Inversions of synthetic umbral flashes: a selection of wavelength sampling

Felipe, T.; Pozuelo, S. Esteban

doi:10.1051/0004-6361/201936679

Cited by 10 publications

(18 citation statements)

References 27 publications

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“…Figure 1 illustrates the development of UFs generated by a propagating wave at the beginning of the simulation. This case is qualitatively comparable to the synthetic UFs analyzed by Bard & Carlsson (2010), Felipe et al (2014Felipe et al ( , 2018a, and Felipe & Esteban Pozuelo (2019). We refer the reader to those papers for a detailed discussion of the formation of UFs.…”

Section: Umbral Flashes From Propagating Wavessupporting

confidence: 77%

“…Accommodating the downflowing UFs in the widely accepted scenario of upward propagating shock waves is a theoretical challenge. Studies employing sophisticated synthesis tools and numerical simulations of the umbral atmosphere have validated the upflowing UF model (Bard & Carlsson 2010;Felipe et al 2014Felipe et al , 2018aFelipe & Esteban Pozuelo 2019). In those simulations, magneto-acoustic waves can propagate from the photosphere to the chromosphere.…”

Section: Introductionmentioning

confidence: 99%

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Downflowing umbral flashes as evidence of standing waves in sunspot umbrae

Felipe

Henriques

Rodríguez

et al. 2021

A&A

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Context. Umbral flashes are sudden brightenings commonly visible in the core of some chromospheric lines. Theoretical and numerical modeling suggests that they are produced by the propagation of shock waves. According to these models and early observations, umbral flashes are associated with upflows. However, recent studies have reported umbral flashes in downflowing atmospheres. Aims. We aim to understand the origin of downflowing umbral flashes. We explore how the existence of standing waves in the umbral chromosphere impacts the generation of flashed profiles. Methods. We performed numerical simulations of wave propagation in a sunspot umbra with the code MANCHA. The Stokes profiles of the Ca II 8542 Å line were synthesized with the NICOLE code. Results. For freely propagating waves, the chromospheric temperature enhancements of the oscillations are in phase with velocity upflows. In this case, the intensity core of the Ca II 8542 Å atmosphere is heated during the upflowing stage of the oscillation. However, a different scenario with a resonant cavity produced by the sharp temperature gradient of the transition region leads to chromospheric standing oscillations. In this situation, temperature fluctuations are shifted backward and temperature enhancements partially coincide with the downflowing stage of the oscillation. In umbral flash events produced by standing oscillations, the reversal of the emission feature is produced when the oscillation is downflowing. The chromospheric temperature keeps increasing while the atmosphere is changing from a downflow to an upflow. During the appearance of flashed Ca II 8542 Å cores, the atmosphere is upflowing most of the time, and only 38% of the flashed profiles are associated with downflows. Conclusions. We find a scenario that remarkably explains the recent empirical findings of downflowing umbral flashes as a natural consequence of the presence of standing oscillations above sunspot umbrae.

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Section: Umbral Flashes From Propagating Wavessupporting

confidence: 77%

Section: Introductionmentioning

confidence: 99%

Downflowing umbral flashes as evidence of standing waves in sunspot umbrae

Felipe

Henriques

Rodríguez

et al. 2021

A&A

Self Cite

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“…The inverted magnetic field strengths were 1.4 kG, 1.4 kG, and 1.3 kG gauss for cases A, B, and C, respectively. tested by Felipe & Esteban Pozuelo (2019), for a slightly better sampling in wavelength selection around the core (55 mÅ versus 73 mÅ in this work). Some very bad fits contribute to the noise visible in the two-dimensional maps analysed.…”

Section: Inversion Resultsmentioning

confidence: 99%

Umbral chromospheric fine structure and umbral flashes modelled as one: The corrugated umbra

Henriques

Nelson

Voort

et al. 2020

A&A

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Context. The chromosphere of the umbra of sunspots features an assortment of dynamic fine structures that are poorly understood and often studied separately. Small-scale umbral brightenings (SSUBs), umbral microjets, spikes or short dynamic fibrils (SDFs), and umbral dark fibrils are found in any observation of the chromosphere with sufficient spatial resolution performed at the correct umbral flash stage and passband. Understanding these features means understanding the dynamics of the umbral chromosphere. Aims. We aim to fully understand the dynamics of umbral chromosphere through analysis of the relationships between distinct observed fine features and to produce complete models that explain both spectral profiles and the temporal evolution of the features. We seek to relate such understanding to umbral flashes. Methods. We studied the spatial and spectral co-evolution of SDFs, SSUBs, and umbral flashes in Ca II 8542 Å spectral profiles. We produced models that generate the spectral profiles for all classes of features using non-local thermodynamic equilibrium radiative transfer with a recent version of the NICOLE inversion code. Results. We find that both bright SSUBs and dark SDF structures are described with a continuous feature in the parameter space that is distinct from the surroundings even in pixel-by-pixel inversions. We find a phase difference between such features and umbral flashes in both inverted line-of-sight velocities and timing of the brightenings. For umbral flashes themselves we resolve, for the first time in inversion-based semi-empirical modelling, the pre-flash downflows, post-flash upflows, and the counter-flows present during the umbral flash phase. We further present a simple time-dependent cartoon model that explains the dynamics and spectral profiles of both fine structure, dark and bright, and umbral flashes in umbral chromospheres. Conclusions. The similarity of the profiles between the brightenings and umbral flashes, the pattern of velocities obtained from the inversions, and the phase relationships between the structures all lead us to put forward that all dynamic umbral chromospheric structures observed to this date are a locally delayed or locally early portion of the oscillatory flow pattern that generates flashes, secondary to the steepening large-scale acoustic waves at its source. Essentially, SSUBs are part of the same shock or merely compression front responsible for the spatially larger umbral flash phenomenon, but out of phase with the broader oscillation.

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“…Such an issue was investigated by Felipe et al [75,76] with synthetic Stokes spectra of the chromospheric 8542 Å line in the presence of umbral flashes. One study [75], focused on the effect of temporal resolution, while another [76] looked at the effect of spectral resolution. The authors find that fine spectral resolution ( δλ ≈ 80 m Å) is required for magnetic field inference, while line scanning within a time period of 16 s can result in inversion results being unreliable in the early stages of an umbral flash.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, the asymmetries induced by the upwardly propagating wave may be varied across the spectra due to this time lag. Such an issue was investigated by Felipe et al [75,76] with synthetic Stokes spectra of the chromospheric 8542 Å line in the presence of umbral flashes. One study [75], focused on the effect of temporal resolution, while another [76] looked at the effect of spectral resolution.…”

Section: (C) Comparison Of Model Parametersmentioning

confidence: 99%

On the effect of oscillatory phenomena on Stokes inversion results

Keys

Steiner

Vigeesh

2020

Phil. Trans. R. Soc. A.

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Stokes inversion codes are crucial in returning properties of the solar atmosphere, such as temperature and magnetic field strength. However, the success of such algorithms to return reliable values can be hindered by the presence of oscillatory phenomena within magnetic wave guides. Returning accurate parameters is crucial to both magnetohydrodynamics (MHD) studies and solar physics in general. Here, we employ a simulation featuring propagating MHD waves within a flux tube with a known driver and atmospheric parameters. We invert the Stokes profiles for the 6301 Å and 6302 Å line pair emergent from the simulations using the well-known Stokes Inversions from Response functions code to see if the atmospheric parameters can be returned for typical spatial resolutions at ground-based observatories. The inversions return synthetic spectra comparable to the original input spectra, even with asymmetries introduced in the spectra from wave propagation in the atmosphere. The output models from the inversions match closely to the simulations in temperature, line-of-sight magnetic field and line-of-sight velocity within typical formation heights of the inverted lines. Deviations from the simulations are seen away from these height regions. The inversions results are less accurate during passage of the waves within the line formation region. The original wave period could be recovered from the atmosphere output by the inversions, with empirical mode decomposition performing better than the wavelet approach in this task. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

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Inversions of synthetic umbral flashes: a selection of wavelength sampling

Cited by 10 publications

References 27 publications

Downflowing umbral flashes as evidence of standing waves in sunspot umbrae

Downflowing umbral flashes as evidence of standing waves in sunspot umbrae

Umbral chromospheric fine structure and umbral flashes modelled as one: The corrugated umbra

On the effect of oscillatory phenomena on Stokes inversion results

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