High-resolution observations of the solar photosphere, chromosphere and transition region. A database of coordinated IRIS and SST observations
L. H. M. Rouppe van der Voort, B. De Pontieu, M. Carlsson, J. de la Cruz Rodriguez, S. Bose, G. Chintzoglou, A. Drews, C. Froment, M. Gosic, D. R. Graham, V. H.… 展开作者
L. H. M. Rouppe van der Voort, B. De Pontieu, M. Carlsson, J. de la Cruz Rodriguez, S. Bose, G. Chintzoglou, A. Drews, C. Froment, M. Gosic, D. R. Graham, V. H. Hansteen, V. M. J. Henriques, S. Jafarzadeh, J. Joshi, L. Kleint, P. Kohutova, T. Leifsen, J. Martinez-Sykora, D. Nobrega-Siverio, A. Ortiz, T. M. D. Pereira, A. Popovas, C. Quintero Noda, A. Sainz Dalda, G. B. Scharmer, D. Schmit, E. Scullion, H. Skogsrud, M. Szydlarski, R. Timmons, G. J. M. Vissers, M. M. Woods, P. Zacharias
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Accepted for publication in Astronomy & Astrophysics (July 21, 2020)
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 a database of co-aligned IRIS and SST datasets that is open for analysis to the scientific community. The database covers a variety of targets including active regions, sunspots, plage, quiet Sun, and coronal holes.
Ellerman bombs are transient brightenings of the extended wings of the solar Balmer lines in emerging active regions. We describe their properties in the ultraviolet lines sampled by the Interface Region Imaging Spectrograph (IRIS), using simultaneous imaging spectroscopy in H$α$ with the Swedish 1-m Solar Telescope (SST) and ultraviolet images from the Solar Dynamics Observatory for Ellerman bomb detection and identification. We select multiple co-observed Ellerman bombs for detailed analysis. The IRIS spectra strengthen the view that Ellerman bombs mark reconnection between bipolar kilogauss…
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…
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 investigate the Interface Region Imaging Spectrograph (IRIS) observations of the quiet-Sun (QS) to understand the propagation of acoustic waves in transition region (TR) from photosphere. We selected a few IRIS spectral lines, which include the photospheric (Mn~{\sc i} 2801.25~Å), chromospheric (Mg~{\sc ii} k 2796.35~Å) and TR (C~{\sc ii} 1334.53~Å), to investigate the acoustic wave propagation.The wavelet cross-spectrum reveals significant coherence (about 70\% locations) between photosphere and chromosphere. Few minutes oscillations (i.e., period range from 1.6 to 4.0 minutes) successfull…
Magnetohydrodynamic (MHD) waves have been considered as energy sources for heating the solar chromosphere and the corona. Although MHD waves have been observed in the solar atmosphere, there are a lack of quantitative estimates on the energy transfer and dissipation in the atmosphere. We performed simultaneous Hinode and IRIS observations of a sunspot umbra to derive the upward energy fluxes at two different atmospheric layers (photosphere and lower transition region) and estimate the energy dissipation. The observations revealed some properties of the observed periodic oscillations in physica…
Predicting the thermodynamics in the chromosphere from the translation of SDO data into the IRIS$^{2}$ inversion results using a visual transformer model
SETI Institute（SETI研究所）；Lockheed Martin Solar & Astrophysics Laboratory（洛克希德·马丁太阳与天体物理学实验室）；Henry M. Gunn Senior High School（亨利·M·冈恩高中）；Lockheed Martin Advanced Technology Center（洛克希德·马丁高级技术中心）
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…
Surges often appear as a result of the emergence of magnetized plasma from the solar interior. Traditionally, they are observed in chromospheric lines such as H$α$ 6563 Åand Ca II 8542 Å. However, whether there is a response to the surge appearance and evolution in the Si IV lines or, in fact, in many other transition region lines has not been studied. In this paper we analyze a simultaneous episode of an H$α$ surge and a Si IV burst that occurred on 2016 September 03 in active region AR12585. To that end, we use coordinated observations from the Interface Region Imaging Spectrograph (IRIS) an…
We present spectroscopic and imaging observations of small-scale reconnection events on the Sun. Using the Interface Region Imaging Spectrograph (IRIS) observations, one reconnection event is first detected as IRIS jets with fast bi-directional velocities in the chromosphere and transition region, which are identified as non-Gaussian broadenings with two extended wings in the line profiles of Si iv, C ii, and Mg ii k. The magnetograms under the IRIS jets from Helioseismic and Magnetic Images exhibit magnetic flux cancellation simultaneously, supporting that the IRIS jets are driven by magnetic…
Transition-region explosive events (EEs) are characterized by non-Gaussian line profiles with enhanced wings at Doppler velocities of 50-150 km/s. They are believed to be the signature of solar phenomena that are one of the main contributors to coronal heating. The aim of this study is to investigate the link of EEs to dynamic phenomena in the transition region and chromosphere in an active region. We analyze observations simultaneously taken by the Interface Region Imaging Spectrograph (IRIS) in the Si IV 1394Å line and the slit-jaw (SJ) 1400Å images, and the Swedish 1-m Solar Telescope (SST)…
We report the results of the Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the solar chromosphere on the southern polar limb. Coordinated observations with the Interface Region Imaging Spectrograph (IRIS) are also conducted. ALMA provided unprecedented high spatial resolution in the millimeter band ($\approx$ 2.0 arcsec) at 100 GHz frequency with a moderate cadence (20 s). The results are as follows: (1) The ALMA 100 GHz images show saw-tooth patterns on the limb, and a comparison with SDO/AIA 171Å images shows a good correspondence of the limbs with each other. (2) The …
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…
Ellerman bombs and UV bursts are transient brightenings that are ubiquitously observed in the lower atmospheres of active and emerging flux regions. Here we present inversion results of SST/CRISP and CHROMIS, as well as IRIS data of such transient events. Combining information from the Mg II h & k, Si IV and Ca II 8542A and Ca II H & K lines, we aim to characterise their temperature and velocity stratification, as well as their magnetic field configuration. We find average temperature enhancements of a few thousand kelvin close to the classical temperature minimum, but localised peak temperatu…
Active chromospheric fibril singularity: Coordinated observations from Solar Orbiter, SST, and IRIS
University of Oslo（奥斯陆大学）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；George Mason University（乔治梅森大学）；Sorbonne Université（索邦大学）；Observatoire de Paris - PSL（巴黎天文台-PSL）；École Polytechnique（巴黎综合理工学院）；Institut Polytechnique de Paris（巴黎理工学院）；CNRS（法国国家科学研究中心）；Stockholm University（斯德哥尔摩大学）；Statkraft AS（Statkraft公司）
Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations. We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated upflows through the photosphere and chromosphere of a quiet Sun internetwork region. We analyzed high spatial and temporal resolution ground- and spaced-based observations of a quiet Sun region. The observations consist of high-cadence time series of wideband and narrowband images of both H-alpha 6563 A and Ca II 8542 A lines o…
The Interface Region Imaging Spectrograph (IRIS) provides spectroscopy and narrow band slit-jaw (SJI) imaging of the solar chromosphere and transition region at unprecedented spatial and temporal resolution. Combined with high-resolution context spectral imaging of the photosphere and chromosphere as provided by the Swedish 1-m Solar Telescope (SST), we can now effectively trace dynamic phenomena through large parts of the solar atmosphere in both space and time. IRIS SJI 1400 images from active regions, which primarily sample the transition region with the Si IV 1394 and 1403 Å lines, reveal …
Using high-resolution transition region (TR) observations taken by the Interface Region Imaging Spectrograph (IRIS) mission, Tian et al. (2014b) revealed numerous short-lived subarcsecond bright dots (BDs) above sunspots (mostly located in the penumbrae), which indicate yet unexplained small-scale energy releases. Moreover, whether these subarcsecond TR brightenings have any signature in the lower atmosphere and how they are formed are still not fully resolved. This paper presents a multi-wavelength study of the TR penumbral BDs using a coordinated observation of a near disk-center sunspot wit…
The plasma contributing to emission from the Sun between the cool chromosphere ($\le 10^4$K) and hot corona ($\ge 10^6$K) has been subjected to many different interpretations. Here we look at the magnetic structure of this transition region (TR) plasma, based upon the implications of CLASP2 data of an active region recently published by Ishikawa et al., and earlier IRIS and SDO data of quiet regions. Ishikawa et al. found that large areas of sunspot plages are magnetically unipolar as measured in the cores of \ion{Mg}{2} resonance lines, formed in the lower transition region under low plasma-$…
Sunspot light bridges (LBs) exhibit a wide range of short-lived phenomena in the chromosphere and transition region. In contrast, we use here data from the Multi-Application Solar Telescope (MAST), the Interface Region Imaging Spectrograph (IRIS), Hinode, the Atmospheric Imaging Assembly (AIA), and the Helioseismic and Magnetic Imager (HMI) to analyze the sustained heating over days in an LB in a regular sunspot. Chromospheric temperatures were retrieved from the the MAST Ca II and IRIS Mg II lines by nonlocal thermodynamic equilibrium inversions. Line widths, Doppler shifts, and intensities w…
Multi-thermal dynamics and transverse oscillations of solar spicules revealed by coordinated SST, IRIS, and SDO observations
Physical Research Laboratory（物理研究实验室）；Udaipur Solar Observatory, Physical Research Laboratory（乌代浦尔太阳观测站，物理研究实验室）；Indian Institute of Technology, Gandhinagar（甘地纳加尔印度理工学院）；Rosseland Centre for Solar Physics, University of Oslo（奥斯陆大学罗斯兰太阳物理中心）；Institute of Theoretical Astrophysics, University of Oslo（奥斯陆大学理论天体物理研究所）
Various bright structures abound in the chromosphere playing an essential role in the dynamics and evolution therein. Tentatively identifying the wave characteristics in the outer solar atmosphere helps to understand this layer better. One of the most significant aspects of these characteristics is the wave phase speed (PS), which is a dominant contribution to solar coronal heating and Energy distribution in the Sun's atmosphere layers. To obtain energy flux (EF), it is necessary to calculate the filling factor (FF) and the PS. In this study, the FF was determined by tracking the size and inte…
Chromospheric evaporation refers to dynamic mass motions in flare loops as a result of rapid energy deposition in the chromosphere. These have been observed as blueshifts in X-ray and extreme-ultraviolet (EUV) spectral lines corresponding to upward motions at a few tens to a few hundreds of km/s. Past spectroscopic observations have also revealed a dominant stationary component, in addition to the blueshifted component, in emission lines formed at high temperatures (~10 MK). This is contradictory to evaporation models predicting predominant blueshifts in hot lines. The recently launched Interf…
Using high-resolution images from 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO), we report the direct evidence of chromospheric reconnection at the polarity inversion line (PIL) between two small opposite polarity sunspots. Small jet-like structures (with velocities of ~20-55 km/s) were observed at the reconnection site before the onset of the first M1.0 flare. The slow rise of untwisting jets was followed by the onset of cool plasma inflow (~10 km/s) at the reconnection site, causing the onset of a two-ribbon flare. The reconnection between two sheared J-shaped cool H$α…
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…
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…
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 C II 133.5 nm multiplet has been observed by NASA's Interface Region Imaging Spectrograph (IRIS) in unprecedented spatial resolution. The aims of this work are to characterize these new observations of the C II lines, place them in context with previous work, and to identify any additional value the C II lines bring when compared with other spectral lines. We make use of wide, long exposure IRIS rasters covering the quiet Sun and an active region. Line properties such as velocity shift and width are extracted from individual spectra and analyzed. The lines have a variety of shapes (mostly …
Nanoflares are regarded as one of the major mechanisms of magnetic energy release and coronal heating in the solar outer atmosphere. We conduct a statistical study on the response of the chromosphere and transition region to nanoflares, as observed by the Interface Region Imaging Spectrograph (IRIS), by using an algorithm for the automatic detection of these events. The initial atmospheric response to these small heating events is observed, with IRIS, as transient brightening at the footpoints of coronal loops heated to high temperatures (>4 MK). For four active regions, observed over 143 hour…
Observations by the Interface Region Imaging Spectrograph (IRIS) in the Mg II h & k spectral lines have provided a new diagnostic window towards the knowledge of the complex physical conditions in the solar chromosphere. Theoretical efforts focused on understanding the behavior of these lines have allowed us to obtain a better and more accurate vision of the chromosphere. These efforts include forward modeling, numerical simulations, and inversions. In this paper, we focus our attention on the uncertainties associated with the thermodynamic model atmosphere obtained after the inversion of the …
NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission will study how the solar atmosphere is energized. IRIS contains an imaging spectrograph that covers the Mg II h&k lines as well as a slit-jaw imager centered at Mg II k. Understanding the observations requires forward modeling of Mg II h&k line formation from 3D radiation-MHD models. We compute the vertically emergent h&k intensity from a snapshot of a dynamic 3D radiation-MHD model of the solar atmosphere, and investigate which diagnostic information about the atmosphere is contained in the synthetic line profiles. We …
Light bridges (LBs) are elongated structures with enhanced intensity embedded in sunspot umbra and pores. We studied the properties of a sample of 60 LBs observed with the Interface Region Imaging Spectrograph (IRIS). Using IRIS near- and far-ultraviolet spectra, we measured the line intensity, width, and Doppler shift; followed traces of LBs in the chromosphere and transition region (TR); and compared LB parameters with umbra and quiet Sun. There is a systematic emission enhancement in LBs compared to nearby umbra from the photosphere up to the TR. Light bridges are systematically displaced t…
Coronal holes (CHs) regions are dark in comparison to the quiet-Sun (QS) at the coronal temperatures. However, at chromospheric and transition region (TR) temperatures, QS and CHs are hardly distinguishable. In this study we have used the \ion{Mg}{2}~2796.35~Å spectral line recorded by the Interface Region Imaging Spectrometer (IRIS) to understand the similarities and differences in the QS and CH at chromospheric levels. Our analysis reveals that the emission from \ion{Mg}{2}~k3 \& k2v that originates in the chromosphere is significantly lower in CH than in QS for the regions with similar magn…
An X1.6 flare occurred in AR 12192 on 2014 October 22 at 14:02 UT and was observed by Hinode, IRIS, SDO, and RHESSI. We analyze a bright kernel which produces a white light (WL) flare with continuum enhancement and a hard X-ray (HXR) peak. Taking advantage of the spectroscopic observations of IRIS and Hinode/EIS, we measure the temporal variation of the plasma properties in the bright kernel in the chromosphere and corona. We found that explosive evaporation was observed when the WL emission occurred, even though the intensity enhancement in hotter lines is quite weak. The temporal correlation…
Dynamics of hot chromospheric plasma of solar flares is a key to understanding of mechanisms of flare energy release and particle acceleration. A moderate M1.0 class flare of 12 June, 2014 (SOL2014-06-12T21:12) was simultaneously observed by NASA's Interface Region Imaging Spectrograph (IRIS), other spacecraft, and also by New Solar Telescope (NST) at the BBSO. This paper presents the first part of our investigation focused on analysis of the IRIS data. Our analysis of the IRIS data in different spectral lines reveals strong redshifted jet-like flow with the speed of ~100 km/s of the chromosph…
IRIS observational approach to the oscillatory and damping nature of network and internetwork chromosphere small-scale brightening (SSBs) and their unusual dynamical and morphological differences in different regions on the solar disk
The C I 135.58 line is located in the wavelength range of NASA's Interface Region Imagin Spectrograph (IRIS) small explorer mission. We here study the formation and diagnostic potential of this line by means of non local-thermodynamic-equilibrium modeling, employing both 1D and 3D radiation-magnetohydrodynamic models. The C I/C II ionization balance is strongly influenced by photoionization by Ly-alpha emission. The emission in the C I 135.58 line is dominated by a recombination cascade and the line forming region is optically thick. The Doppler shift of the line correlates strongly with the v…
Inversion codes allow reconstructing a model atmosphere from observations. With the inclusion of optically thick lines that form in the solar chromosphere, such modelling is computationally very expensive because a non-LTE evaluation of the radiation field is required. In this study, we combine the results provided by these traditional methods with machine and deep learning techniques to obtain similar-quality results in an easy-touse, much faster way. We have applied these new methods to Mg II h&k lines observed by IRIS. As a result, we are able to reconstruct the thermodynamic state (tempera…
The origin of the slow solar wind is still an open issue. It has been suggested that upflows at the edge of active regions (AR) can contribute to the slow solar wind. Here, we compared the upflow region and the AR core and studied how the plasma properties change from the chromosphere via the transition region to the corona. We studied limb-to-limb observations NOAA 12687 (14th - 25th Nov 2017). We analysed spectroscopic data simultaneously obtained from IRIS and Hinode/EIS in six spectral lines. We studied the mutual relationships between the plasma properties for each emission line, as well …
The IRIS Mg II k line serves as a very good tool to diagnose the heating processes in solar flares. Recent studies have shown that apart from the usual red asymmetries which are interpreted as the result of condensation downflows, this line could also show a blue-wing enhancement. To investigate how such a blue asymmetry is formed, we perform a grid of radiative hydrodynamic simulations and calculate the corresponding line profiles. We find that such a spectral feature is likely to originate from the upward plasma motion in the upper chromosphere. However, the formation region that is responsi…
Classic solar models put the Chromosphere-Corona Transition Region (CCTR} at $\sim2$Mm above the $τ_{5000} = 1$ level, whereas rMHD models place it in a wider range of heights. Observational verification is scarce. We review and discuss recent results from various instruments and spectral domains. In SDO and TRACE images spicules appear in emission in the 1600, 1700 and 304 A bands and in absorption in the EUV bands; the latter is due to photo-ionization of H and He I. At the shortest available AIA wavelength and taking into account that the photospheric limb is $\sim0.34$Mm above the $τ_{5000…
The Interface Region Imaging Spectrograph (IRIS) small explorer spacecraft provides simultaneous spectra and images of the photosphere, chromosphere, transition region, and corona with 0.33-0.4 arcsec spatial resolution, 2 s temporal resolution and 1 km/s velocity resolution over a field-of-view of up to 175 arcsec x 175 arcsec. IRIS was launched into a Sun-synchronous orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a 19-cm UV telescope that feeds a slit-based dual-bandpass imaging spectrograph. IRIS obtains spectra in passbands from 1332-1358, 1389-1407 and 2783-2834 Angstrom …
The heating of the chromosphere in internetwork regions remains one of the foremost open questions in solar physics. In the present study we tackle this old problem by using a very high spatial-resolution simulation of quiet-Sun conditions performed with radiative MHD numerical models and IRIS observations. We have expanded a previously existing 3D radiative MHD numerical model of the solar atmosphere, which included self-consistently locally driven magnetic amplification in the chromosphere, by adding ambipolar diffusion and time-dependent non-equilibrium hydrogen ionization to the model. The…
CHROMIS, a new imaging spectrometer at the Swedish 1-m Solar Telescope (SST), can observe the chromosphere in the H and K lines of Ca II at high spatial and spectral resolution. Accurate modeling as well as an understanding of the formation of these lines are needed to interpret the SST/CHROMIS observations. Such modeling is computationally challenging because these lines are influenced by strong departures from local thermodynamic equilibrium, three-dimensional radiative transfer, and partially coherent resonance scattering of photons. We aim to model the CaII H&K lines in 3D model atmosphere…
During solar flares a tremendous amount of magnetic energy is released and transported through the Sun's atmosphere and out into the heliosphere. Despite over a century of study, many unresolved questions surrounding solar flares are still present. Among those are how does the solar plasma respond to flare energy deposition, and what are the important physical processes that transport that energy from the release site in the corona through the transition region and chromosphere? Attacking these questions requires the concert of advanced numerical simulations and high spatial-, temporal-, and s…
Observations of recurrent explosive events (EEs) with time scale of 3-5 minutes are reported. These EEs have been observed with the Interface Region Imaging Spectrograph (IRIS) and have a spatial dimension of $\sim1.5"$ along the slit. The spectral line profiles of \ion{C}{2}~$1335/1336$ Å and \ion{Si}{4}~$1394/1403$ Å become highly broadened both in red as well as blue wings. Several absorption lines on top of the broadened profiles were identified. In addition, emission lines corresponding to neutral lines such as \ion{Cl}{1}~1351.66~Å, \ion{C}{1}~1354.29~Å, and \ion{C}{1}~1355.84~Å were ide…
Acoustic wave heating is believed to contribute significantly to the missing energy input required to maintain the solar chromosphere in its observed state. We studied the propagation of waves above the acoustic cutoff in the upper photosphere into the chromosphere with ultraviolet and optical spectral observations interpreted through comparison with three dimensional radiative magnetohydrodynamic (rMHD) \emph{Bifrost} models to constrain the heating contribution from acoustic waves in the solar atmosphere. Sit-and-stare observations taken with the Interface Region Imaging Spectrograph (IRIS) …
The heating of the solar chromosphere remains one of the most important questions in solar physics. Our current understanding is that small-scale internetwork (IN) magnetic fields play an important role as a heating agent. Indeed, cancellations of IN magnetic elements in the photosphere can produce transient brightenings in the chromosphere and transition region. These bright structures might be the signature of energy release and plasma heating, probably driven by magnetic reconnection of IN field lines. Although single events are not expected to release large amounts of energy, their global …
In the past few years, the ALMA radio telescope has become available for solar observations. ALMA diagnostics of the solar atmosphere are of high interest because of the theoretically expected linear relationship between the brightness temperature at mm wavelengths and the local gas temperature in the solar atmosphere. Key for the interpretation of solar ALMA observations is understanding where in the solar atmosphere the ALMA emission originates. Recent theoretical studies have suggested that ALMA bands at 1.2 (band 6) and 3 mm (band 3) form in the middle and upper chromosphere at significant…
