共查询到20条相似文献，搜索用时 265 毫秒
1.
We review observational studies of solar prominences with some reference to theoretical understandings. We lay emphasis on the following findings: (1) An important discovery was made by Leroy, Bommier, and Sahal-Bréchot concerning the direction of the magnetic field inside some high-altitude, high-latitude prominences, where the field vector points in the opposite direction from the one which would be expected from the potential field calculated from the observed photospheric magnetic field. (2) Landman suggests the possibility of a high total density of 10–11 g cm –3 for the main body of quiescent prominences, 50 times higher than the value hitherto believed. (3) Flow patterns, nearly parallel to the magnetic neutral lines, were detected in the 105 K plasma near and in prominences. (4) Coronal loop structures were found overlying prominences as viewed from X-ray photographs. We propose also an evolutionary scheme by taking the magnetic field topologies into account.The fundamental question why a prominence is present remains basically unanswered. 相似文献
2.
We investigate the formation and support of solar prominences in a quadrupolar magnetic configuration. The prominence is modeled as a current sheet with mass in equilibrium in a two-dimensional field. The model possesses an important property which is now thought to be necessary, namely that the prominence forms within the dip, rather than the dip being created by the prominence.The approach of two bipolar regions of the same sign gives a natural way to form a dip in the magnetic field in a horizontal band above the photospheric polarity inversion line. As the approach proceeds, the height of the dip region decreases but, in agreement with observations, a corridor, free of significant magnetic field, is needed in order to obtain a dip at low heights.Support is achieved locally just as for normal-polarity configurations, so the model avoids the strong self-pinching effect of several inverse-polarity configurations (such as the Kuperus and Raadu model). The role of the strong field component along the prominence axis, which is here modelled by a uniform field in that direction, may well be to provide the necessary thermal properties for prominence formation.The model thus has several attractive features which make it credible for inverse polarity prominences: (i) both the dip and the inverse orientation are naturally present; (ii) prominence formation is by converging rather than shearing motions, in agreement with observations; converging photospheric motions induce a horizontal upward motion in the filament; (iii) the orientation of the axial field, opposite to what is expected from differential rotation, is naturally accounted for; (iv) the observed relation between chromospheric and prominence magnetic field strengths is naturally reproduced; (v) the field configuration is more complex than a simple bipole, in agreement with observations. 相似文献
3.
Summary Conclusion This colloquium on solar prominences - the first ever held - has shown that a major part of activity in prominence research in recent years concentrated on both observation and computation of the magnetic conditions which were found to play a crucial role for the development and the maintainance of prominences. Remarkable progress was made in fine-scale measurements of photospheric magnetic fields around filaments and in internal field measurements in prominences. In addition, important information on the structure of the magnetic fields in the chromosphere adjacent to the filaments may be derived from high resolution photographs of the H fine structure around filaments which have become available recently; unfortunately, an unambiguous determination of the vector field in the chromosphere is not yet possible.It is quite clear, now, that stable filaments extend along neutral lines which divide regions of opposite longitudinal magnetic fields. Different types of neutral lines are possible, depending on the history and relationship of the opposite field regions. There is convincing evidence that the magnetic field in the neighbouring chromosphere may run nearly parallel to the filament axis and that there are two field components in stable prominences: an axial field dominant in the lower parts and a transverse field dominant in the higher parts.Methods for the computation of possible prominence field configurations from measured longitudinal photospheric fields were developed in recent years. In a number of cases (e.g. for loop prominences) the observed configuration could be perfectly represented by a force-free or even a potential field; poor agreement was found between computed and measured field strengths in quiescent prominences. In order to reconcile both of them it is necessary to assume electric currents. Unambiguous solutions will not be found until measurements of the vector field in the photosphere and in the prominences are available.The two-dimensional Kippenhahn-Schlüter model is still considered a useful tool for the study of prominence support and stability. However, a more refined model taking into account both field components and considering also thermal stability conditions is available now. It was proposed that quiescent prominences may form in magnetically neutral sheets in the corona where fields of opposite directions meet.As for the problem of the origin of the dense prominence material there are still two opposite processes under discussion. The injection of material from below, which was mainly applied to loop prominences, has recently been considered also a possible mechanism for the formation of quiescent prominences. On the other hand, the main objections against the condensation mechanism could be removed: it was shown that (1) sufficient material is available in the surrounding corona, and that (2) coronal matter can be condensed to prominence densities and cooled to prominence temperatures in a sufficiently short time.The energy balance in prominences is largely dependent on their fine structure. It seems that a much better radiative loss function for optically thin matter is now available. The problem of the heat conduction can only be treated properly if the field configuration is known. Very little is known on the heating of the corona and the prominence in a complicated field configuration. For the optically thick prominences the energy balance becomes a complicated radiative transfer problem.Still little is known on the first days of prominence development and on the mechanism of first formation which, both, are crucial for the unterstanding of the prominence phenomenon. As a first important step, it was shown in high resolution H photographs that the chromospheric fine structure becomes aligned along the direction of the neutral line already before first filament appearance. More H studies and magnetic field measurements are badly needed.Recent studies have shown that even in stable prominences strong small-scale internal rotational or helical motions exist; they are not yet understood. On the other hand, no generally agreed interpretation of large-scale motions of prominences seems to exist. A first attempt to explain the ascendance of prominences, the Disparitions Brusques, as the result of a kink instability was made recently.New opportunities in prominence research are offered by the study of invisible radiations: X-rays and meterwaves provide important information, not available otherwise, on physical conditions in the coronal surroundings of prominences; EUV observations will provide data on the thin transition layer between the cool prominence and the hot coronal plasma.Mitt. aus dem Fraunhofer Institut No. 111. 相似文献
4.
Oddbjørn Engvold 《Solar physics》1976,49(2):283-295
The fine structure of nonspot prominences are studied from H filtergrams. The size of the smallest prominence structures increases with height above the chromosphere. Some prominences contain structures close to 1/2 arc second, which is the spatial resolution in the present data. The effective thickness of many nonspot prominences ranges between 4 × 107 cm and 1.5 × 108 cm. An apparent downward directed motion is observed in the majority of the prominences. No preferred direction of the motion is seen in regions composed of comparatively large diffuse structures. Some bright threads are visible for 1 hr and longer. Bright knots have an average observed lifetime of about 8 min. The process of condensation and subsequent destruction of prominence fine structure appears to take place on a very short time scale compared to the life time of the regions where prominences may exist. The observed H brightness of the prominences in the present data may be accounted for as scattered chromospheric radiation. 相似文献
5.
The concepts of magnetic reconnection that have been developed in two dimensions need to be generalised to three-dimensional configurations. Reconnection may be defined to occur when there is an electric field (E) parallel to field lines (known as potential singular lines) which are potential reconnection locations and near which the field has an X-type topology in a plane normal to that field line. In general there is a continuum of neighbouring potential singular lines, and which one supports reconnection depends on the imposed flow or electric field. For steady reconnection the nearby flow and electric field are severely constrained in the ideal region by the condition that E = 0 there. Potential singular lines may occur in twisted prominence fields or in the complex magnetic configuration above sources of mixed polarity of an active region or a supergranulation cell. When reconnection occurs there is dynamic MHD behaviour with current concentration and strong plasma jetting along the singular line and the singular surfaces which map onto them. 相似文献
6.
S. Serio G. S. Vaiana G. Godoli S. Motta V. Pirronello R. A. Zappala' 《Solar physics》1978,59(1):65-86
We have analyzed X-ray images of the solar corona obtained by the S-054 telescope on Skylab, together with H filtergrams from the Catania Astrophysical Observatory and EUV and magnetic data, to study the morphology and the evolution of the coronal structures associated with prominences (coronal cavities).X-ray cavities are associated with prominences and are enclosed by series of loops of hot plasma typically higher than 5 × 109 cm. Helmet streamers can be observed only at very large heights (> 1 solar radius). The cavities show a higher luminosity when prominences have temporarily disappeared. The density in one of these X-ray cavities ( 3 × 108cm–3) is insufficient to allow formation of dense ( 1011 cm–3) prominences by local condensation from the corona.Prominences associated with young (up to three solar rotations) and old (greater than eight) magnetic neutral lines are significantly less stable than those associated with middle-aged neutral lines. Downward bending of the top of the inner magnetic loop, necessary in some models of prominences, is not detected in these X-ray observations. The relevance of these results to models of prominence formation is discussed.Presently at Osservatorio Astrofisico di Arcetri, Firenze, Italy. 相似文献
7.
Leroy, Bommier, and Sahal-Bréchot (1984) determined the vector magnetic field in a large sample of quiescent prominences. The direction of the axial component is in general subject to a 180 deg uncertainty. We have selected those prominences in the sample whose field direction is unambiguous. For 95 such prominences, only 3 do not obey the hemispheric preferences of sinistral or dextral filaments, discovered by Martin, Tracadas, and Billamoria (1994). No explanation for the exceptional cases was found.A search of the Ottawa River Solar Observatory archives was made to check on the structural signatures of sinistral and dextral filaments. Of 32 filaments in common with the Leroy data set, 12 were classifiable as sinistral or dextral from their H fine structure and of these, 3 were exceptions to the hemispheric rule.Thus only a small percentage of quiescent filaments disobeys the hemispheric rule. 相似文献
8.
Véronique Bommier Egidio Landi Degl'Innocenti Jean-Louis Leroy Sylvie Sahal-Bréchot 《Solar physics》1994,154(2):231-260
The present paper is devoted to the interpretation of linear polarization data obtained in 14 quiescent prominences with the Pic-du-Midi coronagraph-polarimeter by J. L. Leroy, in the two lines Hei D3 andH quasi-simultaneously. The linear polarization of the lines is due to scattering of the anisotropic photospheric radiation, modified by the Hanle effect due to the local magnetic field. The interpretation of the polarization data in the two lines is able to provide the 3 components of the magnetic field vector, and one extra parameter, namely the electron density, because the linear polarization of H is also sensitive to the depolarizing effect of collisions with the electrons and protons of the medium. Moreover, by using two lines with different optical thicknesses, namely Hei D3, which is optically thin, and H, which is optically thick ( = 1), it is possible to solve the fundamental ambiguity, each line providing two field vector solutions that are symmetrical in direction with respect to the line of sight in the case of the optically thin line, and which have a different symmetry in the case of the optically thick line.It is then possible to determine without ambiguity the polarity of the prominence magnetic field with respect to that of the photospheric field: 12 prominences are found to be Inverse polarity prominences, whereas 2 prominences are found to be Normal polarity prominences. It must be noticed that in 12 of the 14 cases, the line-of-sight component of the magnetic field vector has a Normal polarity (to the extent that the notion of polarity of a vector component is meaningful; no polarity can be derived in the 2 remaining cases); this may explain the controversy between the results obtained with methods based on the Hanle effect with results obtained through the Zeeman effect. A dip of the magnetic field lines across the prominence has been assumed, to which the optically thick H line is sensitive, and the optically thin Hei D3 line is insensitive.For the Inverse prominences, the average field strength is 7.5±1.2 G, the average angle,, between the field vector and the prominence long axis is 36° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 29° ± 20°, and the average electron density is 2.1 × 1010 ± 0.7 × 1010 cm–3. For the Normal prominences, the average field strength is 13.2±2.0 G, the average angle,, between the field vector and the prominence long axis is 53° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 0° ± 20° (horizontal field), and the average electron density is 8.7 × 109 ± 3.0 × 109 cm–3. 相似文献
9.
Helical structures are generally associated with many eruptive solar prominences. Thus, study of their evolution in the solar atmosphere assumes importance. We present a study of a flare-associated erupting prominence of March 11, 1979, with conspicuous helically twisted structure, observed in H line center. We have attempted to understand the role played by twisted force-free magnetic fields in this event. In the analysis, we have assumed that the helical structures visible in H outline the field lines in which prominence tubes are embedded. Untwisting of observed prominence tubes and later, formation of open prominence structures provide evidence of restructuring of the magnetic field configuration over the active region during the course of prominence eruption. Temporal evolution of the force-free parameter is obtained for two main prominence tubes observed to be intertwined in a rope-like structure. Axial electric currents associated with the prominence tubes are estimated to be of the order of 1011 A which decreased with time. Correspondingly, it is estimated that the rate of energy release was 1028 erg s–1 during the prominence eruption. 相似文献
10.
The nature of thin, highly inclined threads observed in quiescent prominences has puzzled solar physicists for a long time. When assuming that the threads represent truly inclined magnetic fields, the supporting mechanism of prominence plasma against gravity has remained an open issue. This paper examines the levitation of prominence plasma exerted by weakly damped MHD waves in nearly vertical magnetic flux tubes. It is shown that the wave damping, and resulting `radiation pressure', caused predominantly by ion-neutral collisions in the `cold' prominence plasma, may balance the acceleration of gravity provided the oscillation frequency is 2 rad s–1 (f0.5 Hz). Such short wave periods may be the result of small-scale magnetic reconnections in the highly fragmentary magnetic field of quiescent prominences. In the proposed model, the wave induced levitation acts predominantly on plasma – neutral gas mixtures. 相似文献
11.
With thespectro-coronagraph and themultichannel subtractive double pass spectrograph (MSDP) at the Pic du Midi Observatory two quiescent prominences were observed simultaneously. From the spectro-coronagraph observations 2D maps of Hei 10830 , Fexiii 10798 and 10747 line intensities were obtained. In addition, we obtained 2D maps of the ratioR of the two iron lines. This ratio is used as a diagnostic for determining the density of the hot coronal plasma surrounding prominences. We found that the electron density is higher at the location of the prominences than in the corona, whereas small regions (40) of lower electron density are unevenly distributed around the prominences indicating that the surrounding corona is highly inhomogeneous. The density of the cavity is reduced by a factor 1.5 compared to the density of the prominence environment (5 × 108 cm–3). We discuss the existence of cavities around these prominences according to the orientation of their axes relative to the line of sight and according to the velocity field inside the prominences. Constraints on models for prominence formation are derived. 相似文献
12.
The development of magnetic field structures which can lead to prominence configurations of the Kuperus-Raadu type is discussed. Starting from streamer type configurations and preserving the total current in the system we find that simple two-dimensional static configurations lead to prominences which in general lie systematically much lower than the heights found from observations. We therefore conclude that either more complex field configurations are needed to explain the recent observations by Leroy et al. (1983) or the initial configurations must be very special. 相似文献
13.
We present measurements of electric fields in quiescent prominences and in a small flare surge, obtained with the CRI electrograph at the NSO/SP 40 cm coronagraph, in 1993 and 1994. Our results on the 9 brightest quiescent prominences enable us to place r.m.s. upper limits ofE
t < 2 – 5 V cm–1 on the component ofE transverse to the line of sight. We show that these upper limits may be difficult to reconcile with non-ideal MHD models of quiescent prominences formed in extended neutral sheets, whether or not the tearing mode instability is present. They do, however, seem consistent with ideal MHD models of prominence support. We point out also that these upper limits are within a factor 4 of the minimum value of anistropic electric field that exists due to motional Stark effect in any thermal plasma permeated by a directed magnetic field.Our data on the flare surge suggest an electric field of intensityE 35 V cm–1, oriented approximately parallel to the inferred magnetic field. This detection ofE
needs to be verified in other flares. But we note that a detectableE
would not be expected in the current interruption flare mechanism, if only a single double layer is present. We show further that the observed relatively narrow, approximately-Gaussian, and only slightly Doppler-shifted Paschen lines, seem inconsistent with the multiple double layers invoked in other models based on the current interruption mechanism. Our detection ofE
does seem consistent with reconnection (including tearing-mode) models of flares, provided the field-aligned electrical conductivity is anomalous over substantial volumes of the plasma circuit joining the reconnecting domain to the photosphere. 相似文献
14.
Properties of a latitude zonal component of the large-scale solar magnetic field are analyzed on the basis of H charts for 1905–1982. Poleward migration of prominences is used to determine the time of reversal of the polar magnetic field for 1870–1905. It is shown that in each hemisphere the polar, middle latitude and equatorial zones of the predominant polarity of large-scale magnetic field can be detected by calculating the average latitude of prominence samples referred to one boundary of the large-scale magnetic field. The cases of a single and three-fold polar magnetic field reversal are investigated. It is shown that prominence samples referred to one boundary of the large-scale magnetic field do not have any regular equatorward drift. They manifest a poleward migration with a variable velocity up to 30 m s-1 depending on the phase of the cycle. The direction of migration is the same for both low-latitude and high-latitude zones. Two different time intervals of poleward migration are found. One lasts from the beginning of the cycle to the time of polar magnetic field reversal and the other lasts from the time of reversal to the time of minimum activity. The velocity of poleward migration of prominences during the first period is from 5 m s-1 to 30 m s-1 and the second period is devoid of regular latitude drift. 相似文献
15.
Ulrich Anzer 《Solar physics》1972,24(2):324-335
A 2-dimensional model of the magnetic field associated with quiescent prominences is presented. The coronal field is assumed to be current-free, currents are only allowed in the photosphere and inside the prominence. The prominence is taken to be infinitely thin. For this model a method is given to calculate the field configuration from the observed normal component of the field both in the photosphere and the prominence. The normal field components are inferred from disc observations and H limb observations. The sheet currents inside the prominence are calculated and the resulting Lorentz force is compared with the gravitational force. Within the range of uncertainty in the total hydrogen density of quiescent prominences it is possible to give models where the gravity is balanced by the Lorentz force. 相似文献
16.
Yngve Öhman 《Solar physics》1973,28(2):399-402
Some comments are presented on the important observations of faint prominences made recently by Dr Jean-Louis Leroy at the Pic du Midi Observatory. The writer draws attention to the very probable connection with faintly luminous H obscuring prominences which appear sometimes as dark lanes and markings in ordinary prominences. 相似文献
17.
A class of 2-D models of solar quiescent prominences, with normal polarity, is presented. These represent an extension to the Kippenhahn-Schlüter model for which the prominence configuration matches smoothly onto an external non-potential coronal solution of a constant field. Using typical prominence values a model is constructed which also matches the coronal conditions. It is found that the magnetic field component along the prominence influences the internal structure of the prominence. A simple extension to the basic models is indicated as a means of taking a lower boundary of the prominence and eliminating parasitic polarities in the photosphere. 相似文献
18.
Kap-Sung Kim 《Solar physics》1988,114(1):47-64
We have calculated the emission spectra of hydrogen and sodium atoms in the cool part of prominence models which satisfy simultaneously the constraints of radiative transfer, statistical equilibrium and charge-particle conservations.In the considered range of our model parameters, emission strengths of H and Nai D lines increase with the temperature and the total number density. Low-pressure models raise the ionization rate highly but yield very weak Nai D line intensities, since these model prominences contain small amounts of free electrons and sodium atoms which have a deep relation with the formation of sodium lines. We find that sodium D lines should be emitted in the high pressure region of prominences, and that their intensities are difficult to attain in the cool core of any model prominence with a temperature as low as 4000 K. In order to explain consistently the spectral emissions of H and Nai D lines observed in quiescent prominences, a total number density higher than 4 x 1011 cm-3 and a temperature over 5000 K are required at least in the cool part of prominences.Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 282. 相似文献
19.
Einar Tandberg-Hanssen 《Solar physics》1970,15(2):359-371
We discuss the longitudinal component of the magnetic field, B
, based on data from about 135 quiescent prominences observed at Climax during the period 1968–1969. The measurements are obtained with the magnetograph which records the Zeeman effect on hydrogen, helium and metal lines. Use of the following lines, H; Hei, D3, Hei, 4471 Å; Nai, Di and D2, leads to the same value for the observed magnetic field component in these prominences. For more than half of the prominences their mean field, B
, satisfy the inequalities 3 G B
8 G, and the overall mean value for all the prominences is 7.3 G. As a rule, the magnetic field enters the prominence on one side and exits on the other, but in traversing the prominence material, the field tends to run along the long axis of the prominence.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
Two possible limiting scenarios are proposed for the production of a coronal mass ejection. In the first the magnetic field around a prominence evolves until it loses equilibrium and erupts, which drives reconnection below the prominence and an eruption of the overlying magnetic arcade. In the second a large-scale magnetic arcade evolves until it loses equilibrium and erupts, thereby causing a prominence to erupt. In general it is likely to be the non-equilibrium of the coupled system which creates the eruption. Furthermore, large quiescent prominences are expected to be centred within the magnetic bubble of a coronal mass ejection whereas when active-region prominences erupt they are likely to be located initially to one side of the bubble.A model is set up for the eruption of a magnetically coupled prominence and coronal mass ejection. This represents a development of the Anzer and Pneuman (1982) model by overcoming two limitations of it, namely that: it is not globally stable initially and so one wonders how it can be set up in a stable way before the eruption; it has reconnection driving the CME whereas recent observations suggest that the reverse may be happening. In our model we assume that magnetic reconnection below the prominence is driven by the eruption and the driver is magnetic non-equilibrium in the coupled prominence-mass ejection system. The prominence is modelled as a twisted flux tube and the mass ejection as an overlying void and magnetic bubble. Two different models of the prominence are considered. In one a globally stable equilibrium becomes unstable when a threshold magnetic flux below the prominence is exceeded and, in the other, equilibrium ceases to exist. In both cases, the prominence and mass-ejection accelerate upwards before reaching constant velocities in a manner that is consistent with observations. It is found that the greater the reconnection that is driven by the eruption, the higher is the final speed. 相似文献