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Helical magnetic flux rope (MFR) is a fundamental structure of corona massejections (CMEs) and has been discovered recently to exist as a sigmoidalchannel structure prior to its eruption in the extreme ultraviolet (EUV) hightemperature passbands of the Atmospheric Imaging Assembly (AIA). However, whenand where the MFR is built up are still elusive. In this paper, we investigatetwo MFRs (MFR1 and MFR2) in detail, whose eruptions produced two energeticsolar flares and CMEs on 2014 April 18 and 2014 September 10, respectively. TheAIA EUV images reveal that for a long time prior to their eruption, both MFR1and MFR2 are under formation, which is probably through magnetic reconnectionbetween two groups of sheared arcades driven by the shearing and convergingflows in the photosphere near the polarity inversion line. At the footpoints ofthe MFR1, the \textit{Interface Region Imaging Spectrograph} Si IV, C II, andMg II lines exhibit weak to moderate redshifts and a non-thermal broadening inthe pre-flare phase. However, a relatively large blueshift and an extremelystrong non-thermal broadening are found at the formation site of the MFR2.These spectral features consolidate the proposition that the reconnection playsan important role in the formation of MFRs. For the MFR1, the reconnectionoutflow may propagate along its legs, penetrating into the transition regionand the chromosphere at the footpoints. For the MFR2, the reconnection probablytakes place in the lower atmosphere and results in the strong blueshift andnon-thermal broadening for the Mg II, C II, and Si IV lines.

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