Solar supergranulation revealed by granule tracking

Abstract

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. Method: Using the 14-Mpixel CALAS camera at the Pic-du-Midi observatory, we obtained a 7.5h-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 2.5Mm up to 250Mm. Results: The kinetic energy density spectrum shows that supergranulation peaks at 36Mm and spans on scales ranging between 20Mm and 75Mm. 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.

4 pages, accepted in Astronomy and Astrophysics (Letters)

References in corpus (4)

• Solar supergranulation as a wavelike phenomenon
• Are granules good tracers of solar surface velocity fields?
• Tracking granules on the Sun's surface and reconstructing horizontal velocity fields: I. the CST algorithm
• Tracking granules at the Sun's surface and reconstructing velocity fields. II. Error analysis

Cited by in corpus (20)

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• On the power spectrum of solar surface flows
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• Stellar mixing length theory with entropy rain
• The Global Solar Dynamo
• Temporal power spectra of the horizontal velocity of the solar photosphere
• Quasi full-disk maps of solar horizontal velocities using SDO/HMI data
• Stochastic coupling of solar photosphere and corona
• Comparison of solar surface flows inferred from time--distance helioseismology and coherent structure tracking using HMI/SDO observations
• The Intensity Profile of the Solar Supergranulation
• Mesoscale dynamics on the Sun's surface from HINODE observations
• Helioseismic Investigation of Modeled and Observed Supergranule Structure
• Structure and evolution of solar supergranulation using SDO/HMI data
• Comparisons of Supergranule Characteristics During the Solar Minima of Cycles 22/23 and 23/24
• Solar supergranular fractal dimension dependence on the Solar cycle phase
• Iterative inversion of synthetic travel times successful at recovering sub-surface profiles of supergranular flows
• Strategies in seismic inference of supergranular flows on the Sun
• Texture of average solar photospheric flows and the donut-like pattern
• Observational characterisation of large-scale transport and horizontal turbulent diffusivity in the quiet Sun