摘要:

To understand the role of reflected particles in the fundamental scalings of the structure of a quasi‐perpendicular shock, we study a simple one‐fluid model for a shock with reflected particles by including appropriate source terms. A reductive perturbation scheme is adopted to obtain the nonlinear evolution equation, yielding a Burgers’ equation for the case of low reflection efficiency. The stability of the shock is investigated and it is found that for a large reflection efficiency, the shock is destabilized. Possible implications for injection and acceleration of pickup‐ions at a quasi‐perpendicular and the heliospheric termination shock are discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809531

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The interaction of magnetohydrodynamic (MHD) waves in space plasmas can be investigated by Lagrangian and Hamiltonian methods. In this paper, we discuss the propagation of non‐WKB waves in a non‐uniform background plasma flow such as the solar wind, by using Lagrangian variational principles for MHD plasmas developed by Newcomb. The Lagrangian methods for the propagation of WKB waves in a non‐uniform background plasma flow developed by Dewar are extended to the case of of non‐WKB waves in a non‐uniform background flow. As part of the analysis, we obtain Noether’s theorem for the combined system of waves and background plasma. This effectively generalizes the form of Noether’s theorem for Lagrangian MHD used by Padhye and Morrison and Padhye in their analysis of Lagrangian, fluid re‐labelling symmetries. Examples of the use of Noether’s theorem, are the derivation of the energy and momentum conservation laws for the total system of waves and background plasma, corresponding respectively to the case of time and space translation symmetries. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809532

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This paper will review some of the origins of exact magnetic reconnection solutions, leading up to fully 3D examples. These are then compared to solutions obtained from dynamic 3D simulations. We find that the analytic steady‐state solutions provide an accurate description of current sheets which form dynamically within a well‐defined domain. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809533

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Kinetic aspects of a collisionless termination shock are discussed in the context of pickup ion injection into a diffusive acceleration mechanism. For the surfing (or multiply reflected ion) mechanism at an almost perpendicular termination shock to be effective the cross‐shock potential has to be of the order of several electron inertial lengths or smaller. Such small scales are only possible for shocks with an ion beta of about 0.1 or less. An alternative mechanism is discussed which is based on the result that pickup ions are easily reflected at quasi‐parallel shocks. Assuming that the termination shock, due to a turbulent upstream magnetic field, is locally quasi‐parallel, pickup ions are efficiently accelerated to several hundreds of keV within about 10 hours, from where a second diffusive process can accelerate them to ACR energies. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809534

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The quasilinear calculation of perpendicular diffusion of cosmic ray particles for weak dynamical magnetic turbulence of arbitrary geometry is presented. Starting from the equations of motion a detailed point‐by‐point derivation of quasilinear Fokker‐Planck coefficients is given. It is shown that, in order to have diffusive behaviour of the Fokker‐Planck coefficients, the existence of a finite correlation time of the magnetic fluctuations is essential. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809535

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The problem of hydrogen neutrals interacting with the heliospheric bow shock region has received considerable attention recently, motivated primarily by the hope that the Voyager spacecraft may soon encounter the first of the heliospheric boundaries. The complexity of the charge exchange interactions has limited our analytic understanding so far. In this work we develop a semi‐analytic one‐dimensional model based upon a double expansion technique to investigate the self‐consistent interaction of shock with neutrals. The underlying method uses the Boltzmann transport equation that describes neutral transport, and is coupled to plasma protons predominantly through charge exchange processes. The gyrotropic distribution function of the neutrals is first expanded in terms of Legendre polynomials followed by associated Laguerre harmonics. The resulting set of equations can be cast into a square matrix whose eigenvalues depend upon sources and the plasma distribution. The interstellar protons, in a high &bgr; limit, are described by a hydrodynamic fluid with source terms that couple neutrals and plasma and further modify both distributions in a self‐consistent manner. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809536

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Conventionally, the heliospheric termination shock (HTS) is regarded as a sharp MHD discontinuity. More recent models suggest that the back‐reaction of energetic cosmic rays accelerated at the HTS will create a broad shock with an extended precursor. Here we suggest that a combination of upstream solar wind disturbances interacting with the HTS, the presence of cosmic ray gradient‐driven instabilities and their coupling to the pickup ion population yields a termination shock that is highly dynamical in both structure and location. We also suggest that the diffusive cosmic ray transport equation used to model particle acceleration at a shock may require modification to account for a highly turbulent velocity component. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809537

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The nature of energetic particle transport needs to be reinvestigated during times of high solar activity when systems of closely spaced fast transient solar wind streams form large regions with strong compressive fluctuations in the solar wind. A nonlinear theory is presented for diffusive energetic particle transport in enhanced mesoscale compressive wave turbulence on which incompressible small‐scale MHD turbulence is superposed. The theory suggests that suprathermal ions such as pickup ions would develop hard power law spectra inside a system of transient flows during solar maximum conditions in the inner heliosphere. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809538

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Cosmic rays can be accelerated so efficiently at shock waves by the first‐order Fermi mechanism that their pressure can be comparable to or exceed that of the thermal gas. Consequently, it was recognized that CRs could modify the structure of the shock itself, typically broadening it by the CR diffusive length scale. Besides modifying the accelerated particle spectrum, the CR pressure gradient across the shock can destabilize short‐wavelength compressive fluctuations (such as acoustic waves), leading to a highly turbulent shock structure. In this paper, we investigate particle acceleration at a turbulence modified shock. We show that the presence of the turbulence can be treated as an effective diffusion coefficient, an effective flow speed and an effective second order Fermi diffusion. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809539

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The transport equation describing the coupling of cosmic rays to the heliospheric plasma is presented, together with an illustrative solution valid at high energies for the solar modulation of galactic cosmic rays (GCR) in both the solar wind and the heliosheath. The nonlinear backreaction of GCR and the anomalous cosmic ray component on the heliospheric flows and magnetic fluctuation spectra are described briefly. Finally, a calculation is presented, which shows that care must be taken in the interpretation of a large component of the particle flux normal to the magnetic field as evidence of a large perpendicular diffusion coefficient. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809540

出版商:AIP    

年代:1904

数据来源: AIP