Anisotropy of the solar network magnetic field around the average supergranule

Langfellner, Jan; Gizon, Laurent; Birch, A. C.

doi:10.1051/0004-6361/201526422

Cited by 13 publications

(19 citation statements)

References 15 publications

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“…This ring of higher cork density stands out more clearly than for the observed magnetic field. The observed network field is stronger on the west side of the average supergranule than on the east side, as we detected in our previous study (Langfellner et al 2015a) and as was later also found by Roudier et al (2016). This observation is successfully reproduced by the cork simulation (run #5).…”

Section: Cork Simulationsupporting

confidence: 88%

Evolution and wave-like properties of the average solar supergranule

Langfellner

Birch

Gizon

2018

A&A

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Context. Solar supergranulation presents us with many mysteries. For example, previous studies in spectral space found that supergranulation has wave-like properties. Aims. Here we study, in real space, the wave-like evolution of the average supergranule over a range of spatial scales (from 10 to 80 Mm). We complement this by characterizing the evolution of the associated network magnetic field. Methods. We use one year of data from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory to measure horizontal near-surface flows near the solar equator by applying time-distance helioseismology (TD) on Dopplergrams and granulation tracking (LCT) on intensity images. The average supergranule outflow (or inflow) is constructed by averaging over 10,000 individual outflows (or inflows). The contemporaneous evolution of the magnetic field is studied with HMI line-of-sight observations. Results. We confirm and extend previous measurements of the supergranular wave dispersion relation to angular wavenumbers in the range 50 < kR < 270. We find a plateau for kR > 120. In real space, larger supergranules undergo oscillations with longer periods and lifetimes than smaller cells. We find excellent agreement between TD and LCT and obtain wave properties that are independent of the tracking rate. The observed network magnetic field follows the oscillations of the supergranular flows with a six-hour time lag. This behavior can be explained by computing the motions of corks carried by the supergranular flows. Conclusions. Signatures of supergranular waves in surface horizontal flows near the solar equator can be observed in real space. These oscillatory flows control the evolution of the network magnetic field, in particular they explain the recently discovered eastwest anisotropy of the magnetic field around the average supergranule. Background flow measurements that we obtain from Doppler frequency shifts do not favor shallow models of supergranulation.

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Section: Cork Simulationsupporting

confidence: 88%

Evolution and wave-like properties of the average solar supergranule

Langfellner

Birch

Gizon

2018

A&A

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“…This is quite surprising because a detailed check of our data alignment did not show any drift, whereas the NE appears to rotate 6% faster. We observe, as Langfellner et al (2015), a greater presence of the NE in the western part (Fig. 16) of the supergranule.…”

Section: Link Between Horizontal Velocities and Magnetic Elementssupporting

confidence: 70%

“…The length scale (30 Mm) and lifetime (24 to 48 h) promote studies with low resolutions DeRosa & Toomre (2004). Statistical averaging over measurements of numerous supergranules (DeGrave & Jackiewicz 2015;Duvall et al 2014;Langfellner et al 2015) allows us to describe global characteristics, but it is difficult to identify the mechanism of supergranule formation because a correspondence between average quantities and the high temporal and spatial processes is missing.…”

Section: Discussionmentioning

confidence: 99%

Relation between trees of fragmenting granules and supergranulation evolution

Roudier

Malherbe

Rieutord

et al. 2016

A&A

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Context. The determination of the underlying mechanisms of the magnetic elements diffusion over the solar surface is still a challenge. Understanding the formation and evolution of the solar network (NE) is a challenge, because it provides a magnetic flux over the solar surface comparable to the flux of active regions at solar maximum. Aims. We investigate the structure and evolution of interior cells of solar supergranulation. From Hinode observations, we explore the motions on solar surface at high spatial and temporal resolution. We derive the main organization of the flows inside supergranules and their effect on the magnetic elements. Methods. To probe the superganule interior cell, we used the trees of fragmenting granules (TFG) evolution and their relations to horizontal flows. Results. Evolution of TFG and their mutual interactions result in cumulative effects able to build horizontal coherent flows with longer lifetime than granulation (1 to 2 h) over a scale up to 12 . These flows clearly act on the diffusion of the intranetwork (IN) magnetic elements and also on the location and shape of the network. Conclusions. From our analysis during 24 h, TFG appear as one of the major elements of the supergranules which diffuse and advect the magnetic field on the Sun's surface. The strongest supergranules contribute the most to magnetic flux diffusion in the solar photosphere.

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“…Here we extent the previous studies on the supergranular brightness excess: How does the convective intensity peak evolve? Does the intensity contrast show an east-west anisotropy, as the magnetic field (Langfellner et al 2015a) or wave travel times (DeGrave & Jackiewicz 2015)? To tackle these questions, we make use of high-quality data from the Helioseismic and Magnetic Imager (HMI) (Schou et al 2012) onboard the SDO spacecraft.…”

Section: Introductionmentioning

confidence: 99%

Intensity contrast of the average supergranule

Langfellner

Birch

Gizon

2016

A&A

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While the velocity fluctuations of supergranulation dominate the spectrum of solar convection at the solar surface, very little is known about the fluctuations in other physical quantities like temperature or density at supergranulation scale. Using SDO/HMI observations, we characterize the intensity contrast of solar supergranulation at the solar surface. We identify the positions of ∼10 4 outflow and inflow regions at supergranulation scales, from which we construct average flow maps and co-aligned intensity and magnetic field maps. In the average outflow center, the maximum intensity contrast is (7.8 ± 0.6) × 10 −4 (there is no corresponding feature in the line-of-sight magnetic field). This corresponds to a temperature perturbation of about 1.1 ± 0.1 K, in agreement with previous studies. We discover an east-west anisotropy, with a slightly deeper intensity minimum east of the outflow center. The evolution is asymmetric in time: the intensity excess is larger 8 hours before the reference time (the time of maximum outflow), while it has almost disappeared 8 hours after the reference time. In the average inflow region, the intensity contrast mostly follows the magnetic field distribution, except for an east-west anisotropic component that dominates 8 hours before the reference time. We suggest that the east-west anisotropy in the intensity is related to the wave-like properties of supergranulation.

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Anisotropy of the solar network magnetic field around the average supergranule

Cited by 13 publications

References 15 publications

Evolution and wave-like properties of the average solar supergranule

Evolution and wave-like properties of the average solar supergranule

Relation between trees of fragmenting granules and supergranulation evolution

Intensity contrast of the average supergranule

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