Dynamics of the Solar Magnetic Network. II. Heating the Magnetized Chromosphere

Hasan, S. S.; Ballegooijen, A. A. van

doi:10.1086/587773

Cited by 90 publications

(109 citation statements)

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“…Recent observations of the chromospheric network are suggestive of Ca ii network grains associated with plasma with quasi-steady heating at heights between 0.5 and 1 Mm inside magnetic flux concentrations (Hasan & van Ballegooijen 2008). Let us now estimate the acoustic energy flux transported into the chromosphere through a single short duration pulse as has been treated in the present paper (the magnetic modes are almost incompressible and not efficient for heating the atmosphere).…”

Section: Discussionmentioning

confidence: 91%

“…This conclusion is emphasized by the fact that the values of Table 2 are temporal maxima: the temporal mean would be lower. In order to be compatible with the observed quasi-steady Ca emission the injection of energy needs to be in the form of sustained short duration pulses as argued by (Hasan & van Ballegooijen 2008) but these pulses could probably not maintain the maximum values of acoustic flux as quoted in Table 2.…”

Section: Discussionmentioning

confidence: 96%

“…They speculated that a well defined interface between the flux sheet and the ambient medium may act as an efficient source of acoustic waves to the surrounding plasma. In a later paper, Hasan & van Ballegooijen (2008) showed that the short period waves that are produced as a result of turbulent motions can be responsible for the heating of the network elements. Cally (2005Cally ( , 2007 provided magneto-acoustic-gravity dispersion relations for waves in a stratified atmosphere with a homogeneous, inclined magnetic field and discussed the process of mode transmission and mode conversion.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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

Vigeesh

Hasan

Steiner

2009

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“…However, the mechanisms by which these different energy fluxes are generated may be different. Hasan & van Ballegooijen (2008) argued that the heating in Ca ii H BPs, caused by weak shocks occurring at short time intervals (less than 100 s) in magnetic flux tubes, is in contrast with the long-period waves which are considered as the spicules driver (De Pontieu et al 2004). Also, by restricting ourselves to small BPs, we may be missing the magnetic features carrying the most energy into the upper atmosphere.…”

Section: Discussionmentioning

confidence: 99%

Structure and dynamics of isolated internetwork Ca II H bright points observed by SUNRISE

Jafarzadeh

Solanki

Feller

et al. 2013

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Aims. We aim to improve our picture of the low chromosphere in the quiet-Sun internetwork by investigating the intensity, horizontal velocity, size and lifetime variations of small bright points (BPs; diameter smaller than 0.3 arcsec) observed in the Ca ii H 3968 Å passband along with their magnetic field parameters, derived from photospheric magnetograms. Methods. Several high-quality time series of disc-centre, quiet-Sun observations from the Sunrise balloon-borne solar telescope, with spatial resolution of around 100 km on the solar surface, have been analysed to study the dynamics of BPs observed in the Ca ii H passband and their dependence on the photospheric vector magnetogram signal.Results. Parameters such as horizontal velocity, diameter, intensity and lifetime histograms of the isolated internetwork and magnetic Ca ii H BPs were determined. Mean values were found to be 2.2 km s −1 , 0.2 arcsec (≈150 km), 1.48 I Ca and 673 s, respectively. Interestingly, the brightness and the horizontal velocity of BPs are anti-correlated. Large excursions (pulses) in horizontal velocity, up to 15 km s −1 , are present in the trajectories of most BPs. These could excite kink waves travelling into the chromosphere and possibly the corona, which we estimate to carry an energy flux of 310 W m −2 , sufficient to heat the upper layers, although only marginally. Conclusions. The stable observing conditions of Sunrise and our technique for identifying and tracking BPs have allowed us to determine reliable parameters of these features in the internetwork. Thus we find, e.g., that they are considerably longer lived than previously thought. The large velocities are also reliable, and may excite kink waves. Although these wave are (marginally) energetic enough to heat the quiet corona, we expect a large additional contribution from larger magnetic elements populating the network and partly also the internetwork.

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“…Photospheric magnetic fields also cause an enhancement of the chromospheric emission, even if the underlying process may be a kind of wave propagation in the end (e.g., Hasan 2000;Rezaei et al 2007a;Beck et al 2008;Hasan & van Ballegooijen 2008;Khomenko et al 2008;Vigeesh et al 2009;Fedun et al 2011). The usage of velocity oscillations to estimate the energy content is in general also less direct than the use of the intensity spectrum.…”

Section: Introductionmentioning

confidence: 99%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2012

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Context. The energy source powering the solar chromosphere is still undetermined, but leaves its traces in observed intensities. Aims. We investigate the statistics of the intensity distributions as a function of the wavelength for Ca ii H and the Ca ii IR line at 854.2 nm to estimate the energy content in the observed intensity fluctuations. Methods. We derived the intensity variations at different heights of the solar atmosphere, as traced by the line wings and line cores of the two spectral lines. We converted the observed intensities to absolute energy units employing reference profiles calculated in non-local thermal equilibrium (NLTE). We also converted the intensity fluctuations to corresponding brightness temperatures assuming LTE. Results. The root-mean-square (rms) fluctuations of the emitted intensity are about 0.6 (1.2) W m −2 ster −1 pm −1 near the core of the Ca ii IR line at 854.2 nm (Ca ii H), corresponding to relative intensity fluctuations of about 20% (30%). For the line wing, we find rms values of about 0.3 W m −2 ster −1 pm −1 for both lines, corresponding to relative fluctuations below 5%. The relative rms values show a local minimum for wavelengths forming at a height of about 130 km, but otherwise increase smoothly from the wing to the core, i.e., from photosphere to chromosphere. The corresponding rms brightness temperature fluctuations are below 100 K for the photosphere and up to 500 K in the chromosphere. The skewness of the intensity distributions is close to zero in the outer line wing and positive throughout the rest of the line spectrum, owing to the frequent occurrence of high-intensity events. The skewness shows a pronounced local maximum at locations with photospheric magnetic fields for wavelengths in-between those of the line wing and the line core (z ≈ 150−300 km), and a global maximum at the very core (z ≈ 1000 km) for both magnetic and field-free locations. Conclusions. The energy content of the intensity fluctuations is insufficient to create a chromospheric temperature rise that would be similar to the one in most reference models of the solar atmosphere. The increase in the rms fluctuations with height indicates the presence of upwardly propagating acoustic waves of increasing oscillation amplitude. The intensity and temperature variations indicate that there is a clear increase in dynamical activity from photosphere towards the chromosphere, but the variations fall short of the magnitude predicted by fully dynamical chromospheric models by a factor of about five. The enhanced skewness between the photosphere and lower solar chromosphere at magnetic locations is indicative of a mechanism that acts solely on magnetized plasma.

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Dynamics of the Solar Magnetic Network. II. Heating the Magnetized Chromosphere

Cited by 90 publications

References 59 publications

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

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

Structure and dynamics of isolated internetwork Ca II H bright points observed by SUNRISE

The energy of waves in the photosphere and lower chromosphere

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