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1.
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
2.
The interaction of interstellar pick-up ions with the solar wind is studied by comparing a model for the velocity distribution function of pick-up ions with actual measurements of He+ ions in the solar wind. The model includes the effects of pitch-ang'e diffusion due to interplanetary Alfvén waves, adiabatic deceleration in the expanding solar wind and the radial variation of the source function. It is demonstrated that the scattering mean free path is in the range 0.1 AU and that energy diffusion can be neglected as compared with adiabatic deceleration. The effects of adiabatic focusing, of the radial variation of the neutral density and of a variation of the solar wind velocity with distance from the Sun are investigated. With the correct choice of these parameters we can model the measured energy spectra of the pick-up ions reasonably well. It is shown that the measured differential energy density of the pick-up ions does not vary with the solar wind velocity and the direction of the interplanetary magnetic field for a given local neutral gas density and ionization rate. Therefore, the comparison of the model distributions with the measurements leads to a quantitative determination of the local interstellar gas density.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988. 相似文献
3.
It has been known for years now that pick-up ions (PUIs) are produced by ionization of interstellar neutral atoms in the heliosphere and are then convected outwards with the solar wind flow as a separate suprathermal ion fluid. Only poorly known is the thermal behaviour of these pick-ups while being convected outwards. On the one hand they drive waves since their distribution function is unstable with respect to wave growth, on the other hand they also experience Fermi-2 energizations by nonlinear wave-particle interactions with convected wave turbulences. Here we will show that this complicated network of interwoven processes can quantitatively be balanced when adequate use is made of transport-kinetic results according to which pick-up ions essentially behave isothermally at their convection to large solar distances. We derive the adequate heat source necessary to maintain this pick-up ion isothermy and use the negative of that source to formulate the enthalpy flow conservation for solar wind protons (SWPs). This takes care of a consistent PUI-induced heat source guaranteeing that the net energy balance in the SWP–PUI two-fluid plasma is satisfied. With this PUI-induced heat input to SWPs we not only obtain the well-observed SWP polytropy, but we can also derive an expression for the percentage of intitial pick-up energy fed into the thermal proton energy. By a first-order evaluation of this expression we then can estimate that, dependent on the actual PUI temperature, about 40 to 50% of the initial pick-up energy is globally passed to solar protons within the inner heliosphere. 相似文献
4.
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
5.
I. G. Richardson S. W. H. Cowley R. J. Hynds
P. W. Daly
T. R. Sanderson
K. -P. Wenzel 《Planetary and Space Science》1988,36(12):1429-1450The properties of energetic (65–95 keV) cometary water-group ions in the extended solar wind pick-up region surrounding comet Giacobini-Zinner are examined using data from the EPAS instrument on the ICE spacecraft. In the outer part of this region, extending from cometocentric distances of several hundred thousand to a few million kilometres (the limit of pick-up ion detectability), it is found that large modulations of the ion flux occur (with JMAX/JMIN 102-103) which are related to the direction of the magnetic field. It is also found that the ions stream in a direction which is intermediate between the directions of the solar wind flow and the E × B drift, and that ions are present at energies somewhat above the local pick-up energy. These properties indicate that the waves which are excited by the unstable “ring-beam” pick-up ion velocity distributions do result in significant scattering of the ions in this region, both in pitch angle and in energy, but that they have insufficient amplitude to scatter the ions into near isotropy in the solar wind frame. Closer to the comet (but still upstream from the bow shock), the ion flux modulations are considerably reduced in amplitude and the ions respond less to the E × B drift, indicating that the ions are scattered nearer to isotropy in this region. Inbound, this transition takes place relatively abruptly at a distance of 4 × 105 km in association with an increase in the solar wind speed, after which the ion flux increases, and ceases to be modulated by the field direction, while the streaming direction is continuously antisolar and unmodulated by the direction of the E × B drift. Outbound, weak vestiges of the ring-beam ion anisotropy are present in the region immediately upstream from the bow shock (at −1 × 105 km), but these become more marked at distances in excess of t4 × 105 km, increasing gradually with increasing distance from the comet. It is shown that the evolution of the ion properties is qualitatively consistent with expectations based on quasi-linear diffusion of the ions by the magnetosonic waves observed during the encounter. 相似文献
6.
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
7.
J. Lemaire 《Planetary and Space Science》1977,25(9):887-890
Assuming that the solar wind plasma is usually non-uniform over distances of 10,000 km or less, it is shown that filamentary plasma elements stretched out from the Sun can penetrate impulsively and become engulfed into the magnetosphere.The diamagnetic effects associated with these plasma inhomogeneities are observed in outer magnetospheres and magnetosheaths as dips or directional discontinuities in the magnetic field measurements. From the mean penetration distances of these diamagnetic plasma elements one can deduce a mean deceleration time, as well as an approximate value of the integrated Pedersen conductivity in the polar cusp of the Earth and Jupiter. 相似文献
8.
Hourly interplanetary proton plasma data, measured by Helios-1 and Helios-2 heliocentric satellites over the period extending between the sunspot minimum and maximum of the 21rst solar cycle are analysed. This analysis gives an emphasis in the presence of a third type solar wind (intermediate) at 450 km s–1, appearing at solar minimum, during which large coronal holes are dominating in the Sun. This type of solar wind is hardly to be observed during the solar maximum period.Both Helios-1 and Helios-2 data give an average speed of the slow solar wind of 350 km s–1 for the period between these two extremes of solar activities.After correlation of the plasma temperature with its speed in different heliocentric distances, it comes out the stronger heating which takes place in distances shorter than 0.6 AU than in distances between 0.6 and 1.0 AU.A different behaviour of the radial proton temperature gradient in different solar activities appears after the calculation of the gradients as a function of solar wind speed and radial distance. 相似文献
9.
Energetic ions from the solar wind, local pick-up ions or magnetospheric plasma ions impact the atmospheres and surfaces of
a number of solar system bodies. These energetic incident ions deposit energy in the gas or solid. This can lead to the ejection
of atoms and molecules, a process referred to as sputtering. In this paper we first describe the physics and chemistry of
atmospheric and surface sputtering. We then apply this to the production of a thin atmosphere on Europa by magnetospheric
ion bombardment of Europa's surface and show that Europa loses more Na atoms than it receives from the Jupiter magnetosphere.
The loss of atmosphere from Mars in earlier epochs by pick-up ion sputtering of that atmosphere is also calculated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
《Planetary and Space Science》2006,54(13-14):1482-1495
Venus has no internal magnetic dynamo and thus its ionosphere and hot oxygen exosphere dominate the interaction with the solar wind. The solar wind at 0.72 AU has a dynamic pressure that ranges from 4.5 nPa (at solar max) to 6.6 nPa (at solar min), and its flow past the planet produces a shock of typical magnetosonic Mach number 5 at the subsolar point. At solar maximum the pressure in the ionospheric plasma is sufficient to hold off the solar wind at an altitude of 400 km above the surface at the subsolar point, and 1000 km above the terminators. The deflection of the solar wind occurs through the formation of a magnetic barrier on the inner edge of the magnetosheath, or shocked solar wind. Under typical solar wind conditions the time scale for diffusion of the magnetic field into the ionosphere is so long that the ionosphere remains field free and the barrier deflects almost all the incoming solar wind. Any neutral atoms of the hot oxygen exosphere that reach the altitude of the magnetosheath are accelerated by the electric field of the flowing magnetized plasma and swept along cycloidal paths in the antisolar direction. This pickup process, while important for the loss of the Venus atmosphere, plays a minor role in the deceleration and deflection of the solar wind. Like at magnetized planets, the Venus shock and magnetosheath generate hot electrons and ions that flow back along magnetic field lines into the solar wind to form a foreshock. A magnetic tail is created by the magnetic flux that is slowed in the interaction and becomes mass-loaded with thermal ions.The structure of the ionosphere is very much dependent on solar activity and the dynamic pressure of the solar wind. At solar maximum under typical solar wind conditions, the ionosphere is unmagnetized except for the presence of thin magnetic flux ropes. The ionospheric plasma flows freely to the nightside forming a well-developed night ionosphere. When the solar wind pressure dominates over the ionospheric pressure the ionosphere becomes completely magnetized, the flow to the nightside diminishes, and the night ionosphere weakens. Even at solar maximum the night ionosphere has a very irregular density structure. The electromagnetic environment of Venus has not been well surveyed. At ELF and VLF frequencies there is noise generated in the foreshock and shock. At low altitude in the night ionosphere noise, presumably generated by lightning, can be detected. This paper reviews the plasma environment at Venus and the physics of the solar wind interaction on the threshold of a new series of Venus exploration missions. 相似文献
11.
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
12.
Frank Verheest 《Astrophysics and Space Science》1987,138(1):209-215
The large differences in drift velocities between the solar wind protons and the picked-up ions of cometary origin cause the Alfvén waves (among others) to become unstable and generate turbulence. A self-consistent treatment of such instabilities has to take into account that these cometary ions affect the solar wind plasma in a decisive way. With the help of a previously developed formalism one finds the correct Alfvén instability criterion, which is here nondispersive, in contrast to recent calculations where the cometary ions are treated as a low-density, high-speed, and non-neutral beam through an otherwise undisturbed solar wind. The true bulk speed of the combined solar wind plus cometary ion plasma clearly shows the mass-loading and deceleration of the solar wind near the cometary nucleus, indicating a bow shock. The instability criterion is also used to determine the region upstream where the Alfvén waves can be unstable, based upon recent observations near comet Halley. 相似文献
13.
It has been hypothesized for quite some time that interplanetary pick-up ions due to energization taking place in the region close to the solar wind termination shock, at some fraction and as an outcome of a complicated chain of processes, eventually are converted into species of the anomalous cosmic-ray particles. For the actual conversion efficiency it is of great importance to know the energy distribution of these pick-up ions upon their arrival at the shock. It turns out that pre-acceleration of these ions during their passage through the heliosphere shall substantially increase their chances to become reflected at the shock into the upstream direction which is a prerequisite for a further climb-up in energy by virtue of Fermi-1 acceleration processes. In this paper we start out from stochastically pre-accelerated pick-up ions and investigate their behaviour at the shock. With the use of adiabatic approaches in the de Hoffman-Teller frame of the shock, we calculate the energy distribution function of the reflected part of pick-up ions. From the calculated distribution functions it turns out that the reflected ions in the average suffer an energy increase by about a factor of 10, still not enough to let them move off the shock by spatial diffusion in the upstream direction. Thus, since converted back into the shock, they can undergo repeated reflections and energy gains till the diffusion-convection limit is reached. As we show in addition, the reflection probability for pick-up ions is about a factor of 10 higher than expected from the present literature and strongly varies with the off-axis angle, pointing to the fact that the termination shock represents a surface with a three-dimensionally varying source strength for the production of anomalous cosmic rays. The ACR source pattern is also expected to vary during the solar cycle and the relevant injection energies are expected to be larger by factors of 10 to 100 than the canonically adopted 1 keV nucl–1.Institute for Problems of Mechanics of the Russian Academy of Sciences, Prospect Vernadskogo 101, 117526, Moscow, Russia. 相似文献
14.
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
15.
The energization of positive ions in front of a cometary bow shock is investigated. Ions produced by ionization of the cometary neutrals interact with the solar wind protons to produce, among other waves, large amplitude oscillations of the ambient magnetic field. Such oscillations are convected towards the comet at the unperturbed solar wind speed far from the shock and at a lower speed closer to the shock (due to the solar wind mass loading) ; hence, they can energize the suprathermal ions by Fermi acceleration. The spatial extension of the acceleration region is of the order of 106 km and the resulting ion energy spectrum is harder than in the Earth's bow shock case. The energization of cometary ions produces an additional deceleration of the solar wind, such that the cometary bow shock of Halley-type comet may be regarded as a “cosmic ray shock”. 相似文献
16.
T.R. McEnulty J.G. Luhmann I. de Pater D.A. Brain A. Fedorov T.L. Zhang E. Dubinin 《Planetary and Space Science》2010,58(14-15):1784-1791
We have used the ion mass analyzer (IMA) and magnetometer (MAG) on Venus Express (VEX) to study escaping O+ during interplanetary coronal mass ejections (ICMEs). Data from 389 VEX orbits during 2006 and 2007 revealed 265 samples of high energy pick-up ion features in 197 separate orbits. Magnetometer data during the same time period showed 17 ICMEs. The interplanetary conditions associated with the ICMEs clearly accelerate the pick-up ions to higher energies at lower altitudes compared to undisturbed solar wind. However, there is no clear dependence of the pick-up ion flux on ICMEs which may be attributed to the fact that this study used data from a period of low solar activity, when ICMEs are slow and weak relative to solar maximum. Alternatively, atmospheric escape rates may not be significantly changed during ICME events. 相似文献
17.
The Apollo-12 ALSEP solar wind spectrometer obtained data from the lunar surface starting November 20, 1969. To a first approximation, the general features of the positive ion flux depend only on the instrument's orientation and location in space relative to the Sun-Earth system. However, there are some detectable effects of the interaction of the solar wind with the local magnetic field and surface, including the deceleration of incident positive ions and the enhancement of fluctuations in the plasma. The expected asymmetry of sunset and sunrise times due to the motion of the Moon about the Sun is not observed. On one occasion, the solar wind was incident on the ALSEP site as early as 36 hr (18°) before sunrise. 相似文献
18.
E. Dubinin D. Winningham J. Woch S. Barabash R. Frahm A.J. Coates J.-A. Sauvaud H. Andersson A. Grigoriev K. Asamura K.S. Hsieh H. Koskinen P. Riihelä T. Säles J. Luhmann R. Cerulli-Irelli M. Maggi D. Williams P. Wurz C. Dierker M. Carter 《Icarus》2006,182(2):343-349
The ASPERA-3 experiment onboard the Mars Express spacecraft revealed, near the wake boundary of Mars, a spatially narrow, strip-like plasma structure composed of magnetosheath-like electrons and planetary ions. The peak electron energy often exceeds the peak energy at the bow shock that indicates a significant heating (acceleration) during the structure formation. It is shown that this structure is formed during efficient plasma penetration into the martian magnetosphere in the region near the terminator. The penetration of sheath electrons and their gradual heating (acceleration) is accompanied by a change of the ion composition from a solar wind plasma to a planetary plasma dominated by oxygen ions. A possible mechanism of plasma inflow to the magnetosphere is discussed. 相似文献
19.
The collision-dominated two-fluid plasma models of the solar wind are shown to become collisionless and subject to microinstabilities at a few solar radii. Assuming that once the plasma is unstable it stays close to marginal stability models of the solar wind are constructed including waves and proton heating. The resulting models have higher velocities and proton temperatures than the collision dominated two fluid models.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献
20.
The numerical integration of hydrodynamics equations with an allowance for thermal conductivity was made using the temperature distribution in the corona situated above the active regions obtained from the damping time of solar radio bursts of Types III and V. It is essential that for the integration path serve the magnetic field lines along which exciters of bursts are moving and accelerated coronal plasma can move freely too.The main result is the discovery of such regions, where the high temperature gradient precludes the possibility of a continuous flow of coronal plasma. These regions, where intense heating and rapid acceleration of the coronal plasma take place, were situated at distances of about 2 R
from the Sun's center. They probably possess the character of weak detonation waves. The waves of cooling can also be present in these regions of discontinuity of the flow. The observations of bursts of Type V at distances up to 6.3 R
gives some evidence that discontinuities of flow of the solar wind of the same nature can possibly arise also in the more remote parts of the solar corona.It is important that the similar jumps of velocity and other parameters of coronal plasma were also discovered earlier in a quite independent way as a result of the interpretation of the solar radio echo data. It can be anticipated that the nonthermal heating of coronal plasma, which was postulated to remove discrepancies between the existing models and observations of solar wind, was localized mainly in these regions thus playing an important role in the formation of the fundamental properties of the interplanetary medium.The obtained results are of preliminary character since there are no reliable and homogeneous data on bursts of Types III and V especially at 20-10 MHz, where the work is difficult due to the man-made interference and also at still lower frequencies, observed by the cosmic probes. We can hope that the filling of this gap allows us to construct a realistic model of outflow of coronal plasma from active regions, which can be successfully compared with the results of direct measurement of parameters of solar wind. 相似文献