"EIT waves" are large-scale disturbances in the solar corona propagating with mean velocities in the range 200-400 km/s. 12 years after their discovery (Thompson et al. 1998) there is still an ongoing debate about the physical nature of the phenomenon: are "EIT waves" indeed proper waves (fast-mode MHD waves) or just signatures related to the erupting CME and associated large-scale magnetic field reconfiguration (so-called "pseudo-wave" hypothesis). One important reason why there is still so much controversy on this subject is the low cadence of the EIT/SOHO instrument (12 min), which does not allow us to properly study the kinematics and dynamics of these events. These limitations are now overcome by a number of full-disk EUV imagers observing the Sun: STEREO EUVI, Proba-2 SWAP, and most recently SDO AIA. The other important reason is the missing plasma diagnostics for "EIT waves".
In the proposed project, we plan to combine EUV imaging observations of "EIT waves" by Proba-2 SWAP and SDO AIA with high cadence (<1 min) in various chromospheric, transition region and coronal spectral lines with high-cadence Hinode EIS spectroscopic sit-and-stare data. Our main aim is to study the plasma motions below the propagating wave fronts with EIS, in transition region and coronal lines together with plasma density diagnostics. To this aim will place the 512 arcsec EIS slit outside an active region (in North-South direction), in order to follow the evolution of EIT waves propagating across the slit. This will allow us to study the plasma conditions, compression ratios and plasma motions related to EIT waves together with their kinematical behaviour. This combined imaging and spectroscopic approach would provide important diagnostics on the physical processes underlying EIT waves, and would be most helpful to pin down the wave vs. non-wave debate. |
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