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.
@article{arxiv.1905.09709,
title = {Different Signatures of Chromospheric Evaporation in Two Solar Flares Observed with IRIS},
author = {Y. Li and M. D. Ding and J. Hong and H. Li and W. Q. Gan},
journal= {arXiv preprint arXiv:1905.09709},
year = {2019}
}