Solar supergranulation revealed by granule tracking

Rieutord, M.; Meunier, N.; Roudier, T.; Rondi, S.; Beigbeder, F.; Parès, L.

doi:10.1051/0004-6361:20079077

Cited by 48 publications

(50 citation statements)

References 12 publications

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“…This change in the peak wavelength does not seem to be an artefact of the smaller field. Indeed, reducing the field on the data of Rieutord et al (2008) to a size comparable to that of the present data, one still obtains a value of 36.4 Mm. The difference seems to result from an intrinsic variability.…”

Section: Horizontal Velocity Fieldssupporting

confidence: 49%

“…Dynamical features at larger scales like the supergranulation pattern are much less understood. Supergranulation is characterised by a horizontal velocity field spanning scales from 15 Mm to 75 Mm according to the recent work of Rieutord et al (2008). Despite several attempts, supergranulation has not been identified in large-eddy or direct numerical simulations (e.g.…”

Section: Introductionmentioning

confidence: 99%

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On the power spectrum of solar surface flows

Rieutord

Roudier

Rincon

et al. 2010

A&A

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113

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Context. The surface of the Sun provides us with a unique and very detailed view of turbulent stellar convection. Studying its dynamics can therefore help us make significant progress in stellar convection modelling. Many features of solar surface turbulence like the supergranulation are still poorly understood. Aims. The aim of this work is to give new observational constraints on these flows by determining the horizontal scale dependence of the velocity and intensity fields, as represented by their power spectra, and to offer some theoretical guidelines to interpret these spectra. Methods. We use long time-series of images taken by the Solar Optical Telescope (SOT) on board the Hinode satellite; we reconstruct both horizontal (by granule tracking) and vertical (by Doppler effect) velocity fields in a field-of-view of ∼ 75×75 Mm 2 . The dynamics in the subgranulation range can be investigated with unprecedented precision thanks to the absence of seeing effects and the use of the modulation transfer function of SOT for correcting the spectra. Results. At small subgranulation scales down to 0.4 Mm the spectral density of kinetic energy associated with vertical motions exhibits a k −10/3 -like power law, while the intensity fluctuation spectrum follows either a k −17/3 or a k −3 -like power law at the two continuum levels investigated (525 and 450 nm respectively). We discuss the possible physical origin of these scalings and interpret the combined presence of k −17/3 and k −10/3 power laws for the intensity and vertical velocity as a signature of buoyancy-driven turbulent dynamics in a strongly thermally diffusive regime. In the mesogranulation range and up to a scale of 25 Mm, we find that the amplitude of the vertical velocity field decreases like λ −3/2 with the horizontal scale λ. This behaviour corresponds to a k 2 spectral power law. Still in the 2.5-10 Mm mesoscale range, we find that intensity fluctuations in the blue continuum also follow a k 2 power law. In passing we show that granule tracking cannot sample scales below 2.5 Mm. We finally further confirm the presence of a significant supergranulation energy peak at 30 Mm in the horizontal velocity power spectrum and show that the emergence of a pore erases this spectral peak. We tentatively estimate the scale height of the vertical velocity field in the supergranulation range and find 1 Mm; this value suggests that supergranulation flows are shallow.

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Section: Horizontal Velocity Fieldssupporting

confidence: 49%

Section: Introductionmentioning

confidence: 99%

On the power spectrum of solar surface flows

Rieutord

Roudier

Rincon

et al. 2010

A&A

Self Cite

113

View full text Add to dashboard Cite

show abstract

“…Supergranulation is readily identified in time-averaged Doppler images (e.g., Hathaway et al 2000), by tracking the motions of individual granules (e.g., Rieutord et al 2008), or by using the correlation between the Ca ii K network and the convergent flow boundaries (e.g., Berrilli et al 1998). The characteristic cell sizes reported depend somewhat on the identification technique employed, ranging from 15 Mm (DeRosa & Toomre 2004) to 25 Mm (Hirzberger et al 2008) or 35 Mm , and may vary with the solar cycle (Berrilli et al 1999;Meunier et al 2008).…”

Section: Introductionmentioning

confidence: 99%

The Intensity Profile of the Solar Supergranulation

Goldbaum¹,

Rast²,

Ermolli³

et al. 2009

ApJ

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We have measured the average radial (cell center to network boundary) profile of the continuum intensity contrast associated with supergranular flows using data from the Precision Solar Photometric Telescope at the Mauna Loa Solar Observatory. After removing the contribution of the network flux elements by the application of masks based on Ca ii K intensity and averaging over more than 10 5 supergranular cells, we find a ∼0.1% decrease in red and blue continuum intensity from the supergranular cell centers outward, corresponding to a ∼1.0 K decrease in brightness temperature across the cells. The radial intensity profile may be caused either by the thermal signal associated with the supergranular flows or a variation in the packing density of unresolved magnetic flux elements. These are not unambiguously distinguished by the observations, and we raise the possibility that the network magnetic fields play an active role in supergranular scale selection by enhancing the radiative cooling of the deep photosphere at the cell boundaries.

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“…The main focus of this work is to present a new method for the treatment of the advection of solar supergranulation by giant cells, which is a large-scale analogue to the observation of granule advection by supergranules (Rieutord et al 2008). Our underlying goal is to provide the methodology for computing more detailed models that allow the exploration of the effects of a giant cell component on simulated supergranulation patterns in conjunction with empirical data.…”

Section: Discussionmentioning

confidence: 99%

“…Previous observations of supergranules have revealed a large array of properties, including (1) their size, shape and their coincidence with the chromospheric network (Simon & Leighton 1964;Küveler 1983); (2) their flow speeds (Küveler 1983;Hathaway et al 2002); and (3) their advection of granules (Rieutord et al 2008). Their Doppler signal also exhibits a superrotation characteristic with respect to the underlying plasma Duvall (1980).…”

Section: Introductionmentioning

confidence: 99%

A method for the treatment of supergranulation advection by giant cells

Williams¹,

Cuntz²

2009

A&A

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Aims. We present a new method for the treatment of the advection of solar supergranulation by giant cells, a large-scale analogue to the observed property of granule advection by supergranules. Methods. The proposed method is derived from a description of solar convection via spherical harmonics and spectral coefficients, allowing the investigation of the influence of a giant cell component on a realistic supergranule signal. Results. We show that a supergranule pattern derived from real data, as well as a simplified test signal, can be advected by a giant cell component of various sizes. Conclusions. The identified behaviour is in analogy to observed supergranulation patterns, including those based on MDI Dopplergrams, which show wavelike supergranulation patterns, even after the removal of the geometric projection effect. Our method is an important step towards the construction of future models involving supergranule flow patterns advected by a giant cell flow. Nevertheless, additional efforts are required to obtain a final verification of giant cells as a separate component of the solar photospheric convection spectrum.

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Solar supergranulation revealed by granule tracking

Cited by 48 publications

References 12 publications

On the power spectrum of solar surface flows

On the power spectrum of solar surface flows

The Intensity Profile of the Solar Supergranulation

A method for the treatment of supergranulation advection by giant cells

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