共查询到20条相似文献，搜索用时 15 毫秒
1.
An analysis, with a representative (canonical) example of solar-flare-generated equatorial disturbances, is presented for the temporal and spatial changes in the solar wind plasma and magnetic field environment between the Sun and one astronomical unit (AU). Our objective is to search for first order global consequences rather than to make a parametric study. The analysis - an extension of earlier planar studies - considers all three plasma velocity and magnetic field components (V r, Vφ, V0, and B r, B0, Bφ) in any convenient heliospheric plane of symmetry such as the ecliptic plane, the solar equatorial plane, or the heliospheric equatorial plane chosen for its ability (in a tilted coordinate system) to order northern and southern hemispheric magnetic topology and latitudinal solar wind flows. Latitudinal velocity and magnetic field gradients in and near the plane of symmetry are considered to provide higher-order corrections of a specialized nature and, accordingly, are neglected, as is dissipation, except at shock waves. The representative disturbance is examined for the canonical case in which one describes the temporal and spatial changes in a homogeneous solar wind caused by a solar-flare-generated shock wave. The ‘canonical’ solar flare is assumed to produce a shock wave that has a velocity of 1000 km s#X2212;1 at 0.08 AU. We have examined all plasma and field parameters at three radial locations: central meridian and 33° W and 90° W of the flare's central meridian. A higher shock velocity (3000 km s#X2212;1) was also used to demonstrate the model's ability to simulate a strongly-kinked interplanetary field. Among the global (first-order) results are the following: (i) incorporation of a small meridional magnetic field in the ambient magnetic spiral field has negligible effect on the results; (ii) the magnetic field demonstrates strong kinking within the interplanetary shocked flow, even reversed polarity that - coupled with low temperature and low density - suggests a viable explanation for observed ‘magnetic clouds’ with accompanying double-streaming of electrons at directions ～ 90° to the heliocentric radius. 相似文献
2.
Based on the event observed by ISEE 3 near the Earth’s orbit at 01:21 UT on April 5, 1979, we investigate the diffusive shock acceleration of ions and the generation of Alfvén waves by accelerated particles near the quasi-parallel parts of interplanetary shock fronts within a quasi-linear approach. The theory is shown to give an excessively high level of Alfvén wave generation by accelerated particles at significant deflection angles of the interplanetary magnetic field from the normal to the shock front. At the Earth’s orbit, the Alfve´ n waves produced by accelerated ions are confined within the frequency range 5 × 10?2?0.5 Hz, and their spectral peak with a wave amplitude δB ≤ B corresponds to a frequency ν = (1?2)×10?2 Hz. The high-frequency part of the wave spectrum (ν ≥ 0.5 Hz) is subjected to damping on thermal protons. The calculated spectra of the accelerated ions and Alfvén waves generated by them reproduce the main features observed in experiments. 相似文献
3.
Preliminary shock experiments at approximately 50 and 250 kb have been carried out with lunar soil and with a dispersion of iron in quartz. The lunar soils acquire remanent magnetization in the Earth's field of order of magnitude 10?3 G cm3 g?1. The remanence exhibited considerable stability against AF demagnetization. Remanence appears to be acquired both during the passage of the shock wave through the material and during post shock cool-down. The higher shock range gave rise to an increase in magnetic viscosity and in the saturation magnetization of the soil, which is most readily explained as due to the generation of fine grained iron. 相似文献
4.
J. B. Singh 《Astrophysics and Space Science》1983,92(1):191-195
A self-similar solution, for the equatorial propagation of axisymmetric point explosion into an inhomogeneous ideal gas permeated by a current-free azimuthal magnetic field, are obtained. The model has been considered here in which the magnetic field is proportional tor ?1, but the total energy of the wave is of the increasing order, not constant. 相似文献
5.
The processes of ion acceleration and Alfvén wave generation by accelerated particles at the Earth’s bow shock are studied within a quasi-linear approach. Steady-state ion and wave spectra are shown to be established in a time of 0.3–4 h, depending on the background level of Alfvénic turbulence in the solar wind. The Alfvén waves produced by accelerated ions are confined within the frequency range 10?2–1 Hz and their spectral peak with a wave amplitude βB ～ B comparable to the interplanetary magnetic field strength B corresponds to the frequency v = (2–3) × 10?2 Hz. The high-frequency part of the wave spectrum (v > 0.2 Hz) undergoes damping by thermal ions. The calculated spectra of the accelerated ions and the Alfvén waves generated by them reproduce the main features observed in experiments. 相似文献
6.
Jun-Ichi Sakai 《Astrophysics and Space Science》1973,23(2):285-300
Nonlinear magnetosonic waves propagating in a magnetic neutral sheet are investigated within the framework of a fluid model. It is shown that the behavior of the magnetosonic waves is governed by a ‘modified Burgers equation’ with an additional termc(η)? due to the relevant slowly varying background plasma parameter (density or magnetic field), $$\frac{{\partial \phi }}{{\partial \eta }}$$ where ?(ξ, η) is the amplitude of the wave, \(\xi = \int {k_x } {\text{d}}x + k_y y - \omega t\) , and η=εx is the coordinate stretched by a smallness parameter ε. When we consider fast magnetosonic waves propagating toward the neutral region across the magnetic field, they grow and undergo rapid steepening after passing through the neutral region; i.e., shock formation is promoted by the background inhomogeneity. By the numerical computation of the above equation, the time evolution is examined for two initial disturbances, the pulse type (gaussian) and the wave train type (sinusoidal wave). The relevance of the interactions between the magnetosonic shock waves and the neutral sheet plasma to a triggering mechanism of sympathetic flares is also suggested. 相似文献
7.
The structure of a hydrogen atom situated in an intense magnetic field is investigated. Three approaches are employed. An elementary Bohr picture establishes a crucial magnetic field strength,H a ?5×109G. Fields in excess ofH a are intense in that they are able to modify the characteristic atomic scales of length and binding energy. A second approach solves the Schrödinger equation by a combination of variational methods and perturbation theory. It yields analytic expressions for the wave functions and energy eigenvalues. A third approach determines the energy eigenvalues by reducing the Schrödinger equation to a one-dimensional wave equation, which is then solved numerically. Energy eigenvalues are tabulated for field strengths of 2×1010G and 2×1012 G. It is found that at 2×1012 G the lowest energy eigenvalue is changed from ?13.6 eV to about ?180 eV in agreement with previous variational computations. 相似文献
8.
Satellite and other observations have shown that H+ densities in the mid-latitude topside ionosphere are greatly reduced during magnetic storms when the plasmapause and magnetic field convection move to relatively low L-values. In the recovery phase of the magnetic storm the convection region moves to higher L-values and replenishment of H+ in the empty magnetospheric field tubes begins. The upwards flow of H+, which arises from O+—H charge exchange, is initially supersonic. However, as the field tubes fill with plasma, a shock front moves downwards towards the ionosphere, eventually converting the upwards flow to subsonic speeds. The duration of this supersonic recovery depends strongly on the volume of the field tube; for example calculations indicate that for L = 5 the time is approximately 22 hours. The subsonic flow continues until diffusive equilibrium is reached or a new magnetic storm begins. Calculations of the density and flux profiles expected during the subsonic phase of the recovery show that diffusive equilibrium is still not reached after an elapsed time of 10 days and correspondingly there is still a net loss of plasma from the ionosphere to the magnetosphere at that time. This slow recovery of the H+ density and flux patterns, following magnetic storms, indicates that the mid-latitude topside ionosphere may be in a continual dynamic state if the storms occur sufficiently often. 相似文献
9.
Intense (? 10 mVm?1) electrostatic plasma waves near the upper hybrid frequency have been observed between ± 50° magnetic latitude during spacecraft plasmapause crossings. We present wave growth rate and three-dimensional convective amplification calculations which suggest how intense upper hybrid (IUH) events can occur over such a wide range of latitudes. The effects of wave refraction are shown to be crucial to the proper calculation of convective amplification.We first calculate upper hybrid wave growth for an IUH event at 10° MLAT during which a complete electron distribution function with a loss cone feature was measured simultaneously with the waves. We show that a parallel density gradient may be necessary to account for the observed amplification. Without such a density gradient, the dipole magnetic field gradient would quickly refract the wave vector component parallel to the local field lines out of the unstable region in wave vector space. Upon mapping the distribution function observed at 10° MLAT to other latitudes by conserving the electrons' magnetic moments, we then find that the mapped distribution could produce large amplification at higher latitudes only if there is an appropriate parallel density gradient. At the equator, the long magnetic field gradient scale length enables large amplitudes to be attained without a density gradient.The results of our UH ray tracing analysis are related to theories and observations of magnetospheric continuum radiation. 相似文献
10.
The unipolar induction mechanism is employed to calculate electric field profiles in the interior of a chemically homogeneous Moon possessing a steep radial thermal gradient characteristic of long-term radioactive heating. The thermal models used are those of Fricker, Reynolds, and Summers. From the magnetic field, the magnetic back pressure upon the solar wind is found. The electric field profile is shown to depend only upon the activation energy,E
o, of the geological material and the radial gradient of the reciprocal temperature. The current is additionally dependent upon the coefficient of the electrical conductivity function but only by a scale factor. Since the Moon is experimentally known to correspond to the case of weak interaction with the solar wind, the magnetic back pressure is calculated without the need for an iterative procedure. The results indicate that a hot Moon can yield sufficient current flow so that the magnetic back pressure is observable as a vestigial limb shock wave using an activation energy of about 2/3 eV together with a conductivity coefficient of about 103 mhos/m. Such matter is approximated by diabase-like composition, although the result that both the activation energy and coefficient enter into the current determination does not rule out the possibility of a match with other similar substances. The calculations are entirely consistent with earlier results which indicated a model where the unipolar current density is dominated by a high impedance surface layer and a strong shock wave is inhibited. In addition to the magnetic back pressure, the integration of the current continuity equation permits current densities and joule heating rates to be calculated, though the magnitude of the latter for present solar wind conditions is not thermally important.On leave from NASA Ames Research Center 相似文献
11.
Chin-Chun Wu Kan Liou R. P. Lepping Angelos Vourlidas Simon Plunkett Dennis Socker S. T. Wu 《Solar physics》2017,292(8):109
At 11:46 UT on 9 September 2011, the Wind spacecraft encountered an interplanetary (IP) fast-forward shock. The shock was followed almost immediately by a short-duration (～?35 minutes) extremely dense pulse (with a peak ～?94 cm?3). The pulse induced an extremely large positive impulse (SYM-H = 74 nT and Dst = 48 nT) on the ground. A close examination of other in situ parameters from Wind shows that the density pulse was associated with i) a spike in the plasma \(\upbeta\) (ratio of thermal to magnetic pressure), ii) multiple sign changes in the azimuthal component of the magnetic field (\(B_{\phi}\)), iii) a depressed magnetic field magnitude, iv) a small radial component of the magnetic field, and v) a large (>?90°) change in the suprathermal (～?255 eV) electron pitch angle across the density pulse. We conclude that the density pulse is associated with the heliospheric plasma sheet (HPS). The thickness of the HPS is estimated to be \({\sim}\,8.2\times10^{5}\ \mbox{km}\). The HPS density peak is about five times the value of a medium-sized density peak inside the HPS (～?18 cm?3) at 1 AU. Our global three-dimensional magnetohydrodynamic simulation results (Wu et al. in J. Geophys. Res. 212, 1839, 2016) suggest that the extremely large density pulse may be the result of the compression of the HPS by an IP shock crossing or an interaction between an interplanetary shock and a corotating interaction region. 相似文献
12.
Sergey G. Moiseenko Gennady S. Bisnovatyi-Kogan 《Astrophysics and Space Science》2007,311(1-3):191-195
2D numerical simulations of magnetorotational (MR) supernova mechanism are described. It is shown that magnetic field is amplified
due to the differential rotation after core collapse. When magnetic pressure reaches some level, a compression wave starts
to move outwards. Moving along steeply decreasing density profile the compression wave transforms quickly into fast MHD shock.
The magnetorotational instability (MRI) was found in our simulations. MRI leads to the exponential growth of the components
of the magnetic field. The MRI significantly reduces MR supernova explosion time. Configuration of the initial magnetic field
qualitatively defines the shape of MR supernova explosion. For the quadrupole-like initial poloidal field the MR supernova
explosion develops mainly along equatorial plane, the dipole-like initial field results in MR supernova developing as mildly
collimated jet along axis of rotation. The explosion energy of MR supernova found in our simulations is ∼0.5–0.6×1051 erg. 相似文献
13.
T.L. Zhang M. Delva M. Volwerk S. Barabash S. Pope K. Kudela Z. Vörös 《Planetary and Space Science》2008,56(6):785-789
In this study, magnetic field measurements obtained by the Venus Express spacecraft are used to determine the bow shock position at solar minimum. The best fit of bow shock location from solar zenith angle 20-120° gives a terminator bow shock location of 2.14 RV (1 RV=6052 km) which is 1600 km closer to Venus than the 2.40 RV determined during solar maximum conditions, a clear indication of the solar cycle variation of the Venus bow shock location. The best fit to the subsolar bow shock is 1.32 RV, with the bow shock completely detached. Finally, a global bow shock model at solar minimum is constructed based on our best-fit empirical bow shock in the sunlit hemisphere and an asymptotic limit of the distant bow shock which is a Mach cone under typical Mach number of 5.5 at solar minimum. We also describe our approach to making the measurements and processing the data in a challenging magnetic cleanliness environment. An initial evaluation of the accuracy of measurements shows that the data are of a quality comparable to magnetic field measurements made onboard magnetically clean spacecraft. 相似文献
14.
I. P. Lopin 《Astronomy Letters》2007,33(6):411-418
The response of an isothermal atmosphere of a thin vertical magnetic flux tube to the presence of an acoustic-gravity wave field in the external medium is considered. The Laplace transform method is used to solve a problem with initial conditions. The structure of the solution for disturbances in the tube is a superposition of forced oscillations at the source frequency and oscillations decaying as ～ t ?3/2 (the so-called wave wake). Both components are analogues of the corresponding disturbances in an external medium with a modified amplitude. The excitation under consideration is shown to be effective in the ranges of external oscillation frequencies 0 mHz ≤ v ≤ 3.3 mHz and v ≥ 6.5 mHz. The time-averaged energy flux density for high-frequency magnetoacoustic-gravity waves in the tube is estimated to be ∝ 3.0 × 107 erg cm?2 s?1, a value of the same order of magnitude as that required for heating local regions in the solar chromosphere, ∝ 107 erg cm?2 s?1. 相似文献
15.
Based on the magnetorotational model of a supernova explosion with core collapse, we investigate the significant processes of neutrino heating of the supernova shock. These processes should be taken into account in self-consistent modeling, since the neutrino heating mechanism is capable of increasing the explosion efficiency. We show that, even in the presence of a strong magnetic field (B ～ 1015 G) in the shock formation region, the heating rate is determined with good accuracy by the absorption and emission of neutrinos in direct URCA processes. Moreover, the influence on them of a magnetic field is reduced to insignificant corrections. 相似文献
16.
17.
S. T. Wu S. Wang M. Dryer A. I. Poland D. G. Sime C. J. Wolfson L. E. Orwig A. Maxwell 《Solar physics》1983,85(2):351-373
Soft X-ray data from the XRP experiment on SMM are used to generate the temperature and density in the flaring region of the 1980, June 29 (18∶21 UT) solar flare. The temporal data (T max ～- 20 × 106 K and n max ～- 4 × 1011 cm?3), together with an assumed velocity, are used to simulate mass injection as the input pulse for the MHD model of Wu et al. (1982a, 1983a). The spatial and temporal coronal response is compared with the ground-based, Mark III K-coronameter observations of the subsequent coronal transient. The simulation produces a spatially-wide, large amplitude, temporarily-steepened MHD wave for either of the two ‘canonical’ magnetic topologies (closed and open), but no shock wave. This result appears to be confirmed by the fact that a type II radio event was observed late in the event for only a few minutes, thereby indicating that a steepening wave with temporary, marginal shock formation, was indeed present. The density enhancements produced by the simulation move away from the Sun at the same velocity observed by the K-coronameter. However, the observation of the coronal transient included a rarefaction that does not appear in the simulation. A probable explanation for this discrepancy is the likelihood that the magnitude and temporal profile of the density of the soft X-ray emitting plasma should not have been used as part of the mass injection pulse. We believe that the temperature profile alone, as suggested by earlier simulations, might have been a necessary and sufficient condition to produce both the compression and rarefaction of the ambient corona as indicated by the K-coronameter data. Hence, the dense plasma observed by XRP was probably confined, for the most part, close to the Sun during the ～ 17 min duration of the observations. 相似文献
18.
A consistent account of plasma turbulence in magnetohydrodynamics equations describing transport processes across the magnetic field is presented. The structure of the perpendicular shock wave generated in the solar atmosphere, as a result of either local disturbance of the magnetic field or dense plasma cloud motion with a frozen-in magnetic field, has been investigated. The region of parameters in the solar atmosphere at which the electron-ion relative drift velocity u exceeds the electron thermal velocity V
eand generation of radio emission becomes possible, has been determined. The plasma turbulence inside the front has been shown, under conditions of solar corona, not to cause the oscillation structure of shock front to break down. Under chromospheric conditions, the shock profile is aperiodical. Then, the condition u > Vecan be satisfied and shock waves having an Alfvén Mach number M which exceeds the critical value M
c 3.3 for aperiodical shock waves can exist (Eselevich et al., 1971a). Arguments are given in favour of the fact that perpendicular shock waves are generated in the Sun's atmosphere when dense plasma clouds, with a frozen-in magnetic field, are expanded. 相似文献
19.
This paper is a demonstration of how the WKB approximation can be used to help solve the linearised 3D MHD equations. Using Charpit’s method and a Runge?–?Kutta numerical scheme, we have demonstrated this technique for a potential 3D magnetic null point, B=[x,ε y,?(ε+1)z]. Under our cold-plasma assumption, we have considered two types of wave propagation: fast magnetoacoustic and Alfvén waves. We find that the fast magnetoacoustic wave experiences refraction towards the magnetic null point and that the effect of this refraction depends upon the Alfvén speed profile. The wave and thus the wave energy accumulate at the null point. We have found that current buildup is exponential and the exponent is dependent upon ε. Thus, for the fast wave there is preferential heating at the null point. For the Alfvén wave, we find that the wave propagates along the field lines. For an Alfvén wave generated along the fan plane, the wave accumulates along the spine. For an Alfvén wave generated across the spine, the value of ε determines where the wave accumulation will occur: fan plane (ε=1), along the x-axis (0<ε<1) or along the y-axis (ε>1). We have shown analytically that currents build up exponentially, leading to preferential heating in these areas. The work described here highlights the importance of understanding the magnetic topology of the coronal magnetic field for the location of wave heating. 相似文献
20.
Recently, the estimation of coronal magnetic field using new methods, such as standoff distance method or density compression ratio method has been reported. In the present work, we utilized the density compression ratio of CME-driven shocks for 10 events at 29 different locations in the upper solar corona (10–26R ⊙) and determined the coronal magnetic field for two different adiabatic indices (γ=4/3 and 5/3). In addition, radial dependence of shock parameters in the corona is studied. It is found that the magnetic field estimated in the above range agree with the general trend. In addition, we obtained a radial profile of magnetic field [B(R)=623R ?1.4] in the entire upper corona (3–30R ⊙) by combining the magnetic field estimated by Kim et al. (Astrophys. J. 746:118, 2012) in the range 3–15R ⊙ and that estimated in the present study in the range (10–26R ⊙). The power-law indices are nearly in agreement with recent results of CME-driven shocks reported in the literature. The results are discussed with the comparison of newly reported coronal magnetic field values obtained by different techniques and found that the power-law relation closely follow the literature values. 相似文献