  We present different signatures of chromospheric evaporation in two solar
flares observed by the Interface Region Imaging Spectrograph (IRIS). In the
B1.6 flare on 2016 December 6 (SOL2016-12-06T10:40), the transition region Si
IV line and the chromospheric C II and Mg II lines show blueshifts with low
velocities up to 20 km/s at the flare loop footpoints in the rise phase,
indicative of a gentle chromospheric evaporation. While in the C1.6 flare on
2015 December 19 (SOL2015-12-19T10:51), the Si IV, C II, and Mg II lines
exhibit redshifts with velocities from several to tens of km/s at the
footpoints, which might suggest an explosive chromospheric evaporation.
Explosive evaporation has been observed in many flares that were captured by
IRIS; however, gentle evaporation, especially manifested as blueshifts in the
cool Si IV, C II, and Mg II lines, has scarcely been reported. Our results
bring some new insights into chromospheric evaporation in the IRIS era.
