抚仙湖太阳观测和研究基地知识库

wThe emergence of active regions (ARs) closely relates to the solar dynamo and dynamical atmospheric phenomena. With high-resolution and long-lasting observations from the New Vacuum Solar Telescope, we report a new dynamic activity phenomenon named "fan-shaped activity (FSA)" in the emerging phase of NOAA AR 12700. The FSAs are clearly observed at Ha wavelengths and are closely related to the dynamics of the adjacent arch filament system (AFS), including thread deformation and material downward motions. On 2018 February 26, the two most representative FSAs appeared around 05:21 UT and 06:03 UT, respectively, and they first ascended and then decayed within around 10 minutes. At the ascending phase, accompanied by the uplifting of an adjacent AFS, each FSA launches up at one end of the AFS and extends for up to similar to 11 Mm. At the decaying phase, the FSA gradually vanishes, and material downflows toward the other end of the AFS are detected. After checking the evolution of the magnetic fields of AR 12700, we find that each FSA is located between the end of an AFS and an adjacent magnetic patch with the same polarity and launches at the onset of the collision and compression between these two magnetic patches. We propose that the collision lifts up the AFS, and then the initially compact AFS laterally expands, resulting in the formation of FSA. A cartoon model is proposed to depict the activities.