Active Region Coronal Rain Event Observed by the Fast Imaging Solar Spectrograph on the NST
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The Fast Imaging Solar Spectrograph (FISS) is being operated on the New Solar Telescope of the Big Bear Solar Observatory. It simultaneously records spectra of Hα and Ca ii 8542 Å lines, and this dual-spectra measurement provides an estimate of the temperature and nonthermal speed components. We observed a loop structure in AR 11305 using the FISS, SDO/AIA, and STEREO/EUVI in 304 Å, and found plasma material falling along the loop from a coronal height into the umbra of a sunspot, which accelerated up to 80 km s−1. We also observed C2 and C7 flare events near the loop. The temperature of the downflows was in the range of 10 000 – 33 000 K, increasing toward the umbra. The temperature of the flow varied with time, and the temperature near the footpoint rose immediately after the C7 flare, but the temperature toward the umbra remained the same. There seemed to be a temporal correlation between the amount of downflow material and the observed C-class flares. The downflows decreased gradually soon after the flares and then increased after a few hours. These high-speed red-shift events occurred continuously during the observations. The flows observed on-disk in Hα and Ca ii 8542 Å appeared as fragmented, fuzzy condensed material falling from the coronal heights when seen off-limb with STEREO/EUVI at 304 Å. Based on these observations, we propose that these flows were an on-disk signature of coronal rain.
KeywordsActive regions Chromosphere Coronal rain Spectroscopic observations
I would like to thank the referee for many critical comments, which improved this manuscript considerably. This research was supported by the National Research Foundation of Korea (355-2012-1-2012R1A6A3A03039815 and 2012R1A2A1A03670387). K. Ahn and W. Cao gratefully acknowledge the support of NSF-CAREER through ATM-0847126.
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