The Magnetic Response of the Solar Atmosphere to Umbral Flashes

Houston, Scott J.; Jess, D. B.; Ramos, A. Asensio; Grant, S. D. T.; Beck, C.; Norton, A. A.; Prasad, S. Krishna

doi:10.3847/1538-4357/aab366

Cited by 45 publications

(50 citation statements)

References 76 publications

(105 reference statements)

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“…The RMSE measured for the magnetic field increases with the length of the wavelength step, although no strong differences are found for wavelength samplings with δλ 85 mÅ. Even in the case of wavelength samplings that give the best results for the magnetic field during the UF, the error is about 200 G. This value is comparable to the magnetic field fluctuations attributed to UFs as reported by several authors (Joshi & de la Cruz Rodríguez 2018;Houston et al 2018).…”

Section: Discussionsupporting

confidence: 64%

Inversions of synthetic umbral flashes: a selection of wavelength sampling

Felipe

Pozuelo

2019

A&A

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Context. Imaging spectrographs are popular instruments used to obtain solar data. They record quasi-monochromatic images at selected wavelength positions. By scanning the spectral range of the line, it is possible to obtain bidimensional maps of the field-of-view with a moderate spectral resolution. Aims. In this work, we evaluate the quality of spectropolarimetric inversions obtained from various wavelength samplings during umbral flashes. Methods. We computed numerical simulations of nonlinear wave propagation in a sunspot and constructed synthetic Stokes profiles in the Ca ii 8542 Å line during an umbral flash using the NLTE code NICOLE. The spectral resolution of the Stokes profiles was downgraded to various cases with differences in the wavelength coverage. A large set of wavelength samplings was analyzed and the performance of the inversions was evaluated by comparing the inferred chromospheric temperature, velocity, and magnetic field with the actual values at the chromosphere of the numerical simulation.Results. The errors in the inverted results depend to a large extent on the location of the wavelength points across the profile of the line. The inferred magnetic field improves with the increase of the spectral resolution. In the case of velocity and temperature, low spectral resolution data produce a match of the inverted atmospheres with the actual values comparable to wavelength samplings with finer resolution, while providing a higher temporal cadence in the data acquisition.Conclusions. We validated the NLTE inversions of spectropolarimetric data from the Ca ii 8542 Å during umbral flashes, during which the atmosphere undergoes sudden dramatic changes due to the propagation of a shock wave. Our results favor the use of fine spectral resolution for analyses that focus on the inference of the magnetic field, whereas the estimation of temperature and velocity fluctuations can be performed with lower spectral resolution.

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Section: Discussionsupporting

confidence: 64%

Inversions of synthetic umbral flashes: a selection of wavelength sampling

Felipe

Pozuelo

2019

A&A

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“…Interestingly, the largest average ∆T (+19.6%) occurs at an optical depth of log 10 τ = −5, corresponding to an approximate geometric height of 1150 km (Maltby et al 1986), which is consistent with examinations of resonantly-amplified fast-mode shocks where Grant et al (2018) found the largest temperature perturbations to be within the range of −5.3 < log 10 τ < −4.6. With this in mind, the pixels we identify as 'active' have clear similarities to previously detected MHD shock phenomena, with characteristics related to the temperature and LOS velocity perturbations closely resembling the signatures synonymous with magnetoacoustic (e.g., Houston et al 2018) and fast-mode (Grant et al 2018) shocks. However, we can now employ the high-precision vector magnetic fields to further categorize the underlying shock behavior.…”

Section: Velocity and Temperature Changessupporting

confidence: 65%

“…The shaded regions indicate the spatially and temporally averaged standard deviations corresponding to offsets between the input and synthetic profiles. The confinement of the wavelengthdependent standard deviations (blue shaded regions in Figure 2) shows statistically a high degree of precision throughout the inversion process, something that is also highlighted by Houston et al (2018). Figure 3 displays the fractional uncertainties for the derived NICOLE parameters.…”

Section: Inversionsmentioning

confidence: 66%

“…where p is the plasma pressure (p = ρk B T /m p µ), k B is the Boltzmann constant, T is the temperature, m p is the mass of a proton, µ is the mean molecular weight (µ = 0.5), and γ is the adiabatic index. Here, an adiabatic index of γ = 1.12 ± 0.01 is utilized, which is consistent with the spectropolarimetric investigation of another chromospheric sunspot by Houston et al (2018). The mean entropy values for all 6964 pixels are displayed in the lower-right panel of Figure 9 as a function of optical depth.…”

Section: Shock Classificationmentioning

confidence: 75%

“…The weights across cycles relative to Stokes I/I c in Q/I c and U/I c were 0.2, 1, and 5, respectively, while in V /I c they were weighted the same as I/I c in each cycle. We apply such weights to Stokes Q/I c and U/I c to better constrain the transverse component of the magnetic field, since this is an important parameter in the classification of umbral shocks and dynamics (Houston et al 2018). The weighting of I/I c and V /I c was kept the same throughout as this resulted in the best overall fits across all Stokes profiles.…”

Section: Inversionsmentioning

confidence: 99%

See 2 more Smart Citations

Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks

Houston

Jess

Keppens

et al. 2020

ApJ

Self Cite

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The formation of shocks within the solar atmosphere remains one of the few observable signatures of energy dissipation arising from the plethora of magnetohydrodynamic waves generated close to the solar surface. Active region observations offer exceptional views of wave behavior and its impact on the surrounding atmosphere. The stratified plasma gradients present in the lower solar atmosphere allow for the potential formation of many theorized shock phenomena. In this study, using chromospheric Ca II 8542Å line spectropolarimetric data of a large sunspot, we examine fluctuations in the plasma parameters in the aftermath of powerful shock events that demonstrate polarimetric reversals during their evolution. Modern inversion techniques are employed to uncover perturbations in the temperatures, line-of-sight velocities, and vector magnetic fields occurring across a range of optical depths synonymous with the shock formation. Classification of these non-linear signatures is carried out by comparing the observationally-derived slow, fast, and Alfvén shock solutions to the theoretical Rankine-Hugoniot relations. Employing over 200 000 independent measurements, we reveal that the Alfvén (intermediate) shock solution provides the closest match between theory and observations at optical depths of log 10 τ = −4, consistent with a geometric height at the boundary between the upper photosphere and lower chromosphere. This work uncovers first-time evidence of the manifestation of chromospheric intermediate shocks in sunspot umbrae, providing a new method for the potential thermalization of wave energy in a range of magnetic structures, including pores, magnetic flux ropes, and magnetic bright points.

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The Fibre Resolved OpticAl and Near-Ultraviolet Czerny–Turner Imaging Spectropolarimeter (francis)

Jess,

Grant,

Bate

et al. 2023

Sol Phys

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The solar physics community is entering a golden era that is ripe with next-generation ground- and space-based facilities, advanced spectral inversion techniques, and realistic simulations that are becoming more computationally streamlined and efficient. With ever-increasing resolving power stemming from the newest observational telescopes, it becomes more challenging to obtain (near-)simultaneous measurements at high spatial, temporal and spectral resolutions, while operating at the diffraction limit of these new facilities. Hence, in recent years there has been increased interest in the capabilities integral field units (IFUs) offer towards obtaining the trifecta of high spatial, temporal and spectral resolutions contemporaneously. To date, IFUs developed for solar physics research have focused on mid-optical and infrared measurements. Here, we present an IFU prototype that has been designed for operation within the near-ultraviolet to mid-optical wavelength range, which enables key spectral lines (e.g., Ca ii H/K, H$\beta $ β , Sr ii, Na i D1/D2, etc.) to be studied, hence providing additional spectral coverage to the instrument suites developed to date. The IFU was constructed as a low-budget proof-of-concept for the upcoming $2\text{ m}$ 2 m class Indian National Large Solar Telescope and employs circular cross-section fibres to guide light into a Czerny–Turner configuration spectrograph, with the resulting spectra captured using a high quantum efficiency scientific CMOS camera. Mapping of each input fibre allows for the reconstruction of two-dimensional spectral images, with frame rates exceeding $20\text{ s}^{-1}$ 20 s − 1 possible while operating in a non-polarimetric configuration. Initial commissioning of the instrument was performed at the Dunn Solar Telescope, USA, during August 2022. The science verification data presented here highlights the suitability of fibre-fed IFUs operating at near-ultraviolet wavelengths for solar physics research. Importantly, the successful demonstration of this type of instrument paves the way for further technological developments to make a future variant suitable for upcoming ground-based and space-borne telescope facilities.

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The Magnetic Response of the Solar Atmosphere to Umbral Flashes

Cited by 45 publications

References 76 publications

Inversions of synthetic umbral flashes: a selection of wavelength sampling

Inversions of synthetic umbral flashes: a selection of wavelength sampling

Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks

The Fibre Resolved OpticAl and Near-Ultraviolet Czerny–Turner Imaging Spectropolarimeter (francis)

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