Statistics of photospheric supergranular cells observed by SDO/HMI

Abstract

The statistics of the photospheric supergranulation pattern were investigated using continuum images observed by Solar Dynamic Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) taken at 6713 Å. The supergranular boundaries can be extracted by tracking photospheric velocity plasma flows. The ball-tracking method in combination with automatic recognition approach were employed to apply on the HMI data gathered over the years 2011–2015. Then, the edge sharpening techniques were exerted on the resultant image to precisely identify the cells borders. To study the fractal dimensionality (FD) of supergranulation, the box counting method was used. We found that the cell sizes follow the log-normal distribution with peak value about 400 Mm2. The five-year mean value of the cells number per unit area (10,000 Mm2) appeared in the solar surface was obtained to be about 19 ± 3. Distribution of the cells orientation presents the power-law behavior. The orientation of supergranular cells (O) and their size (S) follows a power-law function as |O|∝S10.35. We found that the non-roundish cells with smaller and larger sizes than about 650 Mm2 are aligned and perpendicular with the solar rotational velocity on the photosphere, respectively. The FD analysis shows that the supergranular cells form the self-similar patterns.