  We present plasma diagnostics of an EIT wave observed with high cadence in
Hinode/EIS sit-and-stare spectroscopy and SDO/AIA imagery obtained during the
HOP-180 observing campaign on 2011 February 16. At the propagating EIT wave
front, we observe downward plasma flows in the EIS Fe XII, Fe XIII, and Fe XVI
spectral lines (log T ~ 6.1-6.4) with line-of-sight (LOS) velocities up to 20
km/s. These red-shifts are followed by blue-shifts 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 expected increase of the plasma densities at the EIT wave
front estimated from the observed intensity increase lies within the noise
level of our density diagnostics from EIS XIII 202/203 AA line ratios. No
significant LOS plasma motions are observed in the He II line, suggesting that
the wave pulse was not strong enough to perturb the underlying chromosphere.
This is consistent with the finding that no Halpha Moreton wave was associated
with the event. The EIT wave propagating along the EIS slit reveals a strong
deceleration of a ~ -540 m/s2 and a start velocity of v0 ~ 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.
