639 research outputs found
Case Study of Four Homologous Large-Scale Coronal Waves Observed on 2010 April 28 and 29
On 2010 April 28 and 29, the Solar TErrestrial Relations Observatory
B/Extreme Ultraviolet Imager observed four homologous large-scale coronal
waves, the so-called EIT-waves, within 8 hr. All waves emerged from the same
source active region, were accompanied by weak flares and faint coronal mass
ejections, and propagated into the same direction at constant velocities in the
range of ~220-340 km s-1. The last of these four coronal wave events was the
strongest and fastest, with a velocity of 337 +/- 31 km s-1 and a peak
perturbation amplitude of ~1.24, corresponding to a magnetosonic Mach number of
Mms ~ 1.09. The magnetosonic Mach numbers and velocities of the four waves are
distinctly correlated, suggestive of the nonlinear fast-mode magnetosonic wave
nature of the events. We also found a correlation between the magnetic energy
buildup times and the velocity and magnetosonic Mach number
Plasma diagnostics of an EIT wave observed by Hinode/EIS and SDO/AIA
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.Comment: Accepted for ApJ Letter
First observations of a dome-shaped large-scale coronal EUV wave
We present first observations of a dome-shaped large-scale EUV coronal wave,
recorded by the EUVI instrument onboard STEREO-B on January 17, 2010. The main
arguments that the observed structure is the wave dome (and not the CME) are:
a) the spherical form and sharpness of the dome's outer edge and the erupting
CME loops observed inside the dome; b) the low-coronal wave signatures above
the limb perfectly connecting to the on-disk signatures of the wave; c) the
lateral extent of the expanding dome which is much larger than that of the
coronal dimming; d) the associated high-frequency type II burst indicating
shock formation low in the corona. The velocity of the upward expansion of the
wave dome ( km s) is larger than that of the lateral
expansion of the wave ( km s), indicating that the upward
dome expansion is driven all the time, and thus depends on the CME speed,
whereas in the lateral direction it is freely propagating after the CME lateral
expansion stops. We also examine the evolution of the perturbation
characteristics: First the perturbation profile steepens and the amplitude
increases. Thereafter, the amplitude decreases with r, the
width broadens, and the integral below the perturbation remains constant. Our
findings are consistent with the spherical expansion and decay of a weakly
shocked fast-mode MHD wave.Comment: Astrophysical Journal Letters, in pres
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