Motions in the Sun at the Photospheric Level IV. The Equatorial Rotation and Possible Velocity Fields in the Photosphere

Hart, Abraham

doi:10.1093/mnras/114.1.17

Cited by 89 publications

(45 citation statements)

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“…Doppler imaging is the oldest technique used to monitor supergranulation (the first detection by Hart (1954) was on a Doppler signal). A SOHO/MDI view of supergranulation is shown in Figure 2.…”

Section: Dopplergramsmentioning

confidence: 99%

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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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Section: Dopplergramsmentioning

confidence: 99%

“…The story of supergranulation really started in Oxford when Avril B. Hart reported in 1953 the existence of a "noisy" fluctuating velocity field on top of the mean rotation speed of the solar equator that she was measuring (Hart, 1954). Actually, it is most probable that this "noise"was already detected as early as 1915 by Plaskett (1916).…”

Section: Introductionmentioning

confidence: 99%

The Sun’s Supergranulation

Rincon

Rieutord

2010

Living Rev. Solar Phys.

165

132

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“…The solar supergranulation was first observed by Hart (1954) as coherent banded velocity structures with length scales of approximately 75 Mm in line-of-sight Doppler measurements at the Sun's limb. Subsequent work (Leighton et al 1962;Simon & Leighton 1964) concluded that the signal observed by Hart corresponds to a surface-filling cellular pattern of horizontally diverging flows with diameters of approximately 30 Mm, flow speeds of ∼500 m s −1 , and lifetimes of ∼1 day.…”

Section: Introductionmentioning

confidence: 96%

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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“…Supergranulation was discovered by Hart (1954) using Doppler images of the Sun. It appeared as an essentially horizontal flow field at a typical scale of 30 Mm.…”

Section: Introductionmentioning

confidence: 99%

Solar supergranulation revealed by granule tracking

Rieutord

Meunier

Roudier

et al. 2008

A&A

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Context. Supergranulation is a pattern of the velocity field at the surface of the Sun, which has been known about for more than fifty years, however, no satisfactory explanation of its origin has been proposed. Aims. New observational constraints are therefore needed to guide theoretical approaches which hesitate between scenarios that either invoke a large-scale instability of the surface turbulent convection or a direct forcing by buoyancy. Methods. Using the 14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained a 7.5 h-long sequence of high resolution images with unprecedented field size. Tracking granules, we have determined the velocity field at the Sun's surface in great detail from a scale of 2.5 Mm up to 250 Mm. Results. The kinetic energy density spectrum shows that supergranulation peaks at 36 Mm and spans on scales ranging between 20 Mm and 75 Mm. The decrease of supergranular flows in the small scales is close to a k −2 -power law, steeper than the equipartition Kolmogorov one. The probability distribution function of the divergence field shows the signature of intermittency of the supergranulation and thus its turbulent nature.

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Motions in the Sun at the Photospheric Level IV. The Equatorial Rotation and Possible Velocity Fields in the Photosphere

Cited by 89 publications

References 0 publications

The Sun’s Supergranulation

The Sun’s Supergranulation

The Intensity Profile of the Solar Supergranulation

Solar supergranulation revealed by granule tracking

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