摘要:

We study the jumps in the properties of pickup protons across shocks in the distant heliosphere. MHD theory and observational data are used to develop an empirical model for the pickup proton shocks. Three interplanetary shocks identified from high-resolution (192-sec average) plasma and magnetic field data observed from Voyager 2 between 34 and 43 AU are used in this study, these shocks are treated as perpendicular MHD shocks. The solar wind protons and the pickup protons are treated as two distinguished proton species, the model calculates the jumps in temperature for each species separately. The variation of the pickup proton temperature across the shock is very close to the adiabatic relation thatTIis proportional toB. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58825

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Co-rotating interaction regions (CIRs) and their associated shock pairs are dominant structures in the solar wind between the heliocentric distances of 2 and 8 AU. At larger heliocentric distances, these structures undergo a qualitative change. Shocks decay to a point where they are often difficult to detect, and may have little influence on the dynamics of the solar wind. Interaction regions spread and merge, though they appear to retain their identity to surprisingly large distances from the Sun. Solar wind and IMF data from the Pioneer 10, Pioneer 11, and Voyager 2 spacecraft were used to conduct a comprehensive survey of CIRs and their successors between heliocentric distances of 1 and 55 AU over the last two solar cycles. The structure of the solar wind varied in a consistent fashion with heliocentric distances. Similar structures were observed at similar heliocentric distances by all three spacecraft during different portions of the solar cycle. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58727

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We present observations from Voyager 2 of CIRs and merged CIRs in the outer heliosphere. The rather simple characteristics of the CIR-associated changes in plasma, magnetic field, and particles become more complex as observations are made at greater and greater distances. Picked-up ions from charge exchange undoubtedly play an important role in the structure, but the full details are not yet understood. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58728

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Based on Voyager 2 observations, a numerical model of the heliosphere, which includes the mutual interaction of the interstellar medium, solar wind plasma, and interstellar hydrogen, is employed to speculate on the possible crossing of the termination shock by the Voyager spacecraft. The multiple crossings caused by large-scale solar wind fluctuations are studied quantitatively. In the event that Voyager 2 reaches the interstellar medium, the possibility of detecting interstellar ions with the MIT plasma experiment instrument (PLS) is discussed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58729

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Heliospheric energetic hydrogen atoms below 100 keV have been detected at 1 AU with a strong anisotropy toward the heliotail by the instrument CELIAS on SOHO (1). These energetic neutrals are seen as results of anomalous cosmic-ray (ACR) protons transcharging with the local interstellar medium (LISM) in the outer heliosphere. The resulting neutrals then travel on ballistic trajectories, unaffected by the interplanetary magnetic field (IMF), to the inner heliosphere. In the vicinity of the sun, a fraction of these energetic neutrals are ionized again by photoionisation or collision with the solar wind protons and electrons. These energetic protons will then travel along the IMF and contribute to the quiet-time interplanetary energetic proton flux in the energy range below about 100 keV. This contribution should be proportional to the integrated energetic hydrogen atom flux in the heliosphere and therefore the production of energetic neutral hydrogen at the edge of the heliosphere. We estimate the flux upper limit of these energetic protons of heliospheric origin and discuss the possibilities of their observation. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58730

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

With very few exceptions, almost all models describing the interaction of the solar wind with the local interstellar medium (LISM) are essentially steady-state. However, the solar wind ram pressure varies on an 11 year solar cycle period, and the solar wind is traversed by numerous shock waves. It has long been recognized that variation in the solar wind ram pressure can move the termination shock inward and outward on a complementary time scale. We describe here the variation in global heliospheric structure in response to a solar cycle variation in the ram pressure. The models include interstellar neutral hydrogen self-consistently. Also described is the role of ion-neutral friction in driving a “Rayleigh-Taylor-like” instability in the vicinity of the heliospheric nose. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58660

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The heliospheric termination shock must exhibit asymmetry in its shape, due in part to internal latitude variations in the solar wind, and in part to the special directions defined by the external interstellar flow and/or the galactic magnetic field. This asymmetry shows up naturally in numerical simulations of the interaction between the heliosphere and local interstellar medium. However, to date only one analytical treatment of the theory has appeared (Barnes, 1998), which discussed the modification of the shock shape due to solar wind latitude variations in the presence of spherically symmetric outer boundary conditions. In the present report, we discuss an extension and generalization of this theory to an axially symmetric gasdynamic system, in which departure from spherical symmetry may be due either to internal solar wind variations or to the directional properties of the external interstellar medium. It is shown that for steady flow the post-shock region is characterized by an infinite set of quantities that are conserved along streamlines; among these invariants are the stagnation pressure and a quantity closely related to vorticity. Moreover, for a given latitude profile of the (supersonic) solar wind, the geometry of the termination shock uniquely determines the value of these invariants at the points where the streamlines emerge from the shock. In the case of flow into a static interstellar medium for which the appropriate boundary condition is that the stagnation pressure is the same for all streamlines, it can be shown that the location and shape of the termination shock, together with the entire heliosheath flow, are completely determined by the external pressure plus the internal solar wind parameters. However, for even a slightly non-static interstellar flow, or for anisotropy in exterior conditions from any other cause, such as the galactic magnetic field, exterior interstellar plus interior solar-wind conditionsdo not uniquely determinethe heliosheath flow field or the shape of the termination shock. A complete solution requires specification of additional conditions, such as the run of dynamic pressure across the distant wake, or the requirement that the heliosheath flow be vorticity-free. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58826

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Influence of cosmic ray pressure and kinetic stream instability on space plasma dynamics and magnetic structure in the Heliosphere are considered as additional effects to well known effects of solar wind interaction with interstellar medium. It is shown that in the outer Heliosphere are important dynamics effects of galactic cosmic ray pressure on solar wind and interplanetary shock wave propagation as well as on the formation of terminal shock wave of the Heliosphere and subsonic region between Heliosphere and interstellar medium. We determined the behavior of solar wind’s Mach number with taking into account cosmic ray nonlinear processes and show that the transition from supersonic to subsonic region can be gradual or shock wave transition in dependence of cosmic ray pressure gradient in the outer Heliosphere. Investigation of cosmic ray convection-diffusion and drift anisotropies shows that kinetic stream instability effects must be especially important on distances more than 40–60 AU from the Sun: formation of great anisotropy of galactic cosmic rays in about spiral interplanetary magnetic field leads to the Alfven turbulence generation by non isotropic cosmic ray fluxes; generated Alfven turbulence influences on cosmic ray propagation, increases the cosmic ray modulation, decreases the cosmic ray anisotropy and increases the cosmic ray pressure gradient in the outer Heliosphere (the last is also important for terminal shock wave formation). The self-consistent problem is formulated and considered for some noncomplicated case. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58731

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

An overview is given of observations of plasma waves in the heliosphere. To illustrate the range of phenomena involved, we discuss plasma waves in the solar wind and in the planetary magnetospheres as well as heliospheric radio emissions related to the boundary of the Solar System. Intensity of these radio emissions at 2 to 3 kHz detected by the Voyager plasma wave instrument in the outer heliosphere can be explained provided that the electron beams generating Langmuir waves exist in the post-shock plasma due to secondary shocks in the compressed solar wind beyond the termination shock. The field strengths of Langmuir waves required to generate the second harmonic emissions are 50–100 &mgr;V m−1. Alternatively, the emissions are generated in the vicinity of the heliopause. The Voyager 1 and 2 are proceeding toward a likely source region for Langmuir wave and these waves may be observed in situ in thenearfuture. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58732

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We consider the dispersion relation for waves in a cosmic ray modified plasma for the case when the background flow consists of a cosmic ray pressure balance structure, in whichpg+pc=const.wherepcandpgdenote the cosmic ray and thermal gas pressures respectively. The stability analysis shows that waves at an arbitrary point in the flow may be driven unstable if the cosmic ray pressure gradient is sufficiently large to overcome wave damping due to cosmic ray diffusion. Following S. Chalov’s work (1) we analyze the instability of a cosmic ray modified tangential discontinuity. Chalov considered the case wherepc=const.throughout the structure, whereas in our analysis bothpcandpgvary in the direction perpendicular to the surface separating two flow regions. Predictions of the linear theory are compared to numerical simulations. Applications to the stability of the heliopause are discussed. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58827

出版商:AIP    

年代:1999

数据来源: AIP