共查询到20条相似文献，搜索用时 15 毫秒
1.
Cooper John F. Christian Eric R. Richardson John D. Wang Chi 《Earth, Moon, and Planets》2003,92(1-4):261-277
Times for accumulation of chemically significant dosages on icy surfaces of Centaur, Kuiper Belt, and Oort Cloud objects from plasma and energetic ions depend on irradiation position within or outside the heliosphere. Principal irradiation components include solar wind plasma ions, pickup ions from solar UV ionization of interstellar neutral gas, energetic ions accelerated by solar and interplanetary shocks, including the putative solar wind termination shock, and galactic cosmic ray ions from the Local Interstellar Medium (LISM). We present model flux spectra derived from spacecraft data and models for eV to GeV protons at 40 AU, a termination shock position at 85 AU, and in the LISM. Times in years to accumulate dosages ～100 eV per molecule are computed from the spectra as functions of sensible surface depth less than one centimeter at unit density.The collisional resurfacing model of Luu and Jewitt is reconsidered in thecontext of depth-dependent dosage rates from plasma, suprathermal,and higher energy protons, and global exposure, by micrometeoroiddust grain impacts, of moderately irradiated red material below athin crust of heavily irradiated neutral material. This material should be more visible on dynamically `cold’ objects in the ～40 AU region. 相似文献
2.
H.J. Fahr 《Astrophysics and Space Science》2000,274(1-2):35-54
Since about three decades now it is clearly recognized that the interaction of the solar system with the ambient interstellar
medium flow mainly is characterized by its hydrodynamic nature invoking structures like the inner shock, the heliopause and
the outer shock with plasma sheath regions in between. After the pioneering works by Eugene Parker and Vladimir Baranov the
main outlines of this interaction scenario were established, while some discussion on location and geometry of these structures
is still going on till now. Fundamentally new aspects of this interaction problem have meanwhile appeared calling for new
and more consistent calculations. The revisions of the earlier interaction concept starts with the neutral LISM gas component
passing through the solar system. At the occasion of ionizations of this component a medium-energetic plasma component in
form of keV-energetic pick-up ions is created. This component changes the distant solar wind properties by mass-, momentum-,
and energy-loading, by wave generation and lowering the solar wind Mach numbers. Furthermore pick-up ions serve as a seed
population for a high-energetic plasma population with energies between 10 and 100 MeV/nuc called anomalous cosmic rays. This
latter component by means of its pressure gradient not only modifies the solar wind flow but also modulates its termination
shock. In this paper it is shown how the main features of the enlarged interaction scenario change if the above mentioned
multifluid character of the scenario is taken into account. While now we present a `multicolour vision' of the interacting
heliosphere, it should never be forgotten that these modern views only were possible due to the fundamental `black-and-white
vision' already presented by Baranov in the seventieths.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Charge‐transfer is the main process linking neutrals and charged particles in the interaction regions of neutral (or partly ionized) gas with a plasma. In this paper we illustrate the importance of charge‐transfer with respect to the dynamics and the structure of neutral gas‐plasma interfaces. We consider the following phenomena: (1) the heliospheric interface ‐ region where the solar wind plasma interacts with the partly‐ionized local interstellar medium (LISM) and (2) neutral interstellar clouds embedded in a hot, tenuous plasma such as the million degree gas that fills the so‐called “Local Bubble”. In (1), we discuss several effects in the outer heliosphere caused by charge exchange of interstellar neutral atoms and plasma protons. In (2) we describe the role of charge exchange in the formation of a transition region between the cloud and the surrounding plasma based on a two‐component model of the cloud‐plasma interaction. In the model the cloud consists of relatively cold and dense atomic hydrogen gas, surrounded by hot, low density, fully ionized plasma. We discuss the structure of the cloud‐plasma interface and the effect of charge exchange on the lifetime of interstellar clouds. Charge transfer between neutral atoms and minor ions in the plasma produces X‐ray emission. Assuming standard abundances of minor ions in the hot gas surrounding the cold interstellar cloud, we estimate the X‐ray emissivity consecutive to the charge transfer reactions. Our model shows that the charge‐transfer X‐ray emission from the neutral cloud‐plasma interface may be comparable to the diffuse thermal X‐ray emission from the million degree gas cavity itself (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
Martin A. Lee 《Astrophysics and Space Science》1998,264(1-4):497-508
The interaction of interstellar pickup ions with the solar wind termination shock is reviewed and assessed. The pickup ions
mass and momentum load the wind and increase its pressure, effects which decrease the strength of the shock and its distance
from the Sun. The pickup hydrogen may contribute substantially to the "reflected" ion population, which should provide most
of the dissipation at the supercritical quasi-perpendicular shock. A fraction of the pickup ions impinging on the shock is
"injected" into the process of diffusive shock acceleration to form the anomalous cosmic ray component. An injection mechanism
which accounts for the apparent absence of solar wind ions in the anomalous component is "shock surfing", in which pickup
ions which approach the shock slowly may be trapped between the upstream Lorentz force and the shock potential and accelerated
in the motional electric field beyond the energy threshold for diffusive shock acceleration. However, the simplest interpretation
of shock surfing would favor less massive pickup ion species, in contradiction with Voyager observations of anomalous component
composition. A possible extension of the shock surfing mechanism is considered, as well as other injection mechanisms. Finally,
the pressure of the anomalous component may modify the structure of the termination shock, which in turn may influence injection
rates.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
5.
Astronomy Letters - The acceleration of anomalous cosmic rays (ACRs) at the heliospheric termination shock and their influence on the shock structure and location are analyzed in terms of a... 相似文献
6.
The termination shock at the heliospheric boundary is simulated in terms of a two-layer turbulent medium for which the average
radial component of solar wind velocity is nonzero inside the heliosphere and zero for external magnetic inhomogeneities.
Galactic cosmic rays (GCRs) are scattered more strongly in the solar wind than in the interstellar medium. A boundary value
problem for density is defined to describe GCR propagation in the given two-layer medium. The exact analytical solution of
it is derived. The phase density and GCR fluxes in the whole range of the particle energies, as well as the degree of anisotropy
of high-energy GCRs, are determined. The qualitative agreement of theoretical calculations and observed GCR distributions
is obtained. In particular, in the region near the termination shock, an increase in the high-energy particle density and
a decrease in the low-energy particle density are observed. 相似文献
7.
Pter Kirly 《Journal of Astrophysics and Astronomy》2000,21(3-4):431-437
The heliosphere is the region filled with magnetized plasma of mainly solar origin. It extends from the solar corona to well
beyond the planets, and is separated from the interstellar medium by the heliopause. The latter is embedded in a complex and
still unexplored boundary region. The characteristics of heliospheric plasma, fields, and energetic particles depend on highly
variable internal boundary conditions, and also on quasi-stationary external ones. Both galactic cosmic rays and energetic
particles of solar and heliospheric origin are subject to intensity variations over individual solar cycles and also from
cycle to cycle. Particle propagation is controlled by spatially and temporally varying interplanetary magnetic fields, frozen
into the solar wind. An overview is presented of the main heliospheric components and processes, and also of the relevant
missions and data sets. Particular attention is given to flux variations over the last few solar cycles, and to extrapolated
effects on the terrestrial environment. 相似文献
8.
This paper deals with the modeling of the interstellar hydrogen atoms (H atoms) distribution in the heliosphere. We study
influence of the heliospheric interface, that is the region of the interaction between solar wind and local interstellar medium,
on the distribution of the hydrogen atoms in vicinity of the Sun. The distribution of Hatoms obtained in the frame of the
self-consistent kinetic-gasdynamicmodel of the heliospheric interface is compared with a simplified model which assumes Maxwellian
distribution of H atoms at the termination shock and is called often as “hot” model. This comparison shows that the distribution
of H atoms is significantly affected by the heliospheric interface not only at large heliocentric distances, but also in vicinity
of the Sun at ∼1–5 AU. Hence, for analysis of experimental data connected with direct or undirect measurements of the interstellar
atoms one necessarily needs to take into account effects of the heliospheric interface. In this paper we propose a new model
that is relatively simple but takes into account all major effects of the heliospheric interface. This model can be applied
for analysis of backscattered La-alpha radiation data obtained on board of different spacecraft. 相似文献
9.
We numerically analyze a magnetohydrodynamic, steady-state model for the interaction of a spherically symmetric solar wind with a three-component local interstellar medium (LISM), which is composed of plasma, hydrogen atoms, and a magnetic field. The magnetic field is assumed to be parallel to the velocity in the LISM. In this case, the model is axisymmetric. We study the effects of magnetic field on the plasma-flow geometry and on the distribution of hydrogen-atom parameters. In particular, we show that the presence of hydrogen atoms does not affect the qualitative change in the shape of the bow shock, the heliopause, and the solar-wind shock with increasing strength of the interstellar magnetic field. The presence of a magnetic field in the LISM can strongly affect the parameters of the energetic hydrogen atoms originated in the solar wind, although its effect on the “hydrogen wall” observed with the GHRS instrument onboard the HST spacecraft (Linsky and Wood 1996) is marginal. 相似文献
10.
J.G Luhmann 《Planetary and Space Science》2003,51(6):387-392
The MIMI CHEMS Instrument on the Cassini Orbiter detected Jovian pickup ions almost an AU upstream of Jupiter during the 2001 flyby. The clue to their planetary origin is the presence of singly ionized sulfur ions in quantities exceeding those expected from the interstellar gas entering the heliosphere (Nature 415 (2002) 994). Earlier modeling of the extended Jovian neutral gas disk suggested how the combination of the orbiting, localized Jovian source and interplanetary ionization processes should combine to produce a distinctive reservoir for heliospheric pickup ion production, different from its interstellar gas counterpart. Here the expected characteristics of pickup ions from the Jovian source are considered using a simplified model. The results provide an idea of the signatures in physical and phase space that reflect both the initial velocities and directionalities of the parent neutral population. Long-term measurements can easily test for these attributes given sufficient spatial and ion energy coverage. 相似文献
11.
As any comet nears the Sun, gas sublimes from the nucleus taking dust with it. Jupiter family comets are no exception. The neutral gas becomes ionized, and the interaction of a comet with the solar wind starts with ion pickup. This key process is also important in other solar system contexts wherever neutral particles become ionized and injected into a flowing plasma such as at Mars, Venus, Io, Titan and interstellar neutrals in the solar wind. At comets, ion pickup removes momentum and energy from the solar wind and puts it into cometary particles, which are then thermalised via plasma waves. Here we review what comets have shown us about how this process operates, and briefly look at how this can be applied in other contexts. We review the processes of pitch angle and energy scattering of the pickup ions, and the boundaries and regions in the comet-solar wind interaction. We use in-situ measurements from the four comets visited to date by spacecraft carrying plasma instrumentation: 21P/Giacobini-Zinner, 1P/Halley, 26P/Grigg-Skjellerup and 19P/Borrelly, to illustrate the process in action. While, of these, comet Halley is not a Jupiter class comet, it has told us the most about cometary plasma environments. The other comets, which are from the Jupiter family, give an interesting comparison as they have lower gas production rates and less-developed interactions. We examine the prospects for Rosetta at comet Churyumov-Gerasimenko, another Jupiter family comet where a wide range of gas production rates will be studied. 相似文献
12.
Interplanetary pick-up ions originate from ionizations of neutral interstellar atoms in the heliosphere. Over the past periods
it was generally expected that after pick-up by the frozen-in solar wind magnetic fields these ions quickly isotropize in
velocity space by strong pitch- angle scattering, they do, however, not assimilate to the ambient solar wind ions. Meanwhile
careful investigations of pick-up ion data obtained with the plasma analyzers on AMPTE and ULYSSES could clearly reveal that,
especially at periods of flow-aligned fields, noticeably anisotropic distributions must prevail. To better understand the
evolutionary tracks of pick-up ions in interplanetary phase-space we carried out an injection study which takes into account
all relevant convection and diffusion processes, i.e. describing pitch angle scattering, adiabatic cooling, drifts and energy
diffusion. As demonstrated here particles injected at 1 AU establish a distribution function with substantial anisotropies
up to distances beyond 6 AU. Only under the action of fairly strong isotropic turbulence levels a trend towards isotropy can
be recognized. The bulk velocity of the injected pick-up ions turns out to be remarkably smaller than the solar wind velocity.
It also is obvious that pick-ups are strongly spread out from that solar wind plasma parcel into which they were originally
implanted. As one consequence it must be concluded that the derivation of interstellar He gas parameters, using He pick-up
ion flux data, require appreciable caution. Due to anisotropic spatial diffusion the location of the LISM helium cone axis,
i.e. the LISM wind vector, and the LISM helium temperature are hidden in the associated He+pick-up ion flux patterns.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
It is well known that both the galactic and anomalous cosmic rays show positive intensity gradients in the outer heliosphere which are connected with corresponding pressure gradients. Due to an efficient dynamical coupling between the solar wind plasma and these highly energetic media by means of convected MHD turbulences, there exists a mutual interaction between these media. As one consequence of this scenario the enforced pressure gradients influence the distant solar wind expansion. Here we concentrate in our theoretical study on the interaction of the solar wind only with the anomalous cosmic-ray component. We use the standard two-fluid model in which the cosmic-ray fluid modifies the solar wind flow via the cosmic-ray pressure gradient. Then we derive numerical solutions in the following steps: first we calculate an aspherical pressure distribution for the anomalous cosmic rays, describing their diffusion in an unperturbed radial solar wind. Second, we then consider the perturbation of the solar wind flow due to these induced anomalous cosmic-ray pressure gradients. Within this context we especially take account of the action of a non-spherical geometry of the heliospheric shock which may lead to pronounced upwinddownwind asymmetries in the pressures and thereby in the resulting solar wind flows. As we can show in our model, which fits the available observational data, radial decelerations of the distant solar wind by between 5 to 11% are to be expected, however, the deviations of the bulk solar wind flow from the radialdirections are only slightly pronounced. 相似文献
14.
We derive equations for the multipole moments of the distribution function of Galactic cosmic rays with energies 1–20 TeV that experience random scattering by turbulence with a power-law spectrum. We take into account the irregularity of the local interstellar medium (LISM) in the neighborhood of the solar system due to the presence of interstellar clouds, the interstellar wind flow around the heliomagnetosphere, and preceding supernova explosions in the local superbubble. The amplitudes of the second and third harmonics of the cosmic-ray distribution function are expressed in terms of the amplitude of the first harmonic without assuming them to be small compared to the first harmonic. Reconciling their values in magnitude and phase with the observed values requires a significant LISM irregularity, which is consistent with other observational data on the LISM structure. Our model is consistent with the assumption that supernova remnants in the Galactic disk located at distances from the Solar system much larger than the particle transport mean free path are the sources of the particles under consideration. 相似文献
15.
The partially ionized local interstellar medium, before interacting with the heliospheric plasma on the upwind side, most probably undergoes an outer bow shock. After conversion into a sub-magnetosonic plasma flow, it then passes around the heliopause. While the ionized component at the bow shock undergoes abrupt changes of its dynamical properties, the neutral component first continues to flow downstream of the shock with its unperturbed properties. Consequently, the two fluids immediately after the bow shock passage are out of dynamical and thermodynamical equilibrium. Neutral atoms move with a higher bulk velocity and are cooler than the ions. Due to intensive local charge-exchange couplings between neutral atoms and protons these different properties tend to mix each other via momentum and energy exchanges. It turns out that the charge exchange period is shorter than the relaxation period. Hence the distribution functions cannot relax rapidly enough to their highest-entropy forms, i.e. shifted Maxwellians. Here we study the transport processes of newly injected ions in velocity space considering their quasi-linear and non-linear interactions with the ambient MHD turbulence in the plasma interface region. For that purpose we study the turbulence levels in the helio-sheath plasma region. We calculate the expected deviations from equilibrium distributions of ionic and atomic species in the outer heliospheric interface. It clearly turns out from these studies that non-relaxated non-equilibrium distribution functions have to be expected both for O-/H-ions and atoms in this region. This has inherent implications for the diagnostics of interstellar parameters, deduced from observations made further inwards from the interface region. 相似文献
16.
We consider a stationary model of the propagation of galactic cosmic rays (GCR) in the heliosphere and adjacent interstellar space. The heliosphere is assumed to be a two-layer medium consisting of two adjacent regions that are spherically symmetric relative to the sun. The solar wind velocity is supersonic in the inner heliosphere bounded by the standing termination shock, and this velocity is subsonic in the outer heliosphere bounded by the heliosheath. The GCR scattering in these regions is due to different factors characterized by relevant diffusion coefficients. The solar wind velocity is assumed to be zero in the interstellar medium, where the scattering becomes weaker. No particle sources are presumed to exist at the boundaries between the layers. An exact analytical solution of the corresponding mathematical problem can be obtained without essential difficulties, although it is extremely cumbersome. Analytical expressions for the GCR spectra of particles with very high energies (>2500 MeV) and very low energies (<1400 MeV) are obtained for each region of particle propagation. The low-energy particle distribution corresponds to the data obtained by the Voyager spacecraft. It is shown that the low-energy particle density continuously increases from the sun toward the heliospheric boundary, regardless of the scattering mode in the inner and outer parts of the heliosphere. 相似文献
17.
S. V. Chalov 《Astrophysics and Space Science》2018,363(6):124
The process of deceleration of the solar wind downstream of the termination shock is studied on the basis of a one-dimensional multi-component model. It is assumed that the solar wind consists of thermal protons, electrons and interstellar pickup protons. The protons interact with interstellar hydrogen atoms by charge-exchange. Two cases are considered. In the first one, the charge-exchange cross-section for thermal protons and hydrogen atoms is the same as for pickup protons and atoms. Under this condition, there is a strong dependence of the solar wind velocity on the downstream temperature of pickup protons. When the proton temperature is close to 10 keV, the change in the velocity with the distance from the termination shock is similar to that measured on the Voyager 1 spacecraft: linear velocity decrease is accompanied by an extended transition region with near-zero velocity. However, with a more careful approach to the choice of the charge-exchange cross-section, the situation changes dramatically. The strong dependence of the solar wind speed on the pickup proton temperature disappears and the transition region in the heliosheath disappears as well, at least at reasonable distances from the TS. 相似文献
18.
S.V. Chalov 《Astrophysics and Space Science》2000,274(1-2):25-33
It is generally accepted that pick-up ions act as a seed population for anomalous cosmic rays originating at the solar wind
termination shock. We believe that the ion pre-acceleration process operating in the heliosphere up to the termination shock
can be very important to inject the ions into the shock acceleration process. The pick-up ions pre-accelerated by solar wind
turbulences have already a pronounced high energy tail when they reach the shock. Some fraction of these ions can experience
further acceleration up to energies of anomalous cosmic rays by means of shock drift and diffusive acceleration. In the present
paper the shock drift acceleration of pick-up ions suffering multiple reflection due to abrupt changes in both the strength
and direction of the magnetic field through the shock is considered. The reflection process operates for high velocity particles
different from the reflection by the electric cross-shock potential. During the first reflection the mean kinetic energy of
pick-up ions increases by approximately a factor of 10. Reflected particles have highly anisotropic velocity distribution.
Subsequent excursion of the particles in the turbulent upstream flow leads to diffusion in pitch-angle space and, as a result,
the particles can return to the shock again suffering, thus, multiple encounters. In order to describe the motion of particles
in the upstream and down streamparts of the flow we solve the Fokker-Plank transport equation for anisotropic velocity distribution
function.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
We discuss the present status of our understanding of the transport and acceleration of anomalous cosmic rays and the transport
of galactic and CIR-accelerated particles in the heliosphere. Currently, two- and three-dimensional numerical codes can accurately
model many of the observed phenomena – with the major current uncertainties being the values of the parameters such as the
diffusion coefficients and the effects of the poorly understood structure beyond the termination shock. We illustrate the
nature of the phenomena by discussing in detail the response of energetic particles to co-rotating interaction regions, the
acceleration of singly- and multiply-charged anomalous cosmic rays, and the effects of galactic cosmic rays on the structure
of the solar wind and its termination shock.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
The initially supersonic flow of the solar wind passes through a magnetic shock front where its velocity is supposed to be reduced to subsonic values. The location of this shock front is primarily determined by the energy density of the external interstellar magnetic field and the momentum density of the solar wind plasma. Interstellar hydrogen penetrating into the heliosphere undergoes charge exchange processes with the solar wind protons and ionization processes by the solar EUV radiation. This results in an extraction of momentum from the solar wind plasma. Changes of the geometry and the location of the shock front due to this interaction are studied in detail and it is shown that the distance of the magnetic shock front from the Sun decreases from 200 to 80 AU for an increase of the interstellar hydrogen density from 0.1 to 1.0 cm−3. The geometry of the shock front is essentially spherical with a pronounced embayment in the direction opposite to the approach of interstellar matter which depends very much on the temperature of the interstellar gas. Due to the energy loss by the interaction with neutral matter the solar wind plasma reduces its velocity with increasing distance from the Sun. This modifies Parker's solution of a constant solar wind velocity. 相似文献