Dynamics of multi-cored magnetic structures in the quiet Sun

TL;DR

This study investigates the dynamic behavior of multi-cored magnetic structures in the quiet Sun, revealing how granular convection influences flux tube evolution and causes magnetic oscillations driven by granular motions.

Contribution

It provides high-resolution observational evidence that granular flows drive the intensification, fragmentation, and coalescence of magnetic flux tubes in the quiet Sun.

Findings

Flux tubes evolve as a single entity over 23 minutes.

Granular flows cause flux tube intensification and splitting.

Magnetic oscillations are driven by granular motions, not intrinsic flux tube modes.

Abstract

We report on the dynamical interaction of quiet-Sun magnetic fields and granular convection in the solar photosphere as seen by \textsc{Sunrise}. We use high spatial resolution (0\farcs 15--0\farcs 18) and temporal cadence (33 s) spectropolarimetric Imaging Magnetograph eXperiment data, together with simultaneous CN and Ca\,\textsc{ii}\,H filtergrams from \textsc{Sunrise} Filter Imager. We apply the SIR inversion code to the polarimetric data in order to infer the line of sight velocity and vector magnetic field in the photosphere. The analysis reveals bundles of individual flux tubes evolving as a single entity during the entire 23 minute data set. The group shares a common canopy in the upper photospheric layers, while the individual tubes continually intensify, fragment and merge in the same way that chains of bright points in photometric observations have been reported to do. The evolution of the tube cores are driven by the local granular convection flows. They intensify when they are "compressed" by surrounding granules and split when they are "squeezed" between two moving granules. The resulting fragments are usually later regrouped in intergranular lanes by the granular flows. The continual intensification, fragmentation and coalescence of flux results in magnetic field oscillations of the global entity. From the observations we conclude that the magnetic field oscillations first reported by \citet{2011ApJ...730L..37M} correspond to the forcing by granular motions and not to characteristic oscillatory modes of thin flux tubes.