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1.
The structure of the solar corona is dominated by the magnetic field because the magnetic pressure is about four orders of
magnitude higher than the plasma pressure. Due to the high conductivity the emitting coronal plasma (visible, e.g., in SOHO/EIT)
outlines the magnetic field lines. The gradient of the emitting plasma structures is significantly lower parallel to the magnetic
field lines than in the perpendicular direction. Consequently information regarding the coronal magnetic field can be used
for the interpretation of coronal plasma structures. We extrapolate the coronal magnetic field from photospheric magnetic
field measurements into the corona. The extrapolation method depends on assumptions regarding coronal currents, e.g., potential
fields (current-free) or force-free fields (current parallel to magnetic field). As a next step we project the reconstructed
3D magnetic field lines on an EIT-image and compare with the emitting plasma structures. Coronal loops are identified as closed
magnetic field lines with a high emissivity in EIT and a small gradient of the emissivity along the magnetic field. 相似文献
2.
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
3.
Studies of solar flares indicate that the mechanism of flares is magnetic in character and that the coronal magnetic field is a key to understanding solar high-energy phenomena. In our ongoing research we are conducting a systematic study of a large database of observations which includes both coronal structure (from the Soft X-ray Telescope on the Yohkoh spacecraft) and photospheric vector magnetic fields (from the Haleakala Stokes Polarimeter at Mees Solar Observatory). We compare the three-dimensional nonlinear force-free coronal magnetic field, computed from photospheric boundary data, to images of coronal structure. In this paper we outline our techniques and present results for active region AR 7220/7222. We show that the computed force-free coronal magnetic field agrees well with Yohkoh X-ray coronal loops, and we discuss the properties of the coronal magnetic field and the soft X-ray loops. 相似文献
4.
The coronal magnetic field is the primary driver of solar dynamic events. Linear and circular polarization signals of certain infrared coronal emission lines contain information about the magnetic field, and to access this information either a forward or an inversion method must be used. We study three coronal magnetic configurations that are applicable to polar-crown filament cavities by doing forward calculations to produce synthetic polarization data. We analyze these forward data to determine the distinguishing characteristics of each model. We conclude that it is possible to distinguish between cylindrical flux ropes, spheromak flux ropes, and sheared arcades using coronal polarization measurements. If one of these models is found to be consistent with observational measurements, it will mean positive identification of the magnetic morphology that surrounds certain quiescent filaments, which will lead to a better understanding of how they form and why they erupt. 相似文献
5.
Rajendra Shelke 《Journal of Astrophysics and Astronomy》2006,27(2-3):101-112
Coronal holes and interplanetary disturbances are important aspects of the physics of the Sun and heliosphere. Interplanetary
disturbances are identified as an increase in the density turbulence compared with the ambient solar wind. Erupting stream
disturbances are transient large-scale structures of enhanced density turbulence in the interplanetary medium driven by the
high-speed flows of low-density plasma trailing behind for several days. Here, an attempt has been made to investigate the
solar cause of erupting stream disturbances, mapped by Hewish & Bravo (1986) from interplanetary scintillation (IPS) measurements
made between August 1978 and August 1979 at 81.5 MHz. The position of the sources of 68 erupting stream disturbances on the
solar disk has been compared with the locations of newborn coronal holes and/or the areas that have been coronal holes previously.
It is found that the occurrence of erupting stream disturbances is linked to the emergence of new coronal holes at the eruption
site on the solar disk.
A coronal hole is indicative of a radial magnetic field of a predominant magnetic polarity. The newborn coronal hole emerges
on the Sun, owing to the changes in magnetic field configuration leading to the opening of closed magnetic structure into
the corona. The fundamental activity for the onset of an erupting stream seems to be a transient opening of pre-existing closed
magnetic structures into a new coronal hole, which can support highspeed flow trailing behind the compression zone of the
erupting stream for several days. 相似文献
6.
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
7.
With the SDO/AIA instrument, continuous and intermittent plasma outflows are observed on the boundaries of an active region along two distinct open coronal loops. By investigating the temporal sequence magnetograms obtained from HMI/SDO, it is found that a small-scale magnetic reconnection probably plays an important role in the generation of the plasma outflows in the coronal loops. It is found that the origin of the plasma outflows coincides with the locations of the small-scale magnetic fields with mixed polarities, which suggests that the plasma outflows along coronal loops probably results from the magnetic reconnection between the small-scale closed emerging loops and the large-scale open active region coronal loops. 相似文献
8.
Coronal holes (CH) emit significantly less at coronal temperatures than quiet-Sun regions (QS), but can hardly be distinguished in most chromospheric and lower transition region lines. A key quantity for the understanding of this phenomenon is the magnetic field. We use data from SOHO/MDI to reconstruct the magnetic field in coronal holes and the quiet Sun with the help of a potential magnetic model. Starting from a regular grid on the solar surface we then trace field lines, which provide the overall geometry of the 3D magnetic field structure. We distinguish between open and closed field lines, with the closed field lines being assumed to represent magnetic loops. We then try to compute some properties of coronal loops. The loops in the coronal holes (CH) are found to be on average flatter than in the QS. High and long closed loops are extremely rare, whereas short and low-lying loops are almost as abundant in coronal holes as in the quiet Sun. When interpreted in the light of loop scaling laws this result suggests an explanation for the relatively strong chromospheric and transition region emission (many low-lying, short loops), but the weak coronal emission (few high and long loops) in coronal holes. In spite of this contrast our calculations also suggest that a significant fraction of the cool emission in CHs comes from the open flux regions. Despite these insights provided by the magnetic field line statistics further work is needed to obtain a definite answer to the question if loop statistics explain the differences between coronal holes and the quiet Sun. 相似文献
9.
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
10.
An investigation of the large-scale magnetic field variations in the corona prior to and after CME eruptions 总被引：1，自引：0，他引：1
The magnetic field changes in the corona at the site of coronal mass ejections (CMEs) have been investigated using the potential field-source surface model. It is shown that a CME is accompanied by the opening of closed field lines that formed the streamer's helmet base prior to the onset of a coronal disturbance. Two to three days after the appearance of the CME, the field configuration at the location of the coronal ejection reverts approximately to the state pre-existing before the generation of the CME. The appearance of small transient open magnetic tubes has been found after eruption of the coronal mass. These magnetic tubes seem to be the analogs for transient coronal holes.Taking into account the results of calculations of the field changes in the neighbourhood of the CME occurrence site, we have suggested a possible mechanism governing the spatio-temporal correlation between some flares and CMEs. Also, a possible mechanism has been proposed for field reconfiguration in the corona, leading to loss of the equilibrium of the magnetic configuration and to the subsequent generation of a CME in the region of coronal streamer chains separating coronal holes with same-polarity magnetic field. 相似文献
11.
The persistent large-scale coronal magnetic structure associated with a sector boundary appears to consist of a magnetic arcade loop structure extending from one solar polar region to the other in approximately the north-south direction. This structure was inferred from computed coronal magnetic field maps for days on which a stable magnetic sector boundary was near central meridian, based on an interplanetary sector boundary observed to recur during much of 1968 and 1969. 相似文献
12.
Our investigation has been carried using the instruments onboard the Solar Dynamics Observatory (SDO) providing a high resolution of images (AIA photographs and HMI magnetograms). We have investigated the structure and magnetic evolution of several coronal bright points and small scale N-S polarity magnetic fluxes closely associated with them. We also compare the evolution of the magnetic polarities of elementary isolated sources of positive and negative fluxes (magnetic bipoles) and coronal bright points. Tiny (“elementary”) coronal bright points have been detected. A standard coronal bright point is shown to be a group of “elementary” coronal bright points that flare up sequentially. Our investigation shows that a change in the magnetic fluxes of opposite polarities is observed before the flare of a coronal bright point. We show that not all cases of the formation of coronal bright points are described by the magnetic reconnection model. This result has not been considered previously and has not been pointed out by other authors. 相似文献
13.
A method for investigating the differential rotation of the solar corona using the coronal magnetic field as a tracer is proposed. The magnetic field is calculated in the potential approximation from observational data at the photospheric level. The time interval from June 24, 1976, to December 31, 2004, is considered. The magnetic field has been calculated for all latitudes from the equator to ±75? with a 5? step at distances from the base of the corona 1.0 R⊙ to 2.45 R⊙ near the source surface. The coronal rotation periods at 14 distances from the solar center have been determined by the method of periodogram analysis. The coronal rotation is shown to become progressively less differential with increasing heliocentric distance; it does not become rigid even near the source surface. The change in the coronal rotation periods with time is considered. At the cycleminimumthe rotation has been found to bemost differential, especially at small distances from the solar center. The change in coronal rotation with time is consistent with the tilt of the solar magnetic equator. The results from the magnetic field are compared with those obtained from the brightness of the green coronal Fe XIV 530.3 nm line. The consistency between these results confirms the reliability of the proposed method for studying the coronal rotation. Studying the rotation of the coronal magnetic field gives hope for the possibility of using this method to diagnose the differential rotation in subphotospheric layers. 相似文献
14.
Using proxy data for the occurrence of those mass ejections from the solar corona which are directed earthward, we investigate the association between the post-1970 interplanetary magnetic clouds of Klein and Burlaga (1982) and coronal mass ejections. The evidence linking magnetic clouds following shocks with coronal mass ejections is striking; six of nine clouds observed at Earth were preceded an appropriate time earlier by meter-wave type II radio bursts indicative of coronal shock waves and coronal mass ejections occurring near central meridian. During the selected control periods when no clouds were detected near Earth, the only type II bursts reported were associated with solar activity near the limbs. Where the proxy solar data to be sought are not so clearly suggested, that is, for clouds preceding interaction regions and clouds within cold magnetic enhancements, the evidence linking the clouds and coronal mass ejections is not as clear; proxy data usually suggest many candidate mass-ejection events for each cloud. Overall, the data are consistent with and support the hypothesis suggested by Klein and Burlaga that magnetic clouds observed with spacecraft at 1 AU are manifestations of solar coronal mass ejection transients. 相似文献
15.
S. I. Syrovatskii 《Solar physics》1982,76(1):3-20
A model is presented for the penetration into the corona of a new magnetic field of a developing bipolar region and for its interaction with an old large-scale coronal field. An important feature of the model is a reconnection of the old and new fields inside the current sheet arising along the zero line of the total magnetic field calculated in the potential approximation. The magnetic reconnection and accumulation of plasma inside the current sheet can explain the appearance of dense coronal loops and the energy source at their tops. The plasma together with the magnetic lines is flowed into the sheet from both its sides. This fact explains the appearance of coronal cavities above the loops. If the large-scale field gradually decreases with the height, the loop motion is slowed down. The account of the dipolar structure of the magnetic field at large heights explains the possibility of a rapid break of the new field through the corona and the appearance of transients and open field regions - the coronal holes. In this case a fast rising current sheet can be a source of accelerated particles and of type II radio burst, instead of the shock wave considered usually. 相似文献
16.
V. M. Malashchuk V. G. Fainshtein N. N. Stepanian G. V. Rudenko Ya. I. Egorov 《Bulletin of the Crimean Astrophysical Observatory》2012,108(1):70-77
We propose the concept of a large-scale complex of solar formations with an isolated magnetic field. The complex involves a group of coronal holes, active regions, and regions with intermediate characteristics between a coronal hole and the undisturbed (calm) region. An interesting feature of these complexes is the weak connection between the magnetic fields inside and outside the complexes. Most of the lines of the magnetic flux that emerge from the complex prove to be either opened or closed inside the complex. 相似文献
17.
Relation of the coronal green line intensity to magnetic fields and sunspot areas in the solar cycle
The intensity of the green coronal Fe XIV λ530.3-nm line is correlated with sunspot areas and the magnetic field strength calculated for a distance of 1.1R ⊙. The relation of the green line emission to large-scale and local magnetic fields is shown to change differently with cycle phase. Large-scale coronal magnetic fields play a decisive role at the ascending phase, while a slightly higher correlation of the green line intensity with the local magnetic fields of sunspots is observed at the descending phase. Our results can be used to construct and test various solar coronal heating models. 相似文献
18.
The dependence of the position of the solar wind sonic point on the magnetic field in the solar corona during cycle 23 is studied. This dependence is shown to be rather strong in the rising phase and at the cycle maximum. As the coronal magnetic field grows, the distance to the sonic point decreases. Since the distance to the sonic point has been shown previously to anticorrelate with the solar wind speed, the result obtained suggests a strong positive correlation between the later and the coronal magnetic field. The situation changed dramatically two years after the calendar date of the cycle maximum. Beginning in 2004 the solar wind speed ceased to depend on the magnetic field up until the cycle minimum in December 2008. In 2009 a strong dependence of the wind speed on the coronal magnetic field was restored. It is hypothesized that this effect is associated with two different coronal heating mechanisms whose relative efficiency, in turn, depends on the contribution from magnetic fields of different scales. 相似文献
19.
N. V. Karachik E. Minenko I. Sattarov A. A. Pevtsov C. T. Sherdonov 《Astronomische Nachrichten》2014,335(10):1037-1042
Using magnetograms and coronal images from two instruments on board the Solar Dynamics Observatory (SDO), we study structure and evolution of a limited number of coronal bright points (CBPs). Our results show that the relation between CBPs and their magnetic footpoints is not simple. In some cases, CBP may appear as a bright portion of a larger loop (with clearly identifiable footpoints), and in some cases, an isolated CBP may develop between magnetic poles, which might not be the closest ones to each other or which might not be involved in the magnetic flux cancellation. We suggest that the magnetic connectivity responsible for formation of isolated coronal bright points is governed by the orientation of the large‐scale magnetic field. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
探讨了复杂磁结构上空日冕物理状态与磁剪切的关系．结果表明在强磁场的磁中性线上方磁剪切会引起具有强电流和较强等离子体压力的低磁弧．这可解释Ｙｏｈｋｏｈ 卫星的观测结果 相似文献