1202.4360 (David M. Long)
David M. Long
Globally-propagating coronal bright fronts (CBFs) in the solar corona are
among the most dramatic manifestations of solar activity, but are not well
understood despite strong links with both solar flares and coronal mass
ejections. Extreme UltraViolet (EUV) observations from the STEREO and SDO
spacecraft are used here to study their kinematics and morphology. The first
STEREO observations of a CBF are presented, with the pulse observed in all
available EUV passbands (171, 195, 284 and for the first time, 304A). The pulse
displayed similar kinematics in all passbands, although the derived pulse
velocity and acceleration were found to be strongly influenced by the observing
cadence, implying that previous kinematics may have been underestimated.
Different techniques for identifying CBFs and deriving their true kinematics
were tested, with traditional techniques shown to be prone to undefined
user-dependent errors. This was overcome through the development of a
statistically rigorous, semi-automated identification algorithm, which was then
used to determine the kinematics of four CBF events observed by STEREO. All of
the events studied exhibited clear deceleration as well as increases in both
spatial and temporal pulse width, indicating that the CBFs are dispersive. A
CBF pulse observed by both STEREO and SDO was also studied using the algorithm,
with lower initial velocity and weaker deceleration noted in STEREO
observations compared to SDO, reaffirming the effects of image cadence on the
derived kinematics. The kinematics obtained using SDO were highly passband
dependent, suggesting a compressive nature. Significant pulse broadening was
also noted in observations from both spacecraft, allowing the dispersion rate
of the pulse to be determined. These results indicate that coronal bright
fronts are best interpreted as fast-mode magnetoacoustic waves propagating in
an inhomogeneous medium.
View original:
http://arxiv.org/abs/1202.4360
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