共查询到20条相似文献，搜索用时 46 毫秒
1.
The propagation of sonic discontinuity in conducting and radiating atmosphere has been discussed under the influence of magnetic field. The velocity of sonic wave and its termination into shock wave has been obtained. We have also obtained the critical time at which sonic wave terminates into shock wave. There is significant effect of magnetic field on sonic velocity and its termination into shock wave. 相似文献
2.
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
3.
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
4.
Stationary hypersonic flow around a descent vehicle is examined by considering equilibrium and nonequilibrium reactions. We study how physical-chemical processes and shock wave conditions for gas species influence the shock-layer structure. It is shown that conservation conditions of species on the shock wave cause high-temperature and concentration gradients in the shock layer when we calculate spacecraft deceleration trajectory in the atmosphere at 75 km altitude. 相似文献
5.
Onkar Nath 《Astrophysics and Space Science》1989,158(2):183-187
Equations are developed to describe the flow of a rotating atmosphere under force of gravitation heated by an arbitrary distribution of cylindrical shock waves. Solutions are obtained for the outer solar atmosphere with a steady mass motion in which the heat supplied by shock wave is balanced by the convective heat loss due to this motion. It is found that, for very large range of shock strength and frequencies, the temperature profile is similar to that predicted by the constant shock-strength hypothesis. This hypothesis is used as the basis of a model of the outer solar atmosphere starting near the solar atmosphere. 相似文献
6.
The formation of a weak shock at the interaction of the solar wind with the cometary neutral gas is confirmed in a non-stationary gasdynamic model. No shocks will be detectable along the ICE path and if the VEGA/GIOTTO spacecraft enter the cometary atmosphere. A shock can only be expected at an exit from the Halley atmosphere. 相似文献
7.
We investigate the proper method for mathematically simulating the formation of an interplanetary disturbance (IPD) in the subsonic, sub-Alfvénic region near the solar surface within the constraints of one-dimensional hydrodynamic and magnetohydrodynamic (MHD) analyses. We then numerically simulate the subsequent propagation of the IPD through the solar wind critical points in the equatorial plane to the outer corona. We show that, if the IPD is initiated outside the critical points, it always contains both a forward and reverse shock (a shock pair). This result contrasts with observations indicating that shock pairs at 1 AU which can be associated with solar events are rare occurrences in the solar wind. On the other hand, IPDs initiated inside the critical points contain only a forward shock at the leading edge. When the magnetic field is included in the simulation and the IPD is originated inside the critical points, the IPD contains a forward shock at its leading edge followed by large-amplitude, nonlinear, MHD waves which are convected outward by the solar wind. Unlike shock pairs, MHD waves are often observed in the solar wind. Hence, we conclude that physically realistic studies of the propagation of IPD which are assumed to originate near the solar surface must (1) initiate the IPD inside the critical points and (2) include the magnetic field. Although this conclusion is based on a one-dimensional analysis, we speculate that it would be equally valid in multi-dimensions. 相似文献
8.
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
9.
R. C. Srivastava D. Leutloff J. P. Vishwakarma Arun Kumar 《Astrophysics and Space Science》1986,122(1):33-40
Magnetogasdynamic shock waves propagating in a medium of increasing density are discussed. The shock travels in a dense atmosphere. We have used the Runge-Kutta method to obtain a numerical solution of the problem. The distribution of flow variables behind the shock are shown by graphs. 相似文献
10.
Onkar Nath 《Astrophysics and Space Science》1988,146(1):175-182
The self-similar model of propagation of spherical strong shock waves into non-uniform stellar atmosphere under self-gravitation and non-uniform magnetic field is investigated. The disturbances are headed by a shock surface of variable strength. Gas is assumed to be grey and opaque and the shock tobe transparent. 相似文献
11.
There are two distinct regimes of the first-order Fermi acceleration of shocks. The first is a linear (test-particle) regime in which most of the shock energy goes into thermal and bulk motions of the plasma. The second is an efficient regime in which the shock energy goes into accelerated particles. Although the transition region between them is narrow, we identify the factors that drive the system toward a self-organized critical state between those two regimes. Using an analytic solution, we determine this critical state and calculate the spectra and maximum energy of accelerated particles. 相似文献
12.
Self-similar flows, behind a radiation-driven shock wave, have been investigated in non-uniform atmosphere. The total energy content of the flow behind the shock increases due to the absorption of radiation and it is assumed to be time-dependent. 相似文献
13.
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
14.
Under the assumption that type II bursts are excited by strong shock waves it is shown that the velocity determined from dynamic spectrograms should be corrected by a term proportional to the gradient of the shock strength. The magnitude of the correction strongly depends on the properties of the pre-shock atmosphere and the geometry of the shock propagation. 相似文献
15.
作为本系列的最后一篇,本文研究日冕大气中的激波演化.结果表明,日冕背景大气和磁场的非均匀性对激波结构和演化起着决定作用。太阳附近形成的慢激波-快磁声波系统,将在向外传播的过程中演变为以中间激波作为必要组成部分的混合激波。该混合激波在沿电流片传播时能继续维持,而在沿单极开放磁场传播时则进一步演变为纯快激波。 相似文献
16.
J. B. Singh 《Astrophysics and Space Science》1982,87(1-2):347-355
Self-similar flows of self-gravitating gas behind a spherical shock wave which are driven out by a propelling contact surface, propagating in a nonuniform atmosphere at rest, are investigated. The total energy content of the flow between a shock front and contact surface is taken to be time-dependent. In brief, the self-similar homothermal flows of self-gravitating gas behind a shock wave and Roche's model case are also studied in the present paper. 相似文献
17.
Tapas K. Das † 《Monthly notices of the Royal Astronomical Society》2000,318(1):294-302
Introducing a spherical, steady, self-supported pair-plasma pressure-mediated shock surface around a Schwarzschild black hole as the effective physical atmosphere that may be responsible for the generation of astrophysical mass outflows from relativistic quasi-spherical accretion, we calculate the mass outflow rate R ̇ by simultaneously solving the set of equations governing transonic polytropic accretion and isothermal winds. R ̇ is computed in terms of only three inflow parameters, which, we believe, has been done for the first time in our work. We then study the dependence of R ̇ on various inflow as well as shock parameters, and establish the fact that the outflow rate is essentially controlled by the post-shock proton temperature. 相似文献
18.
Self-similar flows of a perfect gas behind the cylindrical shock wave propagating exponentially in an atmosphere whose density varies inversely as the fourth power of shock radius are investigated. The effects of radiation flux has also been taken into consideration. The total energy of the wave is constant. 相似文献
19.
Kazunari Shibata Takara Nishikawa Reizaburo Kitai Yoshinori Suematsu 《Solar physics》1982,75(1-2):99-118
We present a spicule model whose eruption occurs as a result of the sudden pressure enhancement at the bright point located at the root of the spicule. To show this, one dimensional (constant cross sectional) and time dependent hydrodynamic equations are solved numerically in the realistic solar atmosphere extending from the photosphere to the corona. Adiabatic motion is assumed. The pressure enhancement by a bright point at the base of the model atmosphere generates a shock wave. The shock gets stronger as it passes upward through the chromosphere and eventually collides with the chromosphere-corona interface which is a kind of a contact discontinuity. As the result, the interface begins to move upward. We identify the matter following behind this interface as the solar spicule. The model explains many observed features, such as the height and the density of the spicules, although such features have been hitherto considered not to be explained easily by shock theories. 相似文献
20.
Based on model calculations, we show that ion-acoustic oscillations can be excited by heat fluxes in a plasma. We discuss the probable effect of ion-acoustic oscillations on the formation of temperature gradients at critical heat fluxes. The local critical heat flux in the transition region of the solar atmosphere is close to the well-known experimental heat flux from the corona into the chromosphere. 相似文献