Dynamics of the Solar Magnetic Bright Points Derived from Their Horizontal Motions

Abstract

The subarcsecond bright points (BPs) associated with the small-scale magnetic fields in the lower solar atmosphere are advected by the evolution of the photospheric granules. We measure various quantities related to the horizontal motions of the BPs observed in two wavelengths, including the velocity autocorrelation function. A 1 hr time sequence of wideband Hα observations conducted at the Swedish 1 m Solar Telescope (SST) and a 4 hr Hinode G-band time sequence observed with the Solar Optical Telescope are used in this work. We follow 97 SST and 212 Hinode BPs with 3800 and 1950 individual velocity measurements, respectively. For its high cadence of 5 s as compared to 30 s for Hinode data, we emphasize more the results from SST data. The BP positional uncertainty achieved by SST is as low as 3 km. The position errors contribute 0.75 km2 s–2 to the variance of the observed velocities. The raw and corrected velocity measurements in both directions, i.e., (vx , vy ), have Gaussian distributions with standard deviations of (1.32, 1.22) and (1.00, 0.86) km s–1, respectively. The BP motions have correlation times of about 22-30 s. We construct the power spectrum of the horizontal motions as a function of frequency, a quantity that is useful and relevant to the studies of generation of Alfvén waves. Photospheric turbulent diffusion at timescales less than 200 s is found to satisfy a power law with an index of 1.59.