Investigation of mass motions above and around sunspots with highest-resolution observations

Date of Award

Summer 2018

Document Type


Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)



First Advisor

Haimin Wang

Second Advisor

Ju Jing

Third Advisor

Chang Liu

Fourth Advisor

Dale E. Gary

Fifth Advisor

Wenda Cao

Sixth Advisor

Zhen Wu


Studying solar active regions (ARs) is extremely important, as they contain rich information in understanding basic plasma properties, and are also the source of space weather impacting the near-Earth environment. The ultimate understanding of sunspots in solar ARs requires ultra-high resolution observations as well as state-of-the-art modeling of them. The resolution of solar observations is limited by the aperture of solar telescopes, and effect of Earth’s atmosphere. In this dissertation, unprecedented observations were achieved by the 1.6 m Coo de Solar Telescope (CST) at the Big Bear Solar Observatory (BBSO), in combination with a high-order Adaptive Optics (AO) system. The CST observations are supplemented by space observations, especially those from the extremely powerful Solar Dynamic Observatory (SDO), and advanced data processing tools. With above observations, significant findings in three kinds of flow motions around and above sunspots were obtained that could address some fundamental questions:

  • For the first time, unidirectional downflows were found prior to the eruption of a filament in an AR. This drainage effect is interpreted as a driver and precursor to the eruption. Small-scale brightenings at the footpoints of downflows are also observed for the first time due to the high resolution of CST.
  • For the first time, an apparent circular counter-streaming motion of the filament was observed anchored in a sunspot. A careful analysis was conducted to separate two different mechanisms of the discovered motions: the siphon flow for the higher section of the filament from the descending the corona to the sunspot, and leakage of the solar p-mode in the sunspot light bridge.
  • Using data from the newly available GST/NIRIS, moving magnetic features (MMFs) in a sunspot are revealed most clearly with our observations. MMFs were found to originate from the mid-penumbra of the sunspot. Their bipolar magnetic structure and linkage to the sunspot evolution are studied in details.

This study will provide observational inputs for further MHD modeling, and motivate further investigation of fine-scale structures of sunspots when the 4-m Daniel K. Inouye Solar Telescope (DKIST) is online in 2020.