Magnetic Field Characteristics of Moving Magnetic Features during the Sunspot Decay from the Whole Sunspot to Pore

Abstract To understand the relationship between moving magnetic features (MMFs) and the decay of the sunspot, we studied the complete decays of four α -type sunspots based on data from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, focusing on the magnetic properties of same-polarity MMFs at the moment they detach from the sunspots. The main results are as follows: (1) The area and horizontal velocity of MMFs mainly range from 0.4 to 2 MSH and 0.2 to 1.7 km s −1 , with typical values of 0.65 MSH and 0.6 km s −1 , respectively. The dominant ranges for B , B t , B z , and γ are 200–400 G, 75–350 G, 153–297 G, and 20°–60°, respectively. (2) Comparing the pre-pore (the stage before the sunspot transforms into the pore) and pore (after the transformation) stages, the area, horizontal velocity, and B z show similar distribution ranges, while the mean values and ranges of B , B t , and γ decrease significantly. (3) In the pre-pore stage, MMFs predominantly manifest as horizontal MMFs (MMFs that have a horizontal magnetic field (45° < γ < 90°)), whereas in the pore stage, most of them are observed as vertical MMFs (MMFs that have a vertical magnetic field (0° < γ ≤ 45°)). These findings provide observational evidence for the turbulent erosion model of the sunspot decay; the mean vertical magnetic field may be an important parameter for the detachment of MMFs from the sunspots.