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1.
The results of modeling the preflare situation in the solar corona, obtained using a numerical solution for a complete set
of three-dimensional MHD equations, are reviewed. Any assumptions concerning the flare development character or the active
region’s behavior before a flare are not introduced. The initial and boundary conditions on the photosphere are specified
from magnetic field measurements before a flare. The photospheric field sources are approximated by magnetic dipoles. The
usage of the PERESVET program indicated that a current sheet is formed in the vicinity of a singular magnetic field line in
the corona. The sheet is formed due to disturbances coming from the photosphere. The energy necessary for a flare is stored
in the current sheet magnetic field during 2–3 days. The main construction principles of the PERESVET program, which makes
it possible to use the maps of a measured photospheric field as boundary conditions, are presented. 相似文献
2.
The results of a three-dimensional MHD simulation and data obtained using specialized spacecraft made it possible to construct
an electrodynamic model of solar flares. A flare results from explosive magnetic reconnection in a current sheet above an
active region, and electrons accelerated in field-aligned currents cause hard X rays on the solar surface. In this review,
we considered works where the boundary and initial conditions on the photosphere were specified directly from the magnetic
maps, obtained by SOHO MDI in the preflare state, in order to simulate the formation of a current sheet. A numerical solution
of the complete set of MHD equations, performed using the new-generation PERESVET program, demonstrated the formation of several
current sheets before a series of flares. A comparison of the observed relativistic proton spectra and the simulated proton
acceleration along a magnetic field singular line made it possible to estimate the magnetic reconnection rate during a flare
(∼107 cm s−1). Great flares (of the X class) originate after an increase in the active region magnetic flux up to 1022 Mx. 相似文献
3.
4.
A weak active region (NOAA 11158) appeared on the solar disk near the eastern limb. This region increased rapidly and, having reached the magnetic flux higher than 1022 Mx, produced an X-class flare. Only weak field variations at individual points were observed during the flare. An analysis of data with a resolution of 45 s did not indicate any characteristic features in the photospheric field dynamics during the flare. When the flux became higher than 3 × 1022 Mx, active region NOAA 10720 produced six X-class flares. The field remained quiet during these flares. An increase in the magnetic flux above ～1022 Mx is a necessary, but not sufficient, condition for the appearance of powerful flares. Simple active regions do not produce flares. A flare originates only when the field distribution in an active region is complex and lines of polarity inversion have a complex shape. Singular lines of the magnetic field can exist only above such active regions. The current sheets, in the magnetic field of which the solar flare energy is accumulated, originate in the vicinity of these lines. 相似文献
5.
本文提出一种用于研究太阳瞬变扰动在日球空间传播的新坐标系--瞬变源-日球电流片坐标系,并运用该坐标系以瞬变源耀斑为例,分析研究了由地球近空飞船观测到的277个耀斑-激波事件,发现:1.引起行星际激波和地球物理事件的大耀斑（Hα≥2,持续时间>半小时）的频数在耀斑-日球电流片坐标系中呈高斯分布,极值在电流片附近,那种在日面坐标系中随日面纬度呈双峰形的分布看不到了;2.当地球观测者和耀斑位于日球电流片同侧时,耀斑事件频次明显高于它们分处不同侧时的情形;3.激波参数（速度、磁场、密度和温度）呈现了同侧高于异侧,强激波多在同侧观测到;4.激波沿日球电流片方向的传播具有一定优势.上述结果表明,日球电流片的存在对瞬变扰动,如耀斑-激波在日球空间,特别是近太阳的传播可能具有重要影响. 相似文献
6.
《Journal of Atmospheric and Solar》2007,69(3):212-222
We have used a global time-dependent magnetohydrodynamic (MHD) simulation of the magnetosphere and particle tracing calculations to determine the access of solar wind ions to the magnetosphere and the access of ionospheric O+ ions to the storm-time near-Earth plasma sheet and ring current during the September 24–25, 1998 magnetic storm. We found that both sources have access to the plasma sheet and ring current throughout the initial phase of the storm. Notably, the dawnside magnetosphere is magnetically open to the solar wind, allowing solar wind H+ ions direct access to the near-Earth plasma sheet and ring current. The supply of O+ ions from the dayside cusp to the plasma sheet varies because of changes in the solar wind dynamic pressure and in the interplanetary magnetic field (IMF). Most significantly, ionospheric O+ from the dayside cusp loses access to the plasma sheet and ring current soon after the southward turning of the IMF, but recovers after the reconfiguration of the magnetosphere following the passage of the magnetic cloud. On average, during the first 3 h after the sudden storm commencement (SSC), the number density of solar wind H+ ions is a factor of 2–5 larger than the number density of ionospheric O+ ions in the plasma sheet and ring current. However, by 04:00 UT, ∼4 h after the SSC, O+ becomes the dominant species in the ring current and carries more energy density than H+ ions in both the plasma sheet and ring current. 相似文献
7.
The MHD simulations of preflare situation in the corona above the real active region (AR) are performed without any assumptions about the solar flare mechanism. All conditions for simulation are taken from observations. Such approach is directed to understand the flare mechanism. The observed SOHO MDI magnetic maps are used. The special numerical methods are developed and realized in the PERESVET code for numerical simulation in the real time scale. The first results of real time scale MHD simulation during several first minutes are presented. Initiation of current sheet (CS) creation in the vicinity of the magnetic field X-line is shown. The possibilities of real time scale MHD simulation of preflare situation on modern computers using the developed mathematical methods are discussed. 相似文献
8.
《Journal of Atmospheric and Solar》2007,69(3):265-278
Recent observations have quantified the auroral wind O+ outflow in response to magnetospheric inputs to the ionosphere, notably Poynting energy flux and precipitating electron density. For moderate to high activity periods, ionospheric O+ is observed to become a significant or dominant component of plasma pressure in the inner plasma sheet and ring current regions. Using a global circulation model of magnetospheric fields and its imposed ionospheric boundary conditions, we evaluate the global ionospheric plasma response to local magnetospheric conditions imposed by the simulation and evaluate magnetospheric circulation of solar wind H+, polar wind H+, and auroral wind O+. We launch and track the motions of millions of test particles in the global fields, launched at randomly distributed positions and times. Each particle is launched with a flux weighting and perpendicular and parallel energies randomly selected from defined thermal ranges appropriate to the launch point. One sequence is driven by a two-hour period of southward interplanetary magnetic field for average solar wind intensity. A second is driven by a 2-h period of enhanced solar wind dynamic pressure for average interplanetary field. We find that the simulated ionospheric O+ becomes a significant plasma pressure component in the inner plasma sheet and outer ring current region, particularly when the solar wind is intense or its magnetic field is southward directed. We infer that the reported empirical scalings of auroral wind O+ outflows are consistent with a substantial pressure contribution to the inner plasma sheet and plasma source surrounding the ring current. This result violates the common assumption that the ionospheric load is entirely confined to the F layer, and shows that the ionosphere is often an important dynamic element throughout the magnetosphere during moderate to large solar wind disturbances. 相似文献
9.
For electron acceleration during solar flares, it is very important to determine the pitch-angle and energy dependences of the electron distribution function. At present, this cannot be done directly from observations. Therefore, it is necessary to perform a numerical simulation of the propagation of accelerated electrons in the magnetic field of the flare loop (loops) and calculate the X-ray and radio emissions. For the solar flare of November 10, 2002, we have obtained qualitative and quantitative agreements of modeled X-ray and radio maps with the RHESSI satellite and Nobeyama Radioheliograph data. We have determined the flare model parameters that agree with observations. The pitch-angle anisotropy of electrons determined by highly directional functions of the S(α) = cos8(α) type, the energy spectrum consist of two electron populations, the low-energy part of the spectrum up to an energy of break of 350 keV is characterized by a power law with the exponent δ1 = 2.7–2.9, and the energy spectrum is more rigid above 420 keV (δ2 = 2–2.3). 相似文献
10.
文中选了５ 个典型活动区, 分析了这些活动区的磁场, 与活动区相应的ＣＭＥｓ, 太阳爆发事件和太阳质子事件我们发现, 对于Ｅ ≥１０ｍｅＶ 的太阳质子事件有相应的源活动区, 源耀斑和ＣＭＥ; 活动区矢量磁场有剪切, 磁场剪切越强质子事件越强; 多数在质子耀斑发生前出现磁流浮现; 太阳１０ｃｍ 射电爆发持续时间长文中结果还佐证了Ｓｈｅａｌｙ 等的结果： Ｘ 射线耀斑的长持续时间与ＣＭＥ 的发生正相关另外,在５ 个活动区中, 有三个大耀斑发生前没有明显的磁剪切作为它们的先兆, 它们是非质子源耀斑这是Ｍｏｏｒｅ, Ｈａｇｙａｒｄ 和Ｄａｖｉｓ 的磁场强剪切是耀斑产生的必要条件的反例 相似文献
11.
应用二维磁流体动力学模拟方法数值研究了三层电流片中电阻撕裂模不稳定性的特征及磁场重联过程．结果表明，这是一种复杂的非稳态磁场重联．在初期阶段，三个电流片中分别由撕裂模不稳定性引起磁场重联，形成薄而长的磁岛．随着撕裂模不稳定性的非线性发展，每个磁岛的宽度都逐步增大，以至导致新的磁场重联发生．同时，三个电流片的强度都逐渐减弱，且原中心反向电流区最终消失．部分磁能不断地转化为等离子体的热能和动能，引起等离子体的加热和加速．多层电流片中撕裂模不稳定性引起的自发重联，可能对太阳耀斑、日冕加热、太阳风与磁层耦合等有重要影响． 相似文献
12.
The evolution of the microwave radiation from four active regions, where strong X-ray flares (X-class, GOES) occurred in 2011, has been studied. Daily multiwavelength RATAN-600 radio observations of the Sun in the 1.6–8.0 cm range have been used. It has been indicated that the radiosource above the photospheric magnetic field neutral line (above the region with the maximal convergence of the fields opposite in sign) becomes predominant in the structure of the active region microwave radiation one to two days before a powerful flare as in the eruptive events previously studied with RATAN-600. The appearance of such a radiosource possibly reflects the current sheet formation in the corona above the active region. The energy necessary for a flare is stored in the magnetic field of active region, which can be considered as a factor for predicting a powerful flare. 相似文献
13.
The work is devoted to the simulation of recently discovered hard X-ray and gamma radiation sources localized near the top of solar flare loops. The calculations were performed in the context of a model of a flare magnetic loop inhomogeneous with respect to the magnetic field. Two cases of injection were considered: isotropic and anisotropic along the loop axis. The distributions of electrons along the loop are found by solving the nonstationary relativistic kinetic equation in the Fokker-Planck form. Based on the calculated electron distribution functions, the spatial brightness distribution of hard X-ray and gamma radiation has been calculated. Radiation characteristics are compared for different sets of injection parameters. 相似文献
14.
The solar wind velocity distribution in the heliosphere is best represented using a v-map, where velocity contours are plotted in heliographic latitude-longitude coordinates. It has already been established that low-speed regions of the solar wind on the source surface correspond to the maximum bright regions of the K-corona and the neutral line of the coronal magnetic field. In this analysis, v-maps on the source surface for Carrington rotations (CRs) 1787-1795, during 1987, have been prepared using the interplanetary scintillation measurements at Research Institute of Atmospherics (RIA), Nagoya Univ., Japan. These v-maps were then used to study the time evolution of the low-speed (\leq450 km s−1) belt of the solar wind and to deduce the distribution of solar wind velocity on the heliospheric current sheet. The low-speed belt of the solar wind on the source surface was found to change from one CR to the next, implying a time evolution. Instead of a slow and systematic evolution, the pattern of distribution of solar wind changed dramatically at one particular solar rotation (CR 1792) and the distributions for the succeeding rotations were similar to this pattern. The low-speed region, in most cases, was found to be close to the solar equator and almost parallel to it. However, during some solar rotations, they were found to be organised in certain longitudes, leaving regions with longitudinal width greater than 30○ free of low-speed solar wind, i.e. these regions were occupied by solar wind with velocities greater than 450 km s−1. It is also noted from this study that the low-speed belt, in general, followed the neutral line of the coronal magnetic field, except in certain cases. The solar wind velocity on the heliospheric current sheet (HCS) varied in the range 300–585 km s−1 during the period of study, and the pattern of velocity distribution varied from rotation to rotation. 相似文献
15.
The challenges of ‘standard’ model of solar flares motivated by new observations with the spacecrafts and ground-based telescopes are presented. The most important problems are in situ heating of photospheric and chromospheric loop footpoints up to the coronal temperatures without precipitating particle beams accelerated in the corona, and the sunquakes which are unlikely to be explained by the impact of highenergy particles producing hard X-ray emission. There is also the long-standing ‘number problem’ in the physics of solar flares. It is shown that modern observations favored an important role of the electric currents in the energy release processes in the low solar atmosphere. Particle acceleration mechanism in the electric fields driven by the magnetic Rayleigh-Taylor instability in the chromosphere is proposed. The electric current value I ≥ 1010 A, needed for the excitation of super-Dreicer electric fields in the chromosphere is determined. It is shown that both Joule dissipation of the electric currents and the particles accelerated in the chromosphere can be responsible for in situ heating of the low solar atmosphere. Alternative model of the solar flare based on the analogy between the flaring loop and an equivalent electric circuit which is good tool for the electric current diagnostics is presented. Interaction of a current-carrying loop with the partially-ionized plasma of prominence in the context of particle acceleration is considered. The role of plasma radiation mechanism in the sub-THz emission from the chromosphere is discussed. 相似文献
16.
V. V. Zharkova N. S. Meshalkina L. K. Kashapova A. T. Altyntsev A. A. Kuznetsov 《Geomagnetism and Aeronomy》2011,51(8):1029-1040
The kinetics of beam electron precipitation from the top of a loop into the solar atmosphere with density gradients and an
increasing magnetic field have been generally described. The Fokker-Planck equations are solved with regard to Coulomb collisions
and the effect of the electric field induced by this beam. The photon spectra and polarization degree in hard X-ray (10–300
keV) and microwave (1–80 GHz) emissions are simulated under different assumptions regarding the beam electron distribution
function. The simulation results are compared with the flare observations on March 10, 2001, and July 23, 2002, visible at
different position angles. It has been indicated that the coincidence of the theoretical photon spectra with simultaneous
observations of the hard X-ray and microwave emissions of these flares is the best for models that not only take into account
collisions, but also the electric field induced by electron fluxes propagating in flare loops with very weakly or moderately
converging magnetic fields. 相似文献
17.
Tangential discontinuities and the optical analogy for stationary fields IV. High speed fluid sheets
E. N. Parker 《地球物理与天体物理流体动力学》2013,107(4):229-247
Abstract It was shown in the previous paper that a sufficiently strong pressure maximum applied to an equilibrium flux surface, by the fields on either side of the surface, produces a gap in the flux surface. The fields on either side make contact through the gap to produce a surface of tangential discontinuity (current sheet). It is shown in the present paper that there is a high speed sheet of fluid and field sliding over the surface of discontinuity when the applied pressure moves slowly across the flux surface. Conditions in the active X-ray corona of the sun suggest that such sheets are generally present, with velocities of the order of 102 km/sec, but with thicknesses too small to be observed. More substantial high speed sheets of fluid may occur in solar flares. 相似文献
18.
The influence of the spectral nature and position on the solar disk of solar flares related to the production of magnetic effects on earth (from now on, sfe) over a more than 30-year period has been studied. Regarding the spectral issue, we found that the probability of a flare to produce sfe depends on the spectral band in which we observe it, being higher when the flare is important both in Hα and X-ray emissions. On the other hand, Hα and X-ray emissions have been considered in many different divisions of the solar surface and their effectiveness on sfe production have been compared. We found that there is not any privileged region on the solar disk for sfe production. These results end with the controversy generated by distinct conclusions obtained in classical studies on the subject. 相似文献
19.
G. N. Kichigin L. I. Miroshnichenko V. I. Sidorov S. A. Yazev 《Geomagnetism and Aeronomy》2016,56(4):393-400
The analysis of observations of large solar flares made it possible to propose a hypothesis on existence of a skin-layer in magnetic flux ropes of coronal mass ejections. On the assumption that the Bohm coefficient determines the diffusion of magnetic field, an estimate of the skin-layer thickness of ~106 cm is obtained. According to the hypothesis, the electric field of ~0.01–0.1 V/cm, having the nonzero component along the magnetic field of flux rope, arises for ~5 min in the surface layer of the eruptive flux rope during its ejection into the upper corona. The particle acceleration by the electric field to the energies of ~100 MeV/nucleon in the skin-layer of the flux rope leads to their precipitation along field lines to footpoints of the flux rope. The skin-layer presence induces helical or oval chromospheric emission at the ends of flare ribbons. The emission may be accompanied by hard X-ray radiation and by the production of gamma-ray line at the energy of 2.223 MeV (neutron capture line in the photosphere). The magnetic reconnection in the corona leads to a shift of the skin-layer of flux rope across the magnetic field. The area of precipitation of accelerated particles at the flux-rope footpoints expands in this case from the inside outward. This effect is traced in the chromosphere and in the transient region as the expanding helical emission structures. If the emission extends to the spot, a certain fraction of accelerated particles may be reflected from the magnetic barrier (in the magnetic field of the spot). In the case of exit into the interplanetary space, these particles may be recorded in the Earth’s orbit as solar proton events. 相似文献
20.
《Journal of Atmospheric and Solar》2008,70(15):1963-1970
An interpretation of the nature of the sudden ionospheric disturbance in terms of response to X-ray flux enhancement in the band 1–20 Å has been made by many authors. Last decades investigations revealed presence of important qualitative distinctions in spatially temporal pattern of geomagnetic response to solar flares featuring harder radiation spectra (with quanta energies above 100 keV). These distinctions can not be adequately described by classical theory implying ionization growing on E and D ionosperic layers and intensification of Sq-current system. In this respect, solar flare on 4 November 2003 characterizing by existence of two separate (time lag ~45 min) spectral maximums in X-rays range (average quantum energy <100 keV) and in γ-rays range (average quantum energy >100 keV), represents convenient proving ground for study of specifics the geomagnetic response to bursts marked by different hardness. In current article, we show that this flare has a number of unusual features including specific variation of accompanying current system and magnetospheric manifestation that is observed in trapped radiation fluxes and magnetic field on geosynchronous orbit. Possible physical mechanism leading to intensification of magnetospheric–ionospheric current system is discussed. 相似文献