| 其他摘要 | The sunspot decay is an important phenomenon during the evolution of the solaractive region. It is a main mode of the magnetic flux transportation and the evolutionof the solar large scale magnetic field. It is also closely related to variations of thesolar radiation and space weather near the Earth. However, due to the limitation of theobservation technology, the solar convection zone cannot be directly observed, one canspeculate the evolution of sunspots in the solar interior through the performance of thesunspots in the solar atmosphere. As a result, the appearance and interaction of manyfine structures in the sunspot decay process seen still to be controversial, and the sunspotdecay mechanism has not been well understood so far.With the progress of modern science and technology, ground-based (NVST, GST,etc.) and space-based telescopes (SDO, Hinode, etc.) with high temporal and spatialresolution have been put into operation one after another and a large amount of highqualityobservation data are available, this provides us opportunities to study the fineprocess of sunspot decay. In this thesis, based on the data from SDO/HMI, we explorethe issues such as the penumbral magnetic field tending to be vertical, the origin of differentmoving magnetic features (MMFs) and their relationship with the sunspot decay.We first study the complete decay process of an 𝛼-type sunspot located in the active regionNOAA 12411, and then perform a detailed quantitative analysis of the evolution ofits area and vector magnetic field during the decay process. It is shown that the penumbralarea and magnetic flux decay are much faster than that of the umbra. Unlike mostprevious studies, the Gaussian-type decay pattern is more suitable for describing thewhole decay process of sunspot areas. The phenomenon that the penumbral magneticfield becomes gradually more vertical may be explained with the idea that the magneticfield sinks during the decay of the sunspot. It is found that the horizontal magnetic fieldlines of the penumbra first sink below the photosphere, while the vertical field lines areleft, and the penumbral mean brightness becomes darker. The penumbral magnetic fieldtends to be transformed into the umbral magnetic field during the decay of the penumbra.The role of the MMFs evolution in the decay process of two adjacent sunspots (ARNOAA 13023) is investigated then. We compare the physical properties of the MMFsappearing at the penumbral boundary, and sunspot boundary without any penumbra.Their relationship with the magnetic flux decay of the sunspots is studied. It is shownthat despite of the fact that the two sunspots are in close proximity, they do not have thesame decay rates of area and magnetic flux, and the evolution patterns of their vectormagnetic field differ considerably. The penumbral magnetic field of one of the sunspotstends to become vertical, while the other does not. The magnetic flux generation rateof the vertical MMFs is close to the magnetic flux decay rate of the sunspots, while themagnetic flux generation rate of the horizontal MMFs is much larger than the magneticflux decay rate, consistent with the idea that the vertical MMFs are closely related tothe diffusion of the magnetic flux in the sunspots, whereas the horizontal MMFs arenot tightly related to the magnetic flux decay of sunspots. The MMFs appears at theboundary without penumbra generally have the characteristics of strong longitudinalmagnetic field, indicating that most of the MMFs appears here are directly diffused fromthe umbra. On the other hand, most of the MMFs generated at the penumbra boundaryare characterized by a horizontal magnetic field and a weak longitudinal field. Thismeans that the MMFs generated here are the intersection of the horizontal field extendedfrom the penumbra with the solar surface. |
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