Time-Dependent Suppression of Oscillatory Power in Evolving Solar Magnetic Fields

Prasad, S. Krishna; Jess, D. B.; Jain, Rekha; Keys, Peter H.

doi:10.3847/0004-637x/823/1/45

Cited by 9 publications

(11 citation statements)

References 47 publications

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“…Oscillations with similar velocity amplitudes, approximately 0.6 km s −1 , have been shown to be related to the presence of slow magnetoacoustic waves that propagate through multiple layers of the solar atmosphere [35]. Importantly, as can be seen in figure 4, the oscillations demonstrate reduced velocity amplitudes within the confines of the pore structures, where the root mean square (RMS) velocities are less than 100 m s 300-500 m s −1 in the surrounding quiet Sun, which are consistent with previous spectroscopic studies [36][37][38][39][40][41]. To investigate the plasma parameters associated with the detected wave activity, and subsequently evaluate the energy flux, it was imperative to undertake spectropolarimetric inversions of the Si I 10827 Å line.…”

Section: Analysis (A) Bisector Velocity Amplitudessupporting

confidence: 87%

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

Gilchrist-Millar

Jess

Grant

et al. 2020

Phil. Trans. R. Soc. A.

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The suitability of solar pores as magnetic wave guides has been a key topic of discussion in recent years. Here, we present observational evidence of propagating magnetohydrodynamic wave activity in a group of five photospheric solar pores. Employing data obtained by the Facility Infrared Spectropolarimeter at the Dunn Solar Telescope, oscillations with periods of the order of 5 min were detected at varying atmospheric heights by examining Si ɪ 10827 Å line bisector velocities. Spectropolarimetric inversions, coupled with the spatially resolved root mean square bisector velocities, allowed the wave energy fluxes to be estimated as a function of atmospheric height for each pore. We find propagating magnetoacoustic sausage mode waves with energy fluxes on the order of 30 kW m −2 at an atmospheric height of 100 km, dropping to approximately 2 kW m −2 at an atmospheric height of around 500 km. The cross-sectional structuring of the energy fluxes reveals the presence of both body- and surface-mode sausage waves. Examination of the energy flux decay with atmospheric height provides an estimate of the damping length, found to have an average value across all five pores of L d ≈ 268 km, similar to the photospheric density scale height. We find the damping lengths are longer for body mode waves, suggesting that surface mode sausage oscillations are able to more readily dissipate their embedded wave energies. This work verifies the suitability of solar pores to act as efficient conduits when guiding magnetoacoustic wave energy upwards into the outer solar atmosphere. 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 (A) Bisector Velocity Amplitudessupporting

confidence: 87%

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

Gilchrist-Millar

Jess

Grant

et al. 2020

Phil. Trans. R. Soc. A.

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“…A wide distribution of the inclination angles, from vertical to horizontal fields, were observed at chromospheric heights in the datasets under study. Furthermore, the p-mode oscillatory power in the high chromosphere can be suppressed by the presence of strong magnetic fields [17], which is the case in each of the eight datasets. Magneto-acoustic waves have also been shown to considerably dissipate their energy by the mid-chromosphere in small, vertical flux concentrations, such as pores, thus, they are much diminished by the high chromosphere [98][99][100][101].…”

Section: Discussionmentioning

confidence: 76%

“…There have only been a few studies focusing on the dominant frequencies of oscillations in the upper chromosphere. From narrow-band Hα line-core image sequences, Krishna Prasad et al [17] found that the oscillatory power of intensity fluctuations (in the high chromosphere), within an evolving active region, was greatly suppressed within the frequency range of 4-8 mHz (i.e. lack of dominant 3-min oscillations), with some increases found in the 2.7-4.0 mHz range, and a larger power enhancement at even lower frequencies (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…with considerably lower magnetic flux in the former), though their amplitudes, and thus their power, are reduced in the latter [10][11][12]. It has been shown that the power suppression (as well as its spatial extent) increases with the magnetic-field strength and/or geometric height [13][14][15][16][17]. Such power suppression in the high chromosphere, also known as 'magnetic shadows', are thought to be due to the interaction of p-mode oscillations with the embedded magnetic fields (i.e.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Despite being structurally simple, pores are still host to a range of both MHD waves and other dynamic processes (see, for example, Hirzberger et al 2002;Sobotka et al 2013;Freij et al 2014;Krishna Prasad et al 2016;Bharti et al 2020;Stangalini et al 2021). Numerous authors have reported on the confident detection of oscillations in a range of observed quantities within pores, including the measured inten-Send offprint requests to: c.nelson@qub.ac.uk sities (Freij et al 2016;Keys et al 2018), areas (Morton et al 2011;Dorotovič et al 2014;Grant et al 2015), and line-of-sight (LOS) velocities (Fujimura & Tsuneta 2009;Stangalini et al 2012;Cho et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Oscillations In The Line-of-Sight Magnetic Field Strength In A Pore Observed By The GREGOR Infrared Spectrograph (GRIS)

Nelson,

Campbell,

Mathioudakis

2021

Preprint

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Context. Numerous magnetohydrodynamic oscillations have been reported within solar pores over the past decades, including in line-of-sight (LOS) velocities, intensities, and magnetic field strengths. Aims. Our aim is to identify whether high-amplitude oscillations in the LOS magnetic field strength can be detected within a pore located in Active Region 12748 and to investigate which physical mechanisms could be responsible for them. Methods. A solar pore was observed on the 1st September 2019 using the GREGOR Infrared Spectrograph (GRIS) instrument for around one hour. Full-Stokes vectors were sampled in a 37 Å window containing the Fe i 15648.52 Å line (effective Landé g-factor of 3). The LOS magnetic field strength is inferred using the strong-field approximation (SFA). Additionally, the Stokes Inversion based on Response functions (SIR) code is used to gain a more complete understanding the physical properties of the solar atmosphere at the locations of these oscillations. Results. Oscillations of more than 100 G are observed in the LOS magnetic field in the period window between 600-1272 s at three localised (> 1 ′′2 ) regions. These oscillations have coherence across individual regions indicating that jitter cannot account for their occurrence. Longer-period amplitude variations, amplitudes over 200 G, are also detected but these have periods outside of the cone-of-influence. Numerical inversions confirm both oscillations in the LOS magnetic field strength at optical depths of around logτ 5000 =−0.5 (potentially caused by compression) and other effects (e.g., changes in the optical depth or the inclination of the magnetic field) may account for these changes. Conclusions. The oscillations in the separations of the Stokes-V lobes of the 15648.52 Å line appear to be solar in nature. Future work will be required to understand whether these are truly oscillations in the magnetic field strength at a specific depth in the solar atmosphere or whether other effects are responsible for these signatures.

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Time-Dependent Suppression of Oscillatory Power in Evolving Solar Magnetic Fields

Cited by 9 publications

References 47 publications

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

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

Oscillations In The Line-of-Sight Magnetic Field Strength In A Pore Observed By The GREGOR Infrared Spectrograph (GRIS)

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