Diffusion of Magnetic Elements in a Supergranular Cell

Giannattasio, Fabio; Stangalini, M.; Berrilli, F.; Moro, D. Del; Rubio, L. R. Bellot

doi:10.1088/0004-637x/788/2/137

Cited by 36 publications

(71 citation statements)

References 36 publications

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“…From these two plots we can deduce that 1) the smaller the r 0 , the smaller the effective eddy diffusivity Δr 2 /τ for any τ; and 2) the smaller the r 0 , the smaller the value of the effective slope γ; in addition, there is a clear change in the trend for initial separation crossing the value r 0 ∼ 10 Mm, which roughly corresponds to the radius of the ROI. From an observational point of view, 1) and 2) could be interpreted by taking into account the recent results in Orozco Suárez et al (2012) and Giannattasio et al (2014). In those works, the authors showed that the horizontal velocity field within a supergranule is mostly radial and directed from the center to the boundaries.…”

Section: Resultsmentioning

confidence: 86%

Pair separation of magnetic elements in the quiet Sun

Giannattasio¹,

Berrilli²,

Biferale³

et al. 2014

A&A

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The dynamic properties of the quiet Sun photosphere can be investigated by analyzing the pair dispersion of small-scale magnetic fields (i.e., magnetic elements). By using 25 h-long Hinode magnetograms at high spatial resolution (0. 3), we tracked 68 490 magnetic element pairs within a supergranular cell near the disk center. The computed pair separation spectrum, calculated on the whole set of particle pairs independently of their initial separation, points out what is known as a super-diffusive regime with spectral index γ = 1.55 ± 0.05, in agreement with the most recent literature, but extended to unprecedented spatial and temporal scales (from granular to supergranular). Furthermore, for the first time, we investigated here the spectrum of the mean square displacement of pairs of magnetic elements, depending on their initial separation r 0 . We found that there is a typical initial distance above (below) which the pair separation is faster (slower) than the average. A possible physical interpretation of such a typical spatial scale is also provided.

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Section: Resultsmentioning

confidence: 86%

Pair separation of magnetic elements in the quiet Sun

Giannattasio¹,

Berrilli²,

Biferale³

et al. 2014

A&A

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“…Our internetwork γ value is larger than those reported in the literature. In addition to those mentioned above, examples of diffusion indices of internetwork magnetic features are γ=1 (Utz et al 2010), γ=0.96 (Manso Sainz et al 2011), γ=1.59 (Chitta et al 2012, γ=1.20-1.34 (for different length scales; Giannattasio et al 2013), γ=1.69 (PaperI), and γ=1.44 (Giannattasio et al 2014). We note that the γ value in PaperI was determined from migration of magnetic bright points in both internetwork and vicinity of network areas.…”

Section: Discussionmentioning

confidence: 98%

Kinematics of Magnetic Bright Features in the Solar Photosphere

Jafarzadeh¹,

Solanki²,

Cameron³

et al. 2017

ApJS

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Convective flows are known as the prime means of transporting magnetic fields on the solar surface. Thus, small magnetic structures are good tracers of turbulent flows. We study the migration and dispersal of magnetic bright features (MBFs) in intergranular areas observed at high spatial resolution with SUNRISE/IMaX. We describe the flux dispersal of individual MBFs as a diffusion process whose parameters are computed for various areas in the quiet-Sun and the vicinity of active regions from seeing-free data. We find that magnetic concentrations are best described as random walkers close to network areas (diffusion index, 1.0 g = ), travelers with constant speeds over a supergranule ( 1.9 2.0 g = -), and decelerating movers in the vicinity of flux emergence and/or within active regions ( 1.4 1.5 g = -). The three types of regions host MBFs with mean diffusion coefficients of 130 km 2 s −1 , 80-90 km 2 s −1 , and 25-70 km 2 s −1 , respectively. The MBFs in these three types of regions are found to display a distinct kinematic behavior at a confidence level in excess of 95%.

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“…2 was realized by computing the displacement of magnetic elements from the long-duration (∼25 h) data set acquired by Hinode-NFI (Kosugi et al 2007;Tsuneta et al 2008) and used in the analysis by Giannattasio et al (2013Giannattasio et al ( , 2014a. The spatial resolution of this data set is 0.…”

Section: Real Datamentioning

confidence: 99%

“…The tracking algorithm used for the two data sets is the same used in Giannattasio et al (2013Giannattasio et al ( , 2014a and presented in Del Moro (2004) and Berrilli et al (2005). These two data sets combined allow us to explore more consistently the time range from 5 s to 10 000 s. They consistently identify a superdiffusive behaviour (γ 1.4) in the overlapping time range 90 s ≤ t < 500 s. We stress that, to our knowledge, this is the first time that two data sets acquired with rather different instruments and at different sites agree on retrieving γ values consistent within the errors.…”

Section: Real Datamentioning

confidence: 99%

“…Wang & Sheeley 1993;Schrijver et al 1996;Berger et al 1998;Hagenaar et al 1999;Chae et al 2008;Abramenko et al 2011;Chitta et al 2012;Giannattasio et al 2013Giannattasio et al , 2014aJafarzadeh et al 2014) at all accessible spatiotemporal scales, ranging from granulation (diameter 1 Mm and lifetime few minutes; Muller 1999;Hirzberger et al 1999;Del Moro 2004) to super-granulation (diameter 30 Mm and lifetime a day; Raju et al 1999;Srikanth et al 2000;Del Moro et al 2004). …”

Section: Introductionmentioning

confidence: 99%

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Super-diffusion versus competitive advection: a simulation

Moro

Giannattasio

Berrilli

et al. 2015

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Context. Magnetic element tracking is often used to study the transport and diffusion of the magnetic field on the solar photosphere. From the analysis of the displacement spectrum of these tracers, it has recently been agreed that a regime of super-diffusivity dominates the solar surface. Quite habitually this result is discussed in the framework of fully developed turbulence. Aims. However, the debate whether the super-diffusivity is generated by a turbulent dispersion process, by the advection due to the convective pattern, or even by another process is still open, as is the question of the amount of diffusivity at the scales relevant to the local dynamo process. Methods. To understand how such peculiar diffusion in the solar atmosphere takes place, we compared the results from two different data sets (ground-based and space-borne) and developed a simulation of passive tracers advection by the deformation of a Voronoi network.Results. The displacement spectra of the magnetic elements obtained by the data sets are consistent in retrieving a super-diffusive regime for the solar photosphere, but the simulation also shows a super-diffusive displacement spectrum: its competitive advection process can reproduce the signature of super-diffusion. Conclusions. Therefore, it is not necessary to hypothesize a totally developed turbulence regime to explain the motion of the magnetic elements on the solar surface.

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Diffusion of Magnetic Elements in a Supergranular Cell

Cited by 36 publications

References 36 publications

Pair separation of magnetic elements in the quiet Sun

Pair separation of magnetic elements in the quiet Sun

Kinematics of Magnetic Bright Features in the Solar Photosphere

Super-diffusion versus competitive advection: a simulation

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