Discovery of a Temperature-Dependent Upflow in the Plage Region During a Gradual Phase of the X-Class Flare
We present Hinode/EIS raster scan observations of the plage region taken during the gradual phase of the GOES X3.2 flare that occurred on 2006 December 13. The plage region is located 200" east of the flare arcade. The plage region has a small transient coronal hole. The transient coronal hole is strongly affected by an X-class flare, and upflows are observed at its boundary. Multi-wavelength spectral observations allow us to determine velocities from the Doppler shifts at different temperatures. Strong upflows along with stationary plasma have been observed in the FeXV line 284.2Å (log T / K = 6.3) in the plage region. The strong upflows reach almost 150kms-1, which was estimated by a two-component Gaussian fitting. On the other hand, at a lower corona/transition region temperature (HeII, 256.3Å, log T / K = 4.9), very weak upflows, almost stationary, have been observed. We find that these upflow velocities clearly depend on the temperature with the hottest line, FeXV, showing the fastest upflow velocity and the second-highest line, FeXIV, showing the second-highest upflow velocity (130kms-1). All velocities are below the sound speed. The trend of the upflow dependence on temperature dramatically changes at 1MK. These results suggest that heating may have an important role for strong upflow.