共查询到20条相似文献，搜索用时 78 毫秒
1.
J. &#x;afrnkov Z. N me
ek L. P&#x;ech A.A. Samsonov A. Koval K. Andreov 《Planetary and Space Science》2007,55(15):2324-2329
Fast forward interplanetary (IP) shocks have been identified as a source of large geomagnetic disturbances. However, the shocks can evolve in the solar wind, they are modified by interaction with the bow shock and during their propagation through the magnetosheath. A few previous papers refer the inclination and deceleration of the IP shock front in this region. Our contribution continues this effort and presents the study of an IP shock interaction with the bow shock. Since the bow shock is a reversed fast shock, the interaction of the IP shock and bow shock is a problem of interaction of two fast MHD shocks.
We compare profiles of magnetic field and plasma parameters observed by several spacecraft in the solar wind and magnetosheath with the profiles of the same parameters resulting from the MHD numerical model. The MHD model suggests that the interaction of an IP shock with the bow shock results in an inward bow shock displacement that is followed by its outward motion. Such motion will result in an indentation propagating along the bow shock surface. This scenario is confirmed by multipoint observations. Moreover, the model confirms also previous suggestions on the IP shock deceleration in the magnetosheath. 相似文献
2.
It is commonly believed that solar type II bursts are caused by accelerated electrons at a shock front. Holman and Pesses (1983) suggested that electrons creating type II bursts are accelerated by the shock drift mechanism. Zlobec et al. (1993) dealt with a fine structure of type II bursts (herringbones) and suggested a qualitative model where electrons are accelerated by a nearly perpendicular wavy shock front. Using this idea, we developed a model of electron acceleration by such a wavy shock front. Electrons are accelerated by the drift mechanism in the shock layer. Under simplifying assumptions it is possible to obtain an analytical solution of electron motion in the wavy shock front. The calculations show that electrons are rarely reflected more than once at the wavy shock front and that their final energy is mostly 1–3 times the initial one. Their acceleration does not depend significantly on shock spatial parameters. In the present model all electrons are eventually transmitted downstream where they form two downstream beams. Resulting spectral and angular distributions of accelerated electrons are presented and the relevance of the model to the herringbone beams is discussed. 相似文献
3.
Yi-Zhong Fan 《Monthly notices of the Royal Astronomical Society》2009,397(3):1539-1548
Since the launch of the Fermi Gamma-ray Space Telescope on 2008 June 11, significant detections of high-energy emission have been reported only in six gamma-ray bursts (GRBs) until now. In this work we show that the lack of detection of a GeV spectrum excess in almost all GRBs, though somewhat surprising, can be well understood within the standard internal shock model and several alternatives like the photosphere internal shock (gradual magnetic dissipation) model and the magnetized internal shock model. The delay of the arrival of the >100 MeV photons from some Fermi bursts can be interpreted too. We then show that with the polarimetry of prompt emission these models may be distinguishable. In the magnetized internal shock model, a high linear polarization level should be typical. In the standard internal shock model, a high linear polarization level is still possible but much less frequent. In the photosphere internal shock model, the linear polarization degree is expected to be roughly anticorrelated with the weight of the photosphere/thermal component, which may be a unique signature of this kind of model. We also briefly discuss the implications of the current Fermi GRB data on the detection prospects of the prompt PeV neutrinos. The influences of the intrinsic proton spectrum and the enhancement of the neutrino number at some specific energies, due to the cooling of pions (muons), are outlined. 相似文献
4.
Nicole GÜLDEMEISTER Kai WÜNNEMANN Nathanael DURR Stefan HIERMAIER 《Meteoritics & planetary science》2013,48(1):115-133
Generation and propagation of shock waves by meteorite impact is significantly affected by material properties such as porosity, water content, and strength. The objective of this work was to quantify processes related to the shock‐induced compaction of pore space by numerical modeling, and compare the results with data obtained in the framework of the Multidisciplinary Experimental and Modeling Impact Research Network (MEMIN) impact experiments. We use mesoscale models resolving the collapse of individual pores to validate macroscopic (homogenized) approaches describing the bulk behavior of porous and water‐saturated materials in large‐scale models of crater formation, and to quantify localized shock amplification as a result of pore space crushing. We carried out a suite of numerical models of planar shock wave propagation through a well‐defined area (the “sample”) of porous and/or water‐saturated material. The porous sample is either represented by a homogeneous unit where porosity is treated as a state variable (macroscale model) and water content by an equation of state for mixed material (ANEOS) or by a defined number of individually resolved pores (mesoscale model). We varied porosity and water content and measured thermodynamic parameters such as shock wave velocity and particle velocity on meso‐ and macroscales in separate simulations. The mesoscale models provide additional data on the heterogeneous distribution of peak shock pressures as a consequence of the complex superposition of reflecting rarefaction waves and shock waves originating from the crushing of pores. We quantify the bulk effect of porosity, the reduction in shock pressure, in terms of Hugoniot data as a function of porosity, water content, and strength of a quartzite matrix. We find a good agreement between meso‐, macroscale models and Hugoniot data from shock experiments. We also propose a combination of a porosity compaction model (ε–α model) that was previously only used for porous materials and the ANEOS for water‐saturated quartzite (all pore space is filled with water) to describe the behavior of partially water‐saturated material during shock compression. Localized amplification of shock pressures results from pore collapse and can reach as much as four times the average shock pressure in the porous sample. This may explain the often observed localized high shock pressure phases next to more or less unshocked grains in impactites and meteorites. 相似文献
5.
A model of self-similar propagation of shock waves driven by a flare energy release in a non-uniform atmosphere has been considered. The total energy content of the model is assumed to be increased with time within the inner expanding surface and shock front. Finally the variation of velocity, pressure, density, and energy of the model have been discussed. The gas is assumed to be grey and opaque. 相似文献
6.
Abstract— We present a model for the thermal processing of particles in shock waves typical of the solar nebula. This shock model improves on existing models in that the dissociation and recombination of H2 and the evaporation of particles are accounted for in their effects on the mass, momentum and energy fluxes. Also, besides thermal exchange with the gas and gas‐drag heating, particles can be heated by absorbing the thermal radiation emitted by other particles. The flow of radiation is calculated using the equations of radiative transfer in a slab geometry. We compute the thermal histories of particles as they encounter and pass through the shock. We apply this shock model to the melting and cooling of chondrules in the solar nebula. We constrain the combinations of shock speed and gas density needed for chondrules to reach melting temperatures, and show that these are consistent with shock waves generated by gravitational instabilities in the protoplanetary disk. After their melting, cooling rates of chondrules in the range 10–1000 K h?1 are naturally reproduced by the shock model. Chondrules are kept warm by the reservoir of hot shocked gas, which cools only as fast as the dust grains and chondrules themselves can radiate away the gas's energy. We predict a positive correlation between the concentration of chondrules in a region and the cooling rates of chondrules in that region. This correlation is supported by the unusually high frequency of (rapidly cooled) barred chondrules among compound chondrules, which must have collided preferentially in regions of high chondrule density. We discuss these and other compelling consistencies between the meteoritic record and the shock wave model of chondrule formation. 相似文献
7.
The magnetohydrodynamic model of shock waves has been discussed in an atmosphere with gravitation and radiation. The disturbance is headed by a strong shock of increasing density. The medium ahead of the shock is assumed to be inhomogeneous and at rest. Variation of magnetic field radiation flux, and other flow variables are given in tabular form. 相似文献
8.
The self-similar model of a shock wave, produced on account of an instantaneous release of energy in an inhomogeneous self-gravitating gaseous mass, has been discussed with the help of equations of motion and equilibrium conditions. The disturbances are headed by a shock of variable strength. The variation of velocity density, pressure, and mass have been discussed for the different values of strength of the shock. 相似文献
9.
A model of similarity solution for the propagation of shock waves produced on account of an instantaneous release of energy in an inhomogeneous medium with the effect of radiation has been discussed. The disturbances of the medium are headed by a shock of variable strength. The variations of flow variables have been discussed for the different values of strength of the shock. 相似文献
10.
S. A. Grib 《Astronomy Letters》2010,36(1):59-63
The interaction of traveling fast solar shock waves with other fast shock waves generated previously is considered in terms
of magnetohydrodynamics for various solar wind parameters. The shocks are not piston ones and move freely in the flow. The
magnetic structure in the interplanetary magnetic field emerging after the shock interaction is shown to correspond to the
well-known magnetic configuration commonly observed on spacecraft or the classical Hundhausen R model. A head-on collision of solar shock waves with the boundary of a magnetic cloud is considered. It is pointed out that
a slow shockwave refracted into the magnetic cloud can appear at an oblique collision of the shock with the cloud boundary.
The results clarify our understanding of the available spacecraft data. 相似文献
11.
A laser-driven experiment produces images of dense shocked material by x-ray transmission. The post-shock material is sufficiently
dense that no significant signal passes through the dense layer, and therefore the shock compression cannot be directly measured
by comparing transmitted intensities. One could try to determine the shock compression ratio by observing the ratio of the
total distance travelled by the shock to the dense post-shock layer width, but small deviations of the angle of the shock
with respect to the angle of imaging create large asymmetric errors in observation. A statistical approach to recovering shock
compression by appropriately combining data from several experiments is developed, using fits to a simple model for the shock
and shock tube geometry. 相似文献
12.
Interaction of weak shock waves with a current sheet is investigated by a two-dimensional numerical magnetohydrodynamic model. In accordance with solar coronal conditions, a ratio of thermal to magnetic pressures of 0.1 and a shock Alfvén Mach number slightly above 1 are considered. It is found that even weak shock waves trigger magnetic field reconnection in current sheets. Based on this result, it is suggested that drifting chains of type I radio bursts are radio manifestations of the interactions of weakly super-Alfvénic shock waves with pre-existing current sheets distributed in an active region. This model of type I noise storms is then discussed in connection with the concept of nanoflares (localized reconnections) and the heating of the solar corona. 相似文献
13.
An important contribution to the thermalization of the solar wind ions at the Earth's bow shock for high Mach numbers comes from the reflection of a fraction of these ions from the shock. Previous studies have examined the trajectories of the reflected ions assuming the shock to be an infinite plane. In this paper a model is developed to describe the trajectories of particles after reflection for a variety of shock geometries. Of particular interest are the initial conditions which allow the particle to return to the shock with a greater normal velocity than at first encounter, or to return to the shock at all. The effects of the magnetic field direction and the curvature of the shock on particle trajectories are discussed for cylindrical and spherical shock geometries and compared to those for a planar shock. 相似文献
14.
A nonlinear model of cosmic-ray acceleration at the shock fronts in the supernova remnants W28, W44, and IC433 is investigated. The hydrodynamic evolution of a supernova remnant, including the shock modification by the pressure of accelerated particles and the streaming instability of particles upstream of the shock propagating in a partially ionized interstellar gas, is modeled. The electromagnetic radiation generated by accelerated particles is calculated and compared with observations in a wide range of photon energies. 相似文献
15.
The results of numerical modeling of meteoroids' interaction with Earth's atmosphere are presented. We model the entry in two dimensions and then interpolate the results into a 3‐D model to calculate interaction of shock waves with the surface. Maximum shock pressures, wind speeds, and areas subjected to substantial overpressure are calculated for oblique impacts of asteroids and comets. We show that vertical impacts produce a smaller damage zone on the surface than oblique ones. Damage caused by shock waves covers an order of magnitude larger area than any other hazardous effects. The function of energy release in the atmosphere, which is traditionally used in meteoritics, has a limited application if cosmic bodies are larger than tens of meters in diameter: at each time moment energy is smoothed along a substantial length of the trajectory; both emitted radiation (routinely used for calibration of semi‐analytical models) and shock wave amplitude are complex functions of temperature–density distributions in atmosphere. 相似文献
16.
Takashi Yamamoto 《Planetary and Space Science》1976,24(11):1073-1080
Models of acceleration of auroral electrons by electrostatic shock waves are considered based on the model electron beam, calculated by Evans (1974), to account for the observed precipitating electron fluxes. Electron populations in our models include a primary accelerated beam, originating from the plasma sheet, the secondary electrons and the energy-degraded and backscattered primary electrons produced by precipitating electrons of that beam. We find a feasible electrostatic shock model with appropriate ion populations from considerations on the conditions for the existence of shock solutions. 相似文献
17.
G. P. Zank 《Astrophysics and Space Science》1988,140(2):301-324
A multiple scales analysis is used to derive a mixed Burgers-Korteweg-de Vries (BKdV) equation in the long wavelength regime for a two-fluid MHD model used to describe cosmic-ray acceleration by the first-order Fermi process in astrophysical shocks. The BKdV equation describes the time evolution of weak shocks in the theory of diffusive shock acceleration for all possible cosmic-ray pressures. Previous work on weak shocks in the cosmic-ray MHD model has assumed that dissipation alone is sufficient to balance nonlinearity, but, as cosmic-ray pressures become small, the weak shock becomes discontinous. By including Hall current effects into the MHD model, the low cosmic-ray pressure limit leads smoothly into solitary wave behaviour. For low cosmic-ray pressures, the shock has a downstream oscillatory precursor which is smoothed into the standard Taylor shock profile with increasing cosmic-ray pressure. As a by-product of the perturbation analysis, a dissipative KdV equation is derived. In conclusion, dispersive effects on Alfvén waves are discussed and a modulational stability analysis is presented. 相似文献
18.
《New Astronomy》2021
Energetic particles fluxes measured by spacecraft in the heliosphere are frequently observed to peak during interplanetary shock crossings, suggesting the shock to be the source of acceleration. It has been shown that the shape of the energetic particle fluxes, upstream and downstream of the shock, is affected by energetic particle transport properties. In this study we make a comparison among a number of shock crossings observed by the ACE spacecraft, and the energetic particle fluxes derived by a test-particle numerical model in the vicinity of a planar shock. We find that observations are in good agreement with a particle density profile obtained in the simulation by assuming superdiffusive transport both upstream and downstream of the shock region. 相似文献
19.
Onkar Nath 《Solar physics》1991,136(2):263-268
A model is presented of a solar atmosphere which is heated by the periodic passage of shock waves. The outer atmosphere rotates and is assumed not to affect the strength of the shock waves. This constant shock strength hypothesis is used as the basis of the model of the outer solar atmosphere. From the model it is concluded that the chromospheric temperature rise and flow Mach number are slightly affected by the rotation of the atmosphere. 相似文献
20.
本文专门讨论II型超新星瞬发爆炸模型中的激波形成点、激波波阵面的位置、激波速度和激波能量等一系列的问题 .研究发现在外星核区除存在首级激波外 ,还存在次级激波 ;激波波阵面的准确位置应在熵变化的最大点和外星核区中人为粘性压的最大点之间 ;并给出激波能量的不同定义量之间的大小关系 相似文献