<i>The Solar Chromosphere</i>

Bray, R. J.; Loughhead, R. E.; Chapman, Robert D.

doi:10.1063/1.3128990

Cited by 131 publications

(76 citation statements)

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“…The relevant equations can be found, e.g., in Mihalas & Toomre (1981, 1982 and in Bray & Loughhead (1974). See also Paper II.…”

Section: Wave Propagationmentioning

confidence: 99%

On acoustic and gravity waves in the solar photosphere and their energy transport

Kneer¹,

González

2011

A&A

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Aims. We study acoustic and atmospheric gravity waves in the quiet Sun to estimate their energy transport to the chromosphere. Methods. A two-dimensional time sequence from quiet Sun disc centre was analysed with simultaneous spectroscopic observations in Fe i 5576 Å and Fe i 5434 Å (both with Landé factor g = 0). We calculated response functions of the velocities for the line minimum shifts and atmospheric transmissions of waves for the two lines. For this, NLTE line formation in granular and intergranular model atmospheres from numerical simulations were performed. For the interpretation of the observed waves and for the estimates of energy fluxes, we assumed adiabatic propagation of plane waves in an isothermal model atmosphere. Fourier analyses of intensity and velocity fluctuations were carried out. They yield power, phase, and coherence as functions of frequency ν (from temporal Fourier transforms) and in the k h −ν plane (from three-dimensional transforms). The power spectra, together with the mass densities at velocity formation heights, give then the energy fluxes. Results. The rms velocities found here in the acoustic and gravity wave domains are lower by a factor ∼1.5 as in earlier work. We therefore admit a factor of 2 for an upward correction of the estimated fluxes. For acoustic waves we find: 1) upward propagating waves are present on the Sun with frequencies up to 14−15 mHz (periods U ≈ 70 s); 2) the approximation of plane adiabatic waves in an isothermal atmosphere appears adequate for estimating the energy fluxes; 3) the acoustic energy fluxes are in the same range as found in our earlier work from ground-based, two-dimensional spectroscopy, 1500−3100 W m −2 at an atmospheric height of ∼380 km and 1300−2700 W m −2 at 570 km. The energy flux carried by gravity waves is difficult to determine. We find: 1) phase and coherence spectra between continuum and velocity fluctuations show that convective overshoot and gravity waves are superimposed. We account for the convective flows using these coherence spectra. 2) At low frequencies, the vertical wavelength Λ z can be short ( 300 km), yielding large corrections for atmospheric transmissions (factors >100). We thus exclude from the flux estimates waves with |k z | > 20 Mm −1 and with vertical group velocities υ gr,z < 0.3 km s −1 . They are likely to be strongly reduced in amplitude by radiative damping. 3) With these caveats, the energy fluxes carried by gravity waves are found in the range of 4000−8200 W m −2 at 380 km and 700−1400 W m −2 at 570 km. Gravity waves thus also contribute to the energy transport into the chromosphere.

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“…The relevant equations can be found, e.g., in Mihalas & Toomre (1981, 1982 and in Bray & Loughhead (1974). See also Paper II.…”

Section: Wave Propagationmentioning

confidence: 99%

On acoustic and gravity waves in the solar photosphere and their energy transport

Kneer¹,

González

2011

A&A

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“…They are small-scale jet-like features of relatively cool and dense material located at the boundaries of supergranular cells, ejected from the lower chromosphere at speeds of about 10-40 km s −1 (Tsiropoula & Tziotziou 2004;Rouppe van der Voort et al 2007). A number of earlier studies suggest that bright and dark mottles correspond to phenomena in the lower and upper chromospheres, respectively (Bray 1969), while others believe that the difference in brightness indicates different parts of the same structure (Beckers 1968(Beckers , 1972Banos & Macris 1970;Bray & Loughhead 1974;Sterling et al 1993). Mottles are often considered as the disk representation of chromospheric spicules (Hansteen et al 2006;Rouppe van der Voort et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Transverse Oscillations in Chromospheric Mottles

Kuridze

Morton

Erdélyi

et al. 2012

ApJ

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A number of recent investigations have revealed that transverse waves are ubiquitous in the solar chromosphere. The vast majority of these have been reported in limb spicules and active region fibrils. We investigate long-lived, quiet-Sun, on-disk features such as chromospheric mottles (jet-like features located at the boundaries of supergranular cells) and their transverse motions. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope. The data set is comprised of simultaneous imaging in the Hα core, Ca ii K, and G band of an on-disk quiet-Sun region. Time-distance techniques are used to study the characteristics of the transverse oscillations. We detect over 40 transverse oscillations in both bright and dark mottles, with periods ranging from 70 to 280 s, with the most frequent occurrence at ∼165 s. The velocity amplitudes and transverse displacements exhibit characteristics similar to limb spicules. Neighboring mottles oscillating in-phase are also observed. The transverse oscillations of individual mottles are interpreted in terms of magnetohydrodynamic kink waves. Their estimated periods and damping times are consistent with phase mixing and resonant mode conversion.

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“…Using the full nonlinear expression for the energy flux, it is not easily possible to identify the amount of energy carried by the magnetic and acoustic waves. Following Bogdan et al (2003), we instead consider the wave flux using the expression given by Bray & Loughhead (1974) that represents the net transport of energy into the atmosphere:…”

Section: Energy Transportmentioning

confidence: 99%

Wave propagation and energy transport in the magnetic network of the Sun

Vigeesh

Hasan

Steiner

2009

A&A

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Aims. We investigate wave propagation and energy transport in magnetic elements, which are representatives of small scale magnetic flux concentrations in the magnetic network on the Sun. This is a continuation of earlier work by Hasan et al. (2005, ApJ, 631, 1270. The new features in the present investigation include a quantitative evaluation of the energy transport in the various modes and for different field strengths, as well as the effect of the boundary-layer thickness on wave propagation. Methods. We carry out 2D MHD numerical simulations of magnetic flux concentrations for strong and moderate magnetic fields for which β (the ratio of gas to magnetic pressure) on the tube axis at the photospheric base is 0.4 and 1.7, respectively. Waves are excited in the tube and ambient medium by a transverse impulsive motion of the lower boundary.Results. The nature of the modes excited depends on the value of β. Mode conversion occurs in the moderate field case when the fast mode crosses the β = 1 contour. In the strong field case the fast mode undergoes conversion from predominantly magnetic to predominantly acoustic when waves are leaking from the interior of the flux concentration to the ambient medium. We also estimate the energy fluxes in the acoustic and magnetic modes and find that in the strong field case, the vertically directed acoustic wave fluxes reach spatially averaged, temporal maximum values of a few times 10 6 erg cm −2 s −1 at chromospheric height levels. Conclusions. The main conclusions of our work are twofold: firstly, for transverse, impulsive excitation, flux tubes/sheets with strong fields are more efficient than those with weak fields in providing acoustic flux to the chromosphere. However, there is insufficient energy in the acoustic flux to balance the chromospheric radiative losses in the network, even for the strong field case. Secondly, the acoustic emission from the interface between the flux concentration and the ambient medium decreases with the width of the boundary layer.

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The Solar Chromosphere

Cited by 131 publications

References 0 publications

On acoustic and gravity waves in the solar photosphere and their energy transport

On acoustic and gravity waves in the solar photosphere and their energy transport

Transverse Oscillations in Chromospheric Mottles

Wave propagation and energy transport in the magnetic network of the Sun

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