Motions of Isolated<i>G</i>‐Band Bright Points in the Solar Photosphere

Nisenson, P.; Ballegooijen, A. A. van; Wijn, A. G. de; Sütterlin, P.

doi:10.1086/368067

Cited by 71 publications

(105 citation statements)

References 33 publications

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“…Our internetwork features appear to live less long than (photospheric) network BPs which last on average 1080 s (Muller 1983), however, a comparable mean lifetime of 9.2 min for network GBPs was found by Nisenson et al (2003). In addition, we showed that the Ca ii H BPs move horizontally with an average speed of 2.2 km s −1 .…”

Section: Discussionmentioning

confidence: 46%

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

Jafarzadeh

Solanki

Feller

et al. 2013

A&A

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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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Section: Discussionmentioning

confidence: 46%

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

Jafarzadeh

Solanki

Feller

et al. 2013

A&A

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“…Such short duration motions are expected to be generated by the turbulent motion in the convectively unstable subsurface layers where the flux sheet is rooted. In terms of the analysis by Cranmer & van Ballegooijen (2005) of the kinematics of G-band bright points, this motion rather corresponds to a short, single step of their "random walk phase", for which these authors use a rms velocity of 0.89 km s −1 with a correlation time of bright-point motions of 60 s in accordance with the measurements of Nisenson et al (2003). The cases with higher velocities (see Table 2) would rather be representative of the "jump phase" for which Cranmer & van Ballegooijen (2005) use a velocity of 5 km s −1 with a duration of 20 s. This motion generates magnetoacoustic waves in the flux sheet.…”

Section: Methods and Boundary Conditionsmentioning

confidence: 97%

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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“…However, network time scales are well known to vary substantially in the range from min to many hours (e.g. Liu et al 1994;Muller 1994;Berger & Title 1996;Berger et al 1998;Nisenson et al 2003).…”

Section: Autocorrelation Analysismentioning

confidence: 99%

On the fine structure of the quiet solar Ca II K atmosphere

Tritschler

Schmidt

Uitenbroek³

et al. 2006

A&A

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Aims. We investigate the morphological, dynamical, and evolutionary properties of the internetwork and network fine structure of the quiet sun at disk centre.Methods. The analysis is based on a ∼6 h time sequence of narrow-band filtergrams centred on the inner-wing Ca ii K 2v reversal at 393.3 nm. To examine the temporal evolution of network and internetwork areas separately we employ a double-Gaussian decomposition of the mean intensity distribution. An autocorrelation analysis is performed to determine the respective characteristic time scales. In order to analyse statistical properties of the fine structure we apply image segmentation techniques. Results. The results for the internetwork are related to predictions derived from numerical simulations of the quiet sun. The average evolutionary time scale of the internetwork in our observations is 52 s. Internetwork grains show a tendency to appear on a mesh-like pattern with a mean cell size of ∼4-5 arcsec. Based on this size and the spatial organisation of the mesh we speculate that this pattern is related to the existence of photospheric downdrafts as predicted by convection simulations. The image segmentation shows that typical sizes of both network and internetwork grains are in the order of 1.6 arcsec.

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Motions of IsolatedG‐Band Bright Points in the Solar Photosphere

Cited by 71 publications

References 33 publications

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

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

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

On the fine structure of the quiet solar Ca II K atmosphere

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