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1.
Formation of a Flare-Productive Active Region: Observation and Numerical Simulation of NOAA AR 11158
We present a comparison of the Solar Dynamics Observatory (SDO) analysis of NOAA Active Region (AR) 11158 and numerical simulations of flux-tube emergence, aiming to investigate the formation process of this flare-productive AR. First, we use SDO/Helioseismic and Magnetic Imager (HMI) magnetograms to investigate the photospheric evolution and Atmospheric Imaging Assembly (AIA) data to analyze the relevant coronal structures. Key features of this quadrupolar region are a long sheared polarity inversion line (PIL) in the central δ-sunspots and a coronal arcade above the PIL. We find that these features are responsible for the production of intense flares, including an X2.2-class event. Based on the observations, we then propose two possible models for the creation of AR 11158 and conduct flux-emergence simulations of the two cases to reproduce this AR. Case 1 is the emergence of a single flux tube, which is split into two in the convection zone and emerges at two locations, while Case 2 is the emergence of two isolated but neighboring tubes. We find that, in Case 1, a sheared PIL and a coronal arcade are created in the middle of the region, which agrees with the AR 11158 observation. However, Case 2 never builds a clear PIL, which deviates from the observation. Therefore, we conclude that the flare-productive AR 11158 is, between the two cases, more likely to be created from a single split emerging flux than from two independent flux bundles. 相似文献
2.
The nature of three-dimensional reconnection when a twisted flux tube erupts during an eruptive flare or coronal mass ejection is considered. The reconnection has two phases: first of all, 3D “zipper reconnection” propagates along the initial coronal arcade, parallel to the polarity inversion line (PIL); then subsequent quasi-2D “main-phase reconnection” in the low corona around a flux rope during its eruption produces coronal loops and chromospheric ribbons that propagate away from the PIL in a direction normal to it. One scenario starts with a sheared arcade: the zipper reconnection creates a twisted flux rope of roughly one turn (\(2\pi \) radians of twist), and then main-phase reconnection builds up the bulk of the erupting flux rope with a relatively uniform twist of a few turns. A second scenario starts with a pre-existing flux rope under the arcade. Here the zipper phase can create a core with many turns that depend on the ratio of the magnetic fluxes in the newly formed flare ribbons and the new flux rope. Main phase reconnection then adds a layer of roughly uniform twist to the twisted central core. Both phases and scenarios are modeled in a simple way that assumes the initial magnetic flux is fragmented along the PIL. The model uses conservation of magnetic helicity and flux, together with equipartition of magnetic helicity, to deduce the twist of the erupting flux rope in terms the geometry of the initial configuration. Interplanetary observations show some flux ropes have a fairly uniform twist, which could be produced when the zipper phase and any pre-existing flux rope possess small or moderate twist (up to one or two turns). Other interplanetary flux ropes have highly twisted cores (up to five turns), which could be produced when there is a pre-existing flux rope and an active zipper phase that creates substantial extra twist. 相似文献
3.
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
4.
G. Valori L. M. Green P. Démoulin S. Vargas Domínguez L. van Driel-Gesztelyi A. Wallace D. Baker M. Fuhrmann 《Solar physics》2012,278(1):73-97
We study the flux emergence process in NOAA active region 11024, between 29 June and 7 July 2009, by means of multi-wavelength
observations and nonlinear force-free extrapolation. The main aim is to extend previous investigations by combining, as much
as possible, high spatial resolution observations to test our present understanding of small-scale (undulatory) flux emergence,
whilst putting these small-scale events in the context of the global evolution of the active region. The combination of these
techniques allows us to follow the whole process, from the first appearance of the bipolar axial field on the east limb, until
the buoyancy instability could set in and raise the main body of the twisted flux tube through the photosphere, forming magnetic
tongues and signatures of serpentine field, until the simplification of the magnetic structure into a main bipole by the time
the active region reaches the west limb. At the crucial time of the main emergence phase high spatial resolution spectropolarimetric
measurements of the photospheric field are employed to reconstruct the three-dimensional structure of the nonlinear force-free
coronal field, which is then used to test the current understanding of flux emergence processes. In particular, knowledge
of the coronal connectivity confirms the identity of the magnetic tongues as seen in their photospheric signatures, and it
exemplifies how the twisted flux, which is emerging on small scales in the form of a sea-serpent, is subsequently rearranged
by reconnection into the large-scale field of the active region. In this way, the multi-wavelength observations combined with
a nonlinear force-free extrapolation provide a coherent picture of the emergence process of small-scale magnetic bipoles,
which subsequently reconnect to form a large-scale structure in the corona. 相似文献
5.
We study the physical state of the photosphere at about 30 minutes before and at the onset of a 2N/M2 two-ribbon solar flare.
Semiempirical photospheric models are obtained for two Hα-kernels with the help of the SIR inversion code described by Ruiz
Cobo and del Toro Iniesta (Astrophys. J.
398, 375, 1992). The models derived from the inversion reproduce spectral observations in seven Fraunhofer lines. The inferred models show
variations in all photospheric parameters both before and at the onset of the flare relative to the quiet-Sun model. The temperature
enhancement in the upper photospheric layers is found in the atmospheres in both kernels. The dynamical structure in the models
reveals the variations at the onset of the flare relative to the preflaring ones. The inferred atmospheres show some difference
in the thermodynamical parameters of two kernels. 相似文献
6.
The aim of this paper is to look at the magnetic helicity structure of an emerging active region and show that both emergence and flaring signatures are consistent with a same sign for magnetic helicity. We present a multiwavelength analysis of an M1.6 flare occurring in the NOAA active region 10365 on 27 May 2003, in which a large new bipole emerges in a decaying active region. The diverging flow pattern and the “tongue” shape of the magnetic field in the photosphere with elongated polarities are highly suggestive of the emergence of a twisted flux tube. The orientation of these tongues indicates the emergence of a flux tube with a right-hand twist (i.e., positive magnetic helicity). The flare signatures in the chromosphere are ribbons observed in Hα by the MSDP spectrograph in the Meudon solar tower and in 1600 Å by TRACE. These ribbons have a J shape and are shifted along the inversion line. The pattern of these ribbons suggests that the flare was triggered by magnetic reconnection at coronal heights below a twisted flux tube of positive helicity, corresponding to that of the observed emergence. It is the first time that such a consistency between the signatures of the emerging flux through the photosphere and flare ribbons has been clearly identified in observations. Another type of ribbons observed during the flare at the periphery of the active region by the MSDP and SOHO/EIT is related to the existence of a null point, which is found high in the corona in a potential field extrapolation. We discuss the interpretation of these secondary brightenings in terms of the “breakout” model and in terms of plasma compression/heating within large-scale separatrices. 相似文献
7.
A statistical study is carried out to investigate the detailed relationship between rotating sunspots and the emergence of
magnetic flux tubes. This paper presents the velocity characteristics of 132 sunspots in 95 solar active regions. The rotational
characteristics of the sunspots are calculated from successive SOHO/MDI magnetograms by applying the Differential Affine Velocity
Estimator (DAVE) technique (Schuck, 2006, Astrophys. J.
646, 1358). Among 82 sunspots in active regions exhibiting strong flux emergence, 63 showed rotation with rotational angular
velocity larger than 0.4° h−1. Among 50 sunspots in active regions without well-defined flux emergence, 14 showed rotation, and the rotation velocities
tend to be slower, compared to those in emerging regions. In addition, we investigated 11 rotating sunspot groups in which
both polarities show evidence for co-temporary rotation. In seven of these cases the two polarities co-rotate, while the other
four are found to be counter-rotating. Plausible reasons for the observed characteristics of the rotating sunspots are discussed. 相似文献
8.
V. V. Grechnev A. N. Afanasyev A. M. Uralov I. M. Chertok M. V. Eselevich V. G. Eselevich G. V. Rudenko Y. Kubo 《Solar physics》2011,273(2):461-477
On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal
transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (Astrophys. J. Lett.
716, L57, 2010) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded
to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a
freely expanding coronal shock wave, including correspondence with the fast-mode speed distribution, while the transient sweeping
over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption.
Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law
fit matches the expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the
dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected
far from the eruption region. 相似文献
9.
Using RHESSI and some auxiliary observations we examine possible connections between the spatial and temporal structure of
nonthermal hard X-ray (HXR) emission sources from the two-ribbon flares of 29 May 2003 and 19 January 2005. In each of these
events quasi-periodic pulsations (QPP) with time period of 1 – 3 minutes are evident in both hard X rays and microwaves. The
sources of nonthermal HXR emission are situated mainly at the footpoints of the flare arcade loops observed by TRACE and the
SOHO/EIT instrument in the EUV range. At least one of the sources moves systematically during and after the QPP phase in each
flare. The sources move predominantly parallel to the magnetic inversion line during the 29 May flare and along flare ribbons
during the QPP phase of both flares. By contrast, the sources start to show movement perpendicular to the flare ribbons with
velocity comparable to that along the ribbons’ movement after the QPP phase. The sources of each pulse are localized in distinct
parts of the ribbon during the QPP phase. The measured velocity of the sources and the estimated energy release rate do not
correlate well with the flux of the HXR emission calculated from these sources. The sources of microwaves and thermal HXRs
are situated near the apex of the flare loop arcade and are not stationary either. Almost all of the QPP as well as some pulses
of nonthermal HXR emission during the post-QPP phase reveal soft – hard – soft spectral behavior, indicating separate acts
of electron acceleration and injection. In our opinion at least two different flare scenarios based on the Nakariakov et al. (2006, Astron. Astrophys.
452, 343) model and on the idea of current-carrying loop coalescence are suitable for interpreting the observations. However,
it is currently not possible to choose between them owing to observational limitations. 相似文献
10.
The sunspot-associated sources at the frequency of 17 GHz give information on plasma parameters in the regions of magnetic
field about B=2000 G at the level of the chromosphere-corona transition region. The observations of short period (from one to ten minutes)
oscillations in sunspots reflect propagation of magnetohydrodynamic (MHD) waves in the magnetic flux tubes of the sunspots.
We investigate the oscillation parameters in active regions in connection with their flare activity. We confirm the existence
of a link between the oscillation spectrum and flare activity. We find differences in the oscillations between pre-flare and
post-flare phases. In particular, we demonstrate a case of powerful three-minute oscillations that start just before the burst.
This event is similar to the cases of the precursors investigated by Sych et al. (Astron. Astrophys.
505, 791, 2009). We also found well-defined eight-minute oscillations of microwave emission from sunspot. We interpret our observations
in terms of a relationship between MHD waves propagating from sunspots and flare processes. 相似文献
11.
The generally accepted scenario for the events leading up to a two-ribbon flare is that a magnetic arcade (supporting a plage filament) responds to the slow photospheric motions of its footpoints by evolving passively through a series of (largely) force-free equilibria. At some critical amount of shear the configuration becomes unstable and erupts outwards. Subsequently, the field closes back down in the manner modelled by Kopp and Pneuman (1976); but the main problem has been to explain the eruptive instability.The present paper analyses the magnetohydrodynamic stability of several possible arcade configurations, including the dominant stabilizing effect of line-tying at the photospheric footpoints. One low-lying force-free structure is found to be stable regardless of the shear; also some of the arcades that lie on the upper branch of the equilibrium curves are shown to be stable. However, another force-free configuration appears more likely to represent the preflare structure. It consists of a large flux tube, anchored at its ends and surrounded by an arcade, so that the field transverse to the arcade axis contains a magnetic island. Such a configuration is found to become unstable when either the length of the structure, the twist of the flux tube, or the height of the island becomes too great; the higher the tube is situated, the smaller is the twist required for instability. 相似文献
12.
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
13.
In this paper we extend previous work of Browning and Priest (1984, 1986) by studying the equilibrium path of twisted and untwisted thin flux tubes in a stratified, isothermal atmosphere using as the ambient field a linear force-free field. When an untwisted flux tube is considered, we find that shearing the magnetic arcade provides a different form to change the parameter which characterizes the external atmosphere, but at the same time this introduces a limitation in the width allowed for the external arcade. Also, the critical width found for the different analytical cases considered is always greater than one arch of the ambient arcade which prevents an eruption inside the arcade. In the case of twisted flux tubes, an analytical solution can be found for the critical
c
, which separates regimes of strong and weak gravity, and the shape of the flux tube is now dependent on , a parameter which represents the magnetic field enhancement of the loop at the photosphere. 相似文献
14.
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
15.
In the framework of ‘microscopic’ theory of black holes (J. Phys. Soc. Jpn. Suppl. B 70, 84, 2001; Astrophys. USSR 4, 659, 1996; 35, 335, 1991, 33, 143, 1990, 31, 345, 1989a; Astrophys. Space Sci. 1, 1992; Dokl. Akad. Nauk USSR 309, 97, 1989b), and references therein, we address the ‘pre-radiation time’ (PRT) of neutrinos from black holes, which implies the lapse
of time from black hole’s birth till radiation of an extremely high energy neutrinos. For post-PRT lifetime, the black hole
no longer holds as a region of spacetime that cannot communicate with the external universe. We study main features of spherical
accretion onto central BH and infer a mass accretion rate onto it, and, further, calculate the resulting PRT versus bolometric
luminosity due to accretion onto black hole. We estimate the PRTs of AGN black holes, with the well-determined masses and
bolometric luminosities, collected from the literature by Woo Jong-Hak and Urry (Astrophys. J. 579, 530, 2002) on which this paper is partially based. The simulations for the black holes of masses M
BH
≃(1.1⋅106
÷4.2⋅109) M
⊙ give the values of PRTs varying in the range of about T
BH
≃(4.3⋅105
÷5.6⋅1011) yr. The derived PRTs for the 60 AGN black holes are longer than the age of the universe (∼13.7 Gyr) favored today. At present,
some of remaining 174 BHs may radiate neutrinos. However, these results would be underestimated if the reservoir of gas for
accretion in the galaxy center is quite modest, and no obvious way to feed the BHs with substantial accretion. 相似文献
16.
We studied the characteristics of the zebra-associated spike-like bursts that were recorded with high time resolution at 1420
MHz in four intervals (from 12:45 to 12:48 UT) during 5 August 2003. Our detailed analysis is based on the selection of more
than 500 such spike-like bursts and it is, at least to our knowledge, the first study devoted to such short-lived bursts.
Their characteristics are different from those pertinent to “normal” spike bursts, as presented in the paper by Güdel and
Benz (Astron. Astrophys.
231, 202, 1990); in particular, their duration (about 7.4 ms at half power) is shorter, so they should be members of the SSS (super short
structures) family (Magdalenić et al., Astrophys. J.
642, L77, 2006). The bursts were generally strongly R-polarized; however, during the decaying part of interval I a low R-polarized and L-polarized
bursts were also present. This change of polarization shows a trend that resembles the peculiar form of the zebra lines in
the spectral dominion (“V” like). A global statistical analysis on the bursts observed in the two polarimetric channels shows
that the highest cross-correlation coefficient (about 0.5) was pertinent to interval I. The zebras and the bursts can be interpreted
by the same double plasma resonance process as proposed by Bárta and Karlicky (Astron. Astrophys.
379, 1045, 2001) and Karlicky et al. (Astron. Astrophys.
375, 638, 2001); in particular, the spikes are generated by the interruption of this process by assumed turbulence (density or magnetic
field variations). This process should be present in the region close to the reconnection site (e.g., in the plasma reconnection outflows) where the density and the magnetic field vary strongly. 相似文献
17.
Recent numerical investigations of wave propagation near coronal magnetic null points (McLaughlin and Hood: Astron. Astrophys.
459, 641, 2006) have indicated how a fast MHD wave partially converts into a slow MHD wave as the disturbance passes from a low-β plasma to a high-β plasma. This is a complex process and a clear understanding of the conversion mechanism requires the detailed investigation
of a simpler model. An investigation of mode conversion in a stratified, isothermal atmosphere with a uniform, vertical magnetic
field is carried out, both numerically and analytically. In contrast to previous investigations of upward-propagating waves
(Zhugzhda and Dzhalilov: Astron. Astrophys.
112, 16, 1982a; Cally: Astrophys. J.
548, 473, 2001), this paper studies the downward propagation of waves from a low-β to high-β environment. A simple expression for the amplitude of the transmitted wave is compared with the numerical solution. 相似文献
18.
We present three-dimensional unsteady modeling and numerical simulations of a coronal active region, carried out within the
compressible single-fluid MHD approximation. We focus on AR 9077 on 14 July 2000, and the triggering of the X5.7 GOES X-ray
class “Bastille Day” flare. We simulate only the lower corona, although we include a virtual photosphere and chromosphere
below. The boundary conditions at the base of this layer are set using temperature maps from line intensities and line-of-sight
magnetograms (SOHO/MDI). From the latter, we generate vector magnetograms using the force-free approximation; these vector
magnetograms are then used to produce the boundary condition on the velocity field using a minimum energy principle (Longcope,
Astrophys. J.
612, 1181, 2004). The reconnection process is modeled through a dynamical hyper-resistivity which is activated when the current exceeds a
critical value (Klimas et al., J. Geophys. Res.
109, 2218, 2004). Comparing the time series of X-ray fluxes recorded by GOES with modeled time series of various mean physical variables
such as current density, Poynting energy flux, or radiative loss inside the active region, we can demonstrate that the model
properly captures the evolution of an active region over a day and, in particular, is able to explain the initiation of the
flare at the observed time. 相似文献
19.
We develop a diagnostic tool for determination of the electron densities in solar prominences using eclipse data. The method
is based on analysis of the hydrogen Balmer-line intensities (namely Hα and Hβ) and the white-light emission due to Thomson
scattering on the prominence electrons. Our approach represents a generalization of the ratio method already used by Koutchmy,
Lebecq, and Stellmacher (Astron. Astrophys.
119, 261, 1983). In this paper we use an extended grid of non-LTE prominence models of Gouttebroze, Heinzel, and Vial (Astron. Astrophys. Suppl. Ser.
99, 513, 1993) and derive various useful relations between prominence radiation properties and electron densities. Simultaneously, an effective
geometrical thickness of the prominence can also be obtained. As an example we apply our general technique to original eclipse
data of Koutchmy, Lebecq, and Stellmacher (Astron. Astrophys.
119, 261, 1983). Finally, we use our results to determine the color of prominences as it should be seen during total eclipses. 相似文献
20.
Solar p modes are one of the dominant types of coherent signals in Doppler velocity in the solar photosphere, with periods showing
a power peak at five minutes. The propagation (or leakage) of these p-mode signals into the higher solar atmosphere is one of the key drivers of oscillatory motions in the higher solar chromosphere
and corona. This paper examines numerically the direct propagation of acoustic waves driven harmonically at the photosphere,
into the nonmagnetic solar atmosphere. Erdélyi et al. (Astron. Astrophys.
467, 1299, 2007) investigated the acoustic response to a single point-source driver. In the follow-up work here we generalise this previous
study to more structured, coherent, photospheric drivers mimicking solar global oscillations. When our atmosphere is driven
with a pair of point drivers separated in space, reflection at the transition region causes cavity oscillations in the lower
chromosphere, and amplification and cavity resonance of waves at the transition region generate strong surface oscillations.
When driven with a widely horizontally coherent velocity signal, cavity modes are caused in the chromosphere, surface waves
occur at the transition region, and fine structures are generated extending from a dynamic transition region into the lower
corona, even in the absence of a magnetic field. 相似文献