Families of fragmenting granules and their relation  to meso– and supergranular flow fields

Roudier, Th.; Lignières, F.; Rieutord, M.; Brandt, Peter; Malherbe, Jean-Marie

doi:10.1051/0004-6361:20030988

Cited by 57 publications

(68 citation statements)

References 17 publications

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“…All Fourier components such that ω/k ≤ V = 6 km s −1 are retained so as to keep only convective motion (Title et al 1989). To detect TFGs, granules were labeled in time as described in Roudier et al (2003).…”

Section: Observations and Data Reductionmentioning

confidence: 99%

Mesoscale dynamics on the Sun's surface from HINODE observations

Roudier¹,

Rieutord

Brito

et al. 2009

A&A

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Aims. The interactions of velocity scales on the Sun's surface, from granulation to supergranulation are still not understood, nor are their interaction with magnetic fields. We thus aim at giving a better description of dynamics in the mesoscale range which lies between the two scales mentioned above. Methods. We analyse a 48 h high-resolution time sequence of the quiet Sun photosphere at the disk center obtained with the Solar Optical Telescope onboard Hinode. The observations, which have a field of view of 100 × 100 , typically contain four supergranules. We monitor in detail the motion and evolution of granules as well as those of the radial magnetic field.Results. This analysis allows us to better characterize Trees of Fragmenting Granules issued from repeated fragmentation of granules, especially their lifetime statistics. Using floating corks advected by measured velocity fields, we show their crucial role in the advection of the magnetic field and in the build up of the network. Finally, thanks to the long duration of the time series, we estimate that the turbulent diffusion coefficient induced by horizontal motion is approximately 430 km 2 s −1 .Conclusions. These results demonstrate that the long living families contribute to the formation of the magnetic network and suggest that supergranulation could be an emergent length scale building up as small magnetic elements are advected and concentrated by TFG flows. Our estimate for the magnetic diffusion associated with this horizontal motion might provide a useful input for mean-field dynamo models.

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Section: Observations and Data Reductionmentioning

confidence: 99%

Mesoscale dynamics on the Sun's surface from HINODE observations

Roudier¹,

Rieutord

Brito

et al. 2009

A&A

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“…The white-light images were used to study horizontal motions of granules in the full 46 × 75 FOV by means of a local Numerous centres of diverging horizontal motions, of average size of 3 , caused mostly by expansion and splitting of granules and commonly associated with mesogranules (Roudier et al 2003;Roudier & Muller 2004), are present in the whole field outside the sunspot. In this paper we call them "rosettas", a term that has been used by several authors like Sobotka et al (1999) or Roudier et al (2002).…”

Section: Motions Of Granules In the Surroundings Of The Sunspotmentioning

confidence: 99%

“…If some of these granules split again, more and more granules are labelled by the same number and form a family. This technique is described in detail by Roudier et al (2003). In total, 269 families living longer than 1 h were detected in the field of view: 131 in the moat (defined in Sect.…”

Section: Families Of Granules In the Surroundings Of The Sunspotmentioning

confidence: 99%

“…The area of the family is the total area covered, in the segmented image, by the granules belonging to the family. Roudier et al (2003) suggested that the long-lived families are fundamental in structuring the horizontal velocity field in the quiet granulation. The collective action of splitting granules generates diverging flows that, after averaging in time, are detected by LCT in the form of mesogranules.…”

Section: Families Of Granules In the Surroundings Of The Sunspotmentioning

confidence: 99%

“…In addition to this systematic drift, granules exhibit local horizontal motions, mostly related to splitting and expansion. In the quiet photosphere far from sunspots, repeatedly splitting granules produce long-lived structures called "families of granules" (Kawaguchi 1980;Roudier et al 2003). Using a feature-tracking technique, the latter authors found that a significant fraction of granules are organized in the form of spatio-temporal "trees of fragmenting granules," equivalent to families of repeatedly splitting granules, originating from a single granule at the beginning.…”

Section: Introductionmentioning

confidence: 99%

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Phase diversity restoration of sunspot images

Bonet¹,

Márquez

Müller

et al. 2005

A&A

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Abstract. Two time series, taken simultaneously in the G-band and in white-light, and corrected for telescope aberrations and turbulence perturbations using the method of phase diversity, are employed to study the motions of granules and G-band bright points (GBPs) in the moat of an old regular sunspot. Local correlation tracking and feature tracking have been utilized for this purpose. A large-scale radial outflow with a mean velocity of 0.51 km s −1 has been measured in the sunspot moat. Centres of diverging horizontal motions, identified with families of granules formed by repeatedly splitting granules, move away from the sunspot. Most of the GBPs in the moat also move outwards through radially orientated "channels" (confined between the borders of adjacent families) with velocities comparable to those of the adjacent granules. However, 6% of the GBPs move faster (>1.4 km s −1 ) than the neighbouring granules. GBPs in the moat are not regularly distributed but they are less frequent on its solar centre side.

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Structure and Evolution of Supergranulation from Local Helioseismology

Hirzberger¹,

Gizon²,

Solanki³

et al. 2008

Helioseismology, Asteroseismology, and MHD Connections

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Supergranulation is visible at the solar surface as a cellular pattern of horizontal outflows. Although it does not show a distinct intensity pattern, it manifests itself indirectly in, for example, the chromospheric network. Previous studies have reported significant differences in the inferred basic parameters of the supergranulation phenomenon. Here we study the structure and temporal evolution of a large sample of supergranules, measured by using local helioseismology and SOHO/MDI data from the year 2000 at solar activity minimum. Local helioseismology with f modes provides maps of the horizontal divergence of the flow velocity at a depth of about 1 Mm. From these divergence maps supergranular cells were identified by using Fourier segmentation procedures in two dimensions and in three dimensions (two spatial dimensions plus time). The maps that we analyzed contain more than 10 5 supergranular cells and more than 10 3 lifetime histories, which makes possible a detailed analysis with high statistical significance. We find that the supergranular cells have a mean diameter of 27.1 Mm. The mean lifetime is estimated to be 1.6 days from the measured distribution of lifetimes (three-dimensional segmentation), with a clear tendency for larger cells to live longer than smaller ones. The pair and mark correlation functions do not show pronounced features on scales larger than the typical cell size, which suggests purely random cell positions. The temporal histories of supergranular cells indicate a smooth evolution from their emergence and growth in the first half of their lives to their decay in the second half of their lives (unlike exploding granules, which reach their maximum size just before they fragment).

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Families of fragmenting granules and their relation to meso– and supergranular flow fields

Cited by 57 publications

References 17 publications

Mesoscale dynamics on the Sun's surface from HINODE observations

Mesoscale dynamics on the Sun's surface from HINODE observations

Phase diversity restoration of sunspot images

Structure and Evolution of Supergranulation from Local Helioseismology

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