Fractal Dimensions of Umbral and Penumbral Regions of Sunspots

The images of sunspots in 16 active regions taken at the University College of the Cayman Islands (UCCI) Observatory on Grand Cayman during June–November 2015 were used to determine their fractal dimensions using the perimeter–area method for the umbral and the penumbral region. Scale-free fractal dimensions of \(2.09 \pm0.42\) and \(1.72 \pm0.4\) were found, respectively. This value was higher than the value determined by Chumak and Chumak (Astron. Astrophys. Trans.10, 329, 1996), who used a similar method, but only for the penumbral region of their sample set. The umbral and penumbral fractal dimensions for the specific sunspots are positively correlated with \(r = 0.58\). Furthermore, a similar time-series analysis was performed on eight images of AR 12403, from 21 August 2015 to 28 August 2015 taken from the Debrecen Photoheliographic Data (DPD). The correlation is \(r = 0.623\) between the umbral and penumbral fractal dimensions in the time series, indicating that the complexity in morphology indicated by the fractal dimension between the umbra and penumbra followed each other in time as well.