Title: Spectroscopic observations and plasma diagnostics of an EIT wave.
Authors: L.K. Harra, A.C. Sterling, P. Gomory, A.M. Veronig, I.W. Kienreich, N. Muhr, B. Vrsnak, M. Temmer, H.P. Warren
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Description: The large-scale disturbances propagating through the solar corona (EIT waves) are still not well understood. Their interpretation can be roughly subdivided into “wave” versus “non-wave” models. In the “non-wave“ models, EIT waves are explained by the large-scale coronal restructuring due to the erupting coronal mass ejection. The “wave“ models describe this phenomenon as real, fast-mode MHD wave. To identify the real mechanism, the spectral observations and consequent plasma diagnostics of EIT waves, i.e. density, temperature and plasma flows at the wave front, are needed. But the existing datasets provided only very limited results up to now. Therefore such type of studies has hitherto been a challenge. In our work, we present plasma diagnostics of the EIT wave based on an extremely unique dataset where we combined high-cadence EUV spectroscopy with ultra-high imaging. At the propagating EIT wave front, we found downward plasma flows with line-of-sight velocities up to 20 km/s followed by blueshifts with upward velocities up to 5 km/s indicating relaxation of the plasma behind the wave front. During the wave evolution, the downward velocity pulse steepens from a few km/s up to 20 km/s and subsequently decays, correlated with the relative changes of the line intensities. The EIT wave under study revealed a strong deceleration of a ~ -540 m/s2 and a start velocity of v ~ 590 km/s. These findings are consistent with the passage of a coronal fast-mode MHD wave, pushing the plasma downward and compressing it at the coronal base, thus preferring “wave” model of the EIT wave.
Reference: The Astrophysical Journal Letters 737, L4 (2011); The Astrophysical Journal Letters 743, L10 (2011)
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Date and Time: 24.5. 2018 12:05:08 CEST
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