A Confined Two-peaked Solar Flare Observed by EAST and SDO

The solar flare is one of the most violent explosions,and can disturb the near-Earth space weather.Except for commonly single-peaked solar flares in soft X-ray,some special flares show intriguing a two-peak feature that is deserved much more attentions.Here,we reported a confined two-peaked solar flare and analyzed the associated eruptions using high-quality observations from Educational Adaptive-optics Solar Telescope and Solar Dynamics Observatory.Before the flare,a magnetic flux rope(MFR)formed through partially tether-cutting reconnection between two sheared arches.The flare occurred after the MFR eruption that was confined by the overlying strong field.Interestingly,a small underlying filament immediately erupted,which was possibly destabilized by the flare ribbon.The successive eruptions were confirmed by the analysis of the emission measure and the reconnection fluxes.Therefore,we suggest that the two peaks of the confined solar flare are corresponding to two episodes of magnetic reconnection during the successive eruptions of the MFR and the underlying filament.

The Precursor Phase of an X-class Flare: Magnetic Reconnection, Powering and Non-thermal Electrons

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.