共查询到20条相似文献，搜索用时 281 毫秒
1.
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
2.
The ionization of hydrogen atoms that penetrate into the heliosphere from the interstellar medium gives rise to a peculiar population of energetic protons (interstellar pickup protons) in the solar wind. The short-wavelength Alfvènic turbulence in the outer heliosphere is entirely attributable to the source associated with the instability of the initial anisotropic pickup proton velocity distribution. The bulk of the generated turbulent energy is subsequently absorbed by the pickup protons themselves through the cyclotron-resonance particle-wave interaction, and only an insignificant fraction of this energy can be transferred to the solar wind protons and heat them up. 相似文献
3.
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
4.
《Planetary and Space Science》1987,35(11):1359-1366
The Low Energy Charged Particle (LECP) experiment on the Voyager 2 spacecraft in the outer heliosphere ( > 10 a.u.) has observed several occasions when there was a peak in the interplanetary ion spectra for ions of energies ∼ 0.5–1.0 MeV. Such enhancements can last for several days, suggesting that at these times particles of these energies dominate the low energy cosmic population in this region of the heliosphere. Two specific cases are discussed. The enhancements seem to be associated with the passage of transient interplanetary shock events, with the ion anisotropies generally showing outflow. The most straight-forward explanation for the observations seems to involve only a propagation effect of ions from the inner to the outer solar system. This conclusion is supported by simple modeling of the propagation of an event observed at 1 a.u. to the spacecraft at ∼ 12 a.u. 相似文献
5.
Zeldovich M. A. Veselovsky I. S. Dmitriev A. V. Logachev Yu. I. 《Solar System Research》2003,37(5):421-426
Quite an unusual behavior of the low-energy ion fluxes measured with the LECP and CRS instruments onboard Voyager 1, which is located in the outer heliosphere at a distance of about 90 AU, has been observed since July 2002 until recently (February 2003). This behavior can be interpreted as a possible manifestation of a combination of the global heliospheric disturbance produced by solar activity and the precursor of the outer heliosphere with its termination shock. The extremely large variability of the enhanced ion fluxes since the second half of 2002 in several energy channels from 0.5 to several MeV/nucleon is presumed to be associated with the sources of their acceleration near the termination shock. The simultaneous increase in the flux of protons with energies above 70 MeV may result from the easier penetration of Galactic cosmic rays because of the reduction in modulation at the declining phase in the current solar cycle 23 after the maximum in 2000 and from an admixture of the anomalous component accelerated at the termination shock. 相似文献
6.
7.
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
8.
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
9.
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
10.
The relative motion of the solar system with respect to the ambient interstellar medium is known to form a plasma interface region where the subsonic interstellar and solar wind plasma flows adapt to a pressure equilibrium surface, called the heliopause. Inside this discontinuity surface the solar plasma is deflected from the upwind to the downwind side, finally escaping from the solar system along a heliospheric tail. Due to continuous charge exchange interactions with interstellar H atoms entering from the tailward flanks of the heliopause tail plasma, originating from shocked solar wind, changes its thermodynamic character by cooling and deceleration while passing along the tail to larger downstream distances. Here we describe this charge-exchange-induced modification of the tail plasma up to a final assimilation into the interstellar plasma. On the other hand neutral H atoms are produced by means of charge exchange interactions in the heliotail with velocities by which these atoms are shot back into the inner heliosphere. We calculate the velocity distribution of such H atoms entering the inner heliosphere from the downwind direction and study their contribution to the H-pick-up ion production in the downwind region. As we show in this paper, total H-pick-up ion production rates in the downwind region are dominated by ionization of such anti-tailward H atoms within the orbit of the earth. They also dominate the pick-up ion energy spectrum beyond 4keV at distances between 1 and 10AU. 相似文献
11.
We have studied the 27-day variations and their harmonics in Galactic cosmic ray (GCR) intensity, solar wind velocity, and interplanetary magnetic field (IMF) components during the recent prolonged solar minimum 23/24. The time evolution of the quasi-periodicity in these parameters connected with the Sun’s rotation reveals that the synodic period of these variations is ≈?26?–?27 days and is stable. This means that the changes in the solar wind speed and the IMF are related to the Sun’s near-equatorial regions in considering the differential rotation of the Sun. However, the solar wind parameters observed near the Earth’s orbit provide only the conditions in the limited local vicinity of the equatorial region in the heliosphere (within ±?7° in latitude). We also demonstrate that the observed period of the GCR intensity connected with the Sun’s rotation increased up to ≈?33?–?36 days in 2009. This means that the process that drives the 27-day GCR intensity variations takes place not only in the limited local surroundings of the equatorial region but in the global 3-D space of the heliosphere, covering also higher latitude regions. A relatively long period (≈?34 days) found for 2009 in the GCR intensity gives possible evidence of the onset of cycle 24 due to active regions at higher latitudes and rotating slowly because of the Sun’s differential rotation. We also discuss the effect of differential rotation on the theoretical model of the 27-day GCR intensity variations. 相似文献
12.
I. S. Veselovsky 《Astrophysics and Space Science》1982,86(1):209-213
Fast-streaming solar-wind plasma with high conductivity screens the heliosphere from the penetration of the interstellar electric and magnetic fields. The simplest model with the constant solar wind conductivity and radial velocity is considered and the boundary electrodynamic problem is solved for static external fields. The results show that screening of the external fields takes place in the heliosphere according to the exponential law. 相似文献
13.
I.G. Richardson 《Planetary and Space Science》1985,33(5):557-569
The possibility of the statistical acceleration of solar wind ions to energies above 10 keV in the vicinity of co-rotating high speed solar wind streams by scattering from hydromagnetic waves is considered. We find that this process may occur only in the compressed fast stream plasma within the interaction region between the stream interface and the trailing edge, and may account for the energetic ion enhancements observed in this region by Richardson and Zwickl (Planet. Space Sci. 32, 1179, 1984). When statistical acceleration occurs in the outer heliosphere, the accelerated ions may provide a source population for acceleration at the co-rotating reverse shock. 相似文献
14.
Robert F. Wimmer-Schweingruber Ralph McNutt Nathan A. Schwadron Priscilla C. Frisch Mike Gruntman Peter Wurz Eino Valtonen 《Experimental Astronomy》2009,24(1-3):9-46
The Sun, driving a supersonic solar wind, cuts out of the local interstellar medium a giant plasma bubble, the heliosphere. ESA, jointly with NASA, has had an important role in the development of our current understanding of the Suns immediate neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of interstellar matter in the heliosphere. Voyager 1 has recently encountered the innermost boundary of this plasma bubble, the termination shock, and is returning exciting yet puzzling data of this remote region. The next logical step is to leave the heliosphere and to thereby map out in unprecedented detail the structure of the outer heliosphere and its boundaries, the termination shock, the heliosheath, the heliopause, and, after leaving the heliosphere, to discover the true nature of the hydrogen wall, the bow shock, and the local interstellar medium beyond. This will greatly advance our understanding of the heliosphere that is the best-known example for astrospheres as found around other stars. Thus, IHP/HEX will allow us to discover, explore, and understand fundamental astrophysical processes in the largest accessible plasma laboratory, the heliosphere. 相似文献
15.
The discovery of a terrestrial planet orbiting Proxima Centauri has led to a lot of papers discussing the possible conditions on this planet. Since the main factors determining space weather in the Solar System are the solar wind and cosmic rays (CRs), it seems important to understand what the parameters of the stellar wind, Galactic and stellar CRs near exoplanets are. Based on the available data, we present our estimates of the stellar wind velocity and density, the possible CR fluxes and fluences near Proxima b. We have found that there are virtually no Galactic CRs near the orbit of Proxima b up to particle energies ~1 TeV due to their modulation by the stellar wind. Nevertheless, more powerful and frequent flares on Proxima Centauri than those on the Sun can accelerate particles to maximum energies ~3150αβ GeV (α, β < 1). Therefore, the intensity of stellar CRs in the astrosphere may turn out to be comparable to the intensity of low-energy CRs in the heliosphere. 相似文献
16.
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
17.
The Interstellar Heliopause Probe: Heliospheric Boundary Explorer Mission to the Interstellar Medium
The Sun, driving a supersonic solar wind, cuts out of the local interstellar medium a giant plasma bubble, the heliosphere. ESA, jointly with NASA, has had an important role in the development of our current understanding of the Suns’ immediate neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of interstellar matter in the heliosphere. Voyager 1 has recently encountered the innermost boundary of this plasma bubble, the termination shock, and is returning exciting yet puzzling data of this remote region. The next logical step is to leave the heliosphere and to thereby map out in unprecedented detail the structure of the outer heliosphere and its boundaries, the termination shock, the heliosheath, the heliopause, and, after leaving the heliosphere, to discover the true nature of the hydrogen wall, the bow shock, and the local interstellar medium beyond. This will greatly advance our understanding of the heliosphere that is the best-known example for astrospheres as found around other stars. Thus, IHP/HEX will allow us to discover, explore, and understand fundamental astrophysical processes in the largest accessible plasma laboratory, the heliosphere. 相似文献
18.
The Bastille Day (14 July) 2000 CME is a fast, halo coronal mass ejection event headed earthward. The ejection reached Earth
on 15 July 2000 and produced a very significant magnetic storm and widespread aurora. At 1 AU the Wind spacecraft recorded a strong forward shock with a speed jump from ∼ 600 to over 1000 km s−1. About 6 months later, this CME-driven shock arrived at Voyager 2 (∼ 63 AU) on 12 January 2001 with a speed jump of ∼ 60 km s−1. This provides a good opportunity to study the shock propagation in the outer heliosphere. In this study, we employ a 2.5-D
MHD numerical model, which takes the interaction of solar wind protons and interstellar neutrals into account, to investigate
the shock propagation in detail and compare the model predictions with the Voyager 2 observations. The Bastille Day CME shock undergoes a dramatic change in character from the inner to outer heliosphere. Its
strength and propagation speed decay significantly with distance. The model results at the location of Voyager 2 are in good agreement with in-situ observations.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014293527951 相似文献
19.
Cravens TE 《The Astrophysical journal》2000,532(2):L153-L156
X-rays should be generated throughout the heliosphere as a consequence of charge transfer collisions between heavy (Z>2) solar wind ions and interstellar neutrals. The high charge state solar wind ions resulting from these collisions are left in highly excited states and emit extreme ultraviolet or soft X-ray photons. This solar wind charge exchange mechanism applied to cometary neutrals has been used to explain the soft X-ray emission observed from comets. A simple model demonstrates that heliospheric X-ray emission can account for about 25%-50% of the observed soft X-ray background intensities. The spatial and temporal variations of heliospheric X-ray emission should reflect variations in the solar wind flux and composition as well as variations in the distribution of interstellar neutrals within the heliosphere. The heliospheric X-ray "background" can perhaps be identified with the "long-term enhancements" in the soft X-ray background measured by ROSAT. 相似文献
20.
Joseph A. Kunc 《Planetary and Space Science》1980,28(8):815-821
The expressions for “survival” probabilities are presented for an atomic hydrogen particle moving on a trajectory from far regions of the heliosphere to the vicinity of the Sun. Three “destroying” processes have been considered; photoionization, charge transfer and electron ionization. The solar wind has been assumed to be a two-flux steady stream radially expanding with constant flow velocity. Recent profiles of solar-wind electron temperature have been used. The results can be useful for theoretical analyses as well as for analysis of spaceflight observations. 相似文献