Characterization of shock wave signatures at millimetre wavelengths from Bifrost simulations

Eklund, Henrik; Wedemeyer, Sven; Snow, Ben; Jess, D. B.; Jafarzadeh, S.; Grant, S. D. T.; Carlsson, Mats; Szydlarski, Mikołaj

doi:10.1098/rsta.2020.0185

Cited by 16 publications

(18 citation statements)

References 46 publications

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“…The dataset (also appeared in Wedemeyer et al [66] and Eklund et al [90]) samples a relatively quiet area at solar disc centre, with a few small network patches of opposite polarities, mostly located towards the top of the FOV, but also with some weaker magnetic patches located close to the centre of the FOV (as seen in the HMI magnetogram). These are observed as excess brightness temperatures in ALMA’s Band 3 images.…”

Section: Analysis and Resultsmentioning

confidence: 99%

An overall view of temperature oscillations in the solar chromosphere with ALMA

Jafarzadeh

Wedemeyer

Fleck

et al. 2020

Phil. Trans. R. Soc. A.

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By direct measurements of the gas temperature, the Atacama Large Millimeter/submillimeter Array (ALMA) has yielded a new diagnostic tool to study the solar chromosphere. Here, we present an overview of the brightness-temperature fluctuations from several high-quality and high-temporal-resolution (i.e. 1 and 2 s cadence) time series of images obtained during the first 2 years of solar observations with ALMA, in Band 3 and Band 6, centred at around 3 mm (100 GHz) and 1.25 mm (239 GHz), respectively. The various datasets represent solar regions with different levels of magnetic flux. We perform fast Fourier and Lomb–Scargle transforms to measure both the spatial structuring of dominant frequencies and the average global frequency distributions of the oscillations (i.e. averaged over the entire field of view). We find that the observed frequencies significantly vary from one dataset to another, which is discussed in terms of the solar regions captured by the observations (i.e. linked to their underlying magnetic topology). While the presence of enhanced power within the frequency range 3–5 mHz is found for the most magnetically quiescent datasets, lower frequencies dominate when there is significant influence from strong underlying magnetic field concentrations (present inside and/or in the immediate vicinity of the observed field of view). We discuss here a number of reasons which could possibly contribute to the power suppression at around 5.5 mHz in the ALMA observations. However, it remains unclear how other chromospheric diagnostics (with an exception of H α line-core intensity) are unaffected by similar effects, i.e. they show very pronounced 3-min oscillations dominating the dynamics of the chromosphere, whereas only a very small fraction of all the pixels in the 10 ALMA datasets analysed here show peak power near 5.5 mHz. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

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Section: Analysis and Resultsmentioning

confidence: 99%

An overall view of temperature oscillations in the solar chromosphere with ALMA

Jafarzadeh

Wedemeyer

Fleck

et al. 2020

Phil. Trans. R. Soc. A.

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“…In particular, Eklund et al [41] found signatures of shock-wave events in Band 3 (2.8–3.3 mm) observations from December 2016, coming to the conclusion that there are numerous small-scale dynamic structures with lifetimes of 43–360 s present in the ALMA field of view (FOV), with excess temperatures of more than 400 K and a correlation between their occurrence and the magnetic field strength. Characterization of such events at millimetre wavelengths has also been studied in detail from numerical simulations [42]. Nindos et al [40] presented a survey of transient brightenings with a mean lifetime of 51.1 s in ALMA Band 3 data observed in March 2017, which show light curves such that their origin is strongly suggested to be thermal, meaning that the observed brightness temperature variations are indeed caused by variations of the gas temperature and not other effects such as optical depth variations.…”

Section: Introductionmentioning

confidence: 99%

High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array

Gómez

Jafarzadeh

Wedemeyer

et al. 2020

Phil. Trans. R. Soc. A.

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We report detection of oscillations in brightness temperature, size and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e. 2 s cadence) with the Atacama large millimetre/ submillimetre array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ± 23 s, respectively. We find anti-correlations between perturbations in brightness, temperature and size of the three features, which suggest the presence of fast sausage-mode waves in these small structures. In addition, the detection of transverse oscillations (although with a larger uncertainty) may also suggest the presence of Alfvénic oscillations which are likely representative of kink waves. This work demonstrates the diagnostic potential of high-cadence observations with ALMA for detecting high-frequency magnetohydrodynamic waves in the solar chromosphere. Such waves can potentially channel a vast amount of energy into the outer atmosphere of the Sun. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

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“…We analyse coronal oscillations in the numerical simulation of magnetic enhanced network spanning from the upper convection zone to the corona (Carlsson et al 2016) using 3D radiation MHD code Bifrost (Gudiksen et al 2011). This simulation was previously used to analyse the oscillatory behaviour of chromospheric fibrils by Leenaarts & Carlsson (2015) and to study signatures of propagating shock waves by Eklund et al (2021).…”

Section: Numerical Modelmentioning

confidence: 99%

Excitation and evolution of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere

Kohutova

Popovas

2021

A&A

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Context. Solar coronal loops are commonly subject to oscillations. Observations of coronal oscillations are used to infer physical properties of the coronal plasma using coronal seismology. Aims. Excitation and evolution of oscillations in coronal loops is typically studied using highly idealised models of magnetic flux tubes. In order to improve our understanding of coronal oscillations, it is necessary to consider the effect of realistic magnetic field topology and evolution. Methods. We study excitation and evolution of coronal oscillations in three-dimensional (3D) self-consistent simulations of solar atmosphere spanning from the convection zone to the solar corona using the radiation-magnetohydrodynamic (MHD) code Bifrost. We use forward-modelled extreme-ultraviolet emission and 3D tracing of magnetic field to analyse the oscillatory behaviour of individual magnetic loops. We further analyse the evolution of individual plasma velocity components along the loops using wavelet power spectra to capture changes in the oscillation periods. Results. Various types of oscillations commonly observed in the corona are present in the simulation. We detect standing oscillations in both transverse and longitudinal velocity components, including higher-order oscillation harmonics. We also show that self-consistent simulations reproduce the existence of two distinct regimes of transverse coronal oscillations: rapidly decaying oscillations triggered by impulsive events and sustained small-scale oscillations showing no observable damping. No harmonic drivers are detected at the footpoints of oscillating loops. Conclusions. Coronal loop oscillations are abundant in self-consistent 3D MHD simulations of the solar atmosphere. The dynamic evolution and variability of individual magnetic loops suggest that we need to re-evaluate our models of monolithic and static coronal loops with constant lengths in favour of more realistic models.

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Characterization of shock wave signatures at millimetre wavelengths from Bifrost simulations

Cited by 16 publications

References 46 publications

An overall view of temperature oscillations in the solar chromosphere with ALMA

An overall view of temperature oscillations in the solar chromosphere with ALMA

High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array

Excitation and evolution of coronal oscillations in self-consistent 3D radiative MHD simulations of the solar atmosphere

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