Magnetic Fields of Solar Active Regions

Wang, Jingxiu

doi:10.1017/s1743921304005034

“…One therefore ends up with an extensive list of combinations like fast kink body modes and slow sausage surface modes 1 . In the structured solar corona, there have been ample observations for modes pertaining to a substantial fraction of these combinations (see the reviews by e.g., Banerjee et al 2007;Nakariakov et al 2016;Wang 2016). In particular, the ubiquity of radial fundamental kink modes has enabled one to seismologically construct the spatial distributions of the magnetic field strength in a substantial portion of some active region (AR, Anfinogentov & Nakariakov 2019) or even across several ARs (Yang et al 2020).…”

Section: Introductionmentioning

confidence: 99%

“…For this purpose, we further assume that l/R and kR are known. Note that it is non-trivial to evaluate the electric resistivity (η) in a photospheric medium (e.g., Wang 1993;Khomenko & Collados 2012;Ni et al 2016). Nonetheless, one can rather safely assume that the resulting R m lies in the range pertaining to the shaded area in Figure 2, given that this range encompasses the rather extreme values of the waveguide radius (R).…”

mentioning

confidence: 99%

“…As such, only the Ohmic resistivity due to electron-neutral and electron-ion collisions was addressed. In reality, the Cowling resistivity due to ion-neutral collisions may be substantially stronger (e.g., Wang 1993, Figure 1). A detailed study on the effects of the Cowling resistivity on photospheric modes is certainly warranted, but is nonetheless left for a future work.…”

mentioning

confidence: 99%

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Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities

Chen

¹

,

Li

²

,

Doorsselaere

³

et al. 2021

ApJ

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Given the recent interest in magnetohydrodynamic (MHD) waves in pores and sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by modeling solar photospheric waveguides with a cylindrical inhomogeneity comprising a uniform interior, a uniform exterior, and a continuous transition layer (TL) in between. Performing an eigen-mode analysis in linear, resistive, gravity-free MHD, our approach is idealized in that, among other things, our equilibrium is structured only in the radial direction. We can nonetheless address two damping mechanisms simultaneously, one being the Ohmic resistivity, and the other being the resonant absorption of SSKMs in the cusp and Alfvén continua. We find that the relative importance of the two mechanisms depends sensitively on the magnetic Reynolds number (R m ). Resonant absorption is the sole damping mechanism for realistically large values of R m , and the cusp resonance in general dominates the Alfvén one unless the axial wavenumbers are at the lower end of the observationally relevant range. We also find that the thin-boundary approximation holds only when the TL-width-to-radius ratios are much smaller than nominally expected. The Ohmic resistivity is far more important for realistically small R m . Even in this case, SSKMs are only marginally damped, with damping-time-to-period-ratios reaching ∼ 10 in the parameter range we examine.

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“…Ohm's law including ambipolar diffusion was previously derived (Cowling 1957;Braginskii 1965;Kubat & Karlicky 1986). Electric conductivity including ambipolar diffusion was also calculated in the solar atmosphere by Kubat & Karlicky (1986), Wang (1993) and Khomenko & Collados (2012), and its effect was studied in the context of Sweet-Parker magnetic reconnection (Ni et al 2007), as well as the plasma heating and electric current decay (Khomenko & Collados 2012). Among these calculations of electric conductivity, the work of Kubat & Karlicky (1986) appears to be the most comprehensive.…”

Section: Introductionmentioning

confidence: 99%

Electric resistivity of partially ionized plasma in the lower solar atmosphere

Chae

¹

,

Litvinenko

²

2021

Res. Astron. Astrophys.

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The lower solar atmosphere is a gravitationally stratified layer of partially ionized plasma. We calculate the electric resistivity in the solar photosphere and chromosphere, which is the key parameter that controls the rate of magnetic reconnection in a Sweet-Parker current sheet. The calculation takes into account the collisions between ions and hydrogen atoms as well as the electron-ion collisions and the electron-hydrogen atom collisions. We find that under the typical conditions of the quiet Sun, electric resistivity is determined mostly by the electron-hydrogen atom collisions in the photosphere, and mostly by the ion-hydrogen collisions, i.e. ambipolar diffusion, in the chromosphere. In magnetic reconnection events with strong magnetic fields, the ambipolar diffusion, however, may be insignificant because the heating by the reconnection itself may lead to the full ionization of hydrogen atoms. We conclude that ambipolar diffusion may be the most important source of electric resistivity responsible for the magnetic flux cancelation and energy release in chromospheric current sheets that can keep a significant fraction of neutral hydrogen atoms.

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“…One therefore ends up with an extensive list of combinations like fast kink body modes and slow sausage surface modes 1 . In the structured solar corona, there have been ample observations for modes pertaining to a substantial fraction of these combinations (see the reviews by e.g., Banerjee et al 2007;Nakariakov et al 2016;Wang 2016). In particular, the ubiquity of radial fundamental kink modes has enabled one to seismologically construct the spatial distributions of the magnetic field strength in a substantial portion of some active region (AR, Anfinogentov & Nakariakov 2019) or even across several ARs (Yang et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Damping of slow surface kink modes in solar photospheric waveguides modeled by one-dimensional inhomogeneities

Chen,

Li,

Van Doorsselaere

et al. 2020

Preprint

0

View full text Add to dashboard Cite

Given the recent interest in magnetohydrodynamic (MHD) waves in pores and sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by modeling solar photospheric waveguides with a cylindrical inhomogeneity comprising a uniform interior, a uniform exterior, and a continuous transition layer (TL) in between. Performing an eigen-mode analysis in linear, resistive, gravity-free MHD, our approach is idealized in that, among other things, our equilibrium is structured only in the radial direction. We can nonetheless address two damping mechanisms simultaneously, one being the Ohmic resistivity, and the other being the resonant absorption of SSKMs in the cusp and Alfvén continua. We find that the relative importance of the two mechanisms depends sensitively on the magnetic Reynolds number (R m ). Resonant absorption is the sole damping mechanism for realistically large values of R m , and the cusp resonance in general dominates the Alfvén one unless the axial wavenumbers are at the lower end of the observationally relevant range. We also find that the thin-boundary approximation holds only when the TL-width-to-radius ratios are much smaller than nominally expected. The Ohmic resistivity is far more important for realistically small R m . Even in this case, SSKMs are only marginally damped, with damping-time-to-period-ratios reaching ∼ 10 in the parameter range we examine.

show abstract

Magnetic Fields of Solar Active Regions

Cited by 5 publications

References 46 publications

Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities

Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities

Electric resistivity of partially ionized plasma in the lower solar atmosphere

Damping of slow surface kink modes in solar photospheric waveguides modeled by one-dimensional inhomogeneities

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