共查询到20条相似文献，搜索用时 31 毫秒
1.
Gaetano Zimbardo Pierluigi Veltri Pierre Pommois 《Astrophysics and Space Science》2001,277(1-2):101-102
The transport of plasma and of energetic particles because of magnetic turbulence is relevant to many space plasmas, ranging
from the planetary magnetospheres to the solar corona and to the heliosphere. Various transport regimes for magnetic field
lines can be obtained depending on the Kubo number. Here we show, by means of a numerical simulation, that the Kubo number
also determines the level of chaos of the field lines. Weak chaos, closed magnetic surfaces, and anomalous transport regimes
are obtained for R≪ 1; widespread chaos, destroyed magnetic surfaces, and quasilinear scaling of the diffusion coefficient for R ≳ 0.3; and global stochasticity as well as percolation scaling of the diffusion coefficient for R≫ 1.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
We present a new model to explain how particles (solar energetic particles; SEPs), accelerated at a reconnection site that is not magnetically connected to the Earth, could eventually propagate along the well-connected open flux tube. Our model is based on the results of a low-β resistive magnetohydrodynamics simulation of a three-dimensional line-tied and initially current-free bipole, which is embedded in a non-uniform open potential field. The topology of this configuration is that of an asymmetric coronal null point, with a closed fan surface and an open outer spine. When driven by slow photospheric shearing motions, field lines, initially fully anchored below the fan dome, reconnect at the null point, and jump to the open magnetic domain. This is the standard interchange mode as sketched and calculated in 2D. The key result in 3D is that reconnected open field lines located in the vicinity of the outer spine keep reconnecting continuously, across an open quasi-separatrix layer, as previously identified for non-open-null-point reconnection. The apparent slipping motion of these field lines leads to formation of an extended narrow magnetic flux tube at high altitude. Because of the slip-running reconnection, we conjecture that if energetic particles would be traveling through, or be accelerated inside, the diffusion region, they would be successively injected along continuously reconnecting field lines that are connected farther and farther from the spine. At the scale of the full Sun, owing to the super-radial expansion of field lines below 3?R ⊙, such energetic particles could easily be injected in field lines slipping over significant distances, and could eventually reach the distant flux tube that is well-connected to the Earth. 相似文献
3.
Tyan Yeh 《Solar physics》1987,107(2):247-262
This paper elucidates the topological relationship between the distribution of polarity neutral lines on the solar surface and the interspersion of closed field lines among open field lines in the corona. The solar surface contains polarity neutral lines, that are spatially nested in a series-and-parallel hierarchy. The corona is partitioned by separatrix surfaces into a corresponding hierarchy of nested magnetic cells. The complexity of the magnetic structure of the corona consists in the embedding of magnetic cells of closed field lines amid open field lines.Polarity neutral lines lie necessarily on the foot surfaces of magnetic cells that are filled with closed field lines. There are two topologically distinct types of magnetic cells of closed field lines: closed and open. Only the open cells are overlain by current sheets. Each of the heliospheric current sheets separates the open field lines encircled by an open cells from the open field lines encircling the cell. Since closed cells have no images in the outer corona, the cell structure of the latter reflects those polarity neutral lines associated with the open cells in the lower corona. Accordingly, there are fewer heliospheric current sheets, as revealed by magnetic neutral lines on the source surface, in interplanetary space than polarity neutral lines on the solar surface. 相似文献
4.
Among all the signatures of solar ejecta in interplanetary space, magnetic clouds are particularly interesting. We have shown that they are associated with solar mass ejections that involve not only coronal heights, but also chromospheric heights and so, they are almost always associated with low-altitude solar activity such as H flares or filament eruptions. As a magnetic cloud is a very large structure, and not all the ejecta found in the interplanetary medium are clouds, it is interesting to investigate the characteristics of the large-scale coronal magnetic structures in the regions where the activity leading to a cloud takes place. In this paper we use Hoeksema's potential field model of the solar magnetosphere to obtain the magnetic structure of the site of the solar events associated with 35 interplanetary magnetic clouds. The position of the related solar activity was determined from the location of the near-surface solar explosive events (flares and filament eruptions) associated with each cloud, obtained in our previous study. We find that the solar activity associated with interplanetary magnetic clouds occurs in regions of low-altitude, magnetically closed structures lying between higher helmets, or between the highest helmets and coronal holes, where the magnetic field lines are longitudinally oriented. 相似文献
5.
We test a new emission mechanism in pulsar magnetospheres, eventually responsible in part for the high level of observed radio radiation. This is carried out by comparing the efficiency of the two-stream instability of Langmuir waves in a pulsar emission region, where the stationary and non-stationary characters of pair plasma outflows produced in the gap region are characterized by two different time-scales. On the shorter time-scale, the Ruderman &38; Sutherland 'sparking' phenomenon leads to the creation of pair plasma clouds, in motion along magnetic field lines, that contain particles with a large spectrum of momenta. The overlapping of particles with different energies produced in successive clouds results in an efficient 'two stream'-like instability. This effect is a consequence of the non-stationary character of the pair plasma produced in the gap region, just above the magnetic poles of the neutron star. On a long time-scale, resulting pair plasma outflows in pulsar magnetospheres can be treated as stationary. In this case, the instability which results from interaction between existing primary beam particles and the pair plasma is negligible, whereas the instability owing to interaction between electrons and positrons of the pair plasma itself, and more precisely to their relative drift motion along curved magnetic field lines, is effective. We derive characteristic features of the triggered instability, using specific distribution functions to describe either particles in the assembly of clouds or relative drifting of electrons and positrons in these same plasma clouds. Although linear and local, our treatment suggests that non-stationary effects may compete with, or even dominate over, drifting effects in parts of pulsar emission regions. 相似文献
6.
Kenneth R. Lang 《Earth, Moon, and Planets》1995,70(1-3):1-20
The Sun is enveloped by a hot, tenuous million-degree corona that expands to create a continuous solar wind that sweeps past all the planets and fills the heliosphere. The solar wind is modulated by strong gusts that are initiated by powerful explosions on the Sun, including solar flares and coronal mass ejections. This dynamic, invisible outer atmosphere of the Sun is currently under observation with the soft X-ray telescope aboard the Yohkoh spacecraft, whose results are presented. We also show observations from the Ulysses spacecraft that is now passing over the solar pole, sampling the solar wind in this region for the first time. Two other spacecraft, Voyager 1 and 2, have recently detected the outer edge of the invisible heliosphere, roughly halfway to the nearest star. Magnetic solar activity, the total radiative output from the Sun, and the Earth's mean global surface temperature all vary with the 11-year sunspot cycle in which the total number of sunspots varies from a maximum to a minimum and back to a maximum again in about 11 years. The terrestrial magnetic field hollows out a protective magnetic cavity, called the magnetosphere, within the solar wind. This protection is incomplete, however, so the Sun feeds an unseen world of high-speed particles and magnetic fields that encircle the Earth in space. These particles endanger spacecraft and astronauts, and also produce terrestrial aurorae. An international flotilla of spacecraft is now sampling the weak points in this magnetic defense. Similar spacecraft have also discovered a new radiation belt, in addition to the familiar Van Allen belts, except fed by interstellar ions instead of electrons and protons from the Sun. 相似文献
7.
Kouichi Hirotani 《Astrophysics and Space Science》2005,297(1-4):81-91
We investigate a stationary pair production cascade in the outer magnetosphere of an isolated, spinning neutron star. The
charge depletion due to global flows of charged particles, causes a large electric field along the magnetic field lines. Migratory
electrons and/or positrons are accelerated by this field to radiate gamma-rays via curvature and inverse-Compton processes.
Some of such gamma-rays collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen
the electric field, which is self-consistently solved together with the energy distribution of particles and gamma-rays at
each point along the field lines. By solving the set of Maxwell and Boltzmann equations, we demonstrate that an external injection
of charged particles at nearly Goldreich-Julian rate does not quench the gap but shifts its position and that the particle
energy distribution cannot be described by a power-law. The injected particles are accelerated in the gap and escape from
it with large Lorentz factors. We show that such escaping particles migrating outside of the gap contribute significantly
to the gamma-ray luminosity for young pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeV observed for
the Vela pulsar can be explained by this component. We also discuss that the luminosity of the gamma-rays emitted by the escaping
particles is naturally proportional to the square root of the spin-down luminosity. 相似文献
8.
V. G. Fainshtein V. M. Malashchuk N. N. Stepanian G. V. Rudenko Ya. I. Egorov 《Bulletin of the Crimean Astrophysical Observatory》2013,109(1):104-110
The magnetic connections of solar formations inside magneto-isolated complexes with areas outside the complexes were determined from the loop structures in the upper chromosphere and corona, as well as from calculations of magnetic field lines. It was found that 65% of the constructed field lines are closed within complexes or not closed on the solar surface, while 35% of the field lines intersect the boundary of the complex. Short field lines that intersect the boundary of the complex often connect the points of low intensity. The ends of the long field lines coincide with ends of the arch structures, whose higher parts are not visible in the 17.1 nm line. The short field lines coincide in position with the loop structures at the corona level. It was shown that there are three types of magnetic field variations depending on the height above the complexes. 相似文献
9.
10.
Kouichi Hirotani Shinpei Shibata 《Monthly notices of the Royal Astronomical Society》2001,325(3):1228-1240
We investigate a stationary particle acceleration zone in the outer magnetosphere of an obliquely rotating neutron star. The charge depletion as a result of global current causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate curvature gamma-rays, some of which collide with the X-rays to materialize as pairs in the gap. As a result of this pair-production cascade, the replenished charges partially screen the electric field, which is self-consistently solved together with the distribution of particles and gamma-rays. If no current is injected at either of the boundaries of the accelerator, the gap is located around the so-called null surface, where the local Goldreich–Julian charge density vanishes. However, we find that the gap position shifts outwards (or inwards) when particles are injected at the inner (or outer) boundary. We apply the theory to the seven pulsars whose X-ray fields are known from observations. We show that the gap should be located near to or outside of the null surface for the Vela pulsar and PSR B1951+32, so that their expected GeV spectrum may be consistent with observations. We then demonstrate that the intrinsically large TeV flux from the outer gap of PSR B0540–69 is absorbed by the magnetospheric infrared photons, causing it to be undetectable. We also point out that the electrodynamic structure and the resultant GeV emission properties of millisecond pulsars are similar to young pulsars. 相似文献
11.
H. Mavromichalaki A. Belehaki X. Rafios I. Tsagouri 《Astrophysics and Space Science》1996,246(1):7-14
Monthly cosmic-ray data from Inuvik (0.16 GV) and Climax (2.96 GV) Neutron Monitor stations has been studied with the aid of solar activity parameters for the time period 1947–1995. Systematic differences in the overall shape of successive 11-year modulation cycles and similarities in the alternate 11-year cycles seem to be related to the polarity reversals of the polar magnetic field of the Sun. This suggests a possible effectiveness of the Hale cycle during even and odd solar activity cycles. Our results can be understood in terms of open and closed models of the heliosphere. Positive north pole of the Sun leads to open heliosphere where particles reach the Earth more easily when their access route is by the heliospheric oolar regions (even cycles) than when they gain access along the current sheet (odd cycles). In this case as the route of access becomes longer due to the waviness of the neutral sheet, the hysteresis effect of cosmic-rays is also longer. This interpretation is explained in terms of different contributions of convection, diffusion and drift mechanisms to the whole modulation process influencing cosmic-ray transport in the heliosphere. 相似文献
12.
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
13.
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
14.
Magnetic flux synoptic charts are critical for a reliable modeling of the corona and heliosphere. Until now, however, these charts were provided without uncertainty estimates. The uncertainties are due to instrumental noise in the measurements and to the spatial variance of the magnetic flux distribution that contributes to each bin in the synoptic chart. We describe here a simple method to compute synoptic magnetic flux maps and their corresponding magnetic flux spatial variance charts that can be used to estimate the uncertainty in the results of coronal models. We have tested this approach by computing a potential-field source-surface model of the coronal field for a Monte Carlo simulation of Carrington synoptic magnetic flux maps generated from the variance map. We show that these uncertainties affect both the locations of source-surface neutral lines and the distributions of coronal holes in the models. 相似文献
15.
We investigate the formation and evolution of isothermal collapse nonuniformity for rotating magnetic interstellar clouds. The initial and boundary conditions correspond to the statement of the problem of homogeneous cloud contraction from a pressure equilibrium with the external medium. The initial uniform magnetic field is collinear with the angular velocity. Fast and slow magnetosonic rarefaction waves are shown to be formed and propagate from the boundary of the cloud toward its center in the early collapse stages. The front of the fast rarefaction wave divides the gas mass into two parts. The density, angular velocity, and magnetic field remain uniform in the inner region and have nonuniform profiles in the outer region. The rarefaction wave front surface can take both prolate and oblate shapes along the rotation axis, depending on the relationship between the initial angular velocity and magnetic field. We derive a criterion that separates the two regimes of rarefaction wave dynamics with the dominant role of electromagnetic and centrifugal forces. Based on analytical estimations and numerical calculations, we discuss possible scenarios for the evolution of collapse nonuniformity for rotating magnetic interstellar clouds. 相似文献
16.
Walter J. Heikkila 《Planetary and Space Science》1978,26(2):121-129
Reconnection involves singular lines called X-lines on the day and night sides of the magnetosphere, and the reconnection rate is proportional to the component of the electric field along the X-line. Although there is some indirect support for this model, nevertheless direct support is totally lacking. However, there are two distinct pieces of clearly contradictory observational evidence on the dayside. First is the failure to account for the implied energy dissipation by the magnetopause current, over 1011 W, which should be easily observable as heating or enhanced flow of the plasma near the magnetopause. In marked contrast to this prediction, HEOS-2 satellite data reveal a plasma with decreased energy density and reduced flow. Second, the boundary of closed magnetic field lines is in the wrong location. In the reconnection process the plasma outflow would cut across open field lines toward higher latitudes; there should be a band of open field lines equatorward of the cleft. Observations of trapped energetic particles indicate closed field lines within the entry layer and cleft. Either one of these pieces of evidence is sufficient by itself to require drastic revision, even rejection, of the reconnection model. There is also contradictory evidence on the night side. The last closed field line capable of trapping energetic particles is poleward of auroral arcs. The implication is that the X-line is at the distant magnetopause, and not in the plasma sheet. Consequently, even if the reconnection process were operative at the nightside X-line, it would be isolated from steady state plasma sheet and auroral processes. On the other hand, substorm phenomena, in which stored magnetic energy is converted into particle kinetic energy, necessarily involve an induced electric field; that is excluded in theories of the reconnection process in which it is assumed that curl E = 0. Nevertheless, the observed easy access of energetic solar flare particles to the polar caps, and especially the preservation of interplanetary anisotropies as differences between the two polar caps, argues strongly for an open magnetosphere, with interconnection between geomagnetic and inter-planetary magnetic field lines. It is suggested that the resolution of this apparent paradox involves electric fields parallel to the magnetic field lines somewhere on the dawn and dusk sides of the magnetosphere, with an equipotential dayside magnetopause. 相似文献
17.
The physics of the heliosphere has seen several exciting developments in the past years since the in situ discovery of the termination shock by Voyager 1 at 94 AU and radio observations of the interaction of GMIRs with the heliopause. The local hydrogen wall ahead of the heliosphere has been inferred from interstellar absorption lines and information about the interstellar magnetic field is now available. This sudden richness of information has lead to a waking realisation about the importance of the heliosphere for long-term space climate and possibly even terrestrial climate. 相似文献
18.
We consider a stationary model of the propagation of galactic cosmic rays (GCR) in the heliosphere and adjacent interstellar space. The heliosphere is assumed to be a two-layer medium consisting of two adjacent regions that are spherically symmetric relative to the sun. The solar wind velocity is supersonic in the inner heliosphere bounded by the standing termination shock, and this velocity is subsonic in the outer heliosphere bounded by the heliosheath. The GCR scattering in these regions is due to different factors characterized by relevant diffusion coefficients. The solar wind velocity is assumed to be zero in the interstellar medium, where the scattering becomes weaker. No particle sources are presumed to exist at the boundaries between the layers. An exact analytical solution of the corresponding mathematical problem can be obtained without essential difficulties, although it is extremely cumbersome. Analytical expressions for the GCR spectra of particles with very high energies (>2500 MeV) and very low energies (<1400 MeV) are obtained for each region of particle propagation. The low-energy particle distribution corresponds to the data obtained by the Voyager spacecraft. It is shown that the low-energy particle density continuously increases from the sun toward the heliospheric boundary, regardless of the scattering mode in the inner and outer parts of the heliosphere. 相似文献
19.
20.
STEREO A and B observations of the radial magnetic field between 1 January 2007 and 31 October 2008 show significant evidence
that in the heliosphere, the ambient radial magnetic field component with any dynamic effects removed is uniformly distributed.
Based on this monopolar nature of the ambient heliospheric field we find that the surface beyond which the magnetic fields
are in the monopolar configuration must be spherical, and this spherical surface can be defined as the inner boundary of the
heliosphere that separates the monopole-dominated heliospheric magnetic field from the multipole-dominated coronal magnetic
field. By using the radial variation of the coronal helmet streamers belts and the horizontal current – current sheet – source
surface model we find that the spherical inner boundary of the heliosphere should be located around 14 solar radii near solar
minimum phase. 相似文献