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Oblique shock

About: Oblique shock is a research topic. Over the lifetime, 6551 publications have been published within this topic receiving 119823 citations.


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TL;DR: In this paper, the authors proposed that galactic shocks propagating through interstellar density fluctuations provide a mechanism for the intermittent replenishment or pumping of the supersonic motions and internal density enhancements observed pervasively within cool atomic and molecular interstellar structures, without necessarily requiring the presence of selfgravity, magnetic fields, or young stars.
Abstract: We propose that galactic shocks propagating through interstellar density fluctuations provide a mechanism for the intermittent replenishment, or "pumping," of the supersonic motions and internal density enhancements observed pervasively within cool atomic and molecular interstellar structures, without necessarily requiring the presence of self-gravity, magnetic fields, or young stars. The shocks are assumed to be due to a variety of galactic sources on a range of scales. An analytic result for the kinematic vorticity generated by a shock passing through a radially stratified two-dimensional isobaric model cloud is derived, assuming that the Mach number is not so large that the cloud is disrupted, and neglecting the shock curvature and cloud distortion. Two-dimensional lattice gas hydrodynamic simulations at modest Mach numbers were used to verify the analytic result. The induced internal velocities are initially a significant fraction of the shock speed divided by the square root of the density contrast, accounting for both the observed line width amplitudes and the apparent cloud-to-cloud line width-density scaling. The line width-size relation could then be interpreted in terms of the well-known power spectrum of a system of shocks. The induced vortical energy should quickly be converted to compressible and MHD modes and so would be difficult to observe directly, even though it would still be the power source for the other modes. The shock pump thus produces density structure without the necessity of any sort of instability. We argue that the shock pump should lead to nested shock-induced structures, providing a cascade mechanism for supersonic "turbulence" and a physical explanation for the fractal-like structure of the cool interstellar medium. The average time between shock exposures for an idealized cloud in our Galaxy is estimated and found to be small enough that the shock pump is capable of sustaining the supersonic motions against readjustment and dissipation, except for the smallest structures. This suggests an explanation of the roughly spatially uniform and nearly sonic line widths in small "dense cores." We speculate that the avoidance of shock pumping may be necessary for a localized region to form stars and that the inverse dependence of probability of avoidance on region size may be an important factor in determining the stellar initial mass function.

58 citations

Journal ArticleDOI
TL;DR: In this article, the contribution of the directly transmitted ions to ion heating in the low-Mach number oblique shock is determined analytically, and the estimate for the maximum downstream temperature of the heated ion distribution, which depends only on the magnetic compression ratio and cross-shock potential, can be verified observationally.
Abstract: The contribution of the directly transmitted ions to ion heating in the low-Mach number oblique shock is determined analytically. We derive approximate expressions for the pressure tensor inside the ramp of a low-Mach number low-β shock. In the thin shock limit the ion state equation p ∝ n³ is recovered within the ramp, which corresponds to the complete demagnetization of ions and effective one-dimensional behavior. We derive the estimate for the maximum downstream temperature of the heated ion distribution, which depends only on the magnetic compression ratio and cross-shock potential, and may be verified observationally.

58 citations

Journal ArticleDOI
TL;DR: In this article, an attempt at a systematic investigation of wave propagation in a metal, treating interactions between elastic and plastic waves, and the formation and propagation of shock waves, in the general case of motions with unidirectional strain arising from an initial smooth loading-unloading pulse was made.
Abstract: This paper is an attempt at a systematic investigation of wave propagation in a metal, treating interactions between elastic and plastic waves, and the formation and propagation of shock waves, in the general case of motions with unidirectional strain arising from an initial smooth loading­ unloading pulse. A stress-strain relation with linear elastic paths and concave-upward plastic paths (where compression is measured as positive) is derived and used so that the elastic wave velocity is uniform, and the plastic wave velocity an increasing function of stress. The analysis is in terms of engineering stress and strain with a Lagrangian co-ordinate system. Analytic solutions to the interactions between different types of continuous waves are developed incorporating an expression for the motion of the elastic-plastic boundary. An analysis of the breakdown of a smooth plastic compression wave into a shock wave is presented, and the propaga­ tion conditions derived. It is shown that the heat dissipated is proportional to the cube of the strain jump, its low value for moderate shock strength suggests that the shock does not appreciably affect the stress-strain relation, an assumption from which a solution for the unloading of a plastic compression front by an overtaking elastic wave, while shock formation is taking place, is derived. A numerical illustration of this solution for a particular pulse in aluminum is given

58 citations

Journal ArticleDOI
TL;DR: In this paper, an examination of the perturbation vectors of waves upstream and downstream from the region of maximum compression in the bow shock on Ogo 5 under particularly steady solar-wind conditions was performed.
Abstract: Results of an examination of the perturbation vectors of waves upstream and downstream from the region of maximum compression in the bow shock on Ogo 5 under particularly steady solar-wind conditions. The polarization of the upstream waves was right-hand circular, and that of the downstream waves left-hand elliptical in the spacecraft frame. By observing that the polarization of the waves remained unchanged as the shock motion swept the wave structure back and forth across the satellite three times in eight minutes, it was found that the waves were not stationary in the shock frame. A study of the methods of determining the shock normal indicates that the normal estimated from a shock model should be superior to the normal based on magnetic coplanarity. The propagation vectors of the waves examined did not coincide with the shock-model normal, the average magnetic field, or the plasma-flow velocity. However, the major axis of the polarization ellipse of the downstream wave was nearly parallel to the upstream propagation vector.

58 citations

Journal ArticleDOI
TL;DR: In this paper, a numerical simulation code was developed to study the steady state acceleration of energetic particles at an oblique shock and explain observed precursors of Forbush decreases of Galactic cosmic rays before the arrival of an interplanetary shock induced by solar activity.
Abstract: We have developed a numerical simulation code that treats the transport and acceleration of charged particles crossing an idealized oblique, nonrelativistic shock within the framework of pitch angle transport using a finite-difference method. We consider two applications: (1) to study the steady state acceleration of energetic particles at an oblique shock and (2) to explain observed precursors of Forbush decreases of Galactic cosmic rays before the arrival of an interplanetary shock induced by solar activity. For the former, we find that there is a jump in the particle intensity at the shock, which is stronger for more oblique shocks. Detailed pitch angle distributions are also presented. The simple model of a Forbush decrease explains the key features of observed precursors, an enhanced diurnal anisotropy extending several mean free paths upstream of the shock and a depletion of particles in a narrow loss cone within ~0.1 mean free path from the shock. Such precursors have practical applications for space weather prediction.

58 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202369
2022142
2021106
202090
201992
2018102