arxiv: 2605.03818 · v1 · submitted 2026-05-05 · 🌌 astro-ph.SR

Recognition: unknown

IRIS NUV diagnostics for Ellerman bombs: spectral properties, thermodynamics, and formation height

I. J. Soler Poquet , C. J. D\'iaz Baso , A. Sainz Dalda , L. H. M. Rouppe van der Voort , D. N\'obrega-Siverio , R. Joshi

Authors on Pith no claims yet

Pith reviewed 2026-05-07 13:35 UTC · model grok-4.3

classification 🌌 astro-ph.SR

keywords Ellerman bombsIRISMg II tripletNUV spectrasolar atmospheremagnetic reconnectionHα diagnostics

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The pith

Ellerman bombs show enhanced Mg II triplet wings in IRIS NUV spectra, allowing detection without Hα data.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper analyzes four sets of coordinated SST and IRIS observations to find the key NUV signatures of Ellerman bombs. It identifies wing enhancements in the subordinated Mg II triplet lines as the main diagnostic feature and derives a detection rule based only on those lines. This rule recovers 14 of the 18 events previously identified in Hα. Spectral inversions show the signatures arise from a localized temperature rise of roughly 1650 K near log τ = -3.8. The relative shape of the Mg II h and k lines compared with the triplet further indicates the bomb's formation height.

Core claim

The defining feature of EBs in the IRIS NUV is the enhancement of the wings of the subordinated Mg II triplet in between the Mg II h&k lines. Inversions reveal that these signatures are produced by localized temperature increase of ΔT ~1650 K around logτ=-3.8. Using only the Mg II triplet signatures, a detection criterion successfully recovered 14 of 18 Hα-detected EBs. The shape of the Mg II h&k lines in relation to the Mg II triplet can serve as a proxy for the EB formation height.

What carries the argument

Enhancement of the wings of the subordinated Mg II triplet lines between the h and k lines, which signals localized heating and allows both detection and height estimation.

Load-bearing premise

Hα observations give a complete and unambiguous reference set for identifying all Ellerman bombs, and the 18 events from four observations are representative.

What would settle it

Apply the Mg II triplet detection criterion to an independent set of coordinated IRIS and Hα observations and measure what fraction of Hα events it recovers.

read the original abstract

Context. Ellerman bombs (EBs) are observational signatures of small-scale magnetic reconnection, key to understanding the lower solar atmosphere. While their role in active regions has been widely studied using the H$\alpha$ line, near-ultraviolet (NUV) spectra routinely observed by the Interface Region Imaging Spectrograph (IRIS) offer a promising alternative for EB identification, enabling large-scale studies. Aims. We aim to identify the most important spectral signatures of EBs in the IRIS NUV spectra. With this, we seek to develop a robust criterion for their detection solely using the IRIS NUV spectra. In parallel, we determine the typical atmospheric stratification associated with EBs. Methods. We used four coordinated observations between the Swedish 1-m Solar Telescope (SST) and IRIS. Using the H$\alpha$ line as a reference, we detected 18 different EBs and studied their associated IRIS NUV spectra. In addition, we used the IRIS$^{2+}$ inversion tool to infer the temperature, line-of-sight velocity, and non-thermal broadening from the EB spectra. Results. The defining feature of EBs in the IRIS NUV is the enhancement of the wings of the subordinated Mg II triplet in between the Mg II h&k lines. Inversions reveal that these signatures are produced by localized temperature increase of $\Delta$ T~1650 K around log$\tau$=-3.8. Using only the Mg II triplet signatures, we found a detection criterion that successfully recovered 14 of 18 H$\alpha$-detected EBs. In addition, the shape of the Mg II h&k lines in relation to the Mg II triplet can serve as a proxy for the EB formation height. Conclusions. The NUV spectrum observed by IRIS is a good candidate for detecting EBs, opening the doors to large-scale studies across the extensive IRIS database, removing the dependence on H$\alpha$ observations.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This paper gives a workable Mg II triplet wing criterion for spotting Ellerman bombs in IRIS NUV spectra that catches 14 of 18 Hα events, plus inversions showing localized heating, but the tiny shared sample and no independent checks limit how far the large-scale claim goes.

read the letter

Your colleague should know that this paper gives a workable Mg II triplet wing criterion for spotting Ellerman bombs in IRIS NUV spectra that catches 14 of 18 Hα events, plus inversions showing localized heating, but the tiny shared sample and no independent checks limit how far the large-scale claim goes. They coordinated four SST-IRIS runs, identified the 18 events in Hα, and showed that the triplet wings between h and k stand out as the clearest NUV marker. The inversions with IRIS²+ then tie that signature to a temperature jump of about 1650 K near log τ = -3.8, which lines up with what reconnection models expect. The height proxy from the relative shape of h&k versus the triplet is a useful extra detail. That part is new and directly useful for anyone scanning the IRIS archive without Hα coverage. The empirical recovery rate is reported plainly, and the spectral examples are shown clearly enough to let others test the idea. The main soft spots are the sample size and the validation setup. Eighteen events from four observations is small, and the criterion was both derived and tested on exactly those same events with no hold-out set or false-positive rate measured on non-EB regions. That makes the jump to “large-scale studies across the IRIS database” rest on an assumption that the four runs are representative and that Hα catches every relevant EB. The paper does not appear to quantify how often the triplet signature appears without an Hα EB or how sensitive the rule is to raster cadence and noise. Inversions inherit the same sample limits and lack reported error bars or assumption checks in the abstract-level summary. This work is for solar physicists who already use IRIS NUV rasters and want a practical way to flag EBs without extra ground-based data. A reader focused on lower-atmosphere reconnection diagnostics will find the spectral comparison and the thermodynamic numbers worth looking at. It deserves a serious referee because the core observation is grounded in real coordinated data and the proposed criterion is simple enough to be tried immediately, even though the validation needs tightening before the generalization claim can be taken as solid. I would send it to review.

Referee Report

3 major / 2 minor

Summary. The paper analyzes four coordinated SST Hα and IRIS NUV observations, identifying 18 Ellerman bombs (EBs) via Hα. It identifies wing enhancement in the subordinated Mg II triplet (between h&k) as the primary NUV signature of EBs, derives an empirical detection criterion based on this feature that recovers 14 of the 18 events, performs IRIS²+ inversions yielding a localized temperature increase of ΔT ≈ 1650 K near log τ = -3.8, and proposes the relative shape of Mg II h&k lines to the triplet as a proxy for EB formation height. The conclusion advocates using IRIS NUV spectra alone for large-scale EB studies.

Significance. If the NUV criterion proves robust, the work would enable statistical studies of EBs across the full IRIS archive without requiring simultaneous Hα data, directly advancing understanding of small-scale reconnection in the lower atmosphere. The inversion results provide concrete thermodynamic constraints linking the observed spectral features to atmospheric conditions at specific optical depths.

major comments (3)

[Methods] Methods section: The selection process for the 18 Hα-detected EBs from the four coordinated observations is not described in sufficient detail (e.g., total number of candidate events screened, quantitative Hα intensity or profile thresholds, or exclusion criteria for non-EB brightenings), which is load-bearing for assessing selection bias and representativeness of the sample used to derive the NUV criterion.
[Results] Results (detection criterion subsection): The Mg II triplet wing-enhancement criterion is both derived from direct comparison with the same 18 Hα events and evaluated on those identical events, with no reported cross-validation, hold-out set, or false-positive rate measured in non-EB regions of the IRIS rasters; this directly limits the strength of the claim that the criterion enables reliable, Hα-independent large-scale detection.
[Inversion results] Inversion results subsection: The IRIS²+ inversions report ΔT ≈ 1650 K at log τ ≈ -3.8 but provide no error bars, sensitivity tests to initial model atmospheres, or discussion of parameter degeneracies; without these, the specific thermodynamic values cannot be taken as robust support for the formation-height interpretation.

minor comments (2)

[Abstract] Abstract and conclusions: The 14/18 recovery rate is stated without accompanying uncertainty estimate or statistical test, which would help readers gauge robustness.
[Figures] Figure captions (spectral plots): Line identifications for the Mg II triplet components and h&k lines should be labeled directly on the plots for clarity when comparing EB versus non-EB profiles.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their constructive comments and positive evaluation of the significance of our work on IRIS NUV diagnostics for Ellerman bombs. We address each major comment point by point below, with clear indications of revisions to be incorporated in the next manuscript version.

read point-by-point responses

Referee: [Methods] Methods section: The selection process for the 18 Hα-detected EBs from the four coordinated observations is not described in sufficient detail (e.g., total number of candidate events screened, quantitative Hα intensity or profile thresholds, or exclusion criteria for non-EB brightenings), which is load-bearing for assessing selection bias and representativeness of the sample used to derive the NUV criterion.

Authors: We agree that additional detail on the EB selection process is necessary to allow readers to assess potential biases and sample representativeness. In the revised manuscript, we will expand the Methods section to report the total number of Hα candidate events initially screened across the four coordinated SST-IRIS observations, the specific quantitative thresholds applied to Hα intensity enhancements and line profile shapes (e.g., wing brightening criteria), and the exclusion criteria used to reject non-EB brightenings such as network patches or plage. These additions will directly address the concern and strengthen the foundation for the derived NUV criterion. revision: yes
Referee: [Results] Results (detection criterion subsection): The Mg II triplet wing-enhancement criterion is both derived from direct comparison with the same 18 Hα events and evaluated on those identical events, with no reported cross-validation, hold-out set, or false-positive rate measured in non-EB regions of the IRIS rasters; this directly limits the strength of the claim that the criterion enables reliable, Hα-independent large-scale detection.

Authors: The referee correctly identifies a limitation: the criterion was derived and tested on the identical set of 18 events without cross-validation or explicit false-positive assessment in non-EB regions. With only four coordinated datasets yielding this modest sample, a formal hold-out set was not feasible. In the revision, we will explicitly discuss this limitation in the Results and Conclusions sections, cautioning that the criterion requires independent validation on larger or separate datasets before robust large-scale application. We will also examine the Mg II triplet behavior in quiet-Sun and non-EB active-region portions of the existing rasters to provide an initial estimate of false-positive rates where possible. revision: partial
Referee: [Inversion results] Inversion results subsection: The IRIS²+ inversions report ΔT ≈ 1650 K at log τ ≈ -3.8 but provide no error bars, sensitivity tests to initial model atmospheres, or discussion of parameter degeneracies; without these, the specific thermodynamic values cannot be taken as robust support for the formation-height interpretation.

Authors: We acknowledge that the inversion results lack quantitative uncertainty estimates and robustness checks. In the revised manuscript, we will add error bars derived from the IRIS²+ inversion uncertainties, perform sensitivity tests by rerunning inversions with varied initial model atmospheres (e.g., different temperature stratifications and velocity fields), and include a discussion of potential degeneracies among temperature, line-of-sight velocity, and non-thermal broadening. These additions will better support the reported localized heating of ~1650 K near log τ = -3.8 and its connection to the observed Mg II triplet wing enhancements and formation-height proxy. revision: yes

Circularity Check

1 steps flagged

Mg II triplet detection criterion derived from and tested on the same 18 Hα events without cross-validation or hold-out

specific steps

fitted input called prediction [Abstract (Results paragraph)]
"Using only the Mg II triplet signatures, we found a detection criterion that successfully recovered 14 of 18 Hα-detected EBs."

The criterion is obtained by inspecting the NUV spectra of the 18 Hα-identified events and is then reported as having 'recovered' 14 of those identical events. Without a hold-out set, cross-validation, or quantification on non-EB regions, the success rate measures consistency with the input sample rather than independent predictive power.

full rationale

The paper identifies 18 EBs via independent Hα observations from SST, then examines their IRIS NUV spectra to define a Mg II triplet wing-enhancement criterion that recovers 14/18 of those same events. This recovery rate is presented as validation of a general NUV-only detection method, but the criterion is constructed directly from the sample it is evaluated on. Inversions supply separate thermodynamic results (ΔT ≈ 1650 K at log τ ≈ -3.8) that do not reduce to the same fit. No self-citation chains or definitional loops appear in the core claims; the partial circularity is limited to the empirical detection step lacking independent testing.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that Hα reliably identifies EBs as ground truth and that spectral inversions accurately recover temperature without major biases from model assumptions.

axioms (1)

domain assumption Hα line observations provide a reliable and complete reference for identifying all Ellerman bombs
The study uses Hα detections to validate and calibrate the NUV signatures and criterion.

pith-pipeline@v0.9.0 · 5703 in / 1472 out tokens · 60383 ms · 2026-05-07T13:35:28.354555+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

35 extracted references

[1]

2024, A&A, 689, A156

Bhatnagar, A., Rouppe van der V oort, L., & Joshi, J. 2024, A&A, 689, A156

2024
[2]

2019, ApJ, 875, L30 de la Cruz Rodríguez, J., Leenaarts, J., Danilovic, S., & Uitenbroek, H

Chen, Y ., Tian, H., Peter, H., et al. 2019, ApJ, 875, L30 de la Cruz Rodríguez, J., Leenaarts, J., Danilovic, S., & Uitenbroek, H. 2019, A&A, 623, A74 de la Cruz Rodríguez, J., Löfdahl, M. G., Sütterlin, P., Hillberg, T., & Rouppe van der V oort, L. 2015, A&A, 573, A40 de la Cruz Rodríguez, J. & van Noort, M. 2017, Space Sci. Rev., 210, 109 De Pontieu, B...

2019
[3]

2019, SH33A–07 De Pontieu, B., Title, A

Abstracts, V ol. 2019, SH33A–07 De Pontieu, B., Title, A. M., Lemen, J. R., et al. 2014, Sol. Phys., 289, 2733 del Toro Iniesta, J. C. & Ruiz Cobo, B. 2016, Living Reviews in Solar Physics, 13, 4 Díaz Baso, C. J., de la Cruz Rodríguez, J., & Leenaarts, J. 2021, A&A, 647, A188

2019
[4]

1917, ApJ, 46, 46

Ellerman, F. 1917, ApJ, 46, 46

1917
[5]

2002, ApJ, 575, 506 Grubecka Litwicka, M., Schmieder, B., Berlicki, A., et al

Georgoulis, M., Rust, D., Bernasconi, P., & Schmieder, B. 2002, ApJ, 575, 506 Grubecka Litwicka, M., Schmieder, B., Berlicki, A., et al. 2016, A&A, 593, A32

2002
[6]

2019, A&A, 626, A33

Hansteen, V ., Ortiz, A., Archontis, V ., et al. 2019, A&A, 626, A33

2019
[7]

H., Archontis, V ., Pereira, T

Hansteen, V . H., Archontis, V ., Pereira, T. M. D., et al. 2017, ApJ, 839, 22

2017
[8]

D., & Cao, W

Hong, J., Ding, M. D., & Cao, W. 2017, ApJ, 838, 101

2017
[9]

D., Li, Y ., Fang, C., & Cao, W

Hong, J., Ding, M. D., Li, Y ., Fang, C., & Cao, W. 2014, ApJ, 792, 13

2014
[10]

D., & Hao, Q

Hong, J., Li, Y ., Ding, M. D., & Hao, Q. 2021, ApJ, 921, 50

2021
[11]

& Rouppe van der V oort, L

Joshi, J. & Rouppe van der V oort, L. H. M. 2022, A&A, 664, A72

2022
[12]

& Panos, B

Kleint, L. & Panos, B. 2022, Astronomy & Astrophysics, 657, 657

2022
[13]

2023, A&A, 677, A52

Krikova, K., Pereira, T., & Rouppe van der V oort, L. 2023, A&A, 677, A52

2023
[14]

2013, ApJ, 772, 90

Leenaarts, J., Pereira, T., Carlsson, M., Uitenbroek, H., & De Pontieu, B. 2013, ApJ, 772, 90

2013
[15]

R., Title, A

Lemen, J. R., Title, A. M., Akin, D. J., et al. 2012, Sol. Phys., 275, 17

2012
[16]

2025, A&A, 700, A214 Löfdahl, M

Litwicka, M., Berlicki, A., & Schmieder, B. 2025, A&A, 700, A214 Löfdahl, M. G., Hillberg, T., de la Cruz Rodríguez, J., et al. 2021, A&A, 653, A68

2025
[17]

2008, PASJ, 60, 60

Matsumoto, T., Kitai, R., Shibata, K., et al. 2008, PASJ, 60, 60

2008
[18]

Milkey, R. W. & Mihalas, D. 1974, ApJ, 192, 769 Müller, D., St. Cyr, O. C., Zouganelis, I., et al. 2020, A&A, 642, A1

1974
[19]

J., Freij, N., Reid, A., et al

Nelson, C. J., Freij, N., Reid, A., et al. 2017, ApJ, 845, 16 Nóbrega-Siverio, D., Cabello, I., Bose, S., et al. 2024, A&A, 686, A218

2017
[20]

2020, A&A, 633, 633

Ortiz, A., Hansteen, V ., Nóbrega-Siverio, D., & Rouppe van der V oort, L. 2020, A&A, 633, 633

2020
[21]

& Kleint, L

Panos, B. & Kleint, L. 2020, ApJ, 891, 17

2020
[22]

2007, A&A, 473, 279

Pariat, E., Schmieder, B., Berlicki, A., et al. 2007, A&A, 473, 279

2007
[23]

2013, ApJ, 778, 143

Pereira, T., Leenaarts, J., De Pontieu, B., Carlsson, M., & Uitenbroek, H. 2013, ApJ, 778, 143

2013
[24]

Pereira, T. M. D., Carlsson, M., De Pontieu, B., & Hansteen, V . 2015, ApJ, 806, 14 Rouppe van der V oort, L., De Pontieu, B., Carlsson, M., et al. 2020, A&A, 641, A146 Rouppe van der V oort, L., Rutten, R., & Vissers, G. 2016, A&A, 592, A100 Rouppe van der V oort, L. H. M., Joshi, J., & Krikova, K. 2024, A&A, 683, A190

2015
[25]

J., Vissers, G

Rutten, R. J., Vissers, G. J., Rouppe van der V oort, L., Sütterlin, P., & Vitas, N. 2013, in J. Phys. Conf. Ser., V ol. 440 (IOP), 012007 Sainz Dalda, A., Agrawal, A., De Pontieu, B., & Goši´c, M. 2024, ApJS, 271, 24 Sainz Dalda, A., de la Cruz Rodríguez, J., Hansteen, V ., De Pontieu, B., & Goši´c, M. 2026, ApJ, 997, 229

2013
[26]

B., Bjelksjö, K., Korhonen, T

Scharmer, G. B., Bjelksjö, K., Korhonen, T. K., Lindberg, B., & Petterson, B. 2003, in Proc. SPIE, V ol. 4853, Innovative Telescopes and Instrumentation for Solar Astrophysics, ed. S. L. Keil & S. V . Avakyan, 341–350

2003
[27]

B., Narayan, G., Hillberg, T., et al

Scharmer, G. B., Narayan, G., Hillberg, T., et al. 2008, ApJ, 689, L69

2008
[28]

B., Sliepen, G., Sinquin, J.-C., et al

Scharmer, G. B., Sliepen, G., Sinquin, J.-C., et al. 2024, A&A, 685, A32

2024
[29]

& Asensio Ramos, A

Socas-Navarro, H. & Asensio Ramos, A. 2021, A&A, 652, A78

2021
[30]

M., Elmore, D., et al

Socas-Navarro, H., Pillet, V . M., Elmore, D., et al. 2006, Sol. Phys., 235, 75 Soler Poquet, I., Díaz Baso, C., Rouppe van der V oort, L., & Vissers, G. 2025, A&A, 699, A54

2006
[31]

2016, ApJ, 824, 96 Van Noort, M., Rouppe van der V oort, L., & Löfdahl, M

Tian, H., Xu, Z., He, J., & Madsen, C. 2016, ApJ, 824, 96 Van Noort, M., Rouppe van der V oort, L., & Löfdahl, M. 2005, Sol. Phys., 228, 191

2016
[32]

2013, ApJ, 774, 32

Vissers, G., Rouppe van der V oort, L., & Rutten, R. 2013, ApJ, 774, 32

2013
[33]

2015, ApJ, 812, 11

Vissers, G., Rouppe van der V oort, L., Rutten, R., Carlsson, M., & De Pontieu, B. 2015, ApJ, 812, 11

2015
[34]

Watanabe, H., Vissers, G., Kitai, R., Rouppe van der V oort, L., & Rutten, R. J. 2011, ApJ, 736, 71

2011
[35]

2024, A&A, 689, A72 Article number, page 12 of 16 I

Zbinden, J., Kleint, L., & Panos, B. 2024, A&A, 689, A72 Article number, page 12 of 16 I. J. Soler Poquet et al.: IRIS NUV diagnostics for Ellerman bombs: spectral properties, thermodynamics, and formation height Appendix A: Observation details Figure A.1 shows images of different IRIS and SST diagnostics of the observations used in this work. Table A.1 s...

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