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

Jafarzadeh, S.; Solanki, S. K.; Feller, A.; Lagg, A.; Pietarila, A.; Danilović, S.; Riethmüller, T. L.; Pillet, V. Martı́nez

doi:10.1051/0004-6361/201220089

Cited by 60 publications

(96 citation statements)

References 88 publications

(156 reference statements)

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“…The observed velocities were as high as 7 km s −1 , average velocities were 1 km s −1 , and the BP lifetime was around 90 s. This study was extended to the upper photosphere/lower chromosphere using the Ca ii K core where delays were found in the motion of BPs between the two layers (Keys et al 2013) along with elevated velocities observed in Ca ii K BPs. A subsequent, independent study of SUNRISE data by Jafarzadeh et al (2013) found similar elevated velocities in Ca ii H BPs. Berger et al (1998) investigated quiet Sun and network BPs and found mean velocities of 1.1 km s −1 and 0.95 km s −1 , respectively.…”

Section: Introductionmentioning

confidence: 73%

Dynamic properties of bright points in an active region

Keys

Mathioudakis

Jess

et al. 2014

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Context. Bright points (BPs) are small-scale, magnetic features ubiquitous across the solar surface. Previously, we have observed and noted their properties for quiet Sun regions. Here, we determine the dynamic properties of BPs using simultaneous quiet Sun and active region data. Aims. The aim of this paper is to compare the properties of BPs in both active and quiet Sun regions and to determine any difference in the dynamics and general properties of BPs as a result of the varying magnetic activity within these two regions. Methods. High spatial and temporal resolution G-band observations of active region AR11372 were obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope. Three subfields of varying polarity and magnetic flux density were selected with the aid of magnetograms obtained from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Bright points within these subfields were subsequently tracked and analysed. Results. It is found that BPs within active regions display attenuated velocity distributions with an average horizontal velocity of ∼0.6 km s −1 , compared to the quiet region which had an average velocity of 0.9 km s −1 . Active region BPs are also ∼21% larger than quiet region BPs and have longer average lifetimes (∼132 s) than their quiet region counterparts (88 s). No preferential flow directions are observed within the active region subfields. The diffusion index (γ) is estimated at ∼1.2 for the three regions. Conclusions. We confirm that the dynamic properties of BPs arise predominately from convective motions. The presence of stronger field strengths within active regions is the likely reason behind the varying properties observed. We believe that larger amounts of magnetic flux will attenuate BP velocities by a combination of restricting motion within the intergranular lanes and by increasing the number of stagnation points produced by inhibited convection. Larger BPs are found in regions of higher magnetic flux density and we believe that lifetimes increase in active regions as the magnetic flux stabilises the BPs.

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Section: Introductionmentioning

confidence: 73%

Dynamic properties of bright points in an active region

Keys

Mathioudakis

Jess

et al. 2014

A&A

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“…This gives us confidence that these MBPs are good tracers of small-scale magnetic elements in the upper layers of the photosphere and the lower chromosphere. These intrinsically magnetic features can be considered to represent the cross-sections of nearly vertical flux tubes (Jafarzadeh 2013) whose positions are influenced by different external forces and are restricted to intergranular lanes. Therefore, although they are not perfect tracers of the horizontal flows, the spatial and temporal scaling of the MBPs' dynamics can still indicate the presence of turbulence in their paths (Lawrence et al 2001).…”

Section: Discussionmentioning

confidence: 99%

“…These MBPs have a mean lifetime of 673 ± 9 s, when measured only for those MBPs whose birth and death times are observable within the course of the time series and inside the images field of view (Jafarzadeh et al 2013). The observed lifetime was found to be 461 ± 9 s on average when all MBPs are considered.…”

Section: Trajectoriesmentioning

confidence: 99%

“…The MBPs under study are located in the quiet-Sun internetwork areas sampled at a height corresponding roughly to the temperature minimum. In particular, we track the motion of these small and intrinsically magnetic features (Jafarzadeh et al 2013, hereafter Paper I) in time series of filtergrams and calculate their trajectories. We compute the sd for each trajectory and measure the corresponding power exponent (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Migration of Ca II H bright points in the internetwork

Jafarzadeh

Cameron

Solanki

et al. 2014

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Context. The migration of magnetic bright point-like features (MBP) in the lower solar atmosphere reflects the dispersal of magnetic flux as well as the horizontal flows of the atmospheric layer they are embedded in.Aims. We analyse trajectories of the proper motion of intrinsically magnetic, isolated internetwork Ca ii H MBPs (mean lifetime 461± 9 s) to obtain their diffusivity behaviour. Methods. We use seeing-free high spatial and temporal resolution image sequences of quiet-Sun, disc-centre observations obtained in the Ca ii H 3968 Å passband of the Sunrise Filter Imager (SuFI) onboard the Sunrise balloon-borne solar observatory. Small MBPs in the internetwork are automatically tracked. The trajectory of each MBP is then calculated and described by a diffusion index (γ) and a diffusion coefficient (D). We also explore the distribution of the diffusion indices with the help of a Monte Carlo simulation. Results. We find γ = 1.69 ± 0.08 and D = 257 ± 32 km 2 s −1 averaged over all MBPs. Trajectories of most MBPs are classified as super-diffusive, i.e. γ > 1, with the determined γ being the largest obtained so far to our knowledge. A direct correlation between D and timescale (τ) determined from trajectories of all MBPs is also obtained. We discuss a simple scenario to explain the diffusivity of the observed, relatively short-lived MBPs while they migrate within a small area in a supergranule (i.e. an internetwork area). We show that the scatter in the γ values obtained for individual MBPs is due to their limited lifetimes. Conclusions. The super-diffusive MBPs can be described as random walkers (due to granular evolution and intergranular turbulence) superposed on a large systematic (background) velocity, caused by granular, mesogranular, and supergranular flows.

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“…Investigations of Stokes profiles observed with Hinode/SP by Orozco et al (2007) and Lites et al (2008) suggest that the magnetic fields in internetwork regions are inclined predominantly horizontally with an average inclination angle of 20 • to the horizontal. However a study of bright points in Ca ii H images observed using SUNRISE/SuFI, which have a mean area close to 0.01 Mm 2 (nearly 100 times smaller than a typical granule), by Jafarzadeh et al (2013) suggests that these magnetic elements in the internetwork regions are predominantly oriented vertically (Jafarzadeh et al 2014b). For a comprehensive review on this topic we refer to Borrero et al (2015, and the references cited therein).…”

Section: Introductionmentioning

confidence: 99%

Statistical evolution of quiet-Sun small-scale magnetic features using Sunrise observations

Anusha¹,

Solanki²,

Hirzberger³

et al. 2017

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The evolution of small magnetic features in quiet regions of the Sun provides a unique window to probing solar magnetoconvection. Here we analyze small scale magnetic features in the quiet Sun, using the high resolution, seeing-free observations from the Sunrise balloon borne solar observatory. Our aim is to understand the contribution of different physical processes, such as splitting, merging, emergence and cancellation of magnetic fields to the rearrangement, addition and removal of magnetic flux in the photosphere. We employ a statistical approach for the analysis and the evolution studies are carried out using a feature tracking technique. In this paper we provide a detailed description of the feature tracking algorithm that we have newly developed and we present the results of a statistical study of several physical quantities. The results on the fractions of the flux in the emergence, appearance, splitting, merging, disappearance and cancellation qualitatively agrees with other recent studies (see e.g., Lamb et al. 2008Lamb et al. , 2013. To summarize, the total flux gained in unipolar appearance is an order of magnitude larger than the total flux gained in emergence. On the other hand, the bi-polar cancellation contributes nearly an equal amount to the loss of magnetic flux as unipolar disappearance. The total flux lost in cancellation is nearly 6 − 8 times larger than the total flux gained in emergence. One big difference between our study and previous similar studies is that thanks to the higher spatial resolution of Sunrise we can track features with fluxes as low as 9 × 10 14 Mx. This flux is nearly an order of magnitude lower than the smallest fluxes of the features tracked in the highest resolution previous studies based on Hinode data. The area and flux of the magnetic features follow power-law type distribution, while the lifetimes show either power-law or exponential type distribution depending on the exact definitions used to define various birth and death events. We also statistically determine the evolution of the flux within the features in the course of their lifetime, finding that this evolution depends very strongly on the birth and death process that the features undergo.

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

Cited by 60 publications

References 88 publications

Dynamic properties of bright points in an active region

Dynamic properties of bright points in an active region

Migration of Ca II H bright points in the internetwork

Statistical evolution of quiet-Sun small-scale magnetic features using Sunrise observations

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