Magnetic flux structuring of the quiet Sun internetwork. Center-to-limb analysis of solar-cycle variations

TL;DR

This study analyzes the small-scale magnetic flux structures in the quiet Sun's internetwork regions over the solar cycle, revealing that a small-scale dynamo operates alongside the global dynamo, with variations depending on latitude and scale.

Contribution

It provides the first detailed analysis of solar-cycle and center-to-limb variations of internetwork magnetic flux structures using Hinode data and spectral analysis techniques.

Findings

Magnetic fluctuation power at small scales remains constant over the solar cycle.

Marginal increase in magnetic fluctuation power at certain scales during solar maximum at low/mid latitudes.

Decreases in magnetic fluctuation power at high latitudes during solar maximum.

Abstract

It is now well established that the quiet Sun contains in total more magnetic flux than active regions and represents an important reservoir of magnetic energy. But the nature and evolution of these fields remain largely unknown. We investigate the solar-cycle and center-to-limb variations of magnetic-flux structures at small scales in internetwork regions of the quiet Sun. We used Hinode SOT/SP data from the irradiance program between 2008 and 2016. Maps of the magnetic-flux density are derived from the center-of gravity method applied to the FeI 630.15 nm and FeI 630.25 nm lines. To correct the maps from the instrumental smearing, we applied a deconvolution method based on a principal component analysis of the line profiles and on a Richardson-Lucy deconvolution of their coefficients. We then performed a spectral analysis of the spatial fluctuations of the magnetic-flux density in 10'' x 10'' internetwork regions spanning a wide range of latitudes. At low and mid latitudes the power spectra do not vary significantly with the solar cycle. However at solar maximum for one scan in the activity belt showing an enhanced network, a marginal increase in the power of the magnetic fluctuations is observed at granular and larger scales in the internetwork. At high latitudes, we observe variations at granular and larger scales where the power decreases at solar maximum. At all the latitudes the power of the magnetic fluctuations at scales smaller than 0.5''remain constant throughout the solar cycle. Our results favor a small-scale dynamo that operates in the internetwork, but they show that the global dynamo also contributes to the internetwork fields.