| Solar flares are one of the most spectacular phenomena in the solar atmosphere and also have a significant impact on human life.While it is generally believed that magnetic reconnection is the mechanism behind them,the exact triggering and energy release processes are still unclear.In this paper,we explore this topic through four observational studies,with the aim of enhancing our understanding of this fascinating phenomenon.The first work is a case study based on a two-ribbon M3.3 class solar flare(SOL2013-08-17T18:16),revealing new dynamic coupling characteristics in the solar atmosphere.It is found that before the flare occurred,a sunspot in the core region of the active region suddenly started shearing motion from an almost stationary state,lasting for about ten hours,while other sunspots in the active region showed no obvious motion.After the flare occurred,the direction of motion of the sunspot suddenly reversed,and the speed was much greater than its shearing speed before the flare.Combining multi-wavelength observations from the photosphere to the corona,the motion of this sunspot before and after the flare provides new and powerful evidence for the theory of photospheric shearing motion triggering flares and magnetic implosion theory.The second work is statistical studies of circular-ribbon flares(CFs).We conducted a comprehensive statistical analysis of 134 CFs from September 2011 to June 2017,including 4 B-class,82 C-class,40 M-class,and 8 X-class flares.The main statistics include the location,area,equivalent radius,duration,1-8 A soft X-ray peak flux,and a series of associated phenomena,such as remote brightening,filament eruption,coronal jet,type Ⅲ radio burst,and coronal mass ejection(CME).We obtained a series of meaningful statistical conclusions:the area and duration conform to lognormal distributions and are positively correlated;the range of equivalent radius is between 6 and 87 Mm,with an average value of 16.8 Mm;the peak flux of 1-8 A soft X-rays follows a power-law distribution with an index of-1.42;57%of CFs are accompanied by remote brightening,and the correlation rate increases with the flare magnitude,with a positive correlation between the length of the remote brightening and its distance from the CF;about half of CFs are associated with type Ⅲ radio bursts and coronal jets,and the correlation rate is independent of the flare magnitude;about 38%of CFs are accompanied by filament eruption,and their correlation rate increases with the flare magnitude;about 28%of CFs are accompanied by CMEs,and there is a positive correlation among their velocity,angular width,and the soft X-ray peak flux of the CF.These statistical results are important for revealing the physical nature of CFs.The third and fourth works studied two important phenomena related to flares,coronal jets and filament eruptions,respectively.We investigated recurrent jets that occurred in the active region 12205 on November 7,2014,in which the acceleration during the rise and fall process was inconsistent with what is usually observed.Through analysis and comparison,we believe that this was caused by the downward pressure gradient force and extra viscous resistance brought by the previous jet.We also conducted a study on a partial filament eruption that occurred in the active region 11236 on June 13,2011.Through multi-perspective analysis of this event,we propose a new mechanism for partial eruptions,which suggests that some of the filament material can escape through magnetic reconnection with open magnetic lines,while the other part is confined to the solar surface due to the presence of closed magnetic lines. |
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