Analysis of quiet-sun turbulence on the basis of SDO/HMI and Goode Solar Telescope data

TL;DR

This study analyzes quiet-sun turbulence using SDO/HMI and Goode Solar Telescope data, revealing consistent magnetic power spectra across different solar regions and insights into the mechanisms of magnetic field generation.

Contribution

It provides a comparative analysis of magnetic power spectra from different instruments and regions, highlighting the role of local turbulent dynamo in quiet-sun magnetic fields.

Findings

Magnetic power spectra exhibit a consistent spectral index of -1 across various quiet-sun regions.

The NIRIS spectrum extends to smaller scales with a slope of -1.2, then steepens to -2.2.

Kolmogorov turbulence accounts for less than 35% of magnetic energy in the studied scale range.

Abstract

We analysed line-of-sight magnetic fields and magnetic power spectra of an undisturbed photosphere using magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) on-board the Solar Dynamic Observatory (SDO) and the Near InfraRed Imaging Spectrapolarimeter (NIRIS) operating at the Goode Solar Telescope (GST) of the Big Bear Solar Observatory. In the NIRIS data revealed the presence of thin flux tubes of 200-400~km in diameter and of field strength of 1000-2000~G. The HMI power spectra determined for a coronal hole, a quiet sun and a plage areas exhibit the same spectral index of -1 on a broad range of spatial scales from 10-20~Mm down to 2.4~Mm. This implies that the same mechanism(s) of magnetic field generation operate everywhere in the undisturbed photosphere. The most plausible one is the local turbulent dynamo. When compared to the HMI spectra, the -1.2 slope of the NIRIS spectrum appears to be more extended into the short spatial range until the cutoff at 0.8-0.9~Mm, after which it continues with a steeper slope of -2.2. Comparison of the observed and Kolmogorov-type spectra allowed us to infer that the Kolmogorov turbulent cascade cannot account for more than 35\% of the total magnetic energy observed in the scale range of 3.5-0.3~Mm. The energy excess can be attributed to other mechanisms of field generation such as the local turbulent dynamo and magnetic super-diffusivity observed in an undisturbed photosphere that can slow down the rate of the Kolmogorov cascade leading to a shallower resulting spectrum.