The Scales of Granulation, Mesogranulation, and Supergranulation

Rast, Mark

doi:10.1086/381221

Cited by 119 publications

(118 citation statements)

References 89 publications

Supporting

Mentioning

114

Contrasting

Unclassified

Order By: Relevance

“…For instance, the spatial correlations between exploding granules may drive a large-scale instability injecting energy at supergranular scales (Rieutord et al 2000); another scenario suggests that granules impose fixed thermal flux boundary conditions, triggering a convection flow at scales larger than granulation (Rincon & Rieutord 2003). Rast (2003) suggested that interacting downwards flows cluster and produce the scale of meso or supergranules. The picture is further complicated by the results of Gizon et al (2003) and Schou (2003) who suggested that supergranulation was associated with a wave pattern; Rast et al (2004) and Lisle et al (2004), using a similar approach, however argued that the spectrum of supergranulation was instead consistent with two nonoscillatory flows identified with the mesogranular and supergranular scales having different rotation rates.…”

Section: Article Published By Edp Sciencesmentioning

confidence: 99%

Mesoscale dynamics on the Sun's surface from HINODE observations

Roudier¹,

Rieutord

Brito

et al. 2009

A&A

View full text Add to dashboard Cite

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.

show abstract

Section: Article Published By Edp Sciencesmentioning

confidence: 99%

Mesoscale dynamics on the Sun's surface from HINODE observations

Roudier¹,

Rieutord

Brito

et al. 2009

A&A

View full text Add to dashboard Cite

show abstract

“…In view of the results coming from high-resolution observations and numerical simulations of magnetoconvection, this time stability cannot not be interpreted as the stability of individual magnetic structures but the stability of the average properties. For example, a strong granular downdraft lives longer than the granules, and during its lifetime, it continuously advects magnetized plasma toward a specific point of the solar surface ( Rast 2003). Observed with low resolution, one would detect a magnetic patch that remains in place for a long period of time, despite the fact that it is formed by many small-scale short-lived magnetic structures that are continuously advected and engulfed by the downdraft.…”

Section: Time Lag Between Ir and Visible Data Setsmentioning

confidence: 99%

Quiet Sun Magnetic Fields from Simultaneous Inversions of Visible and Infrared Spectropolarimetric Observations

Cerdeña

Alméida

Kneer³

2006

ApJ

View full text Add to dashboard Cite

We study the quiet Sun magnetic fields using spectropolarimetric observations of the infrared and visible Fe i lines at 6301.5, 6302.5, 15648, and 15653 8. Magnetic field strengths and filling factors are inferred by the simultaneous fit of the observed Stokes profiles under the MISMA hypothesis. The observations cover an intranetwork region at the solar disk center. We analyze 2280 Stokes profiles whose polarization signals are above noise in the two spectral ranges, which correspond to 40% of the field of view. Most of these profiles can be reproduced only with a model atmosphere including three magnetic components with very different field strengths, which indicates the coexistence of kG and sub-kG fields in our 1B5 resolution elements. We measure an unsigned magnetic flux density of 9.6 G considering the full field of view. Half of the pixels present magnetic fields with mixed polarities in the resolution element. The fraction of mixed polarities increases as the polarization weakens. We compute the probability density function of finding each magnetic field strength. It has a significant contribution of kG field strengths, which concentrates most of the observed magnetic flux and energy. This kG contribution has a preferred magnetic polarity, while the polarity of the weak fields is balanced.

show abstract

“…From numerical experiments, Cattaneo et al (2001) concluded that mesogranules owe their origin to the interaction between granules, while Steiner (2003), also from numerical simulations, found recurrently fragmenting granules that drive a horizontal flow field of mesogranular scale. Similarly, Rast (2003) stated that a simple n-body simulation of the interaction of granular downflow plumes was successful at reproducing the observed spatial and temporal scales of both MG and supergranules. Roudier et al (2003) confirm the suggestions of Straus & Bonaccini (1997) and Rieutord et al (2000), that MG is not a "specific scale of convection" ... "but just the largescale extension of granulation".…”

Section: Introductionmentioning

confidence: 98%

Dynamics of solar mesogranulation

Leitzinger

Brandt

Hanslmeier

et al. 2005

A&A

View full text Add to dashboard Cite

Using a 45.5-h time series of photospheric flow fields generated from a set of high-resolution continuum images (SOHO/MDI) we analyze the dynamics of solar mesogranule features. The series was prepared applying a local correlation tracking algorithm with a 4.8 FWHM window. By computing 1-h running means in time steps of 10 min we generate 267 averaged divergence maps that are segmented to obtain binary maps. A tracking algorithm determines lifetimes and barycenter coordinates of regions of positive divergence defined as mesogranules (MGs). If we analyze features of lifetimes ≥1 h and of areas ≥5 Mm 2 we find a mean drift velocity of 304 m s −1 (with ±1σ variation of 180 m s −1 ), a mean travel distance of 2.5 ± 1.8 Mm, a mean lifetime of 2.6 ± 1.8 h, and a 1/e decay time of 1.6 h for a total of 2022 MGs. The advective motion of MGs within supergranules is seen for 50 to 70% of the long-lived (≥4 h) MGs while the short-lived ones move irregularly. If only the long-lived MGs are further analyzed the drift velocities reduce to 207 m s −1 and the travel distances increase to 4.1 Mm on average, which is an appreciable fraction of the supergranular radius. The results are largely independent of the divergence segmentation level.

show abstract

The Scales of Granulation, Mesogranulation, and Supergranulation

Cited by 119 publications

References 89 publications

Mesoscale dynamics on the Sun's surface from HINODE observations

Mesoscale dynamics on the Sun's surface from HINODE observations

Quiet Sun Magnetic Fields from Simultaneous Inversions of Visible and Infrared Spectropolarimetric Observations

Dynamics of solar mesogranulation

Contact Info

Product

Resources

About