Characterizing motion types of G-band bright points in the quiet Sun

We study the motion 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 do not move during their lifetimes aside, the non-stationary GBPs are categorized into three types based on an index of their motion type. Most GBPs that move in straight or nearly straight lines are categorized as a straight motion type, a few moving in rotary paths into rotary motion, and the others fall into a motion type we called erratic. The mean horizontal velocities are 2.18 +/- 0.08 k m s(-1), 1.63 +/- 0.09 k m s(-1) and 1.33 +/- 0.07 k m s(-1) for straight, erratic and rotary motion types, 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 on a rotary path. The diffusive process is ballistic-, super-and sub-diffusion for straight, erratic and rotary motion types, respectively. The corresponding diffusion index (gamma) and coefficients (K) are 2.13 +/- 0.09 and 850 +/- 37 k m(2) s(-1), 1.82 +/- 0.07 and 331 +/- 24 k m(2) s(-1), and 0.73 +/- 0.19 and 13 +/- 9 k m(2) s(-1). In terms of direction of motion, it is homogeneous and isotropic, and usually persists between neighboring frames, no matter what motion type a GBP is classified as.