摘要:

The Grad‐Shafranov reconstruction technique involves the Grad‐Shafranov equation governing2 12dimensional structures, and the magnetic and plasma measurements from a single spacecraft. It is capable of deriving, quantitatively, a 2D cross section characterizing non‐axisymmetric, cylindrical magnetic structures. Its applications to observations in the inner heliosphere, such as the magnetic flux ropes observed by spacecraft WIND and ACE, are reported. Multi‐spacecraft validation and its application to structures beyond 1 AU are discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809521

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We summarize observational data and present theoretical considerations in order to estimate the relative contributions of suprathermal pick‐up ions neutralized inside and outside the termination shock to the energetic neutral atom (ENA) flux in the energy range 55 – 80 keV/amu detected by the SOHO/CELIAS/HSTOF sensor near Earth’s orbit. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809522

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We study the spatial intensity profiles of galactic cosmic ray protons (H) and &agr;‐particles (He) during the solar minimum periods of 1987 (the so‐called negative drift state) and 1977/1997 (both positive drift states) of the heliosphere. These intensities were measured with the Pioneer, Voyager and IMP spacecraft. The 1997 intensities were so low that one cannot readily explain them, even with the acceleration at the solar wind termination shock (SWTS) and modulation in the heliosheath included. Our heliospheric model is azimuthally symmetric with a spherical shock and heliopause, however, and we infer from its results that more realistic geometries may produce modulation effects that will explain the observations better. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809523

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

There is experimental evidence that the solar wind is populated with nonlinear waves and coherent structures. There is also experimental as well as theoretical evidence that solar wind MHD turbulence can be approximated in terms of dynamic composite two‐dimensional plus slab turbulence. Within this framework turbulence in the heliospheric plasma sheet, for example, is expected to consist of two‐dimensional non‐linear MHD vortex structures plus slab turbulence associated with quasi‐linear Alfven waves. We reexamine energetic particle transport in the heliosphere by taking into account scattering on vortices. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809524

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Observations of cosmic rays and other energetic charged particles in the heliosphere over the past decade have created new challenges to the standard theoretical paradigms for energetic‐particle transport. Certainly, some of these will be resolved using the standard Parker (diffusive) transport equation applied to increasingly sophisticated models of heliospheric phenomena. For example, we can apparently understand the modulation of galactic cosmic rays and the acceleration and transport of galactic cosmic rays in terms of this paradigm. Cosmic‐ray reaction back on the plasma can also fit into this paradigm. However, it is also becoming increasingly clear that in some situations the diffusion approximation is not strictly valid. The scattering mean free paths may be large or there are significant anisotropies. For example, observations of solar energetic‐particle events show non‐diffusive effects, particularly in the early phases. Recently observed enhancements on Voyager 1, attributed to the proximity of the solar‐wind termination shock, show large anisotropies. In the inner heliosphere, the transport mean‐free paths are comparable to the characteristic macroscopic scales, which again makes diffusion models inaccurate. In this overview, the diffusion approximation and more‐general treatments of particle transport are compared. It is concluded that even where the diffusion approximation is not strictly valid, it can be a useful guide to the more complete and complex models. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809525

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Ulysses has by now made two complete out‐of‐ecliptic orbits around the sun. The first encounter of the solar poles occurred in 1994–1995, when the sun was near the minimum of its activity cycle, while the second one was in 2000–2001, when the sun was at solar maximum. To our surprise, energetic particles of all origins at high latitude are not much different from those we observe near the ecliptic for at least these two phases of solar cycle. The latitude gradients of galactic and anomalous cosmic rays are positive but small at the 1994–1995 solar minimum and almost zero at the 2000–2001 solar maximum, while temporal solar cycle variation dominates their flux variation at all latitudes. Solar energetic particles from all large gradual events can be seen at both Ulysses and Earth no matter how large their spatial separations from the solar event are, and the particle flux often reaches a uniform level in the entire inner heliosphere within a few days after event onset and remains so throughout the decay phase that can sometimes last over a month. Energetic particles accelerated by low‐latitude CIRs can appear at high latitudes, far beyond the latitudinal range of CIRs. All these observations suggest that latitudinal transport of energetic particles is quite easy. In addition, because the average magnetic field is radial at the pole, The Ulysses observations indicate that parallel diffusion and drift in the radial direction need to be reduced at the poles relative to their equatorial values. To achieve such behaviors of particle transport, the heliospheric magnetic field needs a significant latitudinal component at the poles. A non‐zero latitudinal magnetic field component can be produced by latitudinal motion of the magnetic field line in solar corona, which can be in form of either random walk suggested by Jokipii or large scale systematic motion suggested by Fisk. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809526

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The physics of magnetic field‐line meandering and the associated energetic‐particle transport in the outer heliosphere is discussed. We assume that the heliospheric magnetic field, which is frozen into the solar‐wind plasma, is composed of both an average and random component. The power in the random component is dominated by spatial scales that are very large (by a few orders of magnitude) compared to the shock thickness. The results from recent numerical simulations are presented. They reveal a number of characteristics which may be related to recent Voyager 1 observations of energetic particles and fields. For instance, low‐energy (tens of keV) particles are seen well upstream of the shock that also have large pitch‐angle anisotropies. Furthermore, low‐energy particles are readily accelerated by the shock, even though their mean‐free paths are very large compared to their gyroradii. When averaging over the entire system, the downstream spectra are qualitatively consistent with the theory of diffusive shock acceleration. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809527

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The recent enhancements of particle fluxes at Voyager‐1 are most likely connected with the closeness of the termination shock (TS). Near the TS, the topology of the magnetic field lines and their connection to the TS may be of primary importance. One can expect the field lines to intersect the TS more than once. Multiple intersection may occur due to a variety of reasons. We consider a model assuming that V‐1 was still in inside the TS, but on a field line that has already intersected the TS between V‐1 and the Sun. We find that this scenario may result in phenomena similar to those observed by Voyager‐1 in 2002–2003: enhanced low‐energy fluxes and large, anti‐sunward, field‐aligned anisotropies may arise in a natural way. The likeliness of the proposed scenario is discussed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809528

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In astrophysical settings, termination shocks where strong stellar wind outflows interact with the surrounding environments tend to take place in dusty regions. Just to name a few, star formation regions, planetary nebulae, supernova remnants and active galactic nuclei are all good examples. Dynamics and evolution of the associated dust clouds could have important influences on the acceleration and composition of energetic particles resulting from the diffusive shock acceleration at the termination shocks. In this note we provide a brief review of previous work predating the recent detection of ACR Mg, Na, Si and S ions which might have originated from the Kuiper belt dust. Their compositional abundance might be diagnostic of the collisional history of the Kupier belt objects. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809529

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We provide a brief description of three examples of nonlinear stationary waves, chosen because they exhibit interesting and unusual properties. The first is the classical ion‐acoustic soliton which, by a suitable admixture of negative heavy ions, can exhibit a rarefractive structure associated with a potential dip. The second is the whistler “oscilliton” which possesses the classical soliton pulse, superimposed on which are fine scale oscillations in the longitudinal and transverse flow speeds. This wave arises from the balance between the sum of the Reynolds stresses of the electrons and protons and the magnetic Maxwell stresses. The inclusion of negatively charged heavy ions also ensures that the left handed proton cyclotron mode may exhibit this type of intricate structure. Finally we discuss the electrostatic‐ion‐cyclotron mode which can possess both soliton (for subsonic speeds) and oscillatory (for supersonic speeds) solutions. In the latter case spiky wave forms can be constructed by a drive towards the sonic point in the compressive phase of the wave. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809530

出版商:AIP    

年代:1904

数据来源: AIP