共查询到20条相似文献，搜索用时 31 毫秒
1.
Hirokazu Yoshimura 《Solar physics》1977,54(1):229-258
The simultaneous enhancement or subsidence of both the high-speed solar wind streams and the galactic cosmic rays in the minimum or the maximum phase of the solar cycle are interpreted in a unified manner by the concept of geometrical evolution of the general magnetic field of the corona-heliomagnetosphere system. The coronal general magnetic field evolves from an open dipole-like configuration in the minimum phase to a closed configuration with many loop-like formations in the maximum phase of the solar cycle. This concept, developed in a theoretical solar-cycle model driven by the dynamo action of the global convection, is examined and found to be valid by studying the evolution of the coronal general magnetic field calculated from the observed surface general magnetic field of 1959–1974. It is also found that the energy density of the poloidal component of the general surface field, from which the coronal field originates, attained a maximum in the maximum phase and showed a evolution with virtually no phase delay with respect to that of the toroidal component of the field, to which the sunspot activity is related. The subsidence of the high-speed solar wind in the maximum phase is understood as a braking of the solar wind streams by the tightly closed and strong coronal field lines in the lower corona in the maximum phase. The field lines of the heliomagnetosphere, which originate from the coronal field lines drawn by the solar wind, are inferred to be also more tightly closed at the heliopause in the maximum phase than in the minimum phase. The decrease of the galactic cosmic rays in the maximum phase (known as the Forbush's negative correlation between the galactic cosmic ray intensity and the solar activity or the Forbush solar-cycle modulation of the galactic cosmic rays) is interpreted as a braking of the cosmic rays by the closed magnetic field lines at the heliopause. The observed phase lag (approximately one year) of the galactic cosmic ray modulation with respect to the evolution of the solar cycle, and the observed absence of the gradient of the total cosmic ray intensity between 1 AU and 8 AU, are discussed to support this view of the cosmic ray modulation at the remote heliopause, and reject other hypotheses to explain the phenomenon in terms of the magnetic irregularities of various kinds carried by the solar wind: The short-term Forbush decrease at a time of a flare shows that the magnetic irregularities can react on the cosmic rays relatively near the Sun if they even played a dominant role in the long-term modulation. The concept of the general magnetic field of the corona and the surface is also used to understand the basic nature of the surface field itself, by comparing the geometry of the calculated coronal field lines with the eclipse photographs of the corona, and by discussing, in the context of the coronal general magnetic field associated with the solar cycle, the process of the emergence of the coronal field lines from the interior and the formation of the transequatorial arches and loops connecting the two hemispheres in the corona. 相似文献
2.
M.J. Laird 《Planetary and Space Science》1978,26(6):595-604
An analytic investigation is made of rays from a source in a magneto-ionic medium for which the magnetic field H and the electron density vary, in a Cartesian co-ordinate system Oxyz, with x alone. The case Hz = 0 is considered in some detail. It is shown that rays in the xy-plane may be focused, and that interference can occur. The geomagnetic field is then represented by a model for which Hy is proportional to x, and the magnetic field lines are parabolas. Observations and theories of magnetospheric chorus, in particular of the gap near one-half the equatorial electron gyrofrequency, are discussed in relation to this model. 相似文献
3.
4.
E. N. Parker 《Astrophysics and Space Science》1973,24(1):279-288
The origin and behavior of cosmic rays in the Galaxy depends crucially upon whether the galactic magnetic field has a closed topology, as does the field of Earth, or whether a major fraction of the lines of force connect into extragalactic space. If the latter, then cosmic rays could be of extragalactic origin, or they could be of galactic origin, detained in the Galaxy by the scattering offered by hydromagnetic waves, etc. If, on the other hand, the field is largely closed, then cosmic rays cannot be of extragalactic origin (at least below 1016 eV). They must be of galactic origin and escape because their collective pressure inflates the galactic field and they push their way out.This paper examines the structure of a galactic field that opens initially into intergalactic space and, with the inclusion of turbulent diffusion, finds no possibility for maintaining a significant magnetic connection with an extragalactic field. Unless some mechanism can be found, we are forced to the conclusion that the field is closed, that cosmic rays are of galactic origin, and that cosmic rays escape from the Galaxy only by pushing their way out. 相似文献
5.
V. S. Ptuskin 《Astrophysics and Space Science》1979,61(2):259-265
A modification of the diffusional motion of cosmic rays in a large scale turbulent field is considered. The partial dragging of particles in the arbitrarily wandering magnetic field lines may lead to the creation of a new regime of diffusion of cosmic rays in the Galaxy. 相似文献
6.
Donald V. Reames 《Solar physics》2010,265(1-2):187-195
We investigate the topology of magnetic clouds using energetic particles from a variety of sources outside the clouds as probes to remotely sense the interconnections of the magnetic field. We find that only a small percentage of field lines in magnetic clouds are truly closed directly to the Sun, so as to exclude particles from an external source. Field lines that are open to the outer heliosphere must be mixed with closed field lines on a fine spatial scale in the clouds to explain the simultaneous observation of anomalous cosmic rays from the outer heliosphere and of counter-streaming suprathermal electrons from the corona. The results of this paper show that, given sufficient time, particles accelerated at shock waves outside magnetic clouds have access to the interior and to a wide region of solar longitude in interplanetary space surrounding the clouds. 相似文献
7.
Freeman D. Miller 《Icarus》1979,37(2):443-456
On photographs taken between 25 December 1969 and 12 January 1970 with the Michigan Curtis Schmidt on Cerro Tololo and the Hamburg Schmidt at the Boyden Observatory, Comet 1969 IX is seen projected on planes nearly perpendicular to its orbit. During this period the Type I tail was free of major structural disturbances, and the faintness of the Type II tail facilitated study of the Type I tail near the lead. Characteristics of the main Type I tail are described in Part II. A classification of the tail forms according as the tail had the form of a fan of rays or a wedge, the orientation of the tail axis, and the angular width of the tail are discussed in Section IIA. In Section IIB the structure of the tail from 26 to 31 December, a period within which a disconnection of the tail took place, is viewed as the possible result of the passage across the comet of an interplanetary magnetic sector boundary, as proposed by Niedner and Brandt (1977, Bull. Amer. Astron. Soc. 4). In Sections IIC and IID waves in rays and the onset of turbulence are considered. Section IIIA is devoted to unusually long and bright off-axis rays; data on longitudinal forms, closing rate to the axis, and photometry of a ray are presented. In Section IIIB the structure of a “plume” of seven nearly parallel rays is related to the configuration of magnetic field lines predicted by Schmidt and Wegmann (1976, IPP Report 6/147). The orientations of the plume rays are consistent with those of the calculated field lines; the inferred rate of generation of the rays is about 1/hr. 相似文献
8.
The point source of neutral gas undergoing ionization and expanding into an uniform magnetic field is considered. Friction
between the neutral and ionized particles results in the formation of the magnetic field barrier and diamagnetic cavity surrounding
the source. At least one neutral point inevitably arises at the boundary of the cavity. When the neutral gas production rate
grows, two neutral points may arise at this boundary. In the vicinity of these points magnetic field lines converge, along
with the plasma flow which is magnetic field aligned in the steady state. As a result, two plasma jets originate from the
neutral points. Possible relation of these jets to cometary rays is discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Mohsen Shadmehri 《Monthly notices of the Royal Astronomical Society》2009,397(3):1521-1527
We study the dynamical effects of cosmic rays (CRs) on thermal instability in the linear regime. CRs and the thermal plasma are treated as two different interacting fluids, in which CRs can diffuse along the magnetic field lines. We show that the growth rate of the magnetothermal condensation mode is reduced because of the existence of CRs, and this stabilizing effect depends on the diffusion coefficient and the ratio of CR pressure to gas pressure. Thus, a slower rate of structure formation via thermal instability is predicted when CRs are considered. 相似文献
10.
Trajectories of solar cosmic rays have been calculated in a static ninth-order coronal magnetic field. It is found that as a result of field curvature and gradients, protons drift across the field lines at a rate of up to 200
2 deg hr–1. These drift rates are of the same order as, but somewhat smaller than, empirically derived rates. Localized enhancements of magnetic field have been inserted into the ninth-order field in order to model (in a highly idealized manner) the effects of the small-scale magnetic features which give rise to X-ray bright points. The motions of the particles in the presence of these scattering centers can be parameterized approximately by a cross-field diffusion coefficient. Our estimates of this coefficient, although crude, overlap with empirical values which have been deduced over a wide range of energies.We propose that coronal propagation of solar cosmic rays has two components. One is independent of particle velocity, and is associated with dynamic field phenomena (such as an expanding magnetic bottle): this is the only component which is important in flares which occur close to the foot-point of the Sun-Earth field line. The second component is velocity dependent, but is independent of mass, and is associated with scattering off (relatively static) magnetic inhomogeneities with scale sizes of at least 500 km: the second component contributes to coronal propagation if the flare occurs more than about 50–60 deg away from the Sun-Earth field line. 相似文献
11.
Anisotropic diffusion of solar cosmic rays 总被引：1，自引：0，他引：1
W. I. Axford 《Planetary and Space Science》1965,13(12):1301-1309
A simple model is described for solar cosmic ray events which appears to be in reasonable accord with observations. The model is based partly on some earlier models, together with the assumption that the diffusion of particles is strongly anisotropic due to the presence of the interplanetary magnetic field. Some remarks concerning the limitations of the diffusion equation are included, and it is pointed out that the propagation of solar cosmic rays might be best described in terms of an analogy to electrical transmission lines rather than to the conduction of heat as is usually done. 相似文献
12.
One dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These
show that cosmic ray streaming drives large amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently
transfered to the perturbed magnetic field of the Alfvén waves. Thus a magnetic field of interstellar values, assumed in models
of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic
field reduces the acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant
resolution to the highest energy galactic cosmic ray problem were the cosmic rays themselves provide the fields necessary
for their acceleration.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
One-, two- and three-dimensional numerical results of the non-linear interaction between cosmic rays and a magnetic field are presented. These show that cosmic ray streaming drives large-amplitude Alfvénic waves. The cosmic ray streaming energy is very efficiently transferred to the perturbed magnetic field of the Alfvén waves, and the non-linear time-scale of the growth of the waves is found to be very rapid, of the order of the gyro-period of the cosmic ray. Thus, a magnetic field of interstellar values, assumed in models of supernova remnant blast wave acceleration, would not be appropriate in the region of the shock. The increased magnetic field reduces the cosmic ray acceleration time and so increases the maximum cosmic ray energy, which may provide a simple and elegant resolution to the highest energy Galactic cosmic ray problem, where the cosmic rays themselves provide the fields necessary for their acceleration. 相似文献
14.
MHD simulation study is performed to investigate magnetic reconnection induced by the Kelvin Helmholtz instability in the parallel configuration of the uniform magnetic field geometry as well as the sheared field geometry. Highly distorted magnetic field lines due to Kelvin Helmholtz instability become reconnected and flattened so that they resume the straight field line structure in the final stage. When the initial magnetic field is sheared, magnetic islands formed as a result of magnetic reconnection are transported toward the weak field region but they soon disappear since these islands are of small scales and suffer strong diffusions. Morphological change in the long term evolution is most dramatic in the small range of magnetic field intensity in both the uniform field case and the sheared field case, which is not too strong to stabilize vortex growing early on or too weak to have negligible effect on the instability. Energy conversion and the momentum transport are also most effective in this small range. 相似文献
15.
E. J. Weber 《Solar physics》1969,9(1):150-159
A model of the solar atmosphere is presented in which we discuss the conservation of angular momentum for the two basic states in which the solar gas can be: namely, either confined by closed field lines or outflowing along open magnetic field lines. It can be shown that the boundary conditions are in general different for these two cases. From this we obtain the results that in the closed configuration the gas can corotate at the solar surface with the magnetic field lines and its angular velocity will then increase with height, whereas for a gas flowing along an open field line the angular velocity will decrease. An exception to the latter case can be found where the open magnetic field lines are strongly nonradial and where the density is a slowly varying function of radius. In such regions the angular velocity may initially increase with height, reach a maximum and then decrease.Kitt Peak National Observatory Contribution No. 439.Operated by The Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
16.
Magnetic reconnection induced by Kelvin Helmholtz instability 总被引：1，自引：0，他引：1
MHD simulation study is performed to investigate magnetic reconnection induced by the Kelvin Helmholtz instability in the initially sheared magnetic field geometry as well as in the uniform magnetic field geometry. Slow mode rarefaction structures seen in the uniform field case are not observed in the sheared field case. Dynamo action is less prominent and the conversion of plasma flow energy into the other forms of energy is also smaller in the sheared field case than in the uniform field case. Momentum transport is mostly due to the hydrodynamic stress in the sheared field case, while the electromagnetic stress is dominant in the uniform field case. The long term evolutions are also markedly different in the two cases. In the uniform field geometry, the magnetic field lines twisted due to the Kelvin Helmholtz instability become reconnected and flattened so that they resume the straight field line structure which resembles the initial field geometry. The magnetic field, however, is not uniform with smaller intensity in the central region where the pressure balance is partially maintained by the enhanced thermal pressure. In the initially sheared magnetic field geometry, magnetic reconnection continues to operate until the end of the simulation and the conversion of the flow energy into the thermal energy is still seen. 相似文献
17.
The resonances that appear in the linear compressible MHD formulation of waves are studied for equilibrium states with flow. The conservation laws and the jump conditions across the resonance point are determined for 1D cylindrical plasmas. For equilibrium states with straight magnetic field lines and flow along the field lines the conserved quantity is the Eulerian perturbation of total pressure. Curvature of the magnetic field lines and/or velocity field lines leads to more complicated conservation laws. Rewritten in terms of the displacement components in the magnetic surfaces parallel and perpendicular to the magnetic field lines, the conservation laws simply state that the waves are dominated by the parallel motions for the modified slow resonance and by the perpendicular motions for the modified Alfvén resonance.The conservation laws and the jump conditions are then used for studying surface waves in cylindrical plasmas. These waves are characterized by resonances and have complex eigenfrequencies when the classic true discontinuity is replaced by a nonuniform layer. A thin non-uniform layer is considered here in an attempt to obtain analytical results. An important result related to earlier work by Hollweg et al. (1990) for incompressible planar plasmas is found for equilibrium states with straight magnetic field lines and straight velocity field lines. For these equilibrium states the incompressible and compressible surface waves have the same frequencies at least in the long wavelength limit and there is an exact correspondence with the planar case. As a consequence, the conclusions formulated by Hollweg et al. still hold for the straight cylindrical case. The effects of curvature are subsequently considered. 相似文献
18.
O. M. El Mekki 《Solar physics》1980,68(1):3-15
Hydromagnetic planetary waves propagating through a zonal flow and a transverse magnetic field both of which are sheared in the vertical direction are studied. It is found that the effect of the transverse magnetic field is to make planetary waves, which characteristically propagate westwards, propagate eastwards in both westerly and easterly zonal flows. It is also shown that at a critical level the rays are guided by the zonal flow only and that the waves are either attenuated or escalated by an exponential factor as they cross a critical level. 相似文献
19.
The hydrostatic equilibrium of the gas field system is studied in the halo. Cosmic-ray distribution is considered independently from the magnetic field on the basis of the diffusion model of the propagation of cosmic rays. We show that the cosmic rays extend in the halo to distances of a few kiloparsecs. The magnetic field decreases slowly with height above the galactic plane. 相似文献
20.
The identification of solar-wind sources is an important question in solar physics. The existing solar-wind models (e.g., the Wang–Sheeley–Arge model) provide the approximate locations of the solar wind sources based on magnetic field extrapolations. It has been suggested recently that plasma outflows observed at the edges of active regions may be a source of the slow solar wind. To explore this we analyze an isolated active region (AR) adjacent to small coronal hole (CH) in July/August 2009. On 1 August, Hinode/EUV Imaging Spectrometer observations showed two compact outflow regions in the corona. Coronal rays were observed above the active-region coronal hole (ARCH) region on the eastern limb on 31 July by STEREO-A/EUVI and at the western limb on 7 August by CORONAS-Photon/TESIS telescopes. In both cases the coronal rays were co-aligned with open magnetic-field lines given by the potential field source surface model, which expanded into the streamer. The solar-wind parameters measured by STEREO-B, ACE, Wind, and STEREO-A confirmed the identification of the ARCH as a source region of the slow solar wind. The results of the study support the suggestion that coronal rays can represent signatures of outflows from ARs propagating in the inner corona along open field lines into the heliosphere. 相似文献