The relationship between vortex flows at different spatial scales and their contribution to the energy balance in the chromosphere is not yet fully understood. We perform three-dimensional (3D) radiation-magnetohydrodynamic (MHD) simulations of a unipolar solar plage region at a spatial resolution of 10 km using the MURaM code. We use the swirling-strength criterion that mainly detects the smallest vortices present in the simulation data. We additionally degrade our simulation data to smooth-out the smaller vortices, so that also the vortices at larger spatial scales can be detected. Vortex flows at various spatial scales are found in our simulation data for different effective spatial resolutions. We conclude that the observed large vortices are likely clusters of much smaller ones that are not yet resolved by observations. We show that the vertical Poynting flux decreases rapidly with reduced effective spatial resolutions and is predominantly carried by the horizontal plasma motions rather than vertical flows. Since the small-scale horizontal motions or the smaller vortices carry most of the energy, the energy transported by vortices deduced from low resolution data is grossly underestimated. In full resolution simulation data, the Poynting flux contribution due to vortices is more than adequate to compensate for the radiative losses in plage, indicating their importance for chromospheric heating.
We analyze observations from the Interface Region Imaging Spectrograph of the Mg II k line, the Mg II UV subordinate lines, and the O I 135.6 nm line to better understand the solar plage chromosphere. We also make comparisons with observations from the Swedish 1 m Solar Telescope of the Hα line, the Ca II 8542 line, and Solar Dynamics Observatory/Atmospheric Imaging Assembly observations of the coronal 19.3 nm line. To understand the observed Mg II profiles, we compare these observations to the results of numerical experiments. The single-peaked or flat-topped Mg II k profiles found in plage i…
We propose and employ a novel empirical method for determining chromospheric plage regions, which seems to better isolate plage from its surrounding regions compared to other methods commonly used. We caution that isolating plage from its immediate surroundings must be done with care in order to successfully mitigate statistical biases that, for instance, can impact quantitative comparisons between different chromospheric observables. Using this methodology, our analysis suggests that 1.25 mm wavelength free-free emission in plage regions observed with ALMA/Band6 may not form in the low chromo…
Our knowledge of the heating mechanisms that are at work in the chromosphere of plage regions remains highly unconstrained from observational studies. The purpose of our study is to estimate the chromospheric heating terms from a plage dataset, characterize their spatio-temporal distribution and set constraints on the heating processes that are at work. We make use of NLTE inversions to infer a model of the photosphere and chromosphere of a plage dataset acquired with the Swedish 1-m Solar Telescope. We use this model atmosphere to calculate the chromospheric radiative losses from H i, Ca ii a…
We study the properties of slow magneto-acoustic waves that are naturally excited due to turbulent convection and investigate their role in the energy balance of a plage region using three dimensional (3D) radiation-MHD simulations. We calculate the horizontally averaged (over the whole domain) frequency power spectra for both longitudinal and vertical (i.e. the component perpendicular to the surface) components of velocity. To compare our results with the observations we degrade the simulation data with Gaussian kernels having FWHM of 100 km and 200 km, and calculate horizontally averaged pow…
Numerical simulations of the solar chromosphere predict a diverse thermal structure with both hot and cool regions. Observations of plage regions in particular feature broader and brighter chromospheric lines, which suggest that they are formed in hotter and denser conditions than in the quiet-Sun, but also implies a non-thermal component whose source is unclear. We revisit the problem of the stratification of temperature and microturbulence in plage now adding millimeter continuum observations provided by ALMA to inversions of near-ultraviolet IRIS spectra as a powerful new diagnostic to dise…
We employ tomographic observations of a small region of plage to study the propagation of waves from the solar photosphere to the chromosphere using a Fourier phase-difference analysis. Our results show the expected vertical propagation for waves with periods of 3 minutes. Waves with 5-minute periods, i.e., above the acoustic cut-off period, are found to propagate only at the periphery of the plage, and only in the direction in which the field can be reasonably expected to expand. We conclude that field inclination is critically important in the leakage of p-mode oscillations from the photosph…
Vortex-flows exist across a broad range of spatial and temporal scales in the solar atmosphere. Small-scale vortices have been proposed to play an important role in energy transport in the solar atmosphere. However, their physical properties remain poorly understood due to the limited spatial resolution of the observations. We aim to explore and analyze the physical properties of small-scale vortices inside magnetic flux tubes using numerical simulations, and to investigate whether they contribute to heating the chromosphere in a plage region. Using the three-dimensional (3D) radiative magneto…
The role of magnetic fields in the chromospheric heating problem remains greatly unconstrained. Most theoretical predictions from numerical models rely on a magnetic configuration, field strength and connectivity whose details have not been well established with observational studies. High-resolution studies of chromospheric magnetic fields in plage are very scarce or non-existent in general. Our aim is to study the stratification of the magnetic field vector in plage regions. We use high-spatial resolution full-Stokes observations acquired with CRISP instrument at the Swedish 1-m Solar Telesc…
In order to investigate the relation between magnetic structures and the signatures of heating in plage regions, we observed a plage region with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3 using the integral field unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. During the GRIS observation, the Interface Region Imaging Spectrograph (IRIS) obtained spectra of the ultraviolet Mg II doublet emitted from the same region. In the periphery of the plage region, within the limited field of view seen by GRIS, we find that the Mg II radiative flux…
Routine ultraviolet imaging of the Sun's upper atmosphere shows the spectacular manifestation of solar activity; yet we remain blind to its main driver, the magnetic field. Here we report unprecedented spectropolarimetric observations of an active region plage and its surrounding enhanced network, showing circular polarization in ultraviolet (Mg II $h$ & $k$ and Mn I) and visible (Fe I) lines. We infer the longitudinal magnetic field from the photosphere to the very upper chromosphere. At the top of the plage chromosphere the field strengths reach more than 300 gauss, strongly correlated with …
We apply the Tenerife Inversion Code (TIC) to the plage spectropolarimetric observations obtained by the Chromospheric LAyer SpectroPolarimeter (CLASP2). These unprecedented data consist of full Stokes profiles in the spectral region around the Mg II h and k lines for a single slit position, with around two thirds of the 200 arcsec slit crossing a plage region and the rest crossing an enhanced network. A former analysis of these data had allowed us to infer the longitudinal component of the magnetic field by applying the weak field approximation (WFA) to the circular polarization profiles, and…
Observations of flare emissions in the optical continuum are very rare. Therefore, the analysis of such observations is useful and may contribute to our understanding of the flaring chromosphere and photosphere. We study the white light continuum emission observed during the X6.9 flare which occurred on August 09, 2011. This emission comes not only from the flare ribbons but also from the nearby plage area. The main aim of this work is to disentangle the flare and plage (facula) emission. We analyzed the spatial, spectral and temporal evolution of the flare and plage properties by analyzing mu…
We present joint observations of the Sun by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS). The observations were made of a solar active region on 2015 December 18 as part of the ALMA science verification effort. A map of the Sun's continuum emission of size $2.4' \times 2.3'$ was obtained by ALMA at a wavelength of 1.25 mm (239 GHz) using mosaicing techniques. A contemporaneous map of size $1.9'\times 2.9'$ was obtained in the Mg II h doublet line at 2803.5Å by IRIS. Both mm/submm$-λ$ continuum emission and ultraviolet (UV) line em…
Magnetic Field Stratification in Active-Region Plage from Ca II K and Ca II 8542 Å Spectropolarimetry
Instituto de Astrofísica de Canarias（加那利天体物理研究所）；Universidad de La Laguna（拉帕鲁纳大学）；Consejo Superior de Investigaciones Científicas（西班牙高等科学研究委员会）；Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系研究所）；Grupo de Estudios en Heliofísica de Mendoza, CONICET, Universidad de Mendoza（门多萨日球学研究组，阿根廷国家科学研究委员会，门多萨大学）；National Astronomical Observatory of Japan（日本国立天文台）
Mapping the longitudinal magnetic field in the atmosphere of an active region plage from the inversion of the near-ultraviolet CLASP2.1 spectropolarimetric data
本研究利用 HanleRT 反演 CLASP2.1 近紫外 Mg II h & k 光谱偏振数据，绘制活动区谱斑与超半影的大气参数及纵向磁场，揭示二者加热机制的异同。
Densely packed coronal loops are rooted in plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plages are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in plages using high resolution observations and simulations. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the SST. These data were inverted to retrieve th…
The chromosphere is a dynamic and complex layer where all the relevant physical processes happen on very small spatio-temporal scales. A few spectral lines that can be used as chromospheric diagnostics give us convoluted information that is hard to interpret without realistic theoretical models. What are the key ingredients that these models need to contain? The magnetic field has a paramount effect on chromospheric structuring. This is obvious from the ubiquitous presence of chromospheric dynamic fibrilar structures visible on the solar disk and at the limb. The numerical experiments presente…
We present observations of the solar chromosphere obtained simultaneously with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS). The observatories targeted a chromospheric plage region of which the spatial distribution (split between strongly and weakly magnetized regions) allowed the study of linear-like structures in isolation, free of contamination from background emission. Using these observations in conjunction with a radiative magnetohydrodynamic 2.5D model covering the upper convection zone all the way to the corona that consid…
How do magnetohydrodynamic waves travel from the fully ionized corona, into and through the underlying partially ionized chromosphere, and what are the consequences for solar flares? To address these questions, we have developed a 2-fluid model (of plasma and neutrals) and used it to perform 1D simulations of Alfvén waves in a solar atmosphere with realistic density and temperature structure. Studies of a range of solar features (faculae, plage, penumbra and umbra) show that energy transmission from corona to chromosphere can exceed 20% of incident energy for wave periods of one second or less…
Aims. To investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere, observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses. Methods. Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and H-alpha lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m Goode Solar Telescope (GST) on 2019 October 3 and in the H-alpha and H-beta lines with the echelle spectrograph attached to the Vacuum Tower Telescope (VTT) on 2018 December 11 and 2019 June …
In our previous article (Priyal et al. in Solar Phys. 289, 127, 2014) we have discussed the details of observations and methodology adopted to analyze the Ca-K spectroheliograms obtained at the Kodaikanal Observatory (KO) to study the variation of Ca-K plage areas, enhanced network (EN), and active network (AN) for Solar Cycles, namely 19, 20, and 21. Now, we have derived the areas of chromospheric features using KO Ca-K spectroheliograms to study the long-term variations of Solar Cycles 14 to 21. The comparison of the derived plage areas from the data obtained at the KO observatory for the pe…
The Mg II h and k lines are among the strongest in the near-ultraviolet solar spectrum and their line core originates in the upper chromosphere, just below the transition region. Consequently, they have become one of the main targets for investigating the magnetism of the upper solar atmosphere. The recent CLASP2 mission obtained unprecedented spectropolarimetric data of these lines in an active region plage, which have already been used to infer the longitudinal component of the magnetic field by applying the weak field approximation. In this paper, we aim at improving our understanding of th…
The Ca-K spectroheliograms obtained at the Kodaikanal observatory (KO) are used to generate a uniform time series using the equal contrast technique (ECT) to study the long and short-term variation in the solar chromosphere. The percentage of plage, Enhanced network (EN), Active network (AN), and Quiet network (QN) area at various latitudes is compared with the activity at 35$^{\circ}$ latitude and also with the sunspot number for the period of 1907 -- 1984. The values of phase differences indicate that the activity begins at $\sim$45$^{\circ}$ latitude and shift progressively to the lower lat…
It has so far proven impossible to reproduce all aspects of the solar plage chromosphere in quasi-realistic numerical models. The magnetic field configuration in the lower atmosphere is one of the few free parameters in such simulations. The literature only offers proxy-based estimates of the field strength, as it is difficult to obtain observational constraints in this region. Sufficiently sensitive spectro-polarimetric measurements require a high signal-to-noise ratio, spectral resolution, and cadence, which are at the limit of current capabilities. We use critically sampled spectro-polarime…
Acoustic and magnetoacoustic waves are considered to be possible agents of chromospheric heating. We present a comparison of deposited acoustic energy flux with total integrated radiative losses in the middle chromosphere of the quiet Sun and a weak plage. The comparison is based on a consistent set of high-resolution observations acquired by the IBIS instrument in the Ca II 854.2 nm line. The deposited acoustic-flux energy is derived from Doppler velocities observed in the line core and a set of 1737 non-LTE 1D hydrostatic semi-empirical models, which also provide the radiative losses. The mo…
We present observational constraints on the solar chromospheric heating contribution from acoustic waves with frequencies between 5 and 50 mHz. We utilize observations from the Dunn Solar Telescope in New Mexico complemented with observations from the Atacama Large Millimeter Array collected on 2017 April 23. The properties of the power spectra of the various quantities are derived from the spectral lines of Ca II 854.2 nm, H I 656.3 nm, and the millimeter continuum at 1.25 mm and 3 mm. At the observed frequencies the diagnostics almost all show a power law behavior, whose particulars (slope, …
The Mg II h&k lines are amongst the best diagnostic tools of the upper solar chromosphere. This region of the atmosphere is of particular interest as it is the lowest region of the Sun's atmosphere where the magnetic field is dominant in the energetics and dynamics, defining its structure. While highly successful in the photosphere and lower to mid chromosphere, numerical models have produced syntheticMg II lines that do not match the observations well. We present a number of large scale models with magnetic field topologies representative of the quiet Sun, ephemeral flux regions and plage, an…
We carry out a theoretical study of the polarization of the solar Mg II h-k doublet (including its extended wings) and the subordinate UV triplet around 280 nm. These lines are of great diagnostic interest, as they encode information on the physical properties of the solar atmosphere from the upper photosphere to the chromosphere-corona transition region. We base our study on radiative transfer calculations of spectral line polarization in one-dimensional models of quiet and plage regions of the solar atmosphere. Our calculations take into account the combined action of atomic polarization, qu…
The heliophysics catalogues published by the Ebro Observatory during 1910--1937 have been converted into a digital format in order to provide the data for computational processing. This has allowed us to study in detail the North-South (N-S) asymmetry of solar activity in that period, focusing on two different structures located at two different layers of the solar atmosphere: sunspots (Photosphere) and solar plages (Chromosphere). The examination of the absolute and normalised N-S asymmetry indices in terms of their monthly sum of occurrences and areas has made possible to find out a cyclic b…
Solar "magnetic tornadoes" are produced by rotating magnetic field structures that extend from the upper convection zone and the photosphere to the corona of the Sun. Recent studies show that such rotating features are an integral part of atmospheric dynamics and occur on a large range of spatial scales. A systematic statistical study of magnetic tornadoes is a necessary next step towards understanding their formation and their role for the mass and energy transport in the solar atmosphere. For this purpose, we have developed a new automatic detection method for chromospheric swirls, i.e. the …
NASA's Interface Region Imaging Spectrograph (IRIS) provides high resolution observations of the solar atmosphere through UV spectroscopy and imaging. Since the launch of IRIS in June 2013, we have conducted systematic observation campaigns in coordination with the Swedish 1-m Solar Telescope (SST) on La Palma. The SST provides complementary high-resolution observations of the photosphere and chromosphere. The SST observations include spectro-polarimetric imaging in photospheric Fe I lines and spectrally-resolved imaging in the chromospheric Ca II 8542 A, H-alpha, and Ca II K lines. We present…
Solar chromosphere and coronal heating is a big question for astrophysics. Daily measurement of 985 solar spectral irradiances (SSIs) at the spectral intervals 1-39 nm and 116-2416 nm during March 1 2003 to October 28 2017 is utilized to investigate phase relation respectively with daily sunspot number, the Mount Wilson Sunspot Index, and the Magnetic Plage Strength Index. All SSIs which form in the whole heated region: the upper photosphere, chromosphere, transition region, and corona are found to be significantly more correlated to weak magnetic activity than to strong magnetic activity, and…
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…
Vortex structures in the Sun's chromosphere are believed to channel energy between different layers of the solar atmosphere. We investigate the nature and dynamics of two small-scale quiet-Sun rotating structures in the chromosphere. We analyse two chromospheric structures that show clear rotational patterns in spectropolarimetric observations taken with the Interferometric Bidimensional Spectrometer (IBIS) at the Ca II 8542 Å~ line. We present the detection of spectropolarimetric signals that manifest the magnetic nature of rotating structures in the chromosphere. Our observations show two lo…
Acoustic and magnetoacoustic waves are among the possible candidate mechanisms that heat the upper layers of solar atmosphere. A weak chromospheric plage near a large solar pore NOAA 11005 was observed on October 15, 2008 in the lines Fe I 617.3 nm and Ca II 853.2 nm with the Interferometric Bidimemsional Spectrometer (IBIS) attached to the Dunn Solar Telescope. Analyzing the Ca II observations with spatial and temporal resolutions of 0.4" and 52 s, the energy deposited by acoustic waves is compared with that released by radiative losses. The deposited acoustic flux is estimated from power spe…
Aims: To study the heating of solar chromospheric magnetic and nonmagnetic regions by acoustic and magnetoacoustic waves, the deposited acoustic-energy flux derived from observations of strong chromospheric lines is compared with the total integrated radiative losses. Methods: A set of 23 quiet-Sun and weak-plage regions were observed in the Mg II k and h lines with the Interface Region Imaging Spectrograph (IRIS). The deposited acoustic-energy flux was derived from Doppler velocities observed at two different geometrical heights corresponding to the middle and upper chromosphere. A set of sca…
Aims: We demonstrate the universal character of the quiet-Sun chromosphere among inactive stars (solar-type and giants). By assessing the main physical processes, we shed new light on some common observational phenomena. Methods: We discuss measurements of the solar Mt. Wilson S-index, obtained by the Hamburg Robotic Telescope around the extreme minimum year 2009, and compare the established chromospheric basal Ca II K line flux to the Mt. Wilson S-index data of inactive ("flat activity") stars, including giants. Results: During the unusually deep and extended activity minimum of 2009, the Sun…
We present the results of contemporaneous spectroscopic and photometric monitoring of the young solar-type star HD171488 (Prot~1.337 d) aimed at studying surface inhomogeneities at photospheric/chromospheric levels. Echelle FOCES spectra (R~40000) and Johnson photometry have been performed in 2006. Spectral type, rotational velocity, metallicity, and gravity were determined using a code developed by us. The metallicity was measured from the analysis of iron lines. The spectral subtraction technique was applied to the most relevant chromospheric diagnostics included in the FOCES spectral range …
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…
Connectivity between the solar photosphere and chromosphere in a vortical structure. Observations of multi-phase, small-scale magnetic field amplification
Highly turbulent nature of convection on the Sun causes strong multi-scale interaction of subsurface layers with the photosphere and chromosphere. According to realistic 3D radiative MHD numerical simulations ubiquitous small-scale vortex tubes are generated by turbulent flows below the visible surface and concentrated in the intergranular lanes. The vortex tubes can capture and amplify magnetic field, penetrate into chromospheric layers and initiate quasi-periodic flow eruptions that generates Alfvénic waves, transport mass and energy into the solar atmosphere. The simulations revealed high-s…
We review (i) observations and numerical simulations of vortical flows in the solar atmosphere and (ii) measurements of the horizontal magnetic field in quiet Sun regions. First, we discuss various manifestations of vortical flows and emphasize the role of magnetic fields in mediating swirling motion created near the solar surface to the higher layers of the photosphere and to the chromosphere. We reexamine existing simulation runs of solar surface magnetoconvection with regard to vortical flows and compare to previously obtained results. Second, we review contradictory results and problems as…
In this work, a state-of-the-art vortex detection method, Instantaneous Vorticity Deviation, is applied to locate three-dimensional vortex tube boundaries in numerical simulations of solar photospheric magnetoconvection performed by the MURaM code. We detected three-dimensional vortices distributed along intergranular regions and displaying coned shapes that extend from the photosphere to the low chromosphere. Based on a well-defined vortex center and boundary, we were able to determine averaged radial profiles and thereby investigate the dynamics across the vortical flows at different height …
