摘要
In this paper,we report three interesting phenomena that occurred during the precursor phase of the X1.6 class flare on 2014 September 10.(1) The magnetic reconnection initiating the flare occurs between one of the two J-shaped magnetic flux ropes that constitute a sigmoidal structure and the overlying sheared magnetic arcade that runs across the sigmoid over its middle part.The reconnection formed an erupting structure that ultimately leads to flare onset.Another J-shaped magnetic flux rope remains unaffected during the whole eruption.The phenomenon is revealed by the observation made by the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory(SDO)at 94 and 131 A.(2) Being simultaneously with starting time of the precursor,photospheric vertical electric current(VEC) around the footpoint region of the overlying magnetic arcade underwent an obvious increase,as observed by the Helioseismic and Magnetic Imager(HMI) on board SDO.By only taking into account the VEC with current density over 3σ value(1σ:10 mA m^(-2)),we are able to pick out precursor-associated VEC increase starting from nearly the level of zero.We regard it as a kind of powering process for the magnetic reconnection between the two magnetic loops.(3) With high-resolution narrow-band Helium 10830 A images taken by Goode Solar Telescope at Big Bear Solar Observatory(BBSO),we observe a narrow absorption(dark) front that runs along the erupting magnetic structure(or the erupting hot channel) and moves in the direction of the eruption during the precursor phase.Assuming the excitation mechanism of Helium atoms along the absorption front by non-thermal electrons,the phenomenon shows that the interaction between the erupted hot channel and the overlying(or surrounding)magnetic field has yielded electron acceleration.
基金
supported by the National Natural Science Foundation of China under grants 11773061 and 11790302
supported by the West Young Scholars Programs CAS grant No.2017XBQNXZ-A-007
Nanjing University,Key Lab Modern Astronomy and Astrophysics
No.KLSA 202106 of CAS Key Lab of Solar Activity,NAOC
Key Lab for DMSA,CAS for their support
High-level Flexible Talent Program of Xinjiang Uygur Autonomous Region
supported by NJIT and US NSF AGS-1821294 grant
supported by the Korea Astronomy and Space Science Institute
the Seoul National University
the Key Laboratory of Solar Activities of Chinese Academy of Sciences (CAS)
the Operation,Maintenance and Upgrading Fund of CAS for Astronomical Telescopes and Facility Instruments。
