NASA的界面区域成像光谱仪（IRIS）太空任务将研究太阳大气层是如何被激发的。IRIS包含一个成像摄谱仪，覆盖Mg II h&k线，以及一个以Mg II k为中心的狭缝式成像仪。理解观测结果需要从三维辐射-MHD模型中对Mg II h&k线的形成进行正演模拟。本文是我们进行这种正演模拟的系列文章中的第一篇。讨论了与h&k线形成有关的原子物理学，提出了一个可用于辐射转移计算的典型模型原子，讨论了部分再分布（PRD）和三维辐射转移对出射线轮廓的影响。我们的结论是，Mg II的H&K可以准确地模拟与4级加连续Mg II模型原子。理想情况下，辐射转移计算应在3D中进行，包括PRD效应。在实践中，这目前是不可能的。一个合理的折衷方案是使用1D PRD计算来模拟直到并包括中心发射峰的线轮廓，并使用3D传输（假设完全重新分布）来模拟中心凹陷。
英文摘要：
NASA's Interface Region Imaging Spectrograph (IRIS) space 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 will require forward modeling of Mg II h&k line formation from 3D radiation-MHD models. This paper is the first in a series where we undertake this forward modeling. We discuss the atomic physics pertinent to h&k line formation, present a quintessential model atom that can be used in radiative transfer computations and discuss the effect of partial redistribution (PRD) and 3D radiative transfer on the emergent line profiles. We conclude that Mg II h&k can be modeled accurately with a 4-level plus continuum Mg II model atom. Ideally radiative transfer computations should be done in 3D including PRD effects. In practice this is currently not possible. A reasonable compromise is to use 1D PRD computations to model the line profile up to and including the central emission peaks, and use 3D transfer assuming complete redistribution to model the central depression.
The 133.5 nm lines are important observables for the NASA/SMEX mission Interface Region Imaging Spectrograph (IRIS). To make 3D non-LTE radiative transfer computationally feasible it is crucial to have a model atom with as few levels as possible while retaining the main physical processes. We here develop such a model atom and we study the general formation properties of the C II lines. We find that a nine-level model atom of C I-C III with the transitions treated assuming complete frequency redistribution (CRD) suffices to describe the 133.5 nm lines. 3D scattering effects are important for t…
The formation of IRIS diagnostics. III. Near-ultraviolet Spectra and Images
Mg II h&k线是NASA界面区成像光谱仪（IRIS）的主要色球诊断线。在本系列的前几篇论文中，我们使用了一个真实的三维辐射磁流体动力学模型来详细计算h&k线，并研究了它们的光谱特征与下垫面大气的关系。在这项工作中，我们采用相同的方法来研究如何H&K诊断票价时，考虑到有限分辨率的IRIS和不同的噪声水平。此外，我们调查的诊断潜力的其他几个光球线和近连续区域存在于近紫外（NUV）窗口的IRIS和研究的NUV缝颚图像的形成。我们发现IRIS的仪器分辨率对H&K诊断的质量影响很小，光谱特征与大气性质之间的关系基本不变。峰分离是最受影响的诊断，但主要是由于模拟的局限性。噪声的影响在信噪比（S/N）为20时开始变得明显，但我们表明，通过噪声滤波，至少可以在S/N为5时获得可靠的诊断。NUV窗口中的许多光球线提供了至少八个不同光球高度的速度信息。利用h&k远翼中的无谱线区域，我们得到了至少三个高度的光球温度的良好估计。这两种诊断，特别是后者，甚至可以在S/Ns低至5时获得。
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 …
The O I 135.56 nm line is covered by NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission which studies how the solar atmosphere is energized. We here study the formation and diagnostic potential of this line by means of non-LTE modelling employing both 1D semi-empirical and 3D radiation-Magneto Hydrodynamic (RMHD) models. We study the basic formation mechanisms and derive a quintessential model atom that incorporates the essential atomic physics for the formation of the O I 135.56 nm line. This atomic model has 16 levels and describes recombination cascades through highl…
A triplet of subordinate lines of Mg II exists in the region around the h&k lines. In solar spectra these lines are seen mostly in absorption, but in some cases can become emission lines. The aim of this work is to study the formation of this triplet, and investigate any diagnostic value they can bring. Using 3D radiative magnetohydrodynamic simulations of quiet Sun and flaring flux emergence, we synthesize spectra and investigate how spectral features respond to the underlying atmosphere. We find that emission in the lines is rare and is typically caused by a steep temperature increase in the…
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…
We use 3D radiation magnetohydrodynamic models to investigate how the thermodynamic quantities in the simulation are encoded in observable quantities, thus exploring the diagnostic potential of the 133.5 nm lines. We find that the line core intensity is correlated with the temperature at the formation height but the correlation is rather weak, especially when the lines are strong. The line core Doppler shift is a good measure of the line-of-sight velocity at the formation height. The line width is both dependent on the width of the absorption profile (thermal and non-thermal width) and an opac…
We present joint Hinode/EIS and IRIS observations of Fe XII lines in active regions, both on-disk and off-limb. We use an improved calibration for the EIS data, and find that the 192.4 A / 1349 A observed ratio is consistent with the values predicted by CHIANTI and the coronal approximation in quiescent areas, but not in all active region observations, where the ratio is often lower than expected by up to a factor of about two. We investigate a number of physical mechanisms that could affect this ratio, such as opacity and absorption from cooler material. We find significant opacity in the EIS…
The formation of IRIS diagnostics II. The formation of the Mg II h&k lines in the solar atmosphere
美国宇航局的界面区域成像光谱仪（IRIS）小型探测器任务将研究太阳大气层是如何被激活的。IRIS包含一个成像摄谱仪，覆盖Mg II h&k线，以及一个以Mg II k为中心的狭缝式成像仪。了解的意见，需要从三维辐射MHD模型的Mg II H&K线形成的正演模拟。我们计算垂直出射的H&K强度从一个动态的三维辐射MHD模型的太阳大气的快照，并调查的诊断信息的大气中包含在合成线配置文件。我们发现，中心线低压的多普勒频移强烈相关的垂直速度在光学深度单位，这是典型的位于低于200公里的过渡区（TR）。通过结合h线和k线的多普勒频移，我们可以恢复TR正下方的速度梯度的符号。中心线凹陷的强度与地层高度相关，特别是在几平方微米的子场中。因此，该强度可用于测量过渡区高度的空间变化。线芯发射峰的强度与其形成高度处的温度相关，特别是对于强发射峰。因此，可以将峰值用作温度诊断。蓝色和红色峰值之间的波长差提供了对上部色球层中速度梯度的诊断。蓝峰和红峰的强度比与上色球层的平均速度密切相关。我们的结论是镁II的H&K线是很好的探针的非常上部色球层的过渡区，高度制度，是不可能探测与其他谱线。
Solar spectra of ultraviolet bursts and flare ribbons from the Interface Region Imaging Spectrograph (IRIS) have suggested high electron densities of $>10^{12}$ cm$^{-3}$ at transition region temperatures of 0.1 MK, based on large intensity ratios of Si IV $λ$1402.77 to O IV $λ$1401.16. In this work a rare observation of the weak O IV $λ$1343.51 line is reported from an X-class flare that peaked at 21:41 UT on 2014 October 24. This line is used to develop a theoretical prediction of the Si IV $λ$1402.77 to O IV $λ$1401.16 ratio as a function of density that is recommended to be used in the hig…
The O IV intercombination lines observed by the Interface Region Imaging Spectrograph (IRIS) between 1397 and 1407 A provide useful density diagnostics. This document presents data that address two issues related to these lines: (1) the contribution of S IV to the O IV 1404.8 line; and (2) the range of sensitivity of the O IV 1399.8/1401.2 ratio.
Surges have regularly been observed mostly in H$_α$ 6563~Å and Ca~{\sc ii} 8542~Å. However, surge$'$s response to other prominent lines of the interface-region (Mg~{\sc ii} k 2796.35~Å $\&$ h 2803.52~Å, O~{\sc iv} 1401.15~Å, Si~{\sc iv} 1402.77~Å) is not well studied. Here, the evolution and kinematics of six homologous surges are analysed using IRIS and AIA observations. These surges were observed on 7$^{th}$ July 2014, located very close to the limb. DEM analysis is performed on these surges where the co-existence of cool (log T/K = 6.35) and relatively hot (log T/K = 6.95) components have b…
The intensity of the \oiv~2s$^{2}$ 2p $^{2}$P-2s2p$^{2}$ $^{4}$P and \siv~3 s$^{2}$ 3p $^{2}$P- 3s 3p$^{2}$ $^{4}$ P intercombination lines around 1400~Å~observed with the \textit{Interface Region Imaging Spectrograph} (IRIS) provide a useful tool to diagnose the electron number density ($N_\textrm{e}$) in the solar transition region plasma. We measure the electron number density in a variety of solar features observed by IRIS, including an active region (AR) loop, plage and brightening, and the ribbon of the 22-June-2015 M 6.5 class flare. By using the emissivity ratios of \oiv\ and \siv\ lin…
Helical magnetic flux rope (MFR) is a fundamental structure of corona mass ejections (CMEs) and has been discovered recently to exist as a sigmoidal channel structure prior to its eruption in the extreme ultraviolet (EUV) high temperature passbands of the Atmospheric Imaging Assembly (AIA). However, when and where the MFR is built up are still elusive. In this paper, we investigate two MFRs (MFR1 and MFR2) in detail, whose eruptions produced two energetic solar flares and CMEs on 2014 April 18 and 2014 September 10, respectively. The AIA EUV images reveal that for a long time prior to their er…
In the work described here we investigate atomic processes leading to the formation of emission lines within the IRIS wavelength range at temperatures near $10^5$~K. We focus on (1) non-equilibrium and (2) density-dependent effects influencing the formation and radiative properties of S IV and O IV. These two effects have significant impacts on spectroscopic diagnostic measurements of quantities associated with the plasma that emission lines from S IV and O IV provide. We demonstrate this by examining nanoflare-based coronal heating to determine what the detectable signatures are in transition…
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…
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 …
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…
The Interface Region Imaging Spectrograph(IRIS) with its high spatial and temporal resolution brings exceptional plasma diagnostics of solar chromospheric and coronal activity during magnetic reconnection. The aim of this work is to study the fine structure and dynamics of the plasma at a jet base forming a mini flare between two emerging magnetic fluxes (EMFs) observed with IRIS and the Solar Dynamics Observatory (SDO) instruments. We proceed to a spatio-temporal analysis of IRIS spectra observed in the spectral ranges of Mg II, C II, and Si IV ions. Doppler velocities from Mg II lines are co…
We present results of non-LTE modeling of H-alpha 6563 A and Mg II k&h 2796 A and 2803 A lines. This modeling is important for interpretation of coordinated observations from the recently launched NASA's IRIS mission and from the New Solar Telescope at Big Bear Solar Observatory. Among available codes for the non-LTE modeling, the RH code is chosen as the most appropriate for modeling of the line profiles. The most suitable Hydrogen and Magnesium atomic models are selected by performing several tests of the code. The influence of the ionization degree on the line profiles is also studied. Radi…
Penumbral microjets (PMJs) are short-lived, jet-like objects found in the penumbra of sunspots. They were first discovered in chromospheric lines and have later also been shown to exhibit signals in transition region (TR) lines. Their origin and manner of evolution is not yet settled. We perform a comprehensive analysis of PMJs through the use of spectral diagnostics that span from photospheric to TR temperatures to constrain PMJ properties. We employed high-spatial-resolution Swedish 1-m Solar Telescope observations in the Ca II 8542 Angstrom and H-alpha lines, IRIS slit-jaw images, and IRIS …
The GOES X1 flare SOL2014-10-25T17:08:00 was a three-ribbon solar flare observed with IRIS in the near and far ultraviolet. One of the flare ribbons crossed a sunspot umbra, producing a dramatic, $\sim1000$% increase in the near-ultraviolet (NUV) continuum radiation. We comprehensively analyze the ultraviolet spectral data of the umbral flare brightenings, which provide new challenges for radiative-hydrodynamic modeling of the chromospheric velocity field and the white-light continuum radiation. The emission line profiles in the umbral flare brightenings exhibit redshifts and profile asymmetri…
Spectroscopic observations of prominence eruptions associated with coronal mass ejections (CMEs), although relatively rare, can provide valuable plasma and 3D geometry diagnostics. We report the first observations by the Interface Region Imaging Spectrograph (IRIS) mission of a spectacular fast CME/prominence eruption associated with an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and Doppler velocities of the eruption are 1200 and 460 km/s, respectively. There are two eruption components separated by ~200 km/s in Doppler velocity: a primary, bright component and a secondary, …
Quiescent filaments appear as absorption features on the solar disk when observed in chromospheric lines and at continuum wavelengths in the millimeter (mm) range. Active region (AR) filaments are their small-scale, low-altitude analogues, but they could not be resolved in previous mm observations. This spectral diagnostic can provide insight into the details of the formation and physical properties of their fine threads, which are still not fully understood. Here, we shed light on the thermal structure of an AR filament using high-resolution brightness temperature ($T_{\rm b}$) maps taken wit…
Magnetic reconnection is the key mechanism for energy release in solar eruptions, where the high-temperature emission is the primary diagnostic for investigating the plasma properties during the reconnection process. Non-thermal broadening of high-temperature lines has been observed in both the reconnection current sheet (CS) and flare loop-top regions by UV spectrometers, but its origin remains unclear. In this work, we use a recently developed three-dimensional magnetohydrodynamic (MHD) simulation to model magnetic reconnection in the standard solar flare geometry and reveal highly dynamic p…
The bulk of the radiative output of a solar flare is emitted from the chromosphere, which produces enhancements in the optical and UV continuum, and in many lines, both optically thick and thin. We have, until very recently, lacked observations of two of the strongest of these lines: the Mg II h & k resonance lines. We present a detailed study of the response of these lines to a solar flare. The spatial and temporal behaviour of the integrated intensities, k/h line ratios, line of sight velocities, line widths and line asymmetries were investigated during an M class flare (SOL2014-02-13T01:40)…
The Temperature Diagnostic Properties of the MG I 457.1 NM Line
我们分析了Mg I 457.1 nm谱线的重要形成过程。这条线是一条内部耦合线，并且源函数接近于局部热力学平衡（LTE）值。强耦合到当地的温度和相对较高的人口较低的水平（基态的镁I），使这条线在较低的色球/温度最低区域的温度诊断的理想候选人。由于非LTE电离，将探测的温度与绝对物理高度联系起来并不简单。我们分析了非LTE效应，发现低能级的光电离和级联碰撞复合共同主导电离平衡。适当考虑紫外线的线覆盖效应是获得正确的光电离率的必要条件。识别线中的主要非LTE效应使我们能够构建一个典型的模型原子，非常适合计算要求高的任务，例如全3D和/或时间相关的辐射转移。此外，我们分析了诊断潜力，这条线在类太阳大气中的温度，通过合成线从一系列参数化的大气模式。这些模型都是用固定的有效温度，但在能量方程中加入一个可变的热量项，以获得不同高度的色球温升。我们的结论是，该线具有显着的潜力，在诊断较低的色球层温度结构，特别是对于较冷的大气，如太阳黑子。
Aims: We investigate a new method to for obtaining the plasma parameters of solar prominences observed in the Mgii h&k spectral lines by comparing line profiles from the IRIS satellite to a bank of profiles computed with a one-dimensional non-local thermodynamic equilibrium (non-LTE) radiative transfer code. Methods: Using a grid of 1007 one-dimensional non-LTE radiative transfer models we carry out this new method to match computed spectra to observed line profiles while accounting for line core shifts not present in the models. The prominence observations were carried out by the IRIS satelli…
Spectroscopic observations of solar flares provide critical diagnostics of the physical conditions in the flaring atmosphere. Some key features in observed spectra have not yet been accounted for in existing flare models. Here we report a data-driven simulation of the well-observed X1.0 flare on 2014 March 29 that can reconcile some well-known spectral discrepancies. We analyzed spectra of the flaring region from the Interface Region Imaging Spectrograph (IRIS) in MgII h&k, the Interferometric BIdimensional Spectropolarimeter at the Dunn Solar Telescope (DST/IBIS) in H$α$ 6563 Å and CaII 8542 …
The Mg II h&k lines are powerful diagnostics for studying the solar chromosphere. They have become particularly popular with the launch of the IRIS satellite, and a number of studies that include these lines have lead to great progress in understanding chromospheric heating, in many cases thanks to the support from 3D MHD simulations. In this study we utilize another approach to analyze observations: non-LTE inversions of the Mg II h&k and UV triplet lines including the effects of partial redistribution. Our inversion code attempts to construct a model atmosphere that is compatible with the ob…
Surges are cool and dense ejections typically observed in chromospheric lines and closely related to other solar phenomena like UV bursts or coronal jets. Our aim is to address the current lack of inverted models and diagnostics of surges as well as characterizing their plasma properties. We have analyzed different surges related to UV bursts observed with the Interface Region Imaging Spectrograph (IRIS) on 2016 April. The mid- and low-chromosphere of the surges are examined by getting their representative Mg II h&k line profiles through the k-means algorithm and performing inversions on them …
IRIS performs solar observations over a large range of atmospheric heights, including the chromosphere where the majority of flare energy is dissipated. The strong Mg II h&k spectral lines are capable of providing excellent atmospheric diagnostics, but have not been fully utilized for flaring atmospheres. We aim to investigate whether the physics of the chromosphere is identical for all flare observations by analyzing if there are certain spectra that occur in all flares. To achieve this, we automatically analyze hundreds of thousands of Mg II h&k line profiles from a set of 33 flares, and use…
Chromospheric Flashes in a Solar Pore: Insights from Multi-line Spectropolarimetric Diagnostics
Physical Research Laboratory（物理研究实验室）；Udaipur Solar Observatory, Physical Research Laboratory（乌代浦尔太阳观测台，物理研究实验室）；Indian Institute of Technology, Gandhinagar（甘地纳加尔印度理工学院）；National Solar Observatory (NSO)（国家太阳天文台）；Laboratory for Atmospheric and Space Physics, University of Colorado（科罗拉多大学大气与空间物理实验室）；Instituto de Astrofı́sica de Canarias (IAC)（加那利群岛天体物理学研究所）；Universidad de La Laguna（拉古纳大学）
Context. QPPs are usually detected as spatial displacements of coronal loops in imaging observations or as periodic shifts of line properties in spectroscopic observations. They are often applied for remote diagnostics of magnetic fields and plasma properties on the Sun. Aims. We combine imaging and spectroscopic measurements of available space missions, and investigate the properties of non-damping oscillations at flaring loops. Methods. We used the IRIS to measure the spectrum over a narrow slit. The double-component Gaussian fitting method was used to extract the line profile of Fe XXI 1354…
The nature of flows in tornado-prominences is an open issue. While the AIA imager aboard the Solar Dynamics Observatory (SDO) allowed us to follow the global structure of a tornado-like prominence during five hours, the Interface Region Imaging Spectrograph (IRIS), and the Multi subtractive Double pass spectrograph (MSDP) permitted to obtain plasma diagnostics of its fine structures. We aim to address two questions. Is the observed plasma rotation conceptually acceptable in a flux rope magnetic support configuration with dips? How is the plasma density distributed in the tornado-like prominenc…
