Intensity contrast of the average supergranule

Abstract

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 $\sim 10^4$ 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 $(7.8\pm 0.6)\times 10^{-4}$ (there is no corresponding feature in the line-of-sight magnetic field). This corresponds to a temperature perturbation of about $1.1\pm 0.1$ 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.

arXiv comment5 pages, 3 figures (plus appendix), accepted for publication in A&A

References in corpus (8)

• Observables Processing for the Helioseismic and Magnetic Imager Instrument on the Solar Dynamics Observatory
• Solar supergranulation as a wavelike phenomenon
• On the continuum intensity distribution of the solar photosphere
• Spatially resolved vertical vorticity in solar supergranulation using helioseismology and local correlation tracking
• The Intensity Profile of the Solar Supergranulation
• Helioseismic Investigation of Modeled and Observed Supergranule Structure
• Anisotropy of the solar network magnetic field around the average supergranule
• Understanding the Fe I Line Measurements Returned by the Helioseismic and Magnetic Imager

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