共查询到20条相似文献，搜索用时 453 毫秒
1.
We propose a new model for the initiation of solar coronal mass ejections (CMEs) and CME-associated flares. The model is inferred from observations of a quiescent filament eruption in the north-western quadrant of the solar disk on 4 September 2000. The event was observed with the Siberian Solar Radio Telescope (5.7 GHz), the Nobeyama Radioheliograph (17 GHz) and SOHO/EIT and LASCO. Based on the observations, we suggest that the eruption could be caused by the interaction of two dextral filaments. According to our model, these two filaments merge together to form a dual-filament system tending to form a single long filament. This results in a slow upward motion of the dual-filament system. Its upward expansion is prevented by the attachment of the filaments to the photosphere by filament barbs as well as by overlying coronal arcades. The initial upward motion is caused by the backbone magnetic field (first driving factor) which connects the two merging filaments. Its magnetic flux increases slowly due to magnetic reconnection of the cross-interacting legs of these filaments. If a total length of the dual-filament system is large enough, then the filament barbs detach themselves from the solar surface due to magnetic reconnection between the barbs with oppositely directed magnetic fields. The detachment of the filament barbs completes the formation of the eruptive filaments themselves and determines the helicity sign of their magnetic fields. The appearance of a helical magnetic structure creates an additional upward-directed force (second driving factor). A combined action of these two factors causes acceleration of the dual-filament system. If the lifting force of the two factors is sufficient to substantially extend the overlying coronal magnetic arcade, then magnetic reconnection starts below the eruptive filament in accordance with the classical scheme, and the third driving factor comes into play. 相似文献
2.
Speeds of vertical flows in quiescent solar filaments are typically much less than the local Alfvén speed. This is why the flows in filament barbs can be modeled by perturbing a magnetostatic solution describing a balance between the Lorentz force, gravity, and gas pressure in a barb. This approach explains why some of the flows are neither aligned with the magnetic field nor controlled by gravity. Both the observed upflows and the magnetic field dips in barbs are likely to be caused by photospheric magnetic reconnection. 相似文献
3.
V. A. Perebeinos N. N. Stepanian V. G. Fainshtein G. V. Rudenko 《Bulletin of the Crimean Astrophysical Observatory》2011,107(1):43-50
Height variation of the magnetic field structure over groups of sunspots for heights ranging from the photosphere to the source
surface (R = 2.5 Ro, where Ro is the radius of the Sun) is examined. For all heights, starting from the photospheric level, groups of
sunspot are shown as being independent of long-lived boundaries of large-scale structures rotating with a period shorter than
the Carrington period. At heights of 1–1.5 Ro, there is a clear relation between sunspot groups and boundaries separating
the head and tail sunspots in the groups (the Hale boundaries). The rotation periods of these structures are close to the
Carrington period, their lifespan being less than three to five rotations. The maximal intensity of the solar magnetic field
drops by two orders when height increases from H = 1 to H = 1.1 Ro. Further decrease in intensity proceeds gradually (dropping by one order from H = 1.1 to 2.5 Ro). The results obtained can be considered as evidence that large-scale magnetic field structures and long-lived
boundries between them (the lines dividing polarities of the magnetic field or zero lines) all exist irrespective of sunspot
fields being generated by other sources than sunspots. At the photospheric level, active regions fields are superimposed on
these structures. 相似文献
4.
Recent dedicated Hinode polar region campaigns revealed the presence of concentrated kilogauss patches of the magnetic field in the polar regions of the Sun, which are also shown to be correlated with facular bright points at the photospheric level. In this work, we demonstrate that this spatial intermittency of the magnetic field persists even up to the chromospheric heights. The small-scale bright elements visible in the bright network lanes of the solar network structure as seen in the Ca ii H images are termed network bright points. We use special Hinode campaigns devoted to the observation of polar regions of the Sun to study the polar network bright points during the phase of the last extended solar minimum. We use Ca ii H images of chromosphere observed by the Solar Optical Telescope. For magnetic field information, level-2 data of the spectro-polarimeter is used. We observe a considerable association between the polar network bright points and magnetic field concentrations. The intensity of such bright points is found to be correlated well with the photospheric magnetic field strength underneath with a linear relation existing between them.
相似文献5.
Zhang Hongqi 《Solar physics》1993,144(2):323-340
In this paper, the formation and the measurement of the H line in chromospheric magnetic fields are discussed. The evolution of the chromospheric magnetic structures and the relation with the photospheric vector magnetic fields and chromospheric velocity fields in the flare producing active region AR 5747 are also demonstrated.The chromospheric magnetic gulfs and islands of opposite polarity relative to the photospheric field are found in the flare-producing region. This probably reflects the complication of the magnetic force lines above the photosphere in the active region. The evolution of the chromospheric magnetic structures in the active region is caused by the emergence of magnetic flux from the sub-atmosphere or the shear motion of photospheric magnetic fields. The filaments separate the opposite polarities of the chromospheric magnetic field, but only roughly those of the photospheric field. The filaments also mark the inversion lines of the chromospheric Doppler velocity field which are caused by the relative motion of the main magnetic poles of opposite polarities in the active region under discussion. 相似文献
6.
From 16 to 21 August 2010, a northern (???N60) polar crown filament was observed by Solar Dynamics Observatory (SDO). Employing the six-day SDO/AIA data, we identify 69 barbs, and select 58 of them, which appeared away from the western solar limb (???W60), as our sample. We systematically investigate the evolution of filament barbs. Three different types of apparent formation of barbs are detected, including i)?the convergence of surrounding moving plasma condensations, comprised 55.2?% of our sample, ii)?the flows of plasma condensations from the filament, comprised 37.9?%, and iii)?the plasma injections from the neighboring brightening regions, comprised 6.9?%. We also find three different ways that barb disappear, involving: i)?bi-lateral movements (44.8?%), and ii)?outflowing of barb plasma (27.6?%) results in the disappearance of a barb, as well as iii)?disappearance of a barb is associated with a neighboring brightening (27.6?%). The evolution of the magnetic fields, e.g. emergence and cancellation of magnetic flux, may cause the formation or disappearance of the barb magnetic structures. Barbs exchange plasma condensations with the surrounding atmosphere, filament, and nearby brightenings, leading to the increase or drainage of barb material. Furthermore, we find that all the barbs undergo oscillations. The average oscillation period, amplitude, and velocity are 30?min, 2.4?Mm, and 5.7?km?s?1, respectively. Besides the oscillations, 21 (36?%) barbs manifested sideward motions having an average speed of 0.45?km?s?1. Small-scale wave-like propagating disturbances caused by small-scale brightenings are detected, and the barb oscillations associated with these disturbances are also found. We propose that the kinematics of barbs are influenced or even caused by the evolution of the neighboring photospheric magnetic fields. 相似文献
7.
Reliable measurements of the solar magnetic field are restricted to the level of the photosphere. For about half a century attempts have been made to calculate the field in the layers above the photosphere, i.e. in the chromosphere and in the corona, from the measured photospheric field. The procedure is known as magnetic field extrapolation. In the superphotospheric parts of active regions the magnetic field is approximately force-free, i.e. electric currents are aligned with the magnetic field. The practical application to solar active regions has been largely confined to constant-α or linear force-free fields, with a spatially constant ratio, α, between the electric current and the magnetic field. We review results obtained from extrapolations with constant-α force-free fields, in particular on magnetic topologies favourable for flares and on magnetic and current helicities. Presently, different methods are being developed to calculate non-constant-α or nonlinear force-free fields from photospheric vector magnetograms. We also briefly discuss these methods and present a comparison of a linear and a nonlinear force-free magnetic field extrapolation applied to the same photospheric boundary data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
8.
Because of the progressive decrease in rotation rate of the solar plasma at increasing latitudes, the photospheric foot-points of large-scale closed magnetic structures in the corona, which are originally widely separated in longitude, may ultimately be brought into proximity. Magnetic mergers and reconnections between magnetic fields of opposite polarity are presumed to occur, producing major structural changes in the corona and in the locations of underlying filaments. Thus we believe that the differential rotation phenomenon is essential to understanding both gradual (evolutionary) and sudden (transient) changes in the corona, and that they can occur without any observable change in the photospheric magnetic flux. A process is suggested for the splitting or bifurcation of a high-latitude magnetic structure, producing two separate components at the same latitude, whose rotation rates are influenced by their respective magnetic linkages to other regions on the Sun.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
9.
In this paper, we analyze the relations between photospheric vector magnetic fields, chromospheric longitudinal magnetic fields and velocity fields in a solar active region. Agreements between the photospheric and chromospheric magnetograms can be found in large-scale structures or in the stronger magnetic structures, but differences also can be found in the fine structures or in other places, which reflect the variation of the magnetic force lines from the photosphere to the chromosphere. The chromospheric superpenumbral magnetic field, measured by the Hline, presents a spoke-like structure. It consists of thick magnetic fibrils which are different from photospheric penumbral magnetic fibrils. The outer superpenumbral magnetic field is almost horizontal. The direction of the chromospheric magnetic fibrils is generally parallel to the transverse components of the photospheric vector magnetic fields. The chromospheric material flow is coupled with the magnetic field structure. The structures of the H chromospheric magnetic fibrils in the network are similar to H dark fibrils, and the feet of the magnetic fibrils are located at the photospheric magnetic elements. 相似文献
10.
In this paper, three-dimensional linear force-free field configurations that can be associated with filaments are considered. It is assumed that the field configurations are suitable to represent filaments if they contain magnetic dips. With the photospheric flux distribution chosen to be an arcade with a dextral/sinistral axial component, it is found that dipped configurations exist only for large values of alpha (where, ×B=B). The dips always lie above the polarity inversion line in the centre of the channel between the flux regions. When the dips are viewed from above to a depth of 1 Mm they resemble closely the shape of filaments viewed in absorption on the solar disk. As the magnitude of alpha increases, the horizontal and vertical extent of the dips also increases, giving active-region filaments for low values of alpha and quiescient filaments for high values of alpha. Dextral filaments only form for negative values of alpha and sinistral filaments for positive values of alpha. The portion of the field line that is dipped is always of inverse polarity and the magnitude of the field in the dipped region increases with height, both of which are consistent with Leroy, Bommier, and Sahal-Bréchot (1983). Overlying the region of dips there are arcades of normal polarity which have the correct left-bearing/right-bearing orientation for dextral/sinistral filaments. When the hypothesis of barbs occurring in dipped field lines is used, barbs that branch out of the main axis and to the right/left for dextral/sinistral filaments can be formed around minority polarity elements on either side of the polarity inversion line. No barbs are found around normal polarity elements. The model reproduces many of the observed features of filament channels, filaments and their barbs. 相似文献
11.
Spectroheliograms, obtained in certain Fraunhofer lines with the 82-cm solar image at the Kitt Peak National Observatory, show a bright photospheric network having the following properties:
- It resembles, but does not coincide with, the chromospheric network, the structure of the photospheric network being finer and more delicate than the relatively coarse structure of the chromospheric network.
- It is exactly cospatial with the network of non-sunspot photospheric magnetic fields.
- Its visibility in a given photospheric Fraunhofer line is primarily dependent on the states of ionization and excitation from which the line is formed and secondarily dependent on the Zeemansensitivity of the line-being most visible in low-excitation lines of neutral atoms and least visible in high-excitation lines of singly ionized atoms.
12.
Reversed-polarity structures of chromospheric magnetic fields are magnetic gulfs and islands of opposite polarity relative
to the underlying photospheric fields. In this paper data measured with the Solar Magnetic Field Telescope of the Huairou
Solar Observing Station in Beijing were analyzed. From more than 300 pairs of photospheric magnetograms (in FeI λ5324.19 Å) and relevant chromospheric magnetograms (Hβ λ4861.34 Å), the reality of the reversed-polarity structures is demonstrated. According to an analysis of the fine structure
of the magnetic field in the two layers of active regions, we found that there are probably four different types as follows:
Type A: magnetic islands of opposite polarity corresponding to photospheric fields appear in the chromospheric magnetogram.
Type B: magnetic gulfs of opposite polarity corresponding to photospheric fields appear in the chromospheric magnetogram.
Type C is the reverse of type B. That is, a magnetic gulf of opposite polarity corresponding to the chromospheric field appears
in the photospheric magnetogram.
Type D is the reverse of type A. 相似文献
13.
S. Régnier 《Solar physics》2012,277(1):131-151
In the last decades, force-free-field modelling has been used extensively to describe the coronal magnetic field and to better
understand the physics of solar eruptions at different scales. Especially the evolution of active regions has been studied
by successive equilibria in which each computed magnetic configuration is subject to an evolving photospheric distribution
of magnetic field and/or electric-current density. This technique of successive equilibria has been successful in describing
the rate of change of the energetics for observed active regions. Nevertheless the change in magnetic configuration due to
the increase/decrease of electric current for different force-free models (potential, linear and nonlinear force-free fields)
has never been studied in detail before. Here we focus especially on the evolution of the free magnetic energy, the location
of the excess of energy, and the distribution of electric currents in the corona. For this purpose, we use an idealised active
region characterised by four main polarities and a satellite polarity, allowing us to specify a complex topology and sheared
arcades to the coronal magnetic field but no twisted flux bundles. We investigate the changes in the geometry and connectivity
of field lines, the magnetic energy and current-density content as well as the evolution of null points. Increasing the photospheric
current density in the magnetic configuration does not dramatically change the energy-storage processes within the active
region even if the magnetic topology is slightly modified. We conclude that for reasonable values of the photospheric current
density (the force-free parameter α<0.25 Mm−1), the magnetic configurations studied do change but not dramatically: i) the original null point stays nearly at the same location, ii) the field-line geometry and connectivity are slightly modified, iii) even if the free magnetic energy is significantly increased, the energy storage happens at the same location. This extensive
study of different force-free models for a simple magnetic configuration shows that some topological elements of an observed
active region, such as null points, can be reproduced with confidence only by considering the potential-field approximation.
This study is a preliminary work aiming at understanding the effects of electric currents generated by characteristic photospheric
motions on the structure and evolution of the coronal magnetic field. 相似文献
14.
Several laboratory experiments on magnetic field line reconnection are briefly reviewed. Emphasis is placed on the double inverse pinch device (DIPD) in which magnetic flux is built up during a quiescent reconnection phase and then abruptly transferred during an impulsive reconnection phase. Scaling estimates show that this impulsive phase corresponds to a solar release of 1030 ergs in 102 seconds with the production of GeV potentials. The trigger for the impulsive flare is a conduction mode instability (ion-acoustic) which abruptly changes the resistance of the neutral point region when the reconnection current density reaches a critical value.Some results are presented from another reconnection device which has exactly antiparallel fields at the boundaries. This flat plate device develops one x-type neutral point rather than tearing into many neutral points. The reconnection rate is more quiescent than in the DIPD. A mild conduction mode instability occurs. The results suggest that regions with flattened boundary fields may not be as conducive to flares as regions with more curved fields. 相似文献
15.
High-resolution photographs of the photospheric network taken in the Caii K 3933 Å line and at 4308 Å are analysed in order to study the variation, in latitude and over the sunspot cycle, of its density (the density is defined as the number of network elements - also called facular points - per surface unity). It appears that the density of the photospheric network is not distributed uniformly at the surface of the Sun: on September 1983, during the declining phase of the current activity cycle, it was weakened at both the low (equatorial) and high (polar) active latitudes, while it was tremendously enhanced toward the pole. The density at the equator is varying in antiphase to the sunspot number: it increases by a factor 3 or more from maximum to minimum of activity. As a quantum of magnetic flux is associated to each network element, density variations of the photospheric network express in fact variations of the quiet Sun magnetic flux. It thus results that the quiet Sun magnetic flux is not uniformly distributed in latitude and not constant over the solar cycle: it probably varies in antiphase to the flux in active regions.The variation over the solar cycle and the latitude distribution of photospheric network density are compared to those of X-ray bright points and ephemeral active regions: there are no clear correlations between these three kinds of magnetic features. 相似文献
16.
David L. Glackin 《Solar physics》1974,36(1):51-60
The latitudinal component of solar differential rotation and the possibility of a radial component are discussed and compared to the observed rotational velocities of solar filaments. Our values of rotational rate versus heliographic latitude for 100 points in the solar atmosphere derived from 17 quiescent filaments are comparable to the rates found by d'Azambuja and d'Azambuja (1948). The filament rate is significantly greater than the spot rate (Newton and Nunn, 1951); the difference cannot be accounted for by the poleward migration of filaments and seems to reflect a true radial gradient of rotational velocity in the Sun. We show that filaments in closer proximity to active regions usually exhibit no differential rotation, while those far from active regions generally show it clearly. Comparison with Mt. Wilson photospheric Doppler measurements shows that filaments rotate faster than the general photosphere and that, as is well known, the spot rate exceeds that for the general photosphere. 相似文献
17.
Gary A. Chapman 《Solar physics》1970,13(1):78-84
Photographs of the Sun, recently obtained with a violet interference filter ( 3840 Å), show the photospheric network (or photospheric faculae) with a contrast of typically 20% across the entire solar disk. Since this network is cospatial with photospheric magnetic fields, one is able to determine thepositions (not polarity) of these magnetic fields with fairly modest equipment. Furthermore, numerous dark structures and a faint dark network can be seen through the violet filter. 相似文献
18.
N. R. Sheeley Jr. 《Solar physics》1969,9(2):347-357
A time-lapse sequence of spectroheliograms in the bandhead of CN at λ3883 reveals the following behavior of the photospheric network with time:
- There is a steady flow of bright ‘points’ (? 1000 km in diameter) laterally outward from sunspots at speeds on the order of 1 km·sec?1. After traveling about 10 000 km from a sunspot they either conglomerate to form fragments of the photospheric network or disappear.
- Spatial changes in the network pattern seem to take place by means of the shifting of network fragments laterally on the solar surface. Although most small-scale details are recognizable after 5–10 minutes, within 30 minutes nearly all the details have changed completely. In contrast to this, the large-scale network pattern seems relatively unchanged after 2 1/2 hours.
- Occasionally ‘new’ network, not resulting from the lateral motion of bright features from either previously existing network or sunspots, appears on the solar surface. This process consists of the formation in approximately 10 minutes of bright points and a darker-than-average feature between them. The dark feature disappears in another 5–10 minutes and the bright points separate at a relative speed of a few km·sec?1. If the event is of a sufficiently large magnitude, a sunspot will appear.
19.
Simple analytic models for the passive evolution of arcade-like magnetic fields through a series of force-free equilibria are presented. At the photospheric boundary, the normal magnetic field component is prescribed together with either the longitudinal field component or the photospheric shear. Analytic progress is made by considering either cylindrically symmetric solutions or using the separation of variables technique.
Two distinct cylindrically symmetric force-free fields are obtained that possess the same normal field component and photospheric shear. The scond field contains a magnetic bubble. As the shear increases beyond a critical value, so the magnetic energy of the first configuration exceeds that of the second. The possibility is therefore suggested of an eruption of the first field outwards towards the second. Such an eruptive instability is proposed as the origin of a two-ribbon solar flare.A new analytic solution to the force-free field equations, of separable form, is discovered and it is pointed out that the existence of shear in a magnetic field does not preclude it from being potential.Now at AWRE, Aldermaston, Reading, Berkshire. 相似文献
20.
We developed a code for the reconstruction of nonlinear force-free and non-force-free coronal magnetic fields. The 3D magnetic
field is computed numerically with the help of an optimization principle. The force-free and non-force-free codes are compiled
in one program. The force-free approach needs photospheric vector magnetograms as input. The non-force-free code additionally
requires the line-of-sight integrated coronal density distribution in combination with a tomographic inversion code. Previously
the optimization approach has been used to compute magnetic fields using all six boundaries of a computational box. Here we
extend this method and show how the coronal magnetic field can be reconstructed only from the bottom boundary, where the boundary
conditions are measured with vector magnetographs. The program is planed for use within the Stereo mission. 相似文献