Imaging and Spectroscopic Diagnostics on the Formation of Two Magnetic Flux Ropes Revealed by SDO/AIA and IRIS

摘要: Helical magnetic flux rope (MFR) is a fundamental structure of corona mass ejections (CMEs) and has been discovered recently to exist as sigmoidal channel prior its eruption in the extreme ultraviolet (EUV) high temperature passbands Atmospheric Imaging Assembly (AIA). However, when where MFR built up are still elusive. In this paper, we investigate two MFRs (MFR1 MFR2) detail, whose eruptions produced energetic solar flares CMEs on 2014 April 18 September 10, respectively. The AIA EUV images reveal that for long time their eruption, both MFR1 MFR2 under formation, which probably through reconnection between groups sheared arcades driven by shearing converging flows photosphere near polarity inversion line. At footpoints MFR1, \textit{Interface Region Spectrograph} Si IV, C II, Mg II lines exhibit weak moderate redshifts non-thermal broadening pre-flare phase. relatively large blueshift an extremely strong found at formation site MFR2. These spectral features consolidate proposition plays important role MFRs. For outflow may propagate along legs, penetrating into transition region chromosphere footpoints. MFR2, takes place lower atmosphere results IV lines.