1,694 research outputs found
Fan-spine topology formation through two-step reconnection driven by twisted flux emergence
We address the formation of 3D nullpoint topologies in the solar corona by
combining Hinode/XRT observations of a small dynamic limb event, which occurred
beside a non-erupting prominence cavity, with a 3D zero-beta MHD simulation. To
this end, we model the boundary-driven kinematic emergence of a compact,
intense, and uniformly twisted flux tube into a potential field arcade that
overlies a weakly twisted coronal flux rope. The expansion of the emerging flux
in the corona gives rise to the formation of a nullpoint at the interface of
the emerging and the pre-existing fields. We unveil a two-step reconnection
process at the nullpoint that eventually yields the formation of a broad 3D
fan-spine configuration above the emerging bipole. The first reconnection
involves emerging fields and a set of large-scale arcade field lines. It
results in the launch of a torsional MHD wave that propagates along the
arcades, and in the formation of a sheared loop system on one side of the
emerging flux. The second reconnection occurs between these newly formed loops
and remote arcade fields, and yields the formation of a second loop system on
the opposite side of the emerging flux. The two loop systems collectively
display an anenome pattern that is located below the fan surface. The flux that
surrounds the inner spine field line of the nullpoint retains a fraction of the
emerged twist, while the remaining twist is evacuated along the reconnected
arcades. The nature and timing of the features which occur in the simulation do
qualititatively reproduce those observed by XRT in the particular event studied
in this paper. Moreover, the two-step reconnection process suggests a new
consistent and generic model for the formation of anemone regions in the solar
corona.Comment: Accepted for publication in ApJ, 11 pages and 5 figure
Bending and Shear Stresses Developed by the Instantaneous Arrest of the Root of a Cantilever Beam with a Mass at Its Tip
Major Surge Activity of Super-Active Region NOAA 10484
We observed two surges in H-alpha from the super-active region NOAA 10484.
The first surge was associated with an SF/C4.3 class flare. The second one was
a major surge associated with a SF/C3.9 flare. This surge was also observed
with SOHO/EIT in 195 angstrom and NoRh in 17 GHz, and showed similar evolution
in these wavelengths. The major surge had an ejective funnel-shaped spray
structure with fast expansion in linear (about 1.2 x 10^5 km) and angular
(about 65 deg) size during its maximum phase. The mass motion of the surge was
along open magnetic field lines, with average velocity about 100 km/s. The
de-twisting motion of the surge reveals relaxation of sheared and twisted
magnetic flux. The SOHO/MDI magnetograms reveal that the surges occurred at the
site of companion sunspots where positive flux emerged, converged, and canceled
against surrounding field of opposite polarity. Our observations support
magnetic reconnection models for the surges and jets.Comment: 4 pages, 3 figures; To appear in "Magnetic Coupling between the
Interior and the Atmosphere of the Sun", eds. S.S. Hasan and R.J. Rutten,
Astrophysics and Space Science Series, Springer-Verlag, Heidelberg, Berlin,
200
Observations of Multiple Surges Associated with Magnetic Activities in AR10484 on 25 October 2003
We present a multiwavelength study of recurrent surges observed in H{\alpha},
UV (SOHO/EIT) and Radio (Learmonth, Australia) from the super-active region
NOAA 10484 on 25 October, 2003. Several bright structures visible in H{\alpha}
and UV corresponding to subflares are also observed at the base of each surge.
Type III bursts are triggered and RHESSI X-ray sources are evident with surge
activity. The major surge consists of the bunches of ejective paths forming a
fan-shape region with an angular size of (\approx 65\degree) during its maximum
phase. The ejection speed reaches upto \sim200 km/s. The SOHO/MDI magnetograms
reveal that a large dipole emerges east side of the active region on 18-20
October 2003, a few days before the surges. On October 25, 2003, the major
sunspots were surrounded by "moat regions" with moving magnetic features
(MMFs). Parasitic fragmented positive polarities were pushed by the ambient
dispersion motion of the MMFs and annihilated with negative polarities at the
borders of the moat region of the following spot to produce flares and surges.
A topology analysis of the global Sun using PFSS shows that the fan structures
visible in the EIT 171 A images follow magnetic field lines connecting the
present AR to a preceding AR in the South East. Radio observations of type III
bursts indicate that they are coincident with the surges, suggesting that
magnetic reconnection is the driver mechanism. The magnetic energy released by
reconnection is transformed into plasma heating and provides the kinetic energy
for the ejections. A lack of a radio signature in the high corona suggests that
the surges are confined to follow the closed field lines in the fans. We
conclude that these cool surges may have some local heating effects in the
closed loops, but probably play a minor role in global coronal heating and the
surge material does not escape to the solar wind.Comment: Accepted for the Publication in ApJ; 25 pages, 10 Figures, and 1
Tabl
Magnetic field in atypical prominence structures: Bubble, tornado and eruption
Spectropolarimetric observations of prominences have been obtained with the
THEMIS telescope during four years of coordinated campaigns. Our aim is now to
understand the conditions of the cool plasma and magnetism in `atypical'
prominences, namely when the measured inclination of the magnetic field
departs, to some extent, from the predominantly horizontal field found in
`typical' prominences. What is the role of the magnetic field in these
prominence types? Are plasma dynamics more important in these cases than the
magnetic support? We focus our study on three types of `atypical' prominences
(tornadoes, bubbles and jet-like prominence eruptions) that have all been
observed by THEMIS in the He I D_3 line, from which the Stokes parameters can
be derived. The magnetic field strength, inclination and azimuth in each pixel
are obtained by using the Principal Component Analysis inversion method on a
model of single scattering in the presence of the Hanle effect. The magnetic
field in tornadoes is found to be more or less horizontal, whereas for the
eruptive prominence it is mostly vertical. We estimate a tendency towards
higher values of magnetic field strength inside the bubbles than outside in the
surrounding prominence. In all of the models in our database, only one magnetic
field orientation is considered for each pixel. While sufficient for most of
the main prominence body, this assumption appears to be oversimplified in
atypical prominence structures. We should consider these observations as the
result of superposition of multiple magnetic fields, possibly even with a
turbulent field component.Comment: 13 pages, 9 figure
Propagating Waves Transverse to the Magnetic Field in a Solar Prominence
We report an unusual set of observations of waves in a large prominence
pillar which consist of pulses propagating perpendicular to the prominence
magnetic field. We observe a huge quiescent prominence with the Solar Dynamics
Observatory (SDO) Atmospheric Imaging Assembly (AIA) in EUV on 2012 October 10
and only a part of it, the pillar, which is a foot or barb of the prominence,
with the Hinode Solar Optical Telescope (SOT) (in Ca II and H\alpha lines), Sac
Peak (in H\alpha, H\beta\ and Na-D lines), THEMIS ("T\'elescope
H\'eliographique pour l' Etude du Magn\'etisme et des Instabilit\'es Solaires")
with the MTR (MulTi-Raies) spectropolarimeter (in He D_3 line). The THEMIS/MTR
data indicates that the magnetic field in the pillar is essentially horizontal
and the observations in the optical domain show a large number of horizontally
aligned features on a much smaller scale than the pillar as a whole. The data
is consistent with a model of cool prominence plasma trapped in the dips of
horizontal field lines. The SOT and Sac Peak data over the 4 hour observing
period show vertical oscillations appearing as wave pulses. These pulses, which
include a Doppler signature, move vertically, perpendicular to the field
direction, along thin quasi-vertical columns in the much broader pillar. The
pulses have a velocity of propagation of about 10 km/s, a period about 300 sec,
and a wavelength around 2000 km. We interpret these waves in terms of fast
magneto-sonic waves and discuss possible wave drivers.Comment: Accepted for publication in The Astrophysical Journa
Open questions on prominences from coordinated observations by IRIS, Hinode, SDO/AIA, THEMIS, and the Meudon/MSDP
Context. A large prominence was observed on September 24, 2013, for three
hours (12:12 UT -15:12 UT) with the newly launched (June 2013) Interface Region
Imaging Spectrograph (IRIS), THEMIS (Tenerife), the Hinode Solar Optical
Telescope (SOT), the Solar Dynamic Observatory Atmospheric Imaging Assembly
(SDO/AIA), and the Multichannel Subtractive Double Pass spectrograph (MSDP) in
the Meudon Solar Tower. Aims. The aim of this work is to study the dynamics of
the prominence fine structures in multiple wavelengths to understand their
formation. Methods. The spectrographs IRIS and MSDP provided line profiles with
a high cadence in Mg II and in Halpha lines. Results. The magnetic field is
found to be globally horizontal with a relatively weak field strength (8-15
Gauss). The Ca II movie reveals turbulent-like motion that is not organized in
specific parts of the prominence. On the other hand, the Mg II line profiles
show multiple peaks well separated in wavelength. Each peak corresponds to a
Gaussian profile, and not to a reversed profile as was expected by the present
non-LTE radiative transfer modeling. Conclusions. Turbulent fields on top of
the macroscopic horizontal component of the magnetic field supporting the
prominence give rise to the complex dynamics of the plasma. The plasma with the
high velocities (70 km/s to 100 km/s if we take into account the transverse
velocities) may correspond to condensation of plasma along more or less
horizontal threads of the arch-shape structure visible in 304 A. The steady
flows (5 km/s) would correspond to a more quiescent plasma (cool and
prominence-corona transition region) of the prominence packed into dips in
horizontal magnetic field lines. The very weak secondary peaks in the Mg II
profiles may reflect the turbulent nature of parts of the prominence.Comment: 15 pages, 14 figure
Can we explain non-typical solar flares?
We used multi-wavelength high-resolution data from ARIES, THEMIS, and SDO
instruments, to analyze a non-standard, C3.3 class flare produced within the
active region NOAA 11589 on 2012 October 16. Magnetic flux emergence and
cancellation were continuously detected within the active region, the latter
leading to the formation of two filaments.
Our aim is to identify the origins of the flare taking into account the
complex dynamics of its close surroundings.
We analyzed the magnetic topology of the active region using a linear
force-free field extrapolation to derive its 3D magnetic configuration and the
location of quasi-separatrix layers (QSLs) which are preferential sites for
flaring activity. Because the active region's magnetic field was nonlinear
force-free, we completed a parametric study using different linear force-free
field extrapolations to demonstrate the robustness of the derived QSLs.
The topological analysis shows that the active region presented a complex
magnetic configuration comprising several QSLs. The considered data set
suggests that an emerging flux episode played a key role for triggering the
flare. The emerging flux likely activated the complex system of QSLs leading to
multiple coronal magnetic reconnections within the QSLs. This scenario accounts
for the observed signatures: the two extended flare-ribbons developed at
locations matched by the photospheric footprints of the QSLs, and were
accompanied with flare loops that formed above the two filaments which played
no important role in the flare dynamics.
This is a typical example of a complex flare that can a-priori show standard
flare signatures that are nevertheless impossible to interpret with any
standard model of eruptive or confined flare. We find that a topological
analysis however permitted to unveil the development of such complex sets of
flare signatures.Comment: 13 pages, Accepted in A&
Twisting solar coronal jet launched at the boundary of an active region
A broad jet was observed in a weak magnetic field area at the edge of active
region NOAA 11106. The peculiar shape and magnetic environment of the broad jet
raised the question of whether it was created by the same physical processes of
previously studied jets with reconnection occurring high in the corona. We
carried out a multi-wavelength analysis using the EUV images from the
Atmospheric Imaging Assembly (AIA) and magnetic fields from the Helioseismic
and Magnetic Imager (HMI) both on-board the SDO satellite. The jet consisted of
many different threads that expanded in around 10 minutes to about 100 Mm in
length, with the bright features in later threads moving faster than in the
early ones, reaching a maximum speed of about 200 km s^{-1}. Time-slice
analysis revealed a striped pattern of dark and bright strands propagating
along the jet, along with apparent damped oscillations across the jet. This is
suggestive of a (un)twisting motion in the jet, possibly an Alfven wave. A
topological analysis of an extrapolated field was performed. Bald patches in
field lines, low-altitude flux ropes, diverging flow patterns, and a null point
were identified at the basis of the jet. Unlike classical lambda or
Eiffel-tower shaped jets that appear to be caused by reconnection in current
sheets containing null points, reconnection in regions containing bald patches
seems to be crucial in triggering the present jet. There is no observational
evidence that the flux ropes detected in the topological analysis were actually
being ejected themselves, as occurs in the violent phase of blowout jets;
instead, the jet itself may have gained the twist of the flux rope(s) through
reconnection. This event may represent a class of jets different from the
classical quiescent or blowout jets, but to reach that conclusion, more
observational and theoretical work is necessary.Comment: 12 pages, 9 figures, accepted for publication in A&
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