Characterizing motion types ofG-band bright points in the quiet Sun

Abstract

We study the motions of G-band bright points (GBPs) in the quiet Sun to obtain the characteristics of different motion types. A high resolution image sequence taken with the Hinode/Solar Optical Telescope (SOT) is used, and GBPs are automatically tracked by segmenting 3D evolutional structures in a space-time cube. After putting the GBPs that don't move during their lifetimes aside, the non-stationary GBPs are categorized into three types based on an index of motion type. Most GBPs that move in straight or nearly straight lines are categorized into a straight motion type, a few moving in rotary paths into a rotary motion, and the others fall into a motion type we called erratic. The mean horizontal velocity is 2.18±0.08 km s −1 , 1.63±0.09 km s −1 and 1.33±0.07 km s −1 for straight, erratic and rotary motion type, respectively. We find that a GBP drifts at a higher and constant velocity during its whole life if it moves in a straight line. However, it has a lower and variational velocity if it moves in a rotary path. The diffusive process is ballistic-, super-and sub-diffusion for straight, erratic and rotary motion type, respectively. The corresponding diffusion index (γ) and coefficients (K) are 2.13±0.09 and 850±37 km 2 s −1 , 1.82±0.07 and 331±24 km 2 s −1 , 0.73±0.19 and 13±9 km 2 s −1 . In terms of direction of motion, it is homogeneous and isotropical, and usually persists between neighbouring frames, no matter what motion type a GBP belongs to.

On the Relationship Between G-Band Bright Point Dynamics and Their Magnetic Field Strengths

“…It implies that the majority of GBPs are jostled in a limited area, while the minority are pushed by granules far away. The proportion of stationary GBPs is higher than that reported by Bodnárová, Utz, and Rybák (2014) and Yang et al (2015a). They both indicated that there are about 50% stationary GBPs in a QS region.…”

“…The different spatial samplings were overcome by bicubic interpolations of the NFI images obtaining adjusted NFI images with the spatial sampling of the Gband images. Next, the two time-series were aligned carefully by a high-accuracy solar image registration procedure based on a cross-correlation technique (Yang et al, 2015a): all G-band images in the time-series were aligned to its first image, and the NFI magnetograms were aligned to the G-band images according to the displacement between the simultaneous Stokes I image and the G-band image. To estimate the error of the stretched NFI magnetograms, we have performed the following experiment.…”

“…The motion ranges of all GBPs were measured using the definition by Bodnárová, Utz, and Rybák (2014) and Yang et al (2015a). An index of motion range, M R , is defined as…”

“…Besides that, some authors focused on tracking the rotary or vortex motion of GBPs, which is suggested as a primary candidate mechanism, for energy transport from the interior to the outer layers of the solar atmosphere (Vögler et al, 2005;Bonet et al, 2008;Carlsson, Hansteen, and Gudiksen, 2010;Fedun, Shelyag, and Erdélyi, 2011;Moll, Cameron, and Schüssler, 2011;Shelyag et al, 2011;Moll, Cameron, and Schüssler, 2012;Shelyag et al, 2013). Yang et al (2015a) proposed a path classifying method, and suggested that the motion paths of GBPs could be categorized into three types: straight, rotary, and erratic. In addition, the motion range of GBPs was analyzed and suggested that the majority of GBPs move in a local place (Bodnárová, Utz, and Rybák, 2014;Yang et al, 2015a).…”

“…Yang et al (2015a) proposed a path classifying method, and suggested that the motion paths of GBPs could be categorized into three types: straight, rotary, and erratic. In addition, the motion range of GBPs was analyzed and suggested that the majority of GBPs move in a local place (Bodnárová, Utz, and Rybák, 2014;Yang et al, 2015a).…”