Recovering Thermodynamics from Spectral Profiles observed by IRIS: A Machine and Deep Learning Approach

Dalda, A. Sainz; Rodríguez, J. de la Cruz; Pontieu, Bart De; Gošić, Milan

doi:10.3847/2041-8213/ab15d9

Cited by 73 publications

(56 citation statements)

References 12 publications

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“…The Si iv brightenings are blueshifted, and the chromospheric profiles are highly unusual and show a strong emission increase at shorter wavelengths. These features strongly suggest the presence of highly energetic NTE (inversions with the new IRIS 2 code of Sainz Dalda et al (2019) also support this conclusion, as we will discuss in detail in a follow-up paper), and it is most similar to model E5. This is also compatible with the very weak overlying coronal emission, because models with highly energetic NTE predict very small coronal emission (because most of the energy is dissipated in the chromosphere; see Polito et al 2018 for a more detailed discussion).…”

Section: Discussionsupporting

confidence: 60%

“…In particular, we plan to run RADYN simulations on much finer grid of parameters (as partly discussed in the previous section 4) exploring a larger parameter space (e.g., initial conditions, duration of the heating, combination of TC and NTE, total nanoflare energy, parameters of NTE), and to find the closest matches to the observed spectra by using an automatic algorithm such as e.g., k-means clustering (e.g., Panos et al 2018) or using neural networks (e.g., Osborne et al 2019). This will also be complemented by using the IRIS 2 inversion code of Sainz Dalda et al (2019) for all of our events to obtain further constraints on the initial atmosphere and on the response of the lower atmosphere to small coronal heating events.…”

Section: Discussionmentioning

confidence: 99%

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IRIS Observations of Short-term Variability in Moss Associated with Transient Hot Coronal Loops

Testa

Polito

Pontieu

2020

ApJ

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We observed rapid variability ( 60 s) at the footpoints of transient hot (∼ 8 − 10 MK) coronal loops in active region cores, with the Interface Region Imaging Spectrograph (IRIS). The high spatial (∼ 0.33 ) and temporal ( 5-10 s) resolution is often crucial for the detection of this variability. We show how, in combination with 1D RADYN loop modeling, these IRIS spectral observations of the transition region (TR) and chromosphere provide powerful diagnostics of the properties of coronal heating and energy transport (thermal conduction and/or non-thermal electrons (NTE)). Our simulations of nanoflare heated loops indicate that emission in the Mg ii triplet can be used as a sensitive diagnostic for non-thermal particles. In our events we observe a large variety of IRIS spectral properties (intensity, Doppler shifts, broadening, chromospheric/TR line ratios, Mg ii triplet emission) even for different footpoints of the same coronal events. In several events, we find spectroscopic evidence for NTE (e.g., TR blue-shifts and Mg ii triplet emission) suggesting that particle acceleration can occur even for very small magnetic reconnection events which are generally below the detection threshold of hard X-ray instruments that provide direct detection of emission of non-thermal particles.

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Section: Discussionsupporting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

IRIS Observations of Short-term Variability in Moss Associated with Transient Hot Coronal Loops

Testa

Polito

Pontieu

2020

ApJ

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“…The Mg ii lines alone may not be sufficient to infer accurate chromospheric temperatures and microturbulence due to well-known NLTE effects, but they greatly help us to interpret ALMA observations because they provide complementary information on temperature, LOS velocities, and microturbulence (e.g., de la Cruz Rodríguez et al 2016). Furthermore, fast inversions of the h, k, and UV triplet lines are now easily available through the IRIS 2 database (Sainz Dalda et al 2019). This paper shows that the combination of IRIS and ALMA is a powerful tool for diagnosing a wider range of physical conditions in the atmosphere, and it underscores the need for more coordinated observations and 3D r-MHD simulations of plage and other solar features taking into account nonequilibrium hydrogen ionization to better understand the formation of the IRIS and ALMA diagnostics in chromospheric conditions.…”

Section: Discussionmentioning

confidence: 99%

The multi-thermal chromosphere

Santos

Rodríguez

Leenaarts

et al. 2020

A&A

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Context. Numerical simulations of the solar chromosphere predict a diverse thermal structure with both hot and cool regions. Observations of plage regions in particular typically feature broader and brighter chromospheric lines, which suggests that they are formed in hotter and denser conditions than in the quiet Sun, but also implies a nonthermal component whose source is unclear. Aims. We revisit the problem of the stratification of temperature and microturbulence in plage and the quiet Sun, now adding millimeter (mm) continuum observations provided by the Atacama Large Millimiter Array (ALMA) to inversions of near-ultraviolet Interface Region Imaging Spectrograph (IRIS) spectra as a powerful new diagnostic to disentangle the two parameters. We fit cool chromospheric holes and track the fast evolution of compact mm brightenings in the plage region. Methods. We use the STiC nonlocal thermodynamic equilibrium (NLTE) inversion code to simultaneously fit real ultraviolet and mm spectra in order to infer the thermodynamic parameters of the plasma. Results. We confirm the anticipated constraining potential of ALMA in NLTE inversions of the solar chromosphere. We find significant differences between the inversion results of IRIS data alone compared to the results of a combination with the mm data: the IRIS+ALMA inversions have increased contrast and temperature range, and tend to favor lower values of microturbulence (∼3−6 km s−1 in plage compared to ∼4−7 km s−1 from IRIS alone) in the chromosphere. The average brightness temperature of the plage region at 1.25 mm is 8500 K, but the ALMA maps also show much cooler (∼3000 K) and hotter (∼11 000 K) evolving features partially seen in other diagnostics. To explain the former, the inversions require the existence of localized low-temperature regions in the chromosphere where molecules such as CO could form. The hot features could sustain such high temperatures due to non-equilibrium hydrogen ionization effects in a shocked chromosphere – a scenario that is supported by low-frequency shock wave patterns found in the Mg II lines probed by IRIS.

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“…The entire region around the EB/UV burst phenomena is characterized by broad wings in the Mg ii k2 peaks, both on the blue side of the k2v peak and on the red side of the k2r peak. Spectral inversions of this line using the IRIS 2 package (see http://iris.lmsal.com/iris2/ and Sainz Dalda et al 2019;de la Cruz Rodríguez et al 2016) attribute the broad asymmetric Mg ii h & k peaks most likely to the following factors in the region surrounding the EB/UV burst: a highly turbulent plasma, with turbulent velocities v turb of 10 − 15 km s −1 , covering an area that is larger than the UV burst seen in the other plasma variables like temperature T , line of sight velocity v los , and electron density n e . The maximum of v turb is reached in the lower chromosphere, where log(τ 500 ) ≃ −3 (where the photosphere is defined by the height where the optical depth τ = 1 in the continuum at 500 nm, and thus the notation τ 500 ).…”

Section: A Closer View Of the Uv Burst: Propertiesmentioning

confidence: 99%

Ellerman bombs and UV bursts: reconnection at different atmospheric layers

Ortiz

Hansteen

Nóbrega-Siverio

et al. 2020

A&A

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The emergence of magnetic flux through the photosphere and into the outer solar atmosphere produces, amongst other dynamical phenomena, Ellerman bombs (EBs), which are observed in the wings of Hα and are due to magnetic reconnection in the photosphere below the chromospheric canopy. Signs of magnetic reconnection are also observed in other spectral lines, typical of the chromosphere or the transition region. An example are the UV bursts observed in the transition region lines of Si iv and the upper chromospheric lines of Mg ii. In this work we analyze high cadence, high resolution coordinated observations between the Swedish 1-m Solar Telescope (SST) and the Interface Region Imaging Spectrograph (IRIS) spacecraft. Hα images from the SST provide us with the positions, timings and trajectories of EBs in an emerging flux region. Simultaneous, co-aligned IRIS slit-jaw images at 133 (C ii, transition region), 140 (Si iv, transition region) and 279.6 (Mg ii k, core, upper chromosphere) nm, as well as spectroscopy in the far and near ultraviolet from the fast spectrograph raster, allow us to study the possible chromospheric/transition region counterparts of those EBs. Our main goal is to study the possible temporal and spatial relationship between several reconnection events at different layers in the atmosphere (namely EBs and UV bursts), the timing history between them, and the connection of these dynamical phenomena to the ejection of surges in the chromosphere. We also investigate the properties of an extended UV burst and their variations across the burst domain. Our results suggest a scenario where simultaneous and co-spatial EBs and UV bursts are part of the same reconnection system occurring sequentially along a vertical or nearly vertical current sheet. Heating and bidirectional jets trace the location where reconnection takes place. These results support and expand those obtained from recent numerical simulations of magnetic flux emergence.

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Recovering Thermodynamics from Spectral Profiles observed by IRIS: A Machine and Deep Learning Approach

Cited by 73 publications

References 12 publications

IRIS Observations of Short-term Variability in Moss Associated with Transient Hot Coronal Loops

IRIS Observations of Short-term Variability in Moss Associated with Transient Hot Coronal Loops

The multi-thermal chromosphere

Ellerman bombs and UV bursts: reconnection at different atmospheric layers

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