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1.
Vladislav V. Izmodenov 《Astrophysics and Space Science》2000,274(1-2):55-69
During 30 years, a big theoretical effort to understand the physical processes in the heliospheric interface has followed
the pioneer papers by Parker (1961) and Baranov et al. (1971). The heliospheric interface is a shell formed by the solar wind interaction with the ionized component of the circumsolar
local interstellar medium (LISM). For fully ionized supersonic interstellar plasma two-shocks (the termination shock and the
bow shock) and a contact discontinuity (the heliopause) are formed in the solar wind/LISM interaction. However, LISM consists
of at least of three components additional to plasma: H-atoms, galactic cosmic rays and magnetic field. The interstellar atoms
that penetrate into the solar wind, are ionized there and form pickup ions. A part of the pickup ions is accelerated to high
energies of anomalous cosmic rays (ACRs). ACRs may modify the plasma flow upstream the termination shock and in the heliosheath.
In this short review I summarize current understanding of the physical and gasdynamical processes in the heliospheric interface,
outline unresolved problems and future perspectives.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
As known for a long time, interstellar wind neutral helium atoms deeply penetrate into the inner heliosphere and, when passing through the solar gravity field, form a strongly pronounced helium density cone in the downwind direction. Helium atoms are photoionized and picked-up by the solar wind magnetic field, but as pick-up ions they are not simply convected outwards with the solar wind in radial directions as assumed in earlier publications. Rather they undergo a complicated diffusion-convection process described here by an appropriate kinetic transport equation taking into account adiabatic cooling and focusing, pitch angle scattering and energy diffusion. In this paper, we solve this equation for He+pick-up ions which are injected into the solar wind mainly in the region of the helium cone. We show the resulting He+pick-up ion density profile along the orbit of the Earth in many respects differs from the density profile of the neutral helium cone: depending on solar-wind-entrained Alfvénic turbulence levels, the density maximum when looking from the Earth to the Sun is shifted towards the right side of the cone, the ratio of peak-densities to wing-densities varies and a left-to-right asymmetry of the He+-density profile is pronounced. Derivation of interstellar helium parameters from these He+-structures, such as the local interstellar medium (LISM) wind direction, LISM velocity and LISM temperature, are very much impeded. In addition, the pitch-angle spectrum of He+pick-up ions systematically becomes more anisotropic when passing from the left to the right wing of the cone structure. All effects mentioned are more strongly pronounced in high velocity solar wind compared to the low velocity solar wind. 相似文献
3.
The physical processes in the tail of the region where the solar wind interacts with a partially ionized local interstellar medium are investigated in terms of a self-consistent kinetic-gas-dynamical model. Resonant charge exchange between hydrogen atoms and plasma protons is shown to cause the contact discontinuity to disappear far from the Sun. The solar wind plasma cools down and, as a result, the parameters of the plasma and hydrogen atoms approach the corresponding parameters of the unperturbed interstellar medium at large heliocentric distances. 相似文献
4.
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
5.
It is well known that the neutral component of the local interstellar medium can effectively pass through the plasma interface ahead of the solar system and can penetrate deeply into the inner heliosphere. Here we present a newly-developed theoretical approach to describe the distribution function of LISM neutral hydrogen in the heliosphere, also taking into account time-dependent solar and interstellar boundary conditions. For this purpose we start from a Boltzmann-Vlasov equation, Fourier-transformed with respect to space and time coordinates, in connection with correspondingly transformed solar radiation forces and ionization rates, and then arrive at semi-analytic solutions for the transformed hydrogen velocity distribution function. As interstellar boundary conditions we allow for very general, non-Maxwellian and time-dependent distribution functions to account for the case that some LISM turbulence patterns or nonlinear wave-like shock structures pass over the solar system. We consider this theoretical approach to be an ideal instrument for the synoptic interpretation of huge data samples on interplanetary Ly- resonance glow intensities registered from different celestial directions over extended periods of time. In addition we feel that the theoretical approach presented here, when applied to interplanetary resonance glow data, may permit the detection of genuine fluctuations in the local interstellar medium. 相似文献
6.
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
7.
The model of the solar wind interaction with interstellar medium suggested by Baranovet al. (1970) is developed. In this model (TSM) the presence of two shock waves is assumed, through which the solar wind and interstellar gas pass, the latter moving relative to the Sun at supersonic speed (20 km s–1).The distance between shocks was considered earlier (Baranovet al., 1970; Baranov and Krasnobaev, 1971) to be small compared with their distance from the Sun, due to the hypersonic character of the flow. The structure of the subsonic flow portion may not be taken into account.In the present paper the distribution of the gas parameters in the region between shocks is calculated which, in particular, allows us to estimate the possibility of its experimental detection, observing radio-scintillation on interstellar irregularities (Baranovet al., 1975).The possible influence on the model of galactic hydrogen neutral atoms penetrating into interplanetary medium is estimated. 相似文献
8.
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
9.
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
10.
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
11.
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
12.
It has previously been suggested that the solar wind might terminate at distances of 5 AU to 20 AU from the Sun, and that the solar wind might be drastically slowed down by charge exchange and photoionization of interstellar hydrogen atoms which approach the Sun. However, recent satellite measurements of resonantly scattered Lyman alpha radiation, together with pulsar dispersion and Faraday rotation measures, imply very small values for the interstellar hydrogen density (0.05 cm−3) and magnetic field strength (3 μG). As a result, the solar wind is not expected to be slowed down by more than about 30% inside the termination distance, which is expected to be about 100 AU. 相似文献
13.
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
14.
The solution of the classical problem of two-dimensional magnetohydrodynamic (MHD) interaction between two shocks (the angle between the interacting shocks and the slope of the magnetic field are arbitrary) obtained by Pushkar' (1995) is applied to the problem of interaction between interplanetary shocks and the solar wind termination shock (TS). The self-consistent kinetic-gasdynamic model of solar wind interaction with the supersonic flow of a three-component (electrons, protons, and hydrogen atoms) interstellar medium developed for the axisymmetric, steady-state case by Baranov and Malama (1993) is used as the stationary background against which the physical phenomenon under consideration takes place. The main physical process in this model is the resonant charge exchange between protons and hydrogen atoms. This paper is a natural continuation of our previous papers (Baranov et al. 1996a, 1996b). However, whereas attention in these papers was focused on the TS interaction with an interplanetary forward shock moving away from the Sun, here we consider the TS interaction with an interplanetary reverse shock (RS) moving toward the Sun with a velocity lower than the solar-wind velocity. We show that the TS-RS interaction can give rise to a new TS' that moves toward the Sun, i.e., toward Voyager 1 and Voyager 2. This phenomenon may be responsible for the unexpected suggestion made by some of the scientists that Voyager 1 already crossed TS in the past year. This conclusion was drawn from the interpretation of the intensity, energy spectra, and angular distributions of ions in the energy range from 10 keV to 40 MeV measured from this spacecraft. Our results show that Voyager 1 could cross TS' rather than TS. 相似文献
15.
16.
Structure of the region of solar wind—Interstellar medium interaction and its influence on H atoms penetrating the solar wind 总被引：1，自引：0，他引：1
The structure of the region of interaction between the solar wind and the interstellar medium in the two-shocks model (TSM), first suggested by Baranovet al. (1970), is numerically calculated.For this problem our model is true only for charged particles of the interstellar medium interacting with the solar wind, since the free paths of neutral particles are very long and any hydrodynamical approximation would be incorrect.The shapes of the outer and inner shocks, the shape of the contact surface and the distribution of the parameters inside the interaction region are calculated, and are universal and correct for other astrophysical applications such as interstellar bubbles (Weaveret al., 1977), the stellar wind flow around a globule (Dyson, 1975), the interaction of stellar winds in binaries (Prilutzky and Usov, 1976), and so on.The problem of the effect of the charge exchange of H atoms with interstellar gas protons decelerated by an outer shock on H atoms penetrating the solar system is considered using the calculated results (Wallis, 1975). This effect is shown to influence essentially the estimate of H-atom concentration in the interstellar medium based on theL
-scattering data. 相似文献
17.
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
18.
We numerically simulate the evolution of the plane two-dimensional deformations of a contact discontinuity that is impulsively accelerated by a shock wave. We take into account the effects of radiative cooling and perturbation scale lengths on the dynamics and shape of the forming density inhomogeneities. For moderately intense shocks in a stellar wind and for strong shocks from a supernova, we show that the radiative cooling processes do not affect significantly the growth rate of the initial perturbations and the total mass of the forming condensations. However, the density of the matter compressed by the transmitted shock wave increases dramatically. At the same time, the contribution from long-wavelength perturbations to the deformation of the contact surface decreases significantly. In the case of shock propagation from a supernova, the initial conditions have been found to be a factor that can affect the morphology of the shocked interstellar medium. 相似文献
19.
A transient flow system containing several streams and shocks associated with the Bastille Day 2000 solar event was observed
by the WIND and ACE spacecraft at 1 AU. Voyager 2 (V2) at 63 AU observed this flow system after it moved through the interplanetary medium and into the distant heliosphere,
where the interstellar pickup protons strongly influence the MHD structures and flow dynamics. We discuss the Voyager 2 magnetic and plasma observations of this event. Increases in the magnetic field strength B, density N, temperature T and
speed V were observed at the front of a stream at V2, consistent with presence of a shock related to the Bastille Day shock
at 1 AU. However, the jumps occurred in a 16.9-hour data gap, so that the shock was not observed directly, and the properties
of the candidate shock cannot be determined precisely. The candidate shock was followed by a merged interaction region (MIR)
that moved past V2 for at least 10 days. The first part of this MIR contains a structure that might be a magnetic cloud. Just
ahead of the shock there was an abrupt increase in density associated with a decrease in temperature such that the solar wind
thermal pressure was constant across it. Just behind the shock there was an abrupt decrease in density associated with a net
increase in magnetic field strength. This appears to be a pressure balanced structure in which the interstellar pickup protons
make a significant contribution. 相似文献
20.
Ü.D. Göker 《New Astronomy》2012,17(2):130-136
A Lagrangian Remap (LareXd) Code is employed to investigate the shock wave formation in the current sheet of a solar coronal magnetic loop and its effect on the magnetic reconnection. We constructed the slow shock structure in the presence of viscosity and heat conduction parallel and perpendicular to the magnetic field and pairs of slow shocks propagate away from the central current sheet, the so-called diffusion region. Significant jumps in plasma density, pressure, velocity and magnetic field occur across the main shock while the temperature appears in the foreshock. In the presence of dissipative effects, the distinct jumps disappear and the shock profiles show smooth transition between the downstream and the upstream regions while the plasma density and the pressure show very narrow and a sharp decrease with time. These results can be applied to the heating of the solar corona, the structure of the magnetic reconnection and the solar wind. 相似文献