摘要:

During solar maximum conditions, the heliosphere is highly structured on all spatial scales. It is the purpose of this paper to summarize our current understanding of these structures from global scales to mesoscale, a fraction of 1 AU. We use theoretical considerations, in situ observations near Earth and the Ulysses spacecraft, and global heliosphere calculations to discuss the effects on both global and mesoscales on the three‐dimensional structure of the heliospheric magnetic field and their effects on galactic cosmic rays. These conclusions are in contrast to near‐solar‐minimum‐like heliospheric conditions that are currently assumed in modulation and transport calculations even during solar maximum. The expected complex heliospheric properties should be of major importance for the interpretation of the heliospheric boundary events observed by Voyager 1 since 2002. A companion paper by L. A. Fisk will explore the effects of the mesoscale structures on particle acceleration in the heliospheric boundary region. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809501

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Pickup ions (PUIs) are created from a number of neutral sources both inside and outside the heiosphere. The combination of recent observational and theoretical work has completed the catalog of at least the major sources of Heliospheric PUIs. These PUIs are the seed population for anomalous cosmic rays (ACRs), which are accelerated to high energies at the termination shock (TS). Recently, Voyager 1 (V1) encountered strong intensity enhancements in the energy range where pickup ions are energized into ACRs. These observations may indicate that V1 has already passed beyond the TS into the bath of accelerated pickup ions in the inner heliosheath. However, opposing this conclusion, V1 magnetic field and higher energy particle observations appear very typical. Here, we advance the concept that V1 was in a special region in the heliosphere where the magnetic field is highly distorted due to solar wind shearing and footpoint motions at the Sun. These Favored Acceleration Locations at the Termination Shock (FALTS) efficiently inject pickup ions into diffusive shock acceleration due to slightly increased radial field components in the FALTS field regions. Such regions provide much more direct field‐line connection to the TS than along strongly wound Parker field lines found outside of FALTS. Inside the TS, FALTS naturally enhance fluxes of accelerated pickup ions. Thus, FALTS may be responsible for the V1 observations of energetic particle enhancements. Further, FALTS provide a conduit for an inward electron heat flux from hot electrons beyond the TS, thereby heating the plasma and increasing the electron impact ionization rate. This additional ionization causes mass loading that locally weakens the TS and draws it in toward the Sun. Thus, FALTS can cause both energetic particle intensity enhancements and a weaker, locally drawn in TS; these effects may help explain the otherwise contradictory V1 observations. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809502

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

This paper aims to show that the plasma structures of both the outer heliosphere and of some planetary nebulae whose stars have magnetic field can be discussed under similar MHD physical processes. It is shown that the magnetic pressure force of the toroidal field works azimuthaly to push up the plasma in a polar direction, while at the same time pushing down in an equatoward direction from the region where the toroidal field intensity is maximum. As an example of interplanetary nebulae, the three‐ring structure around SN 1987A observed by the Hubble Space Telescope is discussed. It is shown that this structure is reproduced by a MHD simulation due to magnetic‐pressure effects if we assume that the star has a relatively strong dipole magnetic field and that the stellar wind is fast in the high‐latitude coronal hole region, such as in the case of the Sun. It is also shown for the heliospheric structure that, if the magnetic effect around the equatorial neutral sheet is taken into accout, the global heliospheric structure is not a simple nose‐cone type but a V‐shaped gutter structure along the equatorial plane on the nose‐cone surface of the heliopause. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809503

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

In this paper we discuss configurations of the heliospheric interface shaped by the influence of both the uniform interstellar and the interplanetary (Parker model — Archimedean spiral) magnetic fields in the presence of the neutral particles. Magnetic fields strongly affect the structure and the shape of the heliospheric interface, which becomes asymmetric for any configuration of the interstellar magnetic field (ISMF), for the case where the interplanetary magnetic field (IMF) is included. In particular, the interstellar magnetic field lines may merge with interplanetary magnetic field lines of opposite direction at the heliopause. This may possibly cause a reconnection of the magnetic field lines at the heliopause. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809504

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Heavy elements including He, O, and others are present in the interstellar medium surrounding the heliosphere. They form the source for heavy pickup ions and anomalous cosmic rays in the heliosphere. Kinetic numerical models are used to study the entrance and the heliospheric distribution of neutrals and singly charged ions of helium and oxygen as they interact through charge exchange with the neutral and ionized hydrogen of the heliosphere. A representative hydrogen heliospheric model is used to study the heavy element distributions and charge exchange mean free paths, and obtain key results such as filtration ratios and increased heavy neutral densities (walls). © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809505

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

There is currently a controversy as to whether Voyager 1 has already crossed the termination Shock, the first boundary of the heliosphere. The region between the termination shock and the heliopause, the heliosheath, is one of the most unknown regions theoretically. In the heliosheath magnetic effects are crucial, as the solar magnetic field is compressed at the termination shock by the slowing flow. Recently, our simulations showed that the heliosheath presents remarkable dynamics, with turbulent flows and the presence of a jet flow at the current sheet that is unstable due to magnetohydrodynamic instabilities. In this paper we review these recent results, and present an additional simulation with constant neutral atom background. In this case the jet is still present but with reduced intensity. Further study, e.g., including neutrals and the tilt of the solar rotation from the magnetic axis, is required before we can definitively address how the heliosheath behaves. Already we can say that this region presents remarkable dynamics, with turbulent flows, indicating that the heliosheath might be very different from what we previously thought. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809506

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The interaction of the solar wind with the Very Local Interstellar Medium is affected significantly by collisional charge exchange of interstellar neutral atomic hydrogen and protons in the heliosheath. This interaction provides an additional net momentum toward the Sun, decreasing the size of the heliospheric cavity. The interaction is complicated by time variations in the internal solar wind flow, the presence of both the interstellar and interplanetary magnetic fields, and the large mean free paths for charge exchange. Proper treatment of the problem calls for a fully six‐dimensional, time‐dependent kinetic interaction model, yet computational complexities inherent in such a model have precluded its full implementation. The role of neutral hydrogen and charge exchange has had a long history beginning with Axford et al.. Refinements in measurements and inferences of properties of the interstellar medium have narrowed the relevant parameter space, as the evolving power of computers has made more sophisticated numerical models possible. Nonetheless, fully numerical models remain out of reach. At the same time, the Voyager spacecraft continue their journey to the region where the neutral interactions are important, giving rise to the need for better and better models. While the ion populations can be approximated to first order by convected Maxwellians, neglecting non‐Maxwellian features associated with pickup, the neutral population acquires non‐negligible non‐Maxwellian features due to the large mean free paths for charge exchange. Self‐consistent models require the evaluation of the interaction of the two populations, and the models now employed differ primarily in how the neutrals are treated. These treatments broadly split into kinetic and “modified hydrodynamic” groups, the latter being based upon different assumptions of how to handle the Boltzmann collision operator. Kinetic models have typically been two‐dimensional due to limitations on computer time and/or limited in the numerical statistics associated with the simulations. The hydrodynamic‐like approaches have the advantage of allowing more realistic geometries, but are subject to the criticism that they are not “sufficiently kinetic,” raising questions about their accuracy. The history, current status, and limitations of some of these ideas and approaches provide a backdrop and motivation for further progress. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809507

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The asymmetric propagation through the solar wind of shocks from solar eruptions influences the dynamics of the outer heliosphere. In 2002, these effects — and not the crossing of the termination shock (TS) — may have been responsible for the differences in observations made by Voyager 1 (V1) at 85 AU, 34° North and Voyager 2 (V2) at ∼67 AU, 24° South. We suggest these observations stemmed from two series of solar eruptions that propagated asymmetrically in longitude and primarily to the south. At V1 this led to unusually weak magnetic fields and increased access to particles from two sources: the TS and particles accelerated at the shocks created by the second series of solar eruptions as they propagated outward, passing V2. Because V1 was farther out, these particles showed anisotropies from an interior source. We used the HAFv2 model to study the propagation of the solar events. It predicted: 1) the 1 August 2002 shock observed on V2; 2) the trends in the V2 plasma and magnetic field data in August 2002; and implied 3) an extended period of increased particle transport near V1 in 2002. We estimate that on August 1, 2002 the termination shock was at ∼ 121 AU. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809508

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

At energies below ∼300 MeV/nuc our knowledge of cosmic‐ray spectra outside the heliosphere is obscured by the energy loss that cosmic rays experience during transport through the heliosphere into the inner solar system. This paper compares measurements of secondary electron‐capture isotope abundances and cosmic‐ray spectra from ACE with a simple model of interstellar propagation and solar modulation in order to place limits on the range of interstellar spectra that are compatible with both sets of data. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809509

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The most recent data from Voyager 1 (V1) show that a second event (TS2), apparently associated with the termination shock (TS), is in progress, with spectral characteristics similar to the energetic particle increase observed from 2002.4–2003.1 (TS1). We concentrate on the pressure, composition, and anisotropy profiles of TS1. The magnetic field pressure is significantly smaller than the particle pressure perpendicular to the interplanetary magnetic field (IMF) in the 40–4000 keV range. The composition during the interplanetary shock event (ISE) observed by V1 during 1991 is drastically different from that during TS1 (C/O ∼0.2 for ISE, ∼0.02 for TS1). The dominant anisotropy during TS1 is azimuthally in the outward direction for a Parker spiral field, suggesting a source inward of the spacecraft, while the radial anisotropy is consistent with zero (−0.024 ± 0.02), implying a slow (<50 km/s) plasma flow speed. We conclude that the totality of the data is consistent with V1 being in the heliosheath during TS1. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1809510

出版商:AIP    

年代:1904

数据来源: AIP