Abstract
Chromospheric activities before solar flares provide important clues to the mechanisms that initiate solar flares, but are as yet poorly understood. We report a significant and rapid H\(\upalpha\) line broadening before the solar flare SOL2011-09-29T18:08 that was detected using the unprecedented high-resolution H\(\upalpha\) imaging spectroscopy with the Fast Imaging Solar Spectrograph (FISS) installed on the 1.6 m New Solar Telescope (NST) at Big Bear Solar Observatory. The strong H\(\upalpha\) broadening extends as a blue excursion up to −4.5 Å and as a red excursion up to 2.0 Å, which implies a mixture of velocities in the range of \(-130~\mbox{km}\,\mbox{s}^{-1}\) to 38 km s−1 derived by applying the cloud model, comparable to the highest chromospheric motions reported before. The H\(\upalpha\) blueshifted broadening lasts for about six minutes and is temporally and spatially correlated with the start of a rising filament, which is later associated with the main phase of the flare as detected by the Atmosphere Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The potential importance of this H\(\upalpha\) blueshifted broadening as a preflare chromospheric activity is briefly discussed within the context of the two-step eruption model.
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Acknowledgements
We thank the NASA/SDO team for the photospheric magnetograms and UV/EUV filtergrams, and NASA/Fermi team for the GBM data. We thank Stephen White for the GBSRBS radio data. This work was supported by the National Research Foundation of Korea (NRF-2012R1A2A1A03670387). H. Wang is supported by US NSF under grants AGS 1348513 and 1408703, and NASA under grant NNX13AG13G. E.-k. Lim is supported by the Planetary system research for space exploration from KASI. J. Lee is supported by the BK21 Plus Program (21A20131111123) funded by the Ministry of Education (MOE, Korea) and National Research Foundation of Korea (NRF).
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Cho, K., Lee, J., Chae, J. et al. Strong Blue Asymmetry in H\(\upalpha\) Line as a Preflare Activity. Sol Phys 291, 2391–2406 (2016). https://doi.org/10.1007/s11207-016-0963-5
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DOI: https://doi.org/10.1007/s11207-016-0963-5