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1.
We present a multi-wavelength analysis of an eruption event that occurred in active region NOAA 11093 on 7 August 2010, using
data obtained from SDO, STEREO, RHESSI, and the GONG Hα network telescope. From these observations, we inferred that an upward
slow rising motion of an inverse S-shaped filament lying along the polarity inversion line resulted in a CME subsequent to
a two-ribbon flare. Interaction of overlying field lines across the filament with the side-lobe field lines, associated EUV
brightening, and flux emergence/cancelation around the filament were the observational signatures of the processes leading
to its destabilization and the onset of eruption. Moreover, the time profile of the rising motion of the filament/flux rope
corresponded well with flare characteristics, viz., the reconnection rate and hard X-ray emission profiles. The flux rope was accelerated to the maximum velocity as a CME
at the peak phase of the flare, followed by deceleration to an average velocity of 590 km s−1. We suggest that the observed emergence/cancelation of magnetic fluxes near the filament caused it to rise, resulting in
the tethers to cut and reconnection to take place beneath the filament; in agreement with the tether-cutting model. The corresponding
increase/decrease in positive/negative photospheric fluxes found in the post-peak phase of the eruption provides unambiguous
evidence of reconnection as a consequence of tether cutting. 相似文献
2.
Canceling magnetic features are commonly believed to result from magnetic reconnection in the low atmosphere. According to the Sweet–Parker type reconnection model, the rate of flux cancellation in a canceling magnetic feature is related to the converging speed of each pole. To test this prediction observationally, we have analyzed the time variation of two canceling magnetic features in detail using the high-resolution magnetograms taken by the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). As a result, we have obtained the rate and converging speed of flux cancellation in each feature: 1.3×1018 Mx hr–1 (or 1.1×106 G cm s–1 per unit contact length) and 0.35 km s–1 in the smaller one, and 3.5×1018 Mx hr–1 (1.2×106 G cm s–1) and 0.27 km s–1 in the bigger one. The observed speeds are found to be significantly bigger than the theoretically expected ones, but this discrepancy can be resolved if uncertainty factors such as low area filling factor of magnetic flux and low electric conductivity are taken into account. 相似文献
3.
Wahab Uddin Ramesh Chandra Syed Salman Ali 《Journal of Astrophysics and Astronomy》2006,27(2-3):267-276
We observed 4B/X17.2 flare in Hα from super-active region NOAA 10486 at ARIES, Nainital. This is one of the largest flares
of current solar cycle 23, which occurred near the Sun’s center and produced extremely energetic emission almost at all wavelengths
from γ-ray to radio-waves. The flare is associated with a bright/fast full-halo earth directed CME, strong type II, type III
and type IV radio bursts, an intense proton event and GLE. This flare is well observed by SOHO, RHESSI and TRACE. Our Hα observations
show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south-west direction
of the active region with bright shock front followed by rapid increase in intensity and area of the gigantic flare. The flare
shows almost similar evolution in Hα, EUV and UV. We measure the speed of Hα ribbon separation and the mean value is ∼ 70
km s-1. This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sources at the
flare maximum. In this paper, we also discuss the energetics of active region filament, flare and associated CME. 相似文献
4.
Using data from the Transition Region and Coronal Explorer (TRACE), Solar and Heliospheric Observatory (SOHO), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and Hida Observatory (HO), we present a detailed study of an EUV jet and the associated Hα filament eruption in
a major flare in the active region NOAA 10044 on 29 July 2002. In the Hα line wings, a small filament was found to erupt out
from the magnetic neutral line of the active region during the flare. Two bright EUV loops were observed rising and expanding
with the filament eruption, and both hot and cool EUV plasma ejections were observed to form the EUV jet. The two thermal
components spatially separated from each other and lasted for about 25 minutes. In the white-light corona data, a narrow coronal
mass ejection (CME) was found to respond to this EUV jet. We cannot find obvious emerging flux in the photosphere accounting
for the filament eruption and the EUV jet. However, significant sunspot decay and magnetic-flux cancelation owing to collision
of opposite flux before the events were noticed. Based on the hard X-ray data from RHESSI, which showed evidence of magnetic
reconnection along the main magnetic neutral line, we think that all of the observed dynamical phenomena, including the EUV
jet, filament eruption, flare, and CME, should have a close relation to the flux cancelation in the low atmosphere. 相似文献
5.
In this paper we study the evolution of magnetic fields of a 1F/2.4C solar flare and following magnetic flux cancellation. The data are Big Bear Solar Observatory and SOHO/MDI observations of active region NOAA 8375. The active region produced a multitude of subflares, many of them being clustered along the moat boundary in the area with mixed polarity magnetic fields. The study indicates a possible connection between the flare and the flux cancellation. The cancellation rate, defined from the data, was found to be 3×1019 Mx h–1. We observed strong upward directed plasma flows at the cancellation site. Suggesting that the cancellation is a result of reconnection process, we also found a reconnection rate of 0.5 km s–1, which is a significant fraction of Alfvén speed. The reconnection rate indicates a regime of fast photospheric reconnection happening during the cancellation. 相似文献
6.
Solar filaments show the position of large-scale polarity-inversion lines and are used for the reconstruction of large-scale
solar magnetic field structure on the basis of Hα synoptic charts for the periods that magnetographic measurements are not
available. Sometimes crossing filaments are seen in Hα filtergrams. We analyze daily Hα filtergrams from the archive of Big
Bear Solar Observatory for the period of 1999 – 2003 to find crossing and interacting filaments. A number of examples are
presented and filament patterns are compared with photospheric magnetic field distributions. We have found that all crossing
filaments reveal quadrupolar magnetic configurations of the photospheric field and presume the presence of null points in
the corona. 相似文献
7.
This paper describes a new 2D model for the photospheric evolution of the magnetic carpet. It is the first in a series of
papers working towards constructing a realistic 3D non-potential model for the interaction of small-scale solar magnetic fields.
In the model, the basic evolution of the magnetic elements is governed by a supergranular flow profile. In addition, magnetic
elements may evolve through the processes of emergence, cancellation, coalescence and fragmentation. Model parameters for
the emergence of bipoles are based upon the results of observational studies. Using this model, several simulations are considered,
where the range of flux with which bipoles may emerge is varied. In all cases the model quickly reaches a steady state where
the rates of emergence and cancellation balance. Analysis of the resulting magnetic field shows that we reproduce observed
quantities such as the flux distribution, mean field, cancellation rates, photospheric recycle time and a magnetic network.
As expected, the simulation matches observations more closely when a larger, and consequently more realistic, range of emerging
flux values is allowed (4×1016 – 1019 Mx). The model best reproduces the current observed properties of the magnetic carpet when we take the minimum absolute flux
for emerging bipoles to be 4×1016 Mx. In future, this 2D model will be used as an evolving photospheric boundary condition for 3D non-potential modeling. 相似文献
8.
Jana Kašparová Marian KarlickÝ Eduard P. Kontar Richard A. Schwartz Brian R. Dennis 《Solar physics》2005,232(1-2):63-86
A multi-wavelength spatial and temporal analysis of solar high-energy electrons is conducted using the August 20, 2002 flare
of an unusually flat (γ1 = 1.8) hard X-ray spectrum. The flare is studied using RHESSI, Hα, radio, TRACE, and MDI observations with advanced methods
and techniques never previously applied in the solar flare context. A new method to account for X-ray Compton backscattering
in the photosphere (photospheric albedo) has been used to deduce the primary X-ray flare spectra. The mean electron flux distribution
has been analysed using both forward fitting and model-independent inversion methods of spectral analysis. We show that the
contribution of the photospheric albedo to the photon spectrum modifies the calculated mean electron flux distribution, mainly
at energies below ∼100 keV. The positions of the Hα emission and hard X-ray sources with respect to the current-free extrapolation
of the MDI photospheric magnetic field and the characteristics of the radio emission provide evidence of the closed geometry
of the magnetic field structure and the flare process in low altitude magnetic loops. In agreement with the predictions of
some solar flare models, the hard X-ray sources are located on the external edges of the Hα emission and show chromospheric
plasma heated by the non-thermal electrons. The fast changes of Hα intensities are located not only inside the hard X-ray
sources, as expected if they are the signatures of the chromospheric response to the electron bombardment, but also away from
them. 相似文献
9.
Pankaj Kumar Ablishek K. Srivastava B. Filippov R. Erdélyi Wahab Uddin 《Solar physics》2011,272(2):301-317
We present the multiwavelength observations of a flux rope that was trying to erupt from NOAA AR 11045 and the associated
M-class solar flare on 12 February 2010 using space-based and ground-based observations from TRACE, STEREO, SOHO/MDI, Hinode/XRT, and BBSO. While the flux rope was rising from the active region, an M1.1/2F class flare was triggered near one of its
footpoints. We suggest that the flare triggering was due to the reconnection of a rising flux rope with the surrounding low-lying
magnetic loops. The flux rope reached a projected height of ≈0.15R
⊙ with a speed of ≈90 km s−1 while the soft X-ray flux enhanced gradually during its rise. The flux rope was suppressed by an overlying field, and the
filled plasma moved towards the negative polarity field to the west of its activation site. We found the first observational
evidence of the initial suppression of a flux rope due to a remnant filament visible both at chromospheric and coronal temperatures
that evolved a couple of days earlier at the same location in the active region. SOHO/MDI magnetograms show the emergence
of a bipole ≈12 h prior to the flare initiation. The emerged negative polarity moved towards the flux rope activation site,
and flare triggering near the photospheric polarity inversion line (PIL) took place. The motion of the negative polarity region
towards the PIL helped in the build-up of magnetic energy at the flare and flux rope activation site. This study provides
unique observational evidence of a rising flux rope that failed to erupt due to a remnant filament and overlying magnetic
field, as well as associated triggering of an M-class flare. 相似文献
10.
Jiangtao Su Yu Liu Hiroki Kurokawa Xinjie Mao Shangbin Yang Hongqi Zhang Haimin Wang 《Solar physics》2007,242(1-2):53-63
We present new observations of the interactions of two close, but distinct, Hα filaments and their successive eruptions on
5 November 1998. The magnetic fields of the filaments are both of the sinistral type. The interactions between the two filaments
were initiated mainly by an active filament of one of them. Before the filament eruptions, two dark plasma ejections and chromospheric
brightenings were observed. They indicate that possible magnetic reconnection had occurred between the two filaments. During
the first filament eruption, salient dark mass motions transferring from the left erupting filament into the right one were
observed. The right filament erupted 40 minutes later. This second filament eruption may have been the result of a loss of
stability owing to the sudden mass injection from the left filament. Based on the Hα observations, we have created a sketch
for understanding the interactions between two filaments and accompanying activities. The traditional theory of filament merger
requires that the filaments share the same filament channel and that the reconnection occurs between the two heads, as simulated
by DeVore, Antiochos, and Aulanier (Astrophys. J.
629, 1122, 2005; 646, 1349, 2006). Our interpretation is that the external bodily magnetic reconnection between flux ropes of the same chirality is another
possible way for two filament bodies to coalesce.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
11.
High-cadence, high-resolution magnetograms have shown that the quiet-Sun photosphere is very dynamic in nature. It is comprised
of discrete magnetic fragments which are characterized by four key processes – emergence, coalescence, fragmentation and cancellation.
All of this will have consequences for the magnetic field in the corona above.
The aim of this study is to gauge the effect of the behavior of the photospheric flux fragments on the quiet-Sun corona. By
considering a sequence of observed magnetograms, photospheric flux fragments are represented by a series of point sources
and the resulting potential field arising from them is examined. It is found that the quiet-Sun coronal flux is generally
recycled on time scales considerably shorter than the corresponding time scales for the recycling of photospheric flux. From
the motions of photospheric fragments alone, a recycling time of coronal flux of around 3 h is found. However, it is found
that the amount of reconnection driven by the motions of fragments is comparable to the amount driven by emergence and cancellation
of flux, resulting in a net flux replacement time for the corona of only 1.4 h.
The technique used in this study was briefly presented in a short research letter (R. M. Close et al., Astrophys. J., 612, L81, 2004); here the technique is discussed in far greater depth. Furthermore, an estimate is made of the currents required
to flow along separator field lines in order to sustain the observed heating rates (assuming separator reconnection is the
key mechanism by which the solar corona is heated). 相似文献
12.
Observations and analyses of two similar eruptive prominences on the north-east limb observed on 1980 April 27 at 0231 and
0517 UT, which are associated with the Boulder active region No. 2416 are presented. Both the eruptive prominences gave rise
to white-light coronal transients as observed by C/P experiment of High Altitude Observatory on the Solar Maximum Mission.
Type II and moving type IV radio bursts are reported in association with the first Hα eruptive prominence at 0231 UT.
Both the Hα eruptive prominences showed pulse activity with a quasi-periodicity of about 2–4 min. We estimate a magnetic field
in the eruptive prominence of about 100 G and a build-up rate ∼ 1026 ergs-1. The high build-up rate indicates that the shearing of the photospheric magnetic field, which fed the energy into the filament,
was rapid. It is proposed that fast-moving Hα features must have initiated the observed coronal transients. From Hα, type
II and coronal-transient observations, we estimate a magnetic field of 2.8 G at 1.9R⊙ from the disc centre, which agrees well with the earlier results. 相似文献
13.
We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which
has been reported by Isobe and Tripathi (Astron. Astrophys.
449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption
were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than
a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about
5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation.
The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional
motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers
per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified
the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament
oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was
evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We
also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in
the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium
and oscillated. 相似文献
14.
We present and interpret observations of the preflare phase of the eruptive flare of 15 November, 1991 in NOAA AR 6919. New
flux emerged in this region, indicated by arch filaments in Hα and increasing vertical flux in vector magnetograms. With increasing
frequency before the eruption, transient dark Hα fibrils were observed that crossed Hα bright plage and the magnetic inversion
line to extend from the region of flux emergence to the filament, whose eruption was associated with the flare. These crossing
fibrils were dynamic, and were often associated with sites of propagating torsional motion. These sites propagated from the
region of flux emergence into the filament flux system. We interpret these morphological and dynamic features in terms of
relaxation after magnetic reconnection episodes which create longer field lines within the filament flux system, as envisioned
in the tether cutting model, and transfer twist to it, as well.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005086108043 相似文献
15.
We analyze the role of weak photospheric flux concentrations that evolve in a filament channel, in the triggering of dynamic
changes in the shape of a filament. The high polarimetric sensitivity of THEMIS allowed us to detect weak flux concentrations
(few Gauss) associated with the filament development. The synoptic instruments (MDI, SOLIS) even if their sensitivity is much
less than THEMIS were useful to follow any subsequent strengthening of these flux concentrations after their identification
in the THEMIS magnetograms. We found that (1) the northern part of the filament develops an Hα barb at the same time that
weak minority polarity elements develop near a plage; (2) a section in the southern part of the Hα filament gradually disappears
and later reforms at the same time that several mixed-polarity magnetic elements appear, then subsequently cancel or spread
away from each other. These changes correspond to increases in EUV emission, as observed by TRACE, EIT, and CDS. This suggests
that the plasma is temporarily heated along the filament spine. An idealized sequence of force-free models of this filament
channel, based on plasma-supporting magnetic dips occurring in the windings of a very weakly twisted flux tube, naturally
explains the evolution of its southern part as being due to changes in the topology of the coronal magnetic field as the photospheric
flux concentrations evolve. 相似文献
16.
Maria D. Kazachenko Richard C. Canfield Dana W. Longcope Jiong Qiu 《Solar physics》2012,277(1):165-183
In order to better understand the solar genesis of interplanetary magnetic clouds (MCs), we model the magnetic and topological
properties of four large eruptive solar flares and relate them to observations. We use the three-dimensional Minimum Current Corona model (Longcope, 1996, Solar Phys.
169, 91) and observations of pre-flare photospheric magnetic field and flare ribbons to derive values of reconnected magnetic
flux, flare energy, flux rope helicity, and orientation of the flux-rope poloidal field. We compare model predictions of those
quantities to flare and MC observations, and within the estimated uncertainties of the methods used find the following: The
predicted model reconnection fluxes are equal to or lower than the reconnection fluxes inferred from the observed ribbon motions.
Both observed and model reconnection fluxes match the MC poloidal fluxes. The predicted flux-rope helicities match the MC
helicities. The predicted free energies lie between the observed energies and the estimated total flare luminosities. The
direction of the leading edge of the MC’s poloidal field is aligned with the poloidal field of the flux rope in the AR rather
than the global dipole field. These findings compel us to believe that magnetic clouds associated with these four solar flares
are formed by low-corona magnetic reconnection during the eruption, rather than eruption of pre-existing structures in the
corona or formation in the upper corona with participation of the global magnetic field. We also note that since all four
flares occurred in active regions without significant pre-flare flux emergence and cancelation, the energy and helicity that
we find are stored by shearing and rotating motions, which are sufficient to account for the observed radiative flare energy
and MC helicity. 相似文献
17.
The solar wind conditions at one astronomical unit (AU) can be strongly disturbed by interplanetary coronal mass ejections
(ICMEs). A subset, called magnetic clouds (MCs), is formed by twisted flux ropes that transport an important amount of magnetic
flux and helicity, which is released in CMEs. At 1 AU from the Sun, the magnetic structure of MCs is generally modeled by
neglecting their expansion during the spacecraft crossing. However, in some cases, MCs present a significant expansion. We
present here an analysis of the huge and significantly expanding MC observed by the Wind spacecraft during 9 – 10 November 2004. This MC was embedded in an ICME. After determining an approximate orientation for
the flux rope using the minimum variance method, we obtain a precise orientation of the cloud axis by relating its front and
rear magnetic discontinuities using a direct method. This method takes into account the conservation of the azimuthal magnetic
flux between the inbound and outbound branches and is valid for a finite impact parameter (i.e., not necessarily a small distance between the spacecraft trajectory and the cloud axis). The MC is also studied using dynamic
models with isotropic expansion. We have found (6.2±1.5)×1020 Mx for the axial flux and (78±18)×1020 Mx for the azimuthal flux. Moreover, using the direct method, we find that the ICME is formed by a flux rope (MC) followed
by an extended coherent magnetic region. These observations are interpreted by considering the existence of a previously larger
flux rope, which partially reconnected with its environment in the front. We estimate that the reconnection process started
close to the Sun. These findings imply that the ejected flux rope is progressively peeled by reconnection and transformed
to the observed ICME (with a remnant flux rope in the front part). 相似文献
18.
Ayumi Asai Takaaki Yokoyama Masumi Shimojo Satoshi Masuda Kazunari Shibata 《Journal of Astrophysics and Astronomy》2006,27(2-3):167-173
We report a detailed examination about the relationship between the evolution of the Hα flare ribbons and the released magnetic
energy during the April 10 2001 flare. In the Hα images, several bright kernels are observed in the flare ribbons. We identified
the conjugated foot-points, by analyzing the lightcurves at each Hα kernels, and showed their connectivities during the flare.
Then, based on the magnetic reconnection model, we calculated quantitatively the released energy by using the photospheric
magnetic field strengths and separation speeds of the Hα flare ribbons. Finally, we examined the downward motions which are
observed at the Hα kernels. We found that the stronger the red-asymmetry tends to be associated with the brighter the Hα kernel. 相似文献
19.
We studied the behavior of magnetic field, horizontal motion and helicity in a fast emerging flux region NOAA 10488 which
eventually forms a δ spot. It is found that the rotation of photospheric footpoints forms in the earlier stage of magnetic
flux emergence and the relative shear motion of different magnetic flux systems appears later in this active region (AR).
Therefore the emerging process of the AR can be separated into two phases: rotation and shear. We have computed the magnetic
helicity injected into the corona using the local correlation tracking (LCT) technique. Furthermore we determined the vertical
component of current helicity density and the vertical component of induction electric fields Ez = (V× B)z in the photosphere. Particularly we have presented the comparison of the injection rate of magnetic helicity and the variation
of the current helicity density. The main results are as follows: (1) The strong shear motion (SSM) between the new emerging
flux system and the old one brings more magnetic helicity into the corona than the twisting motions. (2) After the maturity
of the main bipolar spots, their twist decreases and the SSM becomes dominant and the major contributor of magnetic non-potentiality
in the solar atmosphere in this AR. (3) The positions of the maxima of Ez (about 0.1 ∼ 0.2 V cm−1) shift from the twisting areas to the areas showing SSMs as the AR evolved from the rotation phase to the shear one, but
no obvious correlation is found between the kernels of Hα flare and Ez for the M1.6 flare in this AR. (4) The coronal helicity inferred from the horizontal motion of this AR amounts to −6 × 1043 Mx2. It is comparable with the coronal helicity of ARs producing flares with coronal mass ejections (CMEs) or helicity carried
away by magnetic clouds (MCs) reported in previous studies (Nindos, Zhang, and Zhang, 2003; Nindos and Andrews, 2004). In
addition, the formation of the δ configuration in this AR belongs to the third formation type indicated by Zirin and Liggett
(1987), i.e., collision of opposite polarities from different dipoles, and can be naturally explained by the SSM. 相似文献
20.
Integrating 26 624 pairs of video frames, the authors have mapped the circular polarization in an active-region filament against
the solar disk by using a traditional magnetograph working at the Hβ line. This filament, offset the disk center, appeared
at the boundary of three decayed active regions. It was quiet and away from any strong enhanced network. The mapped circular
polarization in the filament has an average polarization degree of 1.1×10−3 with a measurement precision of 4×10−4. The mapping of circular polarization in a filament may provide a supplementary diagnosis of the filament magnetic field,
in addition to the mapping of linear polarization via the Hanle effect. However, the interpretation of the circular polarization
requires treatment of the full quantum problem of Zeeman and non-Zeeman effects of Stokes line profiles. 相似文献