We study the dynamics of plasma along the legs of an arch filament system (AFS) from the chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrarred Spectrograph (GRIS) in the He I 10830 Å range and the Swedish Solar Telescope (La Palma) using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542 Å and Fe I 6173 Å spectral lines. The temporal evolution of the draining of the plasma was followed along the legs of a single arch filament from the chromosphere to the photosphere. The average Doppler velocities inferred at the upper chromosphere from the He I 10830 Å triplet reach velocities up to 20-24~km~s$^{-1}$, in the lower chromosphere and upper photosphere the Doppler velocities reach up to 11~km~s$^{-1}$ and 1.5~km~s$^{-1}$ in the case of the Ca II 8542 Å and Si I 10827 Å spectral lines, respectively. The evolution of the Doppler velocities at different layers of the solar atmosphere (chromosphere and upper photosphere) shows that they follow the same LOS velocity pattern, which confirm the observational evidence that the plasma drains towards the photosphere as proposed in models of AFSs. The Doppler velocity maps inferred from the lower photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not show the same LOS velocity pattern. Thus, there is no evidence that the plasma reaches the lower photosphere. The observations and the nonlinear force-free field extrapolations demonstrate that the magnetic field loops of the AFS rise with time. We found flow asymmetries at different footpoints of the AFS. The NLFFF values of the magnetic field strength give us a clue to explain these flow asymmetries.
We report three-minute oscillations in the solar chromosphere driven by a strong downflow event in a sunspot. We used the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope and the Interface Region Imaging Spectrograph (IRIS). The strong downflow event is identified in the chromospheric and transition region lines above the sunspot umbra. After the event, oscillations occur at the same region. The amplitude of the Doppler velocity oscillations is 2 km/s, and gradually decreases with time. In addition, the period of the oscillations gradually increases from 2.7 minutes to 3.3 minu…
The chromosphere above active regions (ARs) on the Sun hosts magnetized supersonic downflows. Studies of these supersonic downflows help to decipher the magnetic fine structure and dynamics of the chromosphere. We perform a statistical analysis of the magnetized supersonic downflows in a number of ARs and survey their characteristics. We analyze spectro-polarimetric scans of parts of 13 ARs obtained in the infrared He I 10830 Å triplet formed in the upper chromosphere recorded with the GREGOR Infrared Spectrograph (GRIS) mounted at the GREGOR solar telescope. We retrieve the line-of-sight velo…
High-speed downflows have been observed in the solar transition region (TR) and lower corona for many decades. Despite their abundance, it has been hard to find signatures of such downflows in the solar chromosphere. In this work, we target an enhanced network region that shows ample occurrences of rapid spicular downflows in the \halpha\ spectral line that could potentially be linked to high-speed TR downflowing counterparts. We used the $k$-means algorithm to classify the spectral profiles of on-disk spicules in \halpha{} and \cak{} data observed from the Swedish 1-m Solar Telescope (SST) an…
Paper I presents the magnetic structure of a filament that developed in active region (AR) NOAA 10781. In this paper we complement those results with the velocities retrieved from Doppler shifts measured at the chromosphere and the photosphere in the AR filament area. Various inversion methods with different numbers of atmospheric components and different weighting schemes of the Stokes profiles were used. The velocities were calibrated on an absolute scale. A ubiquitous chromospheric downflow is found in the faculae surrounding the filament, with an average velocity of 1.6 km/s. The filament …
The solar coronal heating in quiet Sun (QS) and coronal holes (CH), including solar wind formation, are intimately tied by magnetic field dynamics. Thus, a detailed comparative study of these regions is needed to understand the underlying physical processes. CHs are known to have subdued intensity and larger blueshifts in the corona. This work investigates the similarities and differences between CHs and QS in the chromosphere using the Mg II h & k, C II lines, and transition region using Si IV line, for regions with identical absolute magnetic flux density (|B|). We find CHs to have subdued i…
An active region filament in the upper chromosphere is studied using spectropolarimetric data in He I 10830 A from the GREGOR telescope. A Milne-Eddingon based inversion of the Unno-Rachkovsky equations is used to retrieve the velocity and the magnetic field vector of the region. The plasma velocity reaches supersonic values closer to the feet of the filament barbs and coexist with a slow velocity component. Such supersonic velocities result from the acceleration of the plasma as it drains from the filament spine through the barbs. The line-of-sight magnetic fields have strengths below 200 G i…
Aims. Convective collapse, a theoretically predicted process that intensifies existing weak magnetic fields in the solar atmosphere, was first directly observed in a single event by Nagata et al. (2008) using the high resolution Solar Optical Telescope (SOT) of the Hinode satellite. Using the same space telescope, we performed a statistical analysis of convective collapse events. Methods. Our data sets consist of high resolution time series of polarimetric spectral scans of two iron lines formed in the lower photosphere and filter images in Mg I b2 and Ca II H, spectral lines that are formed i…
Solar flares are rapid energy release phenomena that appear as bright ribbons in the chromosphere and high-temperature loops in the corona, respectively. Supra-arcade Downflows (SADs) are plasma voids that first come out above the flare loops and then move quickly towards the flare loop top during the decay phase of the flare. In our work, we study 20 SADs appearing in three flares. By differential emission measure (DEM) analysis, we calculate the DEM weighted average temperature and emission measure (EM) of the front region and the main body of SADs. It is found that the temperatures of the S…
Solar flares are currently understood as the explosive release of energy stored in the form of stressed magnetic fields. In many cases, the released energy seems to take the form of large numbers of electrons accelerated to high energies or alternatively plasma heated to very high temperatures. The transport of this energy into the remaining portion of the atmosphere results in violent mass motion and strong emission across the electromagnetic spectrum. One important phenomenon observed during flares is the appearance in coronal magnetic loops of large amounts of upflowing, soft X-ray emitting…
Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding …
Context. The solar chromosphere and the lower transition region is believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmo…
Broad-band images of the solar chromosphere in the Ca II H&K line cores around active regions are covered with fine bright elongated structures called bright fibrils. The mechanisms that form these structures and cause them to appear bright are still unknown. We aim to investigate the physical properties, such as temperature, line-of-sight velocity, and microturbulence, in the atmosphere that produces bright fibrils and to compare those to the properties of their surrounding atmosphere. We used simultaneous observations of a plage region in Fe I 6301-2 Å, Ca II 8542 Å, Ca II K, and H$α$ acquir…
We use 3D radiative MHD simulations to investigate the formation and dynamics of small-scale (less than 0.5 Mm in diameter) vortex tubes spontaneously generated by turbulent convection in quiet-Sun regions with initially weak mean magnetic fields. The results show that the vortex tubes penetrate into the chromosphere and substantially affect the structure and dynamics of the solar atmosphere. The vortex tubes are mostly concentrated in intergranular lanes and are characterized by strong (near sonic) downflows and swirling motions that capture and twist magnetic field lines, forming magnetic fl…
Magnetic energy released in the corona by solar flares reaches the chromosphere where it drives characteristic upflows and downflows known as evaporation and condensation. These flows are studied here for the case where energy is transported to the chromosphere by thermal conduction. An analytic model is used to develop relations by which the density and velocity of each flow can be predicted from coronal parameters including the flare's energy flux $F$. These relations are explored and refined using a series of numerical investigations in which the transition region is represented by a simpli…
The hydrogen Lyman lines provide important diagnostic information about the dynamics of the chromosphere, but there have been few systematic studies of their variability during flares. We investigate Doppler shifts in these lines in several flares, and use these to calculate plasma speeds. We use spectral data from the Multiple EUV Grating Spectrograph B (MEGS-B) detector of the Extreme-Ultraviolet Variability Experiment (EVE) instrument on the Solar Dynamics Observatory. MEGS-B obtains full-disk spectra of the Sun at a resolution of 0.1nm in the range 37-105 nm, which we analyse using three i…
Vector magnetic fields of an active region filament in the photosphere and upper chromosphere are obtained from spectro-polarimetric observations recorded with the Tenerife Infrared Polarimeter (TIP II) at the German Vacuum Tower Telescope (VTT). We apply Milne-Eddington inversions on full Stokes vectors of the photospheric Si I 1082.7 nm and the upper chromospheric He I triplet at 1083.0 nm to obtain magnetic field vector and velocity maps in two atmosphere layers. We find that: (1)A complete filament was already present in H$α$ at the beginning of the TIP II data acquisition. Only a partiall…
We study the C8.4 class solar flare SOL2016-05-14T11:34 UT using high-resolution spectral imaging in the Ca ii 8542 Å line obtained with the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope. Spectroscopic inversions of the Ca ii 8542 Å line using the non-LTE code NICOLE are used to investigate the evolution of the temperature and velocity structure in the flare chromosphere. A comparison of the temperature stratification in flaring and non-flaring areas reveals strong footpoint heating during the flare peak in the lower atmosphere. The temperature of the flaring footpoints b…
The Ca II H line is one of the strongest lines in the solar spectrum and provides continuous information on the solar atmosphere from the photosphere to the lower chromosphere. We describe an inversion approach that reproduces observed Ca II H spectra assuming LTE. We developed an inversion strategy based on the SIR code. The approach uses a two-step procedure with an archive of pre-calculated spectra to fit the line core and a subsequent iterative modification to improve the fit in the line wing. Simultaneous spectra in the 630nm range can optionally be used to fix the continuum temperature. …
A dense forest of slender bright fibrils near a small solar active region is seen in high-quality narrowband Ca II H images from the SuFI instrument onboard the Sunrise balloon-borne solar observatory. The orientation of these slender Ca II H fibrils (SCF) overlaps with the magnetic field configuration in the low solar chromosphere derived by magnetostatic extrapolation of the photospheric field observed with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are qualitatively aligned with small-scale loops computed from a novel inversion approach based on best-fit numerical MHD simulat…
Arch filament systems occur in active sunspot groups, where a fibril structure connects areas of opposite magnetic polarity, in contrast to active region filaments that follow the polarity inversion line. We used the GREGOR Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral lines Si I 1082.7 nm, He I 1083.0 nm, and Ca I 1083.9 nm. We focus on the near-infrared calcium line to investigate the photospheric magnetic field and velocities, and use the line core intensities and velocities of the helium line to study the chromospheric plasma. The individual fibrils of the a…
Solar filaments can be formed via chromospheric evaporation followed by condensation in the corona or by the direct injection of cool plasma from the chromosphere to the corona. In this paper, with high-resolution H$α$ data observed by the 1.6 m New Solar Telescope of the Big Bear Solar Observatory on 2015 August 21, we confirmed that an active-region filament is maintained by the continuous injection of cold chromospheric plasma. We find that the filament is rooted along a bright ridge in H$α$, which corresponds to the intersection of a magnetic quasi-separatrix layer with the solar surface. …
Context: Resistive Ohmic dissipation has been suggested as a mechanism for heating the solar chromosphere, but few studies have established this association. Aim: We aim to determine how Ohmic dissipation by electric currents can heat the solar chromosphere. Methods: We combine high-resolution spectroscopic Ca II data from the Dunn Solar Telescope and vector magnetic field observations from the Helioseismic and Magnetic Imager (HMI) to investigate thermal enhancements in a sunspot light bridge. The photospheric magnetic field from HMI was extrapolated to the corona using a non-force-free field…
Supersonic flows observed by THEMIS related to a coronal bright point and filament
Kumaun University（库马翁大学）；Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）；KU Leuven（荷语鲁汶大学）；University of Glasgow（格拉斯哥大学）；LUNEX EMMESI Institut（LUNEX EMMESI研究所）；University of Oslo（奥斯陆大学）；University of Maria Curie-Skłodowska（玛丽亚·居里-斯可洛多夫斯卡大学）
The IBIS data Archive (IBIS-A) stores data acquired with the Interferometric BIdimensional Spectropolarimeter (IBIS), which was operated at the Dunn Solar Telescope of the US National Solar Observatory from 2003 to 2019. The instrument provided series of high-resolution narrowband spectropolarimetric imaging observations of the photosphere and chromosphere in the range 5800$-$8600 Å~ and co-temporal broadband observations in the same spectral range and with the same field of view of the polarimetric data. We present the data currently stored in IBIS-A, as well as the interface utilized to expl…
Bright points (BPs) are manifestations of small magnetic elements in the solar photosphere. Their brightness contrast not only gives insight into the thermal state of the photosphere (and chromosphere) in magnetic elements, but also plays an important role in modulating the solar total and spectral irradiance. Here we report on simultaneous high-resolution imaging and spectropolarimetric observations of BPs using Sunrise balloon-borne observatory data of the quiet Sun at disk center. BP contrasts have been measured between 214 nm and 525 nm, including the first measurements at wavelengths belo…
Infrared spectropolarimetry of a C-class solar flare footpoint plasma -- I. Spectral features and forward modelling
Astronomical Institute, Slovak Academy of Sciences（斯洛伐克科学院天文研究所）；Evgeni Kharadze Georgian National Astrophysical Observatory（叶夫根尼·哈拉泽格鲁吉亚国家天文台）；Space Research Centre, Ilia State University（伊利亚州立大学太空研究中心）；Instituto de Astrofísica de Canarias (IAC)（加那利群岛天体物理学研究所）；Departamento de Astrofísica, Universidad de La Laguna（拉帕拉纳大学天体物理学系）；AG, Institute of Physics, University of Graz（格拉茨大学物理研究所）；National Solar Observatory（美国国家太阳观测台）
The aim of this paper is to analyse the validity of the Dopplergram and lambda-meter techniques for the Doppler diagnostics of solar photospheric velocities using the BaII 4554 A line. Both techniques are evaluated by means of NLTE radiative transfer calculations of the BaII 4554 A line in a three-dimensional hydrodynamical model of solar convection. We consider the cases of spatially unsmeared profiles and the profiles smeared to the resolution of ground-based observations. We find that: (i) Speckle-reconstructed Dopplergram velocities reproduce the ``true'' velocities well at heights around …
In this study, we analyzed a filament system, which expanded between moving magnetic features (MMFs) of a decaying sunspot and opposite flux outside of the active region from the nearby quiet-Sun network. This configuration deviated from a classical arch filament system (AFS), which typically connects two pores in an emerging flux region. Thus, we called this system an extended AFS. We contrasted classical and extended AFSs with an emphasis on the complex magnetic structure of the latter. Furthermore, we examined the physical properties of the extended AFS and described its dynamics and connec…
The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He I 10830 Å triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the He I 10830 Å triplet, which are commonly observed wh…
We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them. We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10830 Å spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS. We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10830 Å tr…
The emergence of active regions (ARs) closely relates to the solar dynamo and the dynamical atmospheric phenomena.With high-resolution and long-lasting observations from the New Vacuum Solar Telescope, we report a new dynamic activity phenomenon named "fan-shaped activity (FSA)" in the emerging phase of NOAA AR 12700. The FSAs are clearly observed at Ha wavelength and are closely related to the dynamics of the adjacent arch filament system (AFS), including threads deformation and materials downward motions. On 2018 February 26, the two most representative FSAs appeared around 05:21 UT and 06:0…
Recent observations suggest that magnetic flux cancellation may play a crucial role in heating the Sun's upper atmosphere (chromosphere, transition region, corona). Here, we intended to validate an analytic model for magnetic reconnection and consequent coronal heating, driven by a pair of converging and cancelling magnetic flux sources of opposite polarities. For this test, we analyzed photospheric magnetic field and multi-wavelength UV/EUV observations of a small-scale flux cancellation event in a quiet-Sun internetwork region over a target interval of 5.2 hr. The observed cancellation event…
Starting from a realistically sheared magnetic arcade connecting chromospheric, transition region to coronal plasma, we simulate the in-situ formation and sustained growth of a quiescent prominence in the solar corona. Contrary to previous works, our model captures all phases of the prominence formation, including the loss of thermal equilibrium, its successive growth in height and width to macroscopic dimensions, and the gradual bending of the arched loops into dipped loops, as a result of the mass accumulation. Our 2.5-dimensional, fully thermodynamically and magnetohydrodynamically consiste…
