  The emergence of active regions (ARs) closely relates to the solar dynamo and
the 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 wavelength and are closely
related to the dynamics of the adjacent arch filament system (AFS), including
threads deformation and materials downward motions. On 2018 February 26, the
two most representative FSAs appeared around 05:21 UT and 06:03 UT,
respectively, and they firstly ascended and then decayed in 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 11 Mm. At the
decaying phase, the FSA gradually vanishes, and materials downflows towards 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.
