Spectroscopic observations of a coronal Moreton wave

Harra L.K.¹, Sterling, A.C.^2,5, Gömöry P.³, Veronig A.M.⁴

¹ UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
² Space Science Office, VP62, NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
³ Astronomical Institute, Slovak Academy of Sciences, SK-05960 Tatranská Lomnica, Slovakia
⁴ Institute of Physics, University of Graz, Universitaetsplatz 5, A-8010 Graz, Austria
⁵ JAXA/Institute of Space and Astronautical Science, Hinode Group, 3-1-1 Yoshinodai, Sagamihara, Chuo-ku, Kanagawa 252-5210, Japan

Abstract:
We observed a coronal wave (EIT wave) on 2011 February 16, using EUV imaging data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) and EUV spectral data from the Hinode/EUV Imaging Spectrometer (EIS). The wave accompanied an M1.6 flare that produced a surge and a coronal mass ejection (CME). EIS data of the wave show a prominent redshifted signature indicating line-of-sight velocities of ~20 km/s or greater. Following the main redshifted wave front, there is a low-velocity period (and perhaps slightly blueshifted), followed by a second redshift somewhat weaker than the first; this progression may be due to oscillations of the EUV atmosphere set in motion by the initial wave front, although alternative explanations may be possible. Along the direction of the EIS slit the wave front's velocity was ~500 km/s, consistent with its apparent propagation velocity projected against the solar disk as measured in the AIA images, and the second redshifted feature had propagation velocities between ~200 and ~500 km/s. These findings are consistent with the observed wave being generated by the outgoing CME, as in the scenario for the classic Moreton wave. This type of detailed spectral study of coronal waves has hitherto been a challenge, but is now possible due to the availability of concurrent AIA and EIS data.