共查询到20条相似文献，搜索用时 609 毫秒
1.
New results from electrophotometric scanning of the solar disk in the HeI λ 10830 Å and Hα lines are presented. The intensity at the center of the HeI λ 10830.30 Å line is 1–3% higher in the regions of coronal holes than in quiescent regions; this is accompanied by a decrease in the size and contrast of the chromospheric network compared to the network in quiescent regions. Our observations in the HeI line revealed chains of “dark points” surrounding coronal holes. The Hα±0.5 observations show increased velocities of ascent near the dark points compared to the velocities inside coronal holes and in quiescent regions. It is proposed that the intensification and acceleration of the flows of solar plasma from the dark points are due to reconnection of the magnetic fields of the bipolar chromospheric network and the predominantly unipolar magnetic field inside the coronal holes. Our observations suggest that the same reconnection process takes place near the temperature minimum, in the presence of certain conditions at the boundary between coronal holes and bipolar active regions. The reconnection process produces plasma flows from the chromosphere to the corona, which are sufficient to form prominences. 相似文献
2.
O. G. Den 《Astronomy Reports》2007,51(2):161-167
Magnetic reconnection for arbitrary magnetic fields without null points is analyzed in the absence of plasma. A potential model field for four sources is considered. A method for the localization of probable reconnection regions using computable differential characteristics of magnetic fields is proposed. Some separator properties are examined, and separator regions are found for the best-known reconnection conditions. 相似文献
3.
We present the results of numerical simulations of the development of a current sheet in the solar corona over a bipolar region during the emergence of two new sunspots arranged collinearly with older spots. Two fronts of increased plasma density form at the boundary of the rising new magnetic flux. One of these is due to the generation of a current sheet, whose magnetic field accumulates energy for a flare. The other front is a branch of the density perturbation, and separates the old and new magnetic fluxes in a region where the magnetic field lines have the same direction on both sides of the boundary. The development of this perturbation is not associated with the energy accumulation in the corona, and hinders observation of the preflare state and complicates analysis of the results. This second front can be interpreted as the eruption of a filament before the onset of the flare. A scheme conservative with respect to magnetic flux was introduced in the Peresvet code that solves the MHD equations, in order to suppress numerical instabilities in regions of large magnetic-field gradients. 相似文献
4.
We have developed a three-dimensional numerical model and applied it to simulate plasma flows in semi-detached binary systems
whose accretor possesses a strong intrinsic magnetic field. The model is based on the assumption that the plasma dynamics
are determined by the slow mean flow, which forms a backdrop for the rapid propagation of MHD waves. The equations describing
the slow motion of matter were obtained by averaging over rapidly propagating pulsations. The numerical model includes the
diffusion of magnetic field by current dissipation in turbulent vortices, magnetic buoyancy, and wave MHD turbulence. A modified
three-dimensional, parallel, numerical code was used to simulate the flow structure in close binary systems with various accretor
magnetic fields, from 105 to 108 G. The conditions for the formation of the accretion disk and the criteria distinguishing the two types of flow corresponding
to intermediate polars and polars are discussed. 相似文献
5.
B. V. Somov 《Astronomy Reports》2011,55(11):962-977
A scenario for hard impulsive flares due to magnetic reconnection and particle acceleration in cosmic plasma is proposed.
The properties of fast reconnection in an appreciably non-equilibrium nagnetosphere of a compact relativistic object, such
as a neutron star, magnetar, or white dwarf, are discussed. Such a magnetosphere could form as the result of the action of
a relativistic shock on the strong magnetic field of the star. An analytical solution is presented for the generalized, two-dimensional
structure, shape, and boundaries of the magnetosphere, together with the magnitudes of the direct and reverse currents in
the reconnecting current layer. The uncompensated magnetic force acting on the reverse current is determined. The characteristic
parameters of the non-equilibrium magnetospheres of compact stellar objects are estimated. The excess magnetic energy of the
magnetosphere is comparable to the mechanical energy carried by the shock at the time of impact. The possible acceleration
of particles to gigantic energies is discussed. 相似文献
6.
O. G. Den 《Astronomy Reports》2008,52(11):931-936
We analyze the flare events of October 28 and May 27, 2003 to examine the possible connection of solar flares with singularities in the differential characteristics of solar magnetic fields. The relation between flares and the behavior of F indicators (which describe structural singularities of the magnetic fields) introduced earlier is analyzed. It is shown that the generation of flares can be associated with self-intersections (or reconnection) of the F = 0 curves, where magnetic reconnection can occur. Consequently, the current sheets generated in such regions can be sources of energy release. 相似文献
7.
Krauz V. I. Mitrofanov K. N. Voitenko D. A. Astapenko G. I. Markoliya A. I. Timoshenko A. P. 《Astronomy Reports》2019,63(2):146-160
Results from experiments on the radial distribution of the magnetic fields in axial plasma flows formed during the compression of a plasma–current sheath carried out at the KPF-4-PHOENIX plasmafocus installation are presented. The plasma flows were generated in a discharge with stationary filling of the chamber with a working gas of argon or hydrogen, and also with a pulsed injection of argon. Analysis of the radial profiles of the magnetic field distribution and their time variations are used to localize regions of trappedmagnetic field, as well as regions where a return current flows at the periphery of the plasma flow. It is shown that the transverse (radial) size of the plasma flow depends on the density of the ambient medium (background gas) through which it propagates. These experiments were carried out in the framework of a project on laboratory simulations of non-relativistic jets from young stars.
相似文献8.
New data for the energy and location of the hard-emission centers of a solar flare agree with an electrodynamic model of a solar flare based on the idea of the accumulation of free magnetic energy in the field of a current sheet. Three-dimensional MHD simulations are used to show that the energy stored in the preflare magnetic field of the current sheet is sufficient for the development of a flare and a coronal mass ejection. The flare and coronal mass ejection result from the explosive decay of the current sheet. The position of the brightness-temperature maximum of the radio emission during the flare coincides with the maximum of the current in the current sheet. The exponential spectrum of relativistic protons generated during the flare is consistent with acceleration by the electric field during the current-sheet decay. 相似文献
9.
The results of three-dimensional MHD numerical simulations are used to investigate the characteristic properties of the magnetic-field
structures in the accretion disks of semi-detached binary systems. It is assumed that the intrinsic magnetic field of the
accretor star is dipolar. Turbulent diffusion of the magnetic field in the disk is taken into account. The SS Cyg system is
considered as an example. The results of the numerical simulations show the intense generation of a predominantly toroidal
magnetic field in the accretion disk. Magnetic zones with well defined structures for the toroidal magnetic field form in
the disk, which are separated by current sheets in which there ismagnetic reconnection and current dissipation. Possible observational
manifestations of such structures are discussed. It is shown that the interaction of a spiral precessional wave with the accretor’s
magnetosphere could lead to quasi-periodic oscillations of the accretion rate. 相似文献
10.
This paper examines the mechanisms for the acceleration of electrons, protons, and ions during solar flares. The acceleration is assumed to occur in two steps. The particles are first pre-accelerated by the electric field of a high-temperature current sheet undergoing magnetic reconnection. A collapsing magnetic trap in the solar corona provides further acceleration. It is shown that the Fermi mechanism accelerates trapped protons and ions even more efficiently than it does electrons. The particles escaping from the trap have energies reaching several GeV. The energy distribution of the accelerated ions is essentially independent of their mass and degree of ionization. 相似文献
11.
E. P. Kurbatov D. V. Bisikalo M. V. Starodubtsev A. Ciardi J. Fuchs A. A. Solov’ev K. F. Burdonov G. Revet S. Chen 《Astronomy Reports》2018,62(8):483-491
Estimates of typical parameters of accretion flows in the representative intermediate polar EX Hydrae, the polar AM Herculis, and the “hot Jupiter” WASP-12b are presented. Dimensionless parameters of astrophysical systems are compared with those of laboratory experiments on laser ablation in magnetic fields. It is shown that laboratory simulations of astrophysical flows is possible in principle, provided that some adjustment to the magnetic field, plasma density, and plasma velocity are made. 相似文献
12.
Some mechanisms for Joule dissipation of electric currents flowing in partially ionized hydrogen plasmas are analyzed in a
three-fluid approximation. It is shown that ambipolar diffusion can be responsible for the annihilation of magnetic flux during
collisions of ions with neutral atoms. The relative influences of the electron conductivity and the Cowling conductivity on
the magnetic-field annihilation rate are examined in the frameworks of the Sweet-Parker reconnection model. The escape of
plasma is an efficient mechanism for cooling current sheetswith thicknesses of hundreds of kilometers in the solar chromosphere.
The origin of the solar chromospheric jets observed by the Hinode spacecraft is discussed. 相似文献
13.
An experimental study of the source and formation of large-scale streams in the solar wind is presented. Radio-astronomical data from 1998 are compared with optical SOHO observations and solar coronal magnetic fields calculated from Zeeman data obtained at the Wilcox Observatory. A correlation between the geometry of the solar-wind transition region and the strength of coronal magnetic fields is revealed. For the moderate heliolatitudes studied, this correlation divides into three branches corresponding to three types of coronal magnetic-field structures: open structures with field lines escaping into interplanetary space, closed structures with loop-like field lines, and intermediate structures including both open and closed configurations. High-speed streams of solar wind originate in regions with open magnetic structures. These structures are connected with the lateral lobes of streamers at moderate heliolatitudes. Low-speed flows originate above closed magnetic structures, typical of the main bodies of streamers. The lowest-speed solar-wind flows are not associated with coronal streamer structures, and originate in coronal regions with intermediate magnetic configurations simultaneously containing open and closed field lines. In these regions, the white-light corona becomes an extended and amorphous area with high luminosity, which stratifies into a radial structure with narrow stripes at higher resolution. 相似文献
14.
The process of post-flare loop formation, including the heating of flux tubes by hot chromospheric sources and their filling with plasma, is demonstrated by simulations in an MHD approximation. The loop is additionally heated at its apex by the interaction of oppositely directed plasma streams. Local coronal heating over the loop is also possible due to magnetic-field-line reconnection. A new version of the PERESVET code that can take into account anisotropy of the thermal conductivity of a plasma in a magnetic field was used for the computations. 相似文献
15.
A. P. Kropotkin 《Astronomy Reports》2011,55(12):1132-1143
The basis is laid out for a theory relating various phenomena in the solar atmosphere, including localized concentrations
of magnetic field at the bases of coronal magnetic arches, chromospheric spicules, twisted coronal magnetic flux tubes, and
flows of energy carried by Alfvén waves propagating upward into the corona. The structure of photospheric currents localized
in the vicinity of supergranule boundaries and excited by convective motions is studied. These currents exist primarily in
a “dynamo layer” of sharply enhanced transverse conductivity, which forms in the weakly ionized thermal photospheric plasma
located in the solar gravitational field. The motions of the electrons and ions in this layer have appreciably different characters:
the ions are collisionly driven by the flows of neutral atoms, while the electrons drift in the crossed electric and magnetic
fields. The electric field supporting the current arises due to the polarization of the electrons and ions. This field also
gives rise to Alfvén perturbations that propagate upward into the corona, together with their associated longitudinal currents.
The character of this “loading” makes the system of fields and currents uniquely defined. Moreover, the momentum flux carried
by these Alfvén waves should be transferred to the cool chromospheric gas, facilitating the vertical ejection of this gas
in the form of spicules, as was first proposed in 1992 by Haerendel. 相似文献
16.
A simple model for a multiscaled MHD dynamo is suggested. The uppermost tier of the model controls the evolution of the large-scale magnetic field, while the lower tiers are responsible for the evolution of the small-scale velocity and magnetic fields. This approach makes it possible to reproduce, e.g., the evolution of the Galactic magnetic field for realistic magnetic Reynolds numbers, which cannot be done using direct, detailed simulations. 相似文献
17.
Yu. V. Balabin É. V. Vashenyuk O. V. Mingalev A. I. Podgorny I. M. Podgorny 《Astronomy Reports》2005,49(10):837-846
Analysis of the relativistic proton spectra of solar flares occurring in the 23rd solar activity cycle derived from data of a worldwide neutron monitor network and numerical modeling both provide evidence for the acceleration of charged particles by an electric field that arises in coronal current sheets during reconnection. The method used to obtain the spectra is based on simulating the response of a neutron monitor to an anisotropic flux of relativistic solar protons with specified parameters and determining the characteristics of the primary relativistic solar protons by fitting model responses to the observations. Studies of the dynamics of the energy spectra distinguish two populations of relativistic protons in solar cosmic-ray events: the so-called fast component, which arrives at the flux front of the solar cosmic rays, followed by the delayed slow component. The fast component is characterized by strong anisotropy and an exponential energy spectrum, in agreement with the spectrum yielded by mathematical modeling of particle acceleration by an electric field directed along the X line of the magnetic field. The slow component, whose propagation is probably diffusive, has a power-law spectrum. 相似文献
18.
Using observational data obtained with the Yohkoh, SOHO, and TRACE satellites, it is shown that the three-dimensional structure of the large solar flare of July 14, 2000 was determined by the topology of the large-scale magnetic field of the active region giving rise to the flare. The locations and shapes of chromospheric ribbons and brightness centers on these ribbons are explained. The observed behavior of the flare is attributed to rapid magnetic reconnection in the corona. The electric field accelerating particles in the reconnecting current sheets is estimated. 相似文献
19.
The flare source of thermal X-rays above a magnetic arch in the corona arises from the dissipation of the magnetic energy
of the current sheet formed at the reconnection of magnetic-field lines. The sources of hard X-rays emitted from the footpoints
of the magnetic arch are beams of electrons accelerated in field-aligned currents induced by the Hall electric field generated
in the current sheet. Both the hard X-rays detected above the active region and the type III radio emission are radiated by
electrons accelerated in the field-aligned currents induced by Alfven waves. The solar cosmic rays are emitted promptly at
the instant of the flare. It is important that the Lorentz electric field accelerates protons along the singular magnetic
X line. The relativistic protons propagate along the interplanetary magnetic field. These protons have exponential spectra,
typical for acceleration occurring in current sheets. A mechanism that is relevant for the generation of delayed cosmic rays,
which demonstrate significant anisotropy and a power-law spectrum with γ ∼5, is also discussed. 相似文献
20.
K. N. Mitrofanov S. S. Anan’ev D. A. Voitenko V. I. Krauz G. I. Astapenko A. I. Markoliya V. V. Myalton 《Astronomy Reports》2017,61(9):775-782
The results of experiments aimed at investigating axial plasma flows forming during the compression of a current–plasma sheath are presented. These experiments were carried out at the KPF-4-PHOENIX plasma-focus installation, as part of a program of laboratory simulations of astrophysical jets. The plasma flows were generated in a discharge when the chamber was filled with the working gas (argon) at initial pressures of 0.5–2 Torr. Experimental data obtained using a magnetic probe and optical diagnostics are compared. The data obtained can be used to determine the location of trapped magnetic field relative to regions of intense optical glow in the plasma flow. 相似文献