times of fast magnetic flux emergence as observed by rising magnetic elements. At these times, the magnetic fields are found to move faster than the corresponding plasma.Comment: 15 pages, 11 figures, 5 equations. Accepted for publication in Astronomy and Astrophysics (A&A

Twisting solar coronal jet launched at the boundary of an active region

A broad jet was observed in a weak magnetic field area at the edge of active region NOAA 11106. The peculiar shape and magnetic environment of the broad jet raised the question of whether it was created by the same physical processes of previously studied jets with reconnection occurring high in the corona. We carried out a multi-wavelength analysis using the EUV images from the Atmospheric Imaging Assembly (AIA) and magnetic fields from the Helioseismic and Magnetic Imager (HMI) both on-board the SDO satellite. The jet consisted of many different threads that expanded in around 10 minutes to about 100 Mm in length, with the bright features in later threads moving faster than in the early ones, reaching a maximum speed of about 200 km s^{-1}. Time-slice analysis revealed a striped pattern of dark and bright strands propagating along the jet, along with apparent damped oscillations across the jet. This is suggestive of a (un)twisting motion in the jet, possibly an Alfven wave. A topological analysis of an extrapolated field was performed. Bald patches in field lines, low-altitude flux ropes, diverging flow patterns, and a null point were identified at the basis of the jet. Unlike classical lambda or Eiffel-tower shaped jets that appear to be caused by reconnection in current sheets containing null points, reconnection in regions containing bald patches seems to be crucial in triggering the present jet. There is no observational evidence that the flux ropes detected in the topological analysis were actually being ejected themselves, as occurs in the violent phase of blowout jets; instead, the jet itself may have gained the twist of the flux rope(s) through reconnection. This event may represent a class of jets different from the classical quiescent or blowout jets, but to reach that conclusion, more observational and theoretical work is necessary.Comment: 12 pages, 9 figures, accepted for publication in A&

Flare Energy Release in the Lower Solar Atmosphere Near the Magnetic Field Polarity Inversion Line

We study flare processes in the solar atmosphere using observational data for a M1-class flare of June 12, 2014, obtained by New Solar Telescope (NST/BBSO) and Helioseismic Magnetic Imager (HMI/SDO). The main goal is to understand triggers and manifestations of the flare energy release in the photosphere and chromosphere using high-resolution optical observations and magnetic field measurements. We analyze optical images, HMI Dopplergrams and vector magnetograms, and use Non-Linear Force-Free Field (NLFFF) extrapolations for reconstruction of the magnetic topology and electric currents. The NLFFF modelling reveals interaction of two magnetic flux ropes with oppositely directed magnetic field in the PIL. These flux ropes are observed as a compact sheared arcade along the PIL in the high-resolution broad-band continuum images from NST. In the vicinity of PIL, the NST H alpha observations reveal formation of a thin three-ribbon structure corresponding to a small-scale photospheric magnetic arcade. The observational results evidence in favor of location of the primary energy release site in the chromospheric plasma with strong electric currents concentrated near the polarity inversion line. In this case, magnetic reconnection is triggered by the interacting magnetic flux ropes forming a current sheet elongated along the PIL.Comment: arXiv admin note: substantial text overlap with arXiv:1604.0538