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

Abstract

The sub-arcsec bright points (BP) 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 auto-correlation 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 on the results from SST data. The BP positional uncertainty achieved by SST is as low as 3 km. The position errors contribute 0.75 km 2 s −2 to the variance of the observed velocities. The raw and corrected velocity measurements in both directions, i.e., (v x , v y ), 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 time scales less than 200 s is found to satisfy a power law with an index of 1.59.

Migration of Ca II H bright points in the internetwork

“…However, the features we studied display a much stronger super-diffusive behaviour. Super-diffusivity has also been reported by Abramenko et al (2011) andChitta et al (2012) in recent investigations. They deduced values of the diffusion index in a given type of region by averaging the displacements over all MBPs.…”

“…They reported the presence of super-diffusivity (as the only observed diffusion regime) for both quiet-Sun and active regions. This super-diffusivity was later confirmed by Chitta et al (2012) by tracking MBPs observed in wideband Hα.…”

Super-diffusion versus competitive advection: a simulation

“…Wang & Sheeley 1993;Schrijver et al 1996;Berger et al 1998;Hagenaar et al 1999;Chae et al 2008;Abramenko et al 2011;Chitta et al 2012;Giannattasio et al 2013Giannattasio et al , 2014aJafarzadeh et al 2014) at all accessible spatiotemporal scales, ranging from granulation (diameter 1 Mm and lifetime few minutes; Muller 1999;Hirzberger et al 1999;Del Moro 2004) to super-granulation (diameter 30 Mm and lifetime a day; Raju et al 1999;Srikanth et al 2000;Del Moro et al 2004). …”

Ultra‐High‐Resolution Observations of MHD Waves in Photospheric Magnetic Structures

“…It is clear that for frequencies >0.02 Hz (<50 s) the observational horizontal motions have more power, highlighting the fact that dynamics on short timescales may be very important in the generation of energetic kink and/or Alfvén wave phenomena. Images adapted from Chitta et al [2012b].…”