The Quest to Understand Supergranulation and Large-Scale Convection in the Sun

Research output: Contribution to journalArticle

Abstract

Surface granulation of the Sun is primarily a consequence of thermal transport in the outer 1 % of the radius. Its typical scale of about 1 - 2 Mm is set by the balance between convection, free-streaming radiation, and the strong density stratification in the surface layers. The physics of granulation is well understood, as demonstrated by the close agreement between numerical simulation, theory, and observation. Superimposed on the energetic granular structure comprising high-speed flows, are larger-scale long-lived flow systems (≈ 300 m s-1) called supergranules. Supergranulation has a typical scale of 24 - 36 Mm. It is not clear if supergranulation results from the interaction of granules or is causally linked to deep convection or a consequence of magneto-convection. Other outstanding questions remain: how deep are supergranules? How do they participate in global dynamics of the Sun? Further challenges are posed by our lack of insight into the dynamics of larger scales in the deep convection region. Recent helioseismic constraints have suggested that convective-velocity amplitudes on large scales may be overestimated by an order of magnitude or more, implying that Reynolds stresses associated with large-scale convection, thought to play a significant role in the sustenance of differential rotation and meridional circulation, might be two orders of magnitude weaker than theory and computation predict. While basic understanding on the nature of convection on global scales and the maintenance of global circulations is incomplete, progress is imminent, given substantial improvements in computation, theory, and helioseismic inferences.

Original languageEnglish (US)
Pages (from-to)3403-3419
Number of pages17
JournalSolar Physics
Volume289
Issue number9
DOIs
StatePublished - 2014

Fingerprint

sun
convection
meridional circulation
Reynolds stress
stratification
surface layer
inference
free convection
physics
energetics
maintenance
surface layers
high speed
radii
radiation
simulation
interactions

Keywords

  • Helioseismology, direct modeling
  • Interior, convective zone
  • Waves, acoustic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The Quest to Understand Supergranulation and Large-Scale Convection in the Sun. / Hanasoge, Shravan; Sreenivasan, Katepalli.

In: Solar Physics, Vol. 289, No. 9, 2014, p. 3403-3419.

Research output: Contribution to journalArticle

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