Photospheric flows measured with TRACE II. Network formation

Krijger, J. M.; Roudier, Th.

doi:10.1051/0004-6361:20030387

Cited by 13 publications

(11 citation statements)

References 25 publications

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“…In the future it would be very useful to perform simulations such as the ones performed by Simon et al (2001) and Krijger & Roudier (2003) by including solar cycle variations of parameters such as the supergranulation size (see Sect. 4.2) in order to help to interpret these new results.…”

Section: Resultsmentioning

confidence: 99%

Statistical properties of magnetic structures: Their dependence on scale and solar activity

Meunier

2003

A&A

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Abstract.A long data set of MDI/SOHO full-disk magnetograms is analyzed in order to provide a large sample of network features as well as active regions associated with their magnetic properties (magnetic flux and magnetic flux density for example). The main objective of the paper is to study the variations of these properties along the solar cycle, and to compare the behavior of the magnetic features at various scales (covering three orders of magnitude in size). I also investigate the dependence of these properties on the activity level in their neighborhood and in the context of their global configuration on the solar disk. This study is important for a better understanding of the emergence and decay of active regions, as well as of the role of the network in the removal of the magnetic flux and in solar irradiance variations. The main results are as follows. (i) I observe a characteristic scale in the range 400-800 Mm 2 (close to the supergranular scale) below which the size and magnetic flux distributions are power laws down to 40 Mm 2 (corresponding to the range 3 × 10 19 -10 21 Mx). This scale increases from solar minimum to solar maximum. The shape of the distributions also suggests a strong similarity between small active regions (below the supergranular scale) and network patches. (ii) The North-South asymmetry in the number of structures, compatible with easier-to-detect leading structures in most cases, surprisingly exhibits a sign reversal for the weakest structures, suggesting a different origin, while the East-West asymmetry is compatible with a predominantly eastward inclination of magnetic flux tubes, including network structures and not only for emerging active regions as suggested by models. (iii) The dependence of the magnetic characterictics on the size of the structures is found to be variable with the activity level, the magnetic flux beeing more concentrated at solar maximum (especially for small features). Small-scale properties are also dependent on the proximity of an active region. The results also show a correlation between the number (or magnetic flux) of network structures and the sunspot cycle, with an amplitude larger than expected from previous results.

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Section: Resultsmentioning

confidence: 99%

Statistical properties of magnetic structures: Their dependence on scale and solar activity

Meunier

2003

A&A

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“…As far as the horizontal velocities are concerned, the tracking of magnetic network elements gives values around 350 m s -1 , close to the estimates derived from granule tracking (Lisle et al, 2000). Krijger and Roudier (2003) found that the chromospheric network is well reproduced by letting magnetic elements that are emerging be passively advected by the surface (supergranulation) flow field. These results suggest that the formation of the magnetic network is in some way related to the supergranulation flow.…”

Section: Supergranulation and The Magnetic Networkmentioning

confidence: 98%

The Sun’s Supergranulation

Rincon

Rieutord

2010

Living Rev. Solar Phys.

165

132

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The Sun's supergranulation refers to a physical pattern covering the surface of the quiet Sun with a typical horizontal scale of approximately 30,000 km and a lifetime of around 1.8 d. Its most noticeable observable signature is as a fluctuating velocity field of 360 m s -1 rms whose components are mostly horizontal. Supergranulation was discovered more than fifty years ago, however explaining why and how it originates still represents one of the main challenges of modern solar physics.A lot of work has been devoted to the subject over the years, but observational constraints, conceptual difficulties and numerical limitations have all concurred to prevent a detailed understanding of the supergranulation phenomenon so far. With the advent of 21st century supercomputing resources and the availability of unprecedented high-resolution observations of the Sun, a stage at which key progress can be made has now been reached. A unifying strategy between observations and modelling is more than ever required for this to be possible.The primary aim of this review is therefore to provide readers with a detailed interdisciplinary description of past and current research on the problem, from the most elaborate observational strategies to recent theoretical and numerical modelling efforts that have all taken up the challenge of uncovering the origins of supergranulation. Throughout the text, we attempt to pick up the most robust findings so far, but we also outline the difficulties, limitations and open questions that the community has been confronted with over the years.In the light of the current understanding of the multiscale dynamics of the quiet photosphere, we finally suggest a tentative picture of supergranulation as a dynamical feature of turbulent magnetohydrodynamic convection in an extended spatial domain, with the aim of stimulating future research and discussions.

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“…Rieutord et al 2000;Krijger & Roudier 2003). The quality of the data (free of atmospheric seeing) and the length of the time sequence allow us to provide a very clear illustration of this phenomenon.…”

Section: Corks and Magnetic Fieldsmentioning

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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Photospheric flows measured with TRACE II. Network formation

Cited by 13 publications

References 25 publications

Statistical properties of magnetic structures: Their dependence on scale and solar activity

Statistical properties of magnetic structures: Their dependence on scale and solar activity

The Sun’s Supergranulation

Mesoscale dynamics on the Sun's surface from HINODE observations

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