171 research outputs found
Sunspot waves and flare energy release
We address a possibility of the flare process initiation and further
maintenance of its energy release due to a transformation of sunspot
longitudinal waves into transverse magnetic loop oscillations with initiation
of reconnection. This leads to heating maintaining after the energy release
peak and formation of a flat stage on the X-ray profile. We applied the
time-distance plots and pixel wavelet filtration (PWF) methods to obtain
spatio-temporal distribution of wave power variations in SDO/AIA data. To find
magnetic waveguides, we used magnetic field extrapolation of SDO/HMI
magnetograms. The propagation velocity of wave fronts was measured from their
spatial locations at specific times. In correlation curves of the 17 GHz (NoRH)
radio emission we found a monotonous energy amplification of 3-min waves in the
sunspot umbra before the 2012 June 7 flare. This dynamics agrees with an
increase in the wave-train length in coronal loops (SDO/AIA, 171 {\AA})
reaching the maximum 30 minutes prior to the flare onset. A peculiarity of this
flare time profile in soft X-rays (RHESSI, 3-25 keV) is maintaining the
constant level of the flare emission for 10 minutes after the short impulse
phase, which indicates at the energy release continuation. Throughout this
time, we found 30-sec period transverse oscillations of the flare loop in the
radio-frequency range (NoRH, 17 GHz). This periodicity is apparently related to
the transformation of propagating longitudinal 3-min waves from the sunspot
into the loop transverse oscillations. The magnetic field extrapolation showed
the existence of the magnetic waveguide (loop) connecting the sunspot with the
energy release region. A flare loop heating can be caused by the interaction
(reconnections) of this transversally oscillating waveguide with the underlying
twisted loops.Comment: 7 pages, 9 figure
Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions
Eruptive solar flares were predicted to generate large-scale vortex flows at
both sides of the erupting magnetic flux rope. This process is analogous to a
well-known hydrodynamic process creating vortex rings. The vortices lead to
advection of closed coronal loops located at peripheries of the flaring active
region. Outward flows are expected in the upper part and returning flows in the
lower part of the vortex. Here, we examine two eruptive solar flares, an
X1.1-class flare SOL2012-03-05T03:20 and a C3.5-class SOL2013-06-19T07:29. In
both flares, we find that the coronal loops observed by the Atmospheric Imaging
Assembly in its 171\,\AA, 193\,\AA, or 211\,\AA~passbands show coexistence of
expanding and contracting motions, in accordance with the model prediction. In
the X-class flare, multiple expanding/contracting loops coexist for more than
35 minutes, while in the C-class flare, an expanding loop in 193\,\AA~appears
to be close-by and co-temporal with an apparently imploding loop arcade seen in
171\,\AA. Later, the 193\,\AA~loop also switches to contraction. These
observations are naturally explained by vortex flows present in a model of
eruptive solar flares.Comment: The Astrophysical Journal, accepte
Slipping magnetic reconnection during an X-Class solar flare observed by SDO/AIA
We present SDO/AIA observations of an eruptive X-class flare of July 12,
2012, and compare its evolution with the predictions of a 3D numerical
simulation. We focus on the dynamics of flare loops that are seen to undergo
slipping reconnection during the flare. In the AIA 131A observations, lower
parts of 10 MK flare loops exhibit an apparent motion with velocities of
several tens of km/s along the developing flare ribbons. In the early stages of
the flare, flare ribbons consist of compact, localized bright transition-region
emission from the footpoints of the flare loops. A DEM analysis shows that the
flare loops have temperatures up to the formation of Fe XXIV. A series of very
long, S-shaped loops erupt, leading to a CME observed by STEREO. The observed
dynamics are compared with the evolution of magnetic structures in the
"standard solar flare model in 3D". This model matches the observations well,
reproducing both the apparently slipping flare loops, S-shaped erupting loops,
and the evolution of flare ribbons. All of these processes are explained via 3D
reconnection mechanisms resulting from the expansion of a torus-unstable flux
rope. The AIA observations and the numerical model are complemented by radio
observations showing a noise storm in the metric range. Dm-drifting pulsation
structures occurring during the eruption indicate plasmoid ejection and
enhancement of reconnection rate. The bursty nature of radio emission shows
that the slipping reconnection is still intermittent, although it is observed
to persist for more than an hour
Slipping magnetic reconnection, chromospheric evaporation, implosion, and precursors in the 2014 September 10 X1.6-class solar flare
© 2016. The American Astronomical Society. All rights reserved.. We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. Slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions toward both ends of the ribbons. Velocities of 20-40 km s-1 are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset of apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the Interface Region Imaging Spectrograph slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures, including localized EUV brightenings as well as nonthermal X-ray emission, are signatures of the flare itself, progressing from the early phase toward the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in three dimensions
Density diagnostics derIVed from the O IV and S IV intercombination lines observed by IRIS
The intensity of the \oiv~2s 2p P-2s2p P and \siv~3
s 3p P- 3s 3p P intercombination lines around
1400~\AA~observed with the \textit{Interface Region Imaging Spectrograph}
(IRIS) provide a useful tool to diagnose the electron number density
() in the solar transition region plasma. We measure the electron
number density in a variety of solar features observed by IRIS, including an
active region (AR) loop, plage and brightening, and the ribbon of the
22-June-2015 M 6.5 class flare. By using the emissivity ratios of \oiv\ and
\siv\ lines, we find that our observations are consistent with the emitting
plasma being near isothermal (log[K] 5) and iso-density
( ~10 cm) in the AR loop. Moreover, high
electron number densities ( ~10 cm) are
obtained during the impulsive phase of the flare by using the \siv\ line ratio.
We note that the \siv\ lines provide a higher range of density sensitivity than
the \oiv\ lines. Finally, we investigate the effects of high densities
( 10 cm) on the ionization balance. In
particular, the fractional ion abundances are found to be shifted towards lower
temperatures for high densities compared to the low density case. We also
explored the effects of a non-Maxwellian electron distribution on our
diagnostic method.VP acknowledges support from the Isaac Newton Studentship, the Cambridge Trust, the IRIS team at Harvard-Smithsonian Centre for Astrophysics and the RS Newton Alumni Programme. GDZ and HEM acknowledge support from the STFC and the RS Newton Alumni Programme. JD acknowledges support from the RS Newton Alumni Programme. JD also acknowledges support from the Grant No. P209/12/1652 of the Grant Agency of the Czech Republic. AG acknowledges the in house research support provided by the Science and Technology Facilities Council. KR is supported by contract 8100002705 from Lockheed-Martin to SAO. IRIS is a NASA small explorer mission developed and operated by LMSAL with mission operations executed at NASA Ames Research Center and major contributions to downlink communications funded by the Norwegian Space Center (NSC, Norway) through an ESA PRODEX contract. AIA data are courtesy of NASA/SDO and the respective science teams. CHIANTI is a collaborative project involving researchers at the universities of Cambridge (UK), George Mason and Michigan (USA). ADAS is a project managed at the University of Strathclyde (UK) and funded through memberships universities and astrophysics and fusion laboratories in Europe and worldwide.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by EDP Sciences
Direct observation of the energy release site in a solar flare by SDO/AIA, Hinode/EIS and RHESSI
We present direct evidence for the detection of the main energy release site
in a non-eruptive solar flare, SOL2013-11-09T06:38UT. This GOES C2.7 event was
characterised by two flaring ribbons and a compact, bright coronal source
located between them, which is the focus of our study. We use imaging from
SDO/AIA, and imaging spectroscopy from RHESSI to characterise the thermal and
non-thermal emission from the coronal source, and EUV spectroscopy from the
Hinode/EIS, which scanned the coronal source during the impulsive peak, to
analyse Doppler shifts in Fe XII and Fe XXIV emission lines, and determine the
source density. The coronal source exhibited an impulsive emission lightcurve
in all AIA filters during the impulsive phase. RHESSI hard X-ray images
indicate both thermal and non-thermal emission at the coronal source, and its
plasma temperature derived from RHESSI imaging spectroscopy shows an impulsive
rise, reaching a maximum at 12-13 MK about 10 seconds prior to the hard X-ray
peak. High redshifts associated with this bright source indicate downflows of
40-250 km/s at a broad range of temperatures, interpreted as loop shrinkage
and/or outflows along the magnetic field. Outflows from the coronal source
towards each ribbon are also observed by AIA images at 171, 193, 211, 304 and
1600 A. The electron density of the source obtained from a Fe XIV line pair is
which is collisionally thick to electrons with energy up to 45-65
keV, responsible for the source's non-thermal X-ray emission. We conclude that
the bright coronal source is the location of the main release of magnetic
energy in this flare, with a geometry consistent with component reconnection
between crossing, current-carrying loops. We argue that the energy that can be
released via reconnection, based on observational estimates, can plausibly
account for the non-thermal energetics of the flare.Comment: 10 pages, 7 figure
3D evolution of a filament disappearance event observed by STEREO
A filament disappearance event was observed on 22 May 2008 during our recent
campaign JOP 178. The filament, situated in the southern hemisphere, showed
sinistral chirality consistent with the hemispheric rule. The event was well
observed by several observatories in particular by THEMIS. One day before the
disappearance, H observations showed up and down flows in adjacent
locations along the filament, which suggest plasma motions along twisted flux
rope. THEMIS and GONG observations show shearing photospheric motions leading
to magnetic flux canceling around barbs. STEREO A, B spacecraft with separation
angle 52.4 degrees, showed quite different views of this untwisting flux rope
in He II 304 \AA\ images. Here, we reconstruct the 3D geometry of the filament
during its eruption phase using STEREO EUV He II 304 \AA\ images and find that
the filament was highly inclined to the solar normal. The He II 304 \AA\ movies
show individual threads, which oscillate and rise to an altitude of about 120
Mm with apparent velocities of about 100 km s, during the rapid
evolution phase. Finally, as the flux rope expands into the corona, the
filament disappears by becoming optically thin to undetectable levels. No CME
was detected by STEREO, only a faint CME was recorded by LASCO at the beginning
of the disappearance phase at 02:00 UT, which could be due to partial filament
eruption. Further, STEREO Fe XII 195 \AA\ images showed bright loops beneath
the filament prior to the disappearance phase, suggesting magnetic reconnection
below the flux rope
On the structure and evolution of a polar crown prominence/filament system
Polar crown prominences are made of chromospheric plasma partially circling
the Suns poles between 60 and 70 degree latitude. We aim to diagnose the 3D
dynamics of a polar crown prominence using high cadence EUV images from the
Solar Dynamics Observatory (SDO)/AIA at 304 and 171A and the Ahead spacecraft
of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195A. Using
time series across specific structures we compare flows across the disk in 195A
with the prominence dynamics seen on the limb. The densest prominence material
forms vertical columns which are separated by many tens of Mm and connected by
dynamic bridges of plasma that are clearly visible in 304/171A two-color
images. We also observe intermittent but repetitious flows with velocity 15
km/s in the prominence that appear to be associated with EUV bright points on
the solar disk. The boundary between the prominence and the overlying cavity
appears as a sharp edge. We discuss the structure of the coronal cavity seen
both above and around the prominence. SDO/HMI and GONG magnetograms are used to
infer the underlying magnetic topology. The evolution and structure of the
prominence with respect to the magnetic field seems to agree with the filament
linkage model.Comment: 24 pages, 14 figures, Accepted for publication in Solar Physics
Journal, Movies can be found at http://www2.mps.mpg.de/data/outgoing/panesar
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