Dispersion of the solar magnetic flux in undisturbed photosphere as derived from SDO/HMI data

TL;DR

This study analyzes magnetic flux dispersion in the undisturbed solar photosphere using SDO/HMI data, revealing different diffusion regimes for small and large magnetic elements in distinct solar regions.

Contribution

It provides new insights into the dispersion behavior and turbulent diffusion coefficients of magnetic elements in the solar photosphere, distinguishing between different size regimes and regions.

Findings

Small elements exhibit super-diffusivity with gamma ~ 1.3.

Large elements show varying diffusion regimes, including sub-diffusivity and super-diffusivity.

Diffusion coefficient saturation suggests a transition from super-diffusive to normal diffusion.

Abstract

To explore the magnetic flux dispersion in the undisturbed solar photosphere, magnetograms acquired by Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO) were utilized. Two areas, a coronal hole area (CH) and an area of super-granulation pattern, SG, were analyzed. We explored the displacement and separation spectra and the behavior of the turbulent diffusion coefficient, $K$. The displacement and separation spectra are very similar to each other. Small magnetic elements (of size 3-100 squared pixels and the detection threshold of 20 Mx sm$^{-2}$) in both CH and SG areas disperse in the same way and they are more mobile than the large elements (of size 20-400 squared pixels and the detection threshold of 130 Mx sm$^{-2}$). The regime of super-diffusivity is found for small elements ($\gamma \approx 1.3 $ and $K$ growing from $\sim$100 to $\sim$ 300 km$^2$ s$^{-1}$). Large elements in the CH area are scanty and show super-diffusion with $\gamma \approx 1.2$ and $K$ = (62-96) km$^2$ s$^{-1}$ on rather narrow range of 500-2200 km. Large elements in the SG area demonstrate two ranges of linearity and two diffusivity regimes: sub-diffusivity on scales (900-2500) km with $\gamma=0.88$ and $K$ decreasing from $\sim$130 to $\sim$100 km$^2$ s$^{-1}$, and super-diffusivity on scales (2500-4800) km with $\gamma \approx 1.3$ and $K$ growing from $\sim$140 to $\sim$200 km$^2$ s$^{-1}$. Comparison of our results with the previously published shows that there is a tendency of saturation of the diffusion coefficient on large scales, i.e., the turbulent regime of super-diffusivity is gradually replaced by normal diffusion.