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We performed coordinated observations of AR 12205, which produced a C-classflare on 2014 November 11, with the Interface Region Imaging Spectrograph(IRIS) and the Domeless Solar Telescope (DST) at Hida Observatory. Usingspectral data in the Si IV 1403 \AA, C II 1335 \AA, and Mg II h and k linesfrom IRIS and the Ca II K, Ca II 8542 \AA, and H$\alpha$ lines from DST, weinvestigated a moving flare kernel during the flare. In the Mg II h line, theleading edge of the flare kernel showed the intensity enhancement in the bluewing, and the smaller intensity of the blue-side peak (h2v) than that of thered-side one (h2r). The blueshift lasted for 9-48 s with a typical speed of10.1 $\pm$ 2.6 km s$^{-1}$ and it was followed by the high intensity and thelarge redshift with a speed of up to 51 km s$^{-1}$ detected in the Mg II hline. The large redshift was a common property for all six lines but theblueshift prior to it was found only in the Mg II lines. A cloud modeling ofthe Mg II h line suggests that the blue wing enhancement with such peakdifference can be caused by a chromospheric-temperature (cool) upflow. Wediscuss a scenario in which an upflow of cool plasma is lifted up by expandinghot plasma owing to the deep penetration of non-thermal electrons into thechromosphere. Furthermore, we found that the blueshift persisted without anysubsequent redshift in the leading edge of the flare kernel during its decayingphase. The cause of such long-lasting blueshift is also discussed.

Blue wing enhancement of the chromospheric Mg II h and k lines in a solar flare