92 research outputs found
Rapid Rotation of an Erupting Prominence and the Associated Coronal Mass Ejection on 13 May 2013
In this paper, we report the multiwavelength observations of an erupting
prominence and the associated CME on 13 May 2013. The event occurs behind the
western limb in the field of view of SDO/AIA. The prominence is supported by a
highly twisted magnetic flux rope and shows rapid rotation in the
counterclockwise direction during the rising motion. The rotation of the
prominence lasts for 47 minutes. The average period, angular speed, and
linear speed are 806 s, 0.46 rad min, and 355 km
s, respectively. The total twist angle reaches 7, which is
considerably larger than the threshold for kink instability. Writhing motion
during 17:4217:46 UT is clearly observed by SWAP in 174 {\AA} and EUVI on
board the behind STEREO spacecraft in 304 {\AA} after reaching an apparent
height of 405\,Mm. Therefore, the prominence eruption is most probably
triggered by kink instability. A pair of conjugate flare ribbons and post-flare
loops are created and observed by STA/EUVI. The onset time of writhing motion
is consistent with the commencement of the impulsive phase of the related
flare. The 3D morphology and positions of the associated CME are derived using
the graduated cylindrical shell (GCS) modeling. The kinetic evolution of the
reconstructed CME is divided into a slow-rise phase (330 km s) and
a fast-rise phase (1005 km s) by the writhing motion. The edge-on
angular width of the CME is a constant (60), while the face-on
angular width increases from 96 to 114, indicating a
lateral expansion. The latitude of the CME source region decreases slightly
from 18 to 13, implying an equatorward
deflection during propagation.Comment: 28 pages, 20 figures, accepted for publication in Solar Physics,
comments are welcom
Early Abnormal Temperature Structure of X-ray Looptop Source of Solar Flares
This Letter is to investigate the physics of a newly discovered phenomenon --
contracting flare loops in the early phase of solar flares. In classical flare
models, which were constructed based on the phenomenon of expansion of flare
loops, an energy releasing site is put above flare loops. These models can
predict that there is a vertical temperature gradient in the top of flare loops
due to heat conduction and cooling effects. Therefore, the centroid of an X-ray
looptop source at higher energy bands will be higher in altitude, for which we
can define as normal temperature distribution. With observations made by {\it
RHESSI}, we analyzed 10 M- or X-class flares (9 limb flares). For all these
flares, the movement of looptop sources shows an obvious U-shaped trajectory,
which we take as the signature of contraction-to-expansion of flare loops. We
find that, for all these flares, normal temperature distribution does exist,
but only along the path of expansion. The temperature distribution along the
path of contraction is abnormal, showing no spatial order at all. The result
suggests that magnetic reconnection processes in the contraction and expansion
phases of these solar flares are different.Comment: 11 pages, 4 figure
Sunspot shearing and sudden retraction motion associated with the 2013 August 17 M3.3 Flare
In this Letter, we give a detailed analysis to the M3.3 class flare that
occurred on August 17, 2013 (SOL2013-08-17T18:16). It presents a clear picture
of mutual magnetic interaction initially from the photosphere to the corona via
the abrupt rapid shearing motion of a small sunspot before the flare, and then
suddenly from the corona back to the photosphere via the sudden retraction
motion of the same sunspot during the flare impulsive phase. About 10 hours
before the flare, a small sunspot in the active region NOAA 11818 started to
move northeast along a magnetic polarity inversion line (PIL), creating a
shearing motion that changed the quasi-static state of the active region. A
filament right above the PIL was activated following the movement of the
sunspot and then got partially erupted. The eruption eventually led to the M3.3
flare. The sunspot was then suddenly pulled back to the opposite direction upon
the flare onset. During the backward motion, the Lorentz force underwent a
simultaneous impulsive change both in magnitude and direction. Its directional
change is found to be conformable with the retraction motion. The observation
provides direct evidence for the role of the shearing motion of the sunspot in
powering and triggering the flare. It especially confirms that the abrupt
motion of a sunspot during a solar flare is the result of a back reaction
caused by the reconfiguration of the coronal magnetic field
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