Post-doctor LI Qiaoling from Department of Physics and Astronomy of Yunnan University, Prof. YAN Xiaoli and their cooperators from Yunnan Observatories of the Chinese Academy of Sciences, studied statistically the decay of eight α-type sunspots for the first time, and the results have been published recently in The Astrophysical Journal.

Sunspots are local strong magnetic field regions on the solar surface. The decay of sunspots is a part of the evolution process of local magnetic fields in the solar atmosphere. Some researches show that the decay of sunspot is closely related to flare activity. By studying the decay process of sunspots during solar flares, it can shed light on understanding the nature of solar flare activity more deeply. Previous statistical studies on sunspot decay tend to focus on the decay rates of the area and magnetic flux of multiple sunspot groups. Up to now, there is almost no statistical study on the decay process of the same type of sunspot.

In order to better understand the decay process of different types of sunspots, LI Qiaoling et al. selected eight typical α-type sunspots in detail and studied their decay process over a 4-day period using the data from Helioseismic and Magnetic Imaging (SDO/HMI) aboard on the Solar Dynamics Observatory (SDO) during 2014 to 2020. The evolution of their photosphere area and magnetic field parameters were analyzed in detail.

It is found that the area and total magnetic flux of α-type sunspots show a near-linear decrease during their decay. Meanwhile, the area decay rate of an individual sunspot is not constant. The area decay of a sunspot can be divided into two stages, a slow and a rapid decay process.

Moreover, according to the difference of the area decay of the penumbra and umbra, the α-type sunspots decay can be classified in three ways: the penumbra and umbra decay synchronously, the penumbra decays first, and the umbra decays first. In addition, the flux decay of the penumbra lags behind the decay of the penumbral area.

This finding suggests that the vertical magnetic field of the sunspot penumbra increases significantly in the early stage of sunspot decay.

 Contact:

YAN Xiaoli, yanxl@ynal.ac.cn

Yunnan Observatories, CAS