Resonant Absorption of Surface Sausage and Surface Kink Modes under Photospheric Conditions

Yu, Dae Jung; Doorsselaere, Tom Van; Goossens, Marcel

doi:10.3847/1538-4357/aa9223

Cited by 22 publications

(59 citation statements)

References 62 publications

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“…Such energy structuring can be attributed to the presence of surface (pores 2, 3 and 4) and body (pores 1 and 5) mode waves, which have only recently been conclusively observed in photospheric imaging data [21]. Previous identifications of surface mode waves have come from theoretical estimations [17,18,58,59]. However, here we clearly show the existence of heightened wave energy towards the edges of the pore boundaries, which has only been made possible by the high spectral, spatial and temporal resolutions of our dataset coupled with modern spectropolarimetric inversion routines.…”

Section: Discussionmentioning

confidence: 99%

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: Discussionmentioning

confidence: 99%

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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“…External gas pressure enhancement -Requires β > 1 in the external medium which is not suitable for a coronal investigation. However, this may represent a flux tube located within the lower layers of the solar atmosphere (see, for example, Yu et al 2017). 2.…”

Section: Methodsmentioning

confidence: 99%

“…However, a radial gradient in the magnetic field strength can also provide the non-constant Alfvén speed profile that is required for a resonant layer to exist. To this end, many studies have demonstrated the mode conversion of MHD waves in the presence of a non-uniform magnetic field (see, for example, Ruderman & Erdélyi 2009;Antolin et al 2015;Giagkiozis et al 2016;Yu et al 2017;Howson et al 2017a). However, in the majority of previous studies, the magnetic field is simply a function of radial position and does not vary along the length of the magnetic structure.…”

Section: Introductionmentioning

confidence: 99%

Resonant absorption in expanding coronal magnetic flux tubes with uniform density

Howson

Moortel

Antolin

et al. 2019

A&A

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Aims. We investigate the transfer of energy between a fundamental standing kink mode and azimuthal Alfvén waves within an expanding coronal magnetic flux tube. We consider the process of resonant absorption in a loop with a non-uniform Alfvén frequency profile but in the absence of a radial density gradient. Methods. Using the three dimensional MHD code, Lare3d, we modelled a transversely oscillating magnetic flux tube that expands radially with height. An initially straight loop structure with a magnetic field enhancement was allowed to relax numerically towards a force-free state before a standing kink mode was introduced. The subsequent dynamics, rate of wave damping and formation of small length scales are considered.Results. We demonstrate that the transverse gradient in Alfvén frequency required for the existence of resonant field lines can be associated with the expansion of a high field-strength flux tube from concentrated flux patches in the lower solar atmosphere. This allows for the conversion of energy between wave modes even in the absence of the transverse density profile typically assumed in wave heating models. As with standing modes in straight flux tubes, small scales are dominated by the vorticity at the loop apex and by currents close to the loop foot points. The azimuthal Alfvén wave exhibits the structure of the expanded flux tube and is therefore associated with smaller length scales close to the foot points of the flux tube than at the loop apex. Conclusions. Resonant absorption can proceed throughout the coronal volume, even in the absence of visible, dense, loop structures. The flux tube and MHD waves considered are difficult to observe and our model highlights how estimating hidden wave power within the Sun's atmosphere can be problematic. We highlight that, for standing modes, the global properties of field lines are important for resonant absorption and coronal conditions at a single altitude will not fully determine the nature of MHD resonances. In addition, we provide a new model in partial response to the criticism that wave heating models cannot self-consistently generate or sustain the density profile upon which they typically rely.

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“…Some previous studies of pore oscillations (Grant et al 2015;Moreels et al 2015a;Freij et al 2016) infer the surface/body characteristics of sausage modes using a combination of semiempirical models, theory, and the derived parameters of the modes from observations. Understanding the surface and body properties, however, is crucial in determining how energy is dissipated by modes in higher regions (Yu et al 2017b). Here, for the first time to our knowledge, we present conclusive, direct evidence for the existence of surface and body modes in photospheric pores supporting sausage modes.…”

Section: Introductionmentioning

confidence: 49%

“…As properties such as magnetic field and density vary rapidly from a pore to its surroundings, pores should support surface and body modes. Recent theoretical work (Yu et al 2017a(Yu et al , 2017b showed that resonant damping of slow surface sausage modes could be efficient under conditions usually observed in pores. Some previous studies of pore oscillations (Grant et al 2015;Moreels et al 2015a;Freij et al 2016) infer the surface/body characteristics of sausage modes using a combination of semiempirical models, theory, and the derived parameters of the modes from observations.…”

Section: Introductionmentioning

confidence: 99%

Photospheric Observations of Surface and Body Modes in Solar Magnetic Pores.

Keys

Morton

Jess

et al. 2019

Preprint

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Over the past number of years, great strides have been made in identifying the various low-order magnetohydrodynamic wave modes observable in a number of magnetic structures found within the solar atmosphere. However, one aspect of these modes that has remained elusive, until now, is their designation as either surface or body modes. This property has significant implications for how these modes transfer energy from the waveguide to the surrounding plasma. Here, for the first time to our knowledge, we present conclusive, direct evidence of these wave characteristics in numerous pores that were observed to support sausage modes. As well as outlining methods to detect these modes in observations, we make estimates of the energies associated with each mode. We find surface modes more frequently in the data, as well as that surface modes appear to carry more energy than those displaying signatures of body modes. We find frequencies in the range of ∼2-12mHz, with body modes as high as 11mHz, but we do not find surface modes above 10mHz. It is expected that the techniques we have applied will help researchers search for surface and body signatures in other modes and in differing structures from those presented here.

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Resonant Absorption of Surface Sausage and Surface Kink Modes under Photospheric Conditions

Cited by 22 publications

References 62 publications

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

Magnetoacoustic wave energy dissipation in the atmosphere of solar pores

Resonant absorption in expanding coronal magnetic flux tubes with uniform density

Photospheric Observations of Surface and Body Modes in Solar Magnetic Pores.

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