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1.
An analysis is made of the Martens-Kuin filament eruption model in relation to observations of coronal mass ejections (CMEs). The field lines of this model are plotted in the vacuum or infinite resistivity approximation with two background fields. The first is the dipole background field of the model and the second is the potential streamer model of Low. The assumption is made that magnetic field evolution dominates compression or other effects which is appropriate for a low- coronal plasma. The Martens-Kuin model predicts that, as the filament erupts, the overlying coronal magnetic field lines rise in a manner inconsistent with observations of CMEs associated with eruptive filaments. Initially, the bright arc of a CME broadens in time much more slowly than the dark cavity between it and the filament, whereas in the model they broaden at the same rate or the bright arc broadens more rapidly than the dark cavity, depending on the background field. Thus, this model and, by generalization the whole class of so-called Kuperus-Raadu configurations in which a neutral point occurs below the filament, are of questionable utility for CME modeling. An alternate case is considered in which the directions of currents in the Martens-Kuin model are reversed resulting in a so-called normal polarity configuration of the filament magnetic field. In this case, a neutral line occurs above the current-carrying filament. The background field lines now distort to support the filament and help eject it. While the vacuum field results make this configuration appear very promising, a full two- or more-dimensional MHD simulation is required to properly analyze the dynamics resulting from this configuration.Presently NRC Senior Research Associate at NOAA, Space Environment Laboratory, Boulder, Colorado, U.S.A.At the NASA National Space Data Center. 相似文献
2.
Tilaye Tadesse Alexei A. Pevtsov T. Wiegelmann P. J. MacNeice S. Gosain 《Solar physics》2014,289(11):4031-4045
Solar eruptive phenomena, like flares and coronal mass ejections (CMEs), are governed by magnetic fields. To describe the structure of these phenomena one needs information on the magnetic flux density and the electric current density vector components in three dimensions throughout the atmosphere. However, current spectro-polarimetric measurements typically limit the determination of the vector magnetic field to only the photosphere. Therefore, there is considerable interest in accurate modeling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data. In this work, we model the coronal magnetic field for global solar atmosphere using nonlinear force-free field (NLFFF) extrapolation codes implemented to a synoptic maps of photospheric vector magnetic field synthesized from the Vector Spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) as boundary condition. Using the resulting three-dimensional magnetic field, we calculate the three-dimensional electric current density and magnetic energy throughout the solar atmosphere for Carrington rotation 2124 using our global extrapolation code. We found that spatially, the low-lying, current-carrying core field demonstrates a strong concentration of free energy in the active-region core, from the photosphere to the lower corona (about 70 Mm). The free energy density appears largely co-spatial with the electric current distribution. 相似文献
3.
The onset stage of coronal mass ejections (CMEs) is difficult to observe and is poorly studied. In spite of their practical importance, methods for CME predictions with sufficient lead times are only in the nascent stages of development. The most probable CME mechanism is a catastrophic loss of equilibrium of a large-scale current system in the corona (a flux rope). A twisted magnetic rope is maintained by the tension of field lines of photospheric sources until parameters of the system reach critical values and the equilibrium is lost. Unfortunately, there is low-density plasma (coronal cavity) in most of the rope volume; thus, it is difficult to observe a rope. However, the lower parts of the helical field lines of a rope are fine traps for the dense cold plasma of prominences. Thus, prominences are the best tracers of flux ropes in the corona. The maximal height up to which the rope is in stable equilibrium can be found by analyzing the distribution of the magnetic field generated by photospheric sources in the corona. Comparing this critical height with the actually observed prominence height, one can estimate the probability of the loss of equilibrium by a magnetic rope with a following eruption of prominences and coronal mass ejections. 相似文献
4.
The finite element method was used to solve a partial differential equation (magnetostatic equation) for multipolar magnetic regions. It is found that the height of magnetic field lines above the magnetic neutral line of a central strong bipolar magnetic field decreases as the field lines' footpoints approach the neutral line and also with increased magnetic shear. Both the electric current density and plasma pressure in the sheared low-lying loops are high. We suggest that the sheared low-lying loops may store the energies of large coronal mass ejections (CMEs) and filament eruptions. In addition, it is found that a lower pressure area exists above the low-lying loops and that it is similar in morphology to a coronal cavity. Above the lower pressure area there is a higher pressure area, which may be the source of CMEs. In this area magnetic shear leads to magnetic reconnection, which may be the cause of high coronal temperature. 相似文献
5.
We present a theoretical study of the formation of a coronal cavity and its relation to a quiescent prominence. We argue that the formation of a coronal cavity is initiated by the condensation of plasma which is trapped by the coronal magnetic field in a closed streamer and which then flows down to the chromosphere along the field lines due to lack of stable magnetic support against gravity. The existence of a coronal cavity depends on the coronal magnetic field strength; with low strength, the plasma density is not high enough for condensation to occur. Furthermore, we suggest that prominence and cavity material is supplied from the chromospheric level. Whether a coronal cavity and a prominence coexist depends on the magnetic field configuration; a prominence requires stable magnetic support.We initiate the study by considering the stability of condensation modes of a plasma in the coronal streamer model obtained by Steinolfson et al. (1982) using a 2-D, time dependent, ideal MHD computer simulation; they calculated the dynamic interaction between outward flowing solar wind plasma and a global coronal magnetic field. In the final steady state, they found a density enhancement in the closed field region with the enhancement increasing with increasing strength of the magnetic field. Our stability calculation shows that if the density enhancement is higher than a critical value, the plasma is unstable to condensation modes. We describe how, depending on the magnetic field configuration, the condensation may produce a coronal cavity and/or initiate the formation of a prominence.NRC Research Associate. 相似文献
6.
Most work on coronal mass ejection (CME) interpretation focuses on the involved active region rather than on the large-scale coronal context. In this paper a global potential-field source-surface model of the coronal magnetic field is used to evaluate the sensitivity of the coronal field configuration to the location, orientation, and strength of a bipolar active region relative to a background polar field distribution. The results suggest that the introduction of antiparallel components between the field of the active region and the background field can cause significant topological changes in the large-scale coronal magnetic field resembling observations during some simple CMEs. Antiparallel components can be introduced in the real corona by the diffusion and convection of photospheric fields, flux emergence, or erupted or shear-induced twist of active-region fields. Global MHD models with time-dependent boundary conditions could easily test the stability of such configurations and the nature of any related transients. 相似文献
7.
Catastrophe of coronal magnetic rope embedded in a partly open multipolar background magnetic field is studied by using a 2-dimensional, 3-component ideal MHD model in spherical coordinates. The background field is composed of three closed bipolar fields of a coronal streamer and an open field with an equatorial current sheet. The magnetic rope lies below the central bipolar field, and it is characterized by its annular and axial magnetic fluxes. For a given annual flux, there is a critical value of the axial flux, and for a given axial flux, there is a critical value of annual flux such that, below the critical value, the magnetic rope is attached to the solar surface and the system stays in equilibrium, but when the critical value is exceeded, the magnetic rope breaks free and erupts upward. This implies that catastrophe can occur in a coronal magnetic rope embedded in a partly open multipolar background magnetic field. Our computation gives a threshold value of magnetic energy that is about 15% greater than the energy of the partly open magnetic field (the central bipolar field open and the fields on either side closed). The excess energy may serve as source for solar explosions such as coronal mass ejections. 相似文献
8.
《Chinese Astronomy and Astrophysics》2007,31(2):128-136
The influence of coronal streamer background with nested and closed magnetic fields on the of the triggering of coronal mass ejections (CMEs) is investigated in the meridian plane. In the coronal streamers’ background magnetic structure there are three small-scale closed magnetic fields, of which the middle one has a direction opposite to that of the global dipolar field of coronal streamers. The trigger model of CMEs emerges from beneath this small-scale closed magnetic field and possesses a concentric circular structure with radius of a = 0.1Rs (Rs being the solar radius). The direction of the magnetic field in the front half of the CME trigger model is opposite to that of the small-scale closed field and is the same as that of the streamers’ global dipolar field. As revealed by numerical simulation, when the ratio of the plasma pressure at the center of the CME trigger model to the boundary pressure is m ≤ 2, then the emerging model can trigger CMEs. When m < 2, then it cannot. The error in this critical value of 2 is less than 1%. 相似文献
9.
Tilaye Tadesse T. Wiegelmann P. J. MacNeice B. Inhester K. Olson A. Pevtsov 《Solar physics》2014,289(3):831-845
Measurements of magnetic fields and electric currents in the pre-eruptive corona are crucial to the study of solar eruptive phenomena, like flares and coronal mass ejections (CMEs). However, spectro-polarimetric measurements of certain photospheric lines permit a determination of the vector magnetic field only at the photosphere. Therefore, there is considerable interest in accurate modeling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data. In this work, we model the coronal magnetic field above multiple active regions with the help of a potential field and a nonlinear force-free field (NLFFF) extrapolation code over the full solar disk using Helioseismic and Magnetic Imager (SDO/HMI) data as boundary conditions. We compare projections of the resulting magnetic field lines with full-disk coronal images from the Atmospheric Imaging Assembly (SDO/AIA) for both models. This study has found that the NLFFF model reconstructs the magnetic configuration closer to observation than the potential field model for full-disk magnetic field extrapolation. We conclude that many of the trans-equatorial loops connecting the two solar hemispheres are current-free. 相似文献
10.
We combine a convectively driven dynamo in a spherical shell with a nearly isothermal density-stratified cooling layer that mimics some aspects of a stellar corona to study the emergence and ejections of magnetic field structures. This approach is an extension of earlier models, where forced turbulence simulations were employed to generate magnetic fields. A spherical wedge is used which consists of a convection zone and an extended coronal region to ???1.5 times the radius of the sphere. The wedge contains a quarter of the azimuthal extent of the sphere and 150° in latitude. The magnetic field is self-consistently generated by the turbulent motions due to convection beneath the surface. Magnetic fields are found to emerge at the surface and are ejected to the coronal part of the domain. These ejections occur at irregular intervals and are weaker than in earlier work. We tentatively associate these events with coronal mass ejections on the Sun, even though our model of the solar atmosphere is rather simplistic. 相似文献
11.
B. C. Low 《Solar physics》1996,167(1-2):217-265
This review puts together what we have learned about coronal structures and phenomenology to synthesize a physical picture of the corona as a voluminous, thermally and electrically highly-conducting atmosphere responding dynamically to the injection of magnetic flux from below. The synthesis describes complementary roles played by the magnetic heating of the corona, the different types of flares, and the coronal mass ejections as physical processes by which magnetic flux and helicity make their way from below the photosphere into the corona, and, ultimately, into interplanetary space. In these processes, a physically meaningful interplay among dissipative magnetohydrodynamic turbulence, ideal ordered flows, and magnetic helicity determines how and when the rich variety of relatively long-lived coronal structures, spawned by the emerged magnetic flux, will evolve quasi-steadily or erupt with the impressive energies characteristic of flares and coronal mass ejections. Central to this picture is the suggestion, based on recent theoretical and observational works, that the the emerged flux may take the form of a twisted flux rope residing principally in the corona. Such a flux rope is identified with the low-density cavity at the base of a coronal helmet, often but not always encasing a quiescent prominence. The flux rope may either be bodily transported into the corona from below the photosphere, or reform out of a state of flaring turbulence under some suitable constraint of magnetic-helicity conservation. The appeal of this synthesis is its physical simplicity and the manner it relates a large set of diverse phenomena into a self-consistent whole. The implications of this view point are discussed.The topics covered are: the large-scale corona; helmet streamers; quiescent prominences; coronal mass ejections; flares and heating; magnetic reconnection and magnetic helicity; and, the hydromagnetics of magnetic flux emergence.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
12.
To quantify changes of the solar coronal field connectivity during eruptive events, one can use magnetic helicity, which is
a measure of the shear or twist of a current-carrying (non-potential) field. To find a physically meaningful quantity, a relative
measure, giving the helicity of a current-carrying field with respect to a reference (potential) field, is often evaluated.
This requires a knowledge of the three-dimensional vector potential. We present a method to calculate the vector potential
for a solenoidal magnetic field as the sum of a Laplacian part and a current-carrying part. The only requirements are the
divergence freeness of the Laplacian and current-carrying magnetic field and the sameness of their normal field component
on the bounding surface of the considered volume. 相似文献
13.
Tilaye Tadesse T. Wiegelmann P. J. MacNeice K. Olson 《Astrophysics and Space Science》2013,347(1):21-27
The magnetic fields in the solar atmosphere structure the plasma, store free magnetic energy and produce a wide variety of active solar phenomena, like flare and coronal mass ejections (CMEs). The distribution and strength of magnetic fields are routinely measured in the solar surface (photosphere). Therefore, there is considerable interest in accurately modeling the 3D structure of the coronal magnetic field using photospheric vector magnetograms. Knowledge of the 3D structure of magnetic field lines also help us to interpret other coronal observations, e.g., EUV images of the radiating coronal plasma. Nonlinear force-free field (NLFFF) models are thought to be viable tools for those task. Usually those models use Cartesian geometry. However, the spherical nature of the solar surface cannot be neglected when the field of view is large. In this work, we model the coronal magnetic field above multiple active regions using NLFFF extrapolation code using vector magnetograph data from the Synoptic Optical Long-term Investigations of the Sun survey (SOLIS)/Vector Spectromagnetograph (VSM) as a boundary conditions. We compare projections of the resulting magnetic field lines solutions with their respective coronal EUV-images from the Atmospheric Imaging Assembly (SDO/AIA) observed on October 15, 2011 and November 13, 2012. This study has found that the NLFFF model in spherical geometry reconstructs the magnetic configurations for several active regions which agrees to some extent with observations. During October 15, 2011 observation, there are substantial number of trans-equatorial loops carrying electric current. 相似文献
14.
The radial oscillations of coaxial magnetic flux tubes with an azimuthal field in the shell modeling current-carrying coronal loops are studied in the cool plasma approximation. Since the concept of current-carrying coronal loops provides a theoretical basis for studying simple loop flares, finding their parameters by means of coronal seismology is a topical problem of modern solar physics. The dispersion equation for radial oscillations is derived and the dispersion curves are constructed. Oscillations with arbitrarily long periods are shown to exist at the fundamental radial mode. 相似文献
15.
Axel Brandenburg Simon Candelaresi Piyali Chatterjee 《Monthly notices of the Royal Astronomical Society》2009,398(3):1414-1422
Using mean-field models with a dynamical quenching formalism, we show that in finite domains magnetic helicity fluxes associated with small-scale magnetic fields are able to alleviate catastrophic quenching. We consider fluxes that result from advection by a mean flow, the turbulent mixing down the gradient of mean small-scale magnetic helicity density or the explicit removal which may be associated with the effects of coronal mass ejections in the Sun. In the absence of shear, all the small-scale magnetic helicity fluxes are found to be equally strong for both large- and small-scale fields. In the presence of shear, there is also an additional magnetic helicity flux associated with the mean field, but this flux does not alleviate catastrophic quenching. Outside the dynamo-active region, there are neither sources nor sinks of magnetic helicity, so in a steady state this flux must be constant. It is shown that unphysical behaviour emerges if the small-scale magnetic helicity flux is forced to vanish within the computational domain. 相似文献
16.
N. S. Shilova 《Solar System Research》2006,40(5):437-440
The cells of photospheric background magnetic fields during Carrington rotation 2009 in October–November 2003 are considered. The small number of large sunspots and the high activity on the Sun in this period allow the correspondence between the activity of background field cells (flares) and the appearance of coronal mass ejections (CMEs) observed with the LASCO coronagraphs to be established without statistical analyses. The sunspots of opposite polarities in one background field cell are shown to serve as the legs of the same CME. The separation between them is close to 30°. 相似文献
17.
When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic
field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside
the source surface (Schatten, Wilcox, and Ness, 1969) or by limiting the interaction to thin current sheets between oppositely
directed field regions (Wolfson, 1985). Yet observations and numerical MHD calculations suggest the presence of non-force-free
volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed
and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This
work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the
magnetostatic equilibria developed by Bogdan and Low (1986) and the current-sheet modeling technique developed by Schatten
(1971). The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at
the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field
and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet
model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coronal helmet
structures better than the current-sheet model. 相似文献
18.
The most pertinent effect of the currents in the coronal-interplanetary space is their alteration of the magnetic topology to form configurations of open field lines. The important currents seem to be those in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines in the coronal helmet-streamer structures. Thus, the coronal-interplanetary space may be regarded as being partitioned by current-sheets into several piecewise current-free regions. These current sheets overlie the photospheric neutral lines, where the vertical component of the magnetic field reverses its polarity on the solar surface. But, their locations and strengths are determined by force balance between the magnetic field and the gas pressure in the coronal-interplanetary space. Since the pressure depends on the flow velocity of the solar wind and the solar wind channels along magnetic flux tubes, there is a strong magnetohydrodynamic coupling between the magnetic field and the solar wind. The sheetcurrent approach presented in this paper seems to be a reasonable way to account for this complicated interaction.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
19.
《Chinese Astronomy and Astrophysics》2007,31(2):146-163
Magnetic clouds (MCs) belong to an important subset of interplanetary coronal mass ejections. The identification of their boundaries is always a problem in the studies of MCs. This paper discusses a method to identify the boundaries of MCs by coordinate transformation. Instead of the conventional GSE (Geocentric Solar Ecliptic) coordinate system, the interplanetary magnetic field data are converted into a cloud natural coordinate system, in which the profile of the MC as a magnetic flux tube is clearly displayed. Then, combining with the plasma properties of the MC, the boundary of the cloud can be identified easily. Six observed MCs are analyzed using this method, and the results show that this method is feasible and can reduce the uncertainty in the identification of MC boundaries. 相似文献
20.
C. H. Mandrini P. Demoulin B. Schmieder E. E. Deluca E. Pariat W. Uddin 《Solar physics》2006,238(2):293-312
A major two-ribbon X17 flare occurred on 28 October 2003, starting at 11:01 UT in active region NOAA 10486. This flare was
accompanied by the eruption of a filament and by one of the fastest halo coronal mass ejections registered during the October–November
2003 strong activity period. We focus on the analysis of magnetic field (SOHO/MDI), chromospheric (NainiTal observatory and
TRACE), and coronal (TRACE) data obtained before and during the 28 October event. By combining our data analysis with a model
of the coronal magnetic field, we concentrate on the study of two events starting before the main flare. One of these events,
evident in TRACE images around one hour prior to the main flare, involves a localized magnetic reconnection process associated
with the presence of a coronal magnetic null point. This event extends as long as the major flare and we conclude that it
is independent from it. A second event, visible in Hα and TRACE images, simultaneous with the previous one, involves a large-scale
quadrupolar reconnection process that contributes to decrease the magnetic field tension in the overlaying field configuration;
this allows the filament to erupt in a way similar to that proposed by the breakout model, but with magnetic reconnection
occurring at Quasi-Separatrix Layers (QSLs) rather than at a magnetic null point.
Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users. 相似文献