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1.
The properties of the solar wind including magnetic fields, plasma, and plasma waves are briefly reviewed with emphasis on conditions near and beyond the orbit of Jupiter. An extrapolation of the steady-state wind to large distances, evolution of disturbances and structure, modulation of cosmic rays, interactions with planetary bodies (bow shocks and magnetosheaths), and interactions with interstellar neutral helium and hydrogen are briefly discussed. Some comments on instrumentation requirements to observationally define the above phenomena are also included.This is one of the publications by the Science Advisory Group.  相似文献   

2.
An account is given of the observations and theoretical ideas concerning the role of kinetic processes in the solar wind. This includes, first of all, the measurements on distribution functions of plasma electrons and protons, the relation of the observed non-thermal electron features with the concept of an exospheric expansion of the solar corona, and the connection of non-thermal proton distributions with bulk flow inhomogeneities of the wind. A discussion is given of the present understanding of the connection between observed features of the particle distributions and anomalous values of some plasma transport coefficients, which in turn determine the actual values of macroscopic plasma parameters.A further topic of the review is that of possible kinetic processes occurring within small scale structures in the solar wind, like collisionless shocks, various types of discontinuities and D-sheets.  相似文献   

3.
Acceleration of the solar wind   总被引:2,自引:0,他引:2  
In this review, we discuss critically recent research on the acceleration of the solar wind, giving emphasis to high-speed solar wind streams emanating from solar coronal holes. We first explain why thermally driven wind models constrained by solar and interplanetary observations encounter substantial difficulties in explaining high speed streams. Then, through a general discussion of energy addition to the solar wind above the coronal base, we indicate a possible resolution of these difficulties. Finally, we consider the question of what role MHD waves might play in transporting energy through the solar atmosphere and depositing it in the solar wind, and we conclude by examining, in a simple way, the specific mechanism of solar wind acceleration by Alfvén waves and the related problem of accelerating massive stellar winds with Alfvén waves.Paper presented at the IX-th Lindau Workshop The Source Region of the Solar Wind.On leave from the Auroral Observatory, Institute of Mathematical and Physical Sciences, University of Tromsø, N-9001 Tromsø, Norway.The National Center for Atmospheric Research is sponsored by the National Science Foundation.  相似文献   

4.
5.
Data on composition in the solar wind are summarized and compared with best estimates of abundances in the outer convective zone of the Sun. Several mechanisms of element and isotope fractionation are discussed in relation to observed abundances and their variations.The evidence available so far indicates that in addition to ion fractionation in the corona there is a separation mechanism operating at low solar altitude that affects solar wind composition. It is suggested that the systematic depletion of helium observed in the solar wind is in part caused by ion-neutral separation in the chromosphere-transition zone. Conditions for this mechanism to be effective are discussed. It is shown that ion-neutral separation is much more pronounced than ion-ion separation under these conditions. Therefore, this mechanism should fractionate elements according to the rate at which first ionization occurs. This implies that isotope fractionation by this mechanism is minor.Ion-neutral separation may be responsible for the general depletion that is observed in the slow interstream solar wind as well as in the fast streams coming out of coronal holes. However, the occurrences of very low He/H ratios are probably caused in the corona.Paper presented at the IX-th Lindau Workshop The Source Region of the Solar Wind.  相似文献   

6.
Pneuman  G. W. 《Space Science Reviews》1986,43(1-2):105-138
In this review, we consider the central physical aspects pertinent to the acceleration of the solar wind. Special importance is placed on the high-speed streams since the properties of these structures seem to strain the various theoretical explanations the most. Heavy emphasis is also given to the observations — particularly as to what constraints they place on the theories. We also discuss certain sporadic events such as spicules, macrospicules, X-ray bright points, and outflows seen in the EUV associated with the explosive events, jets, and coronal bullets which could be of relevance to this problem.Three theoretical concepts pertaining to the solar wind acceleration process are examined — purely thermal acceleration with and without extended heating, acceleration due to Alfvén wave pressure, and diamagnetic acceleration. Emphasis is given to how well these theories meet the constraints imposed by the observations. Diamagnetism is argued to be a powerful ingredient in solar wind theory, both in the light of observed sporatic outflows seen in the chromosphere and transition region and also because of its effectiveness in increasing the flow speed and producing strong acceleration near the Sun in line with coronal hole observations.  相似文献   

7.
This paper is a review of the basic theoretical dynamical properties of an atmosphere with an extended temperature strongly bound by gravity. The review begins with the historical developments leading up to the realization that the only dynamical equilibrium of an atmosphere with extended temperature is supersonic expansion. It is shown that sufficient conditions for supersonic expansion are T(r) declining asymptotically less rapidly than 1/r, or the density at the base of the corona being less than N b given by (40) if no energy is available except through thermal conductivity, or the temperature falling within the limits given by (18) if T N -1 throughout the corona. Less extended temperatures lead to equilibria which are subsonic or static. The hypothetical case of a corona with no energy supply other than thermal conduction from its base is considered at some length because the equations may be solved by analytical methods and illustrate the transition from subsonic to supersonic equilibrium as the temperature becomes more extended. Comparison with the actual corona shows that the solar corona is actively heated for some distance into space by wave dissipation.The dynamical stability of the expanding atmosphere is demonstrated, and in a later section the radial propagation of acoustic and Alfvén waves through the atmosphere and wind is worked out. The calculations show that the magnetometer will probably detect waves more easily than the plasma instrument, but that both are needed to determine the mode and direction of the wave. An observer in the wind at the orbit of Earth can listen to disturbances generated in the corona near the sun and in turbulent regions in interplanetary space.The possibility that the solar corona is composed of small-scale filaments near the sun is considered. It is shown that such filamentary structure would not be seen at the orbit of Earth. It is pointed out that the expansion of a non-filamentary corona seems to lead to too high a calculated wind density at the orbit of Earth to agree with the present observations, unless T(r) is constant or increases with r. A filamentary corona, on the other hand, would give the observed wind density for declining T(r).It is shown that viscosity plays no important role in the expansion of an atmosphere either with or without a weak magnetic field. The termination of the solar wind, presumably between 10–103 AU, is discussed briefly. The interesting development here is the interplanetary L recently observed, which may come from the interstellar neutral hydrogen drifting into the outer regions of the solar wind.Theory is at the present time concerned with the general dynamical principles which pertain to the expansion equilibrium of an atmosphere. It is to be expected that the rapid progress of direct observations of the corona and wind will soon permit more detailed studies to be carried out. It is important that the distinction between detailed empirical models and models intended to illustrate general principles be kept clearly in mind at all times.This work was supported by the National Aeronautics and Space Administration under Grant NASA-NsG-96-60.  相似文献   

8.
As the solar wind flows out from the coronal base the coulomb collision frequencies rapidly become small and particle-particle collisions can no longer maintain local statistical equilibrium. At 1 AU the particle distribution functions have important non-Maxwellian characteristics and the firehose instability, a cyclotron resonance whistler-mode instability, and several heat flux current instabilities should be operative. Superthermal particle populations also provide large wave levels, and other forms of enhanced plasma turbulence develop at shock fronts and discontinuities. This report contains a review of the theoretical concepts and a progress report on the experimental study of interplanetary wave-particle interactions.Prepared for Space Science Reviews.  相似文献   

9.
The solar wind carves a cavity in the flow of interstellar H atoms through the solar system by charge-exchange ionization. The resulting Ly- sky pattern depends on the latitude distribution of the solar wind flux and velocity. We review how the solar wind characteristics (mass flux latitude distribution) can be retrieved from Ly- observations, yielding a new remote sensing method of solar wind studies, through UV optical measurements.  相似文献   

10.
11.
An overview of the solar wind termination shock is presented including: its place in the heliosphere and its origin; its structure including the role of interstellar pickup ions and galactic and anomalous cosmic rays; its inferred location based on Lyman- backscatter, Voyager radio signals, and anomalous cosmic rays; its shape and movement.  相似文献   

12.
13.
Theoretical studies of the solar wind phenomenon   总被引:1,自引:1,他引:0  
This paper is a review of current theoretical topics concerning the solar wind. Broadly speaking the questions outstanding at the present time concern the loss of angular momentum to the sun, the origin of the fluctuations observed in the wind at the orbit of earth, conditions in the wind in regions yet unvisited by spacecraft (inside the orbit of Venus, beyond the orbit of Mars, and out of the plane of the ecliptic), conditions at the terminus of the wind, etc. The question of angular momentum loss is important in understanding the evolution of the sun to its present form with a slowly rotating surface. Evidence from both comet and spacecraft observations of the wind indicate that the rate at which angular momentum is being carried away by the solar wind is very large, of the order of 1031 dyne/cm in the gas flow and half as much by the interplanetary magnetic field. But theory cannot account for more than about 1030 dynes/cm in the gas without special assumptions.The fluctuations presently observed in the wind at the orbit of earth have scales ranging upward from 102 km. Their presence is puzzling because fluctuations with scales less than about 106 km are not expected to survive from the sun. Presumably, therefore, the fluctuations are generated by the velocity differences of more than 100 km/sec in the wind from different regions in the solar corona and by instabilities produced by the anisotropy of the electrons of the wind plasma.Conditions in the wind at places far removed from the orbit of earth can be inferred from the behavior of cosmic rays. The evidence is that the wind becomes relatively placid beyond about 5 AU, extending from there out to 30–300 AU without much small-scale turbulence. There are also some suggestions that the wind may perhaps be less turbulent toward the sun from 1 AU, and that the wind may be faster and more turbulent at higher solar latitudes. But the ambiguity of the situation does not permit a firm conclusion on this yet.  相似文献   

14.
Ulysses measurements of the solar wind electron heat flux as a function of heliographic latitude are presented. The latitudinal in the electron heat flux presented have been normalized by the radial gradient in the electron heat flux obtained during the in-ecliptic phase of the Ulysses mission (qe R–3.0). We find no significant variation in electron heat flux with latitude.  相似文献   

15.
Hada  Tohru  Koga  Daiki  Yamamoto  Eiko 《Space Science Reviews》2003,107(1-2):463-466
Large amplitude MHD waves are commonly found in the solar wind. Nonlinear interactions between the MHD waves are likely to produce finite correlation among the wave phases. For discussions of various transport processes of energetic particles, it is fundamentally important to determine whether the wave phases are randomly distributed (as assumed in quasi-linear theories) or they have a finite coherence. Using a method based on a surrogate data technique and a fractal analysis, we analyzed Geotail magnetic field data (provided by S. Kokubun and T. Nagai through DARTS at the Institute of Space and Astronautical Science) to evaluate the phase coherence among the MHD waves in the earth's foreshock region. The correlation of wave phases does exist, indicating that the nonlinear interactions between the waves is in progress. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

16.
A critical review of the interstellar hydrogen in the heliosphere will be presented. Recent Sun-interstellar matter interaction model improvements, a non-stationary flow and a flexible latitude dependence, will be discussed. We also consider the influence of heliospheric interface on neutral flow and the remaining refinements, which could help to better interpret the results of the SWAN experiment on board SOHO.  相似文献   

17.
This paper summarizes space probe observations relevant to the determination of the large-scale, three-dimensional structure of the solar wind and its solar cycle variations. Observations between 0.6 and 5 AU reveal very little change in the average solar-wind velocity, but a pronounced decrease in the spread of velocities about the average. The velocity changes may be accompanied by a transfer of energy from the electrons to the protons. The mass flux falls off approximately as the inverse square of distance as expected for spherically symmetric flow. Measurements of the interplanetary magnetic field show that the spiral angle is well defined over this entire range of distances, but there is some evidence that the spiral may wind up more slowly with distance from the Sun than predicted by Parker's model. The variances or noise in the field and plasma have also been measured as a function of radial distance.During the rising portion of the solar-activity cycle, the solar-wind velocity showed a pronounced positive correlation with solar latitude over the range ±7°. Several other plasma parameters which have been found generally to correlate (or anticorrelate) with velocity also showed a latitude variation; these parameters include the density, percent helium, and azimuthal flow direction. The average polarity and the north-south component of the magnetic field depend on the solar hemisphere in which the measurements are made.Dependence on the phase of the solar-activity cycle can be found in the data on the number of high speed streams, the proton density, the percent helium, and the magnetic-field strength and polarity.  相似文献   

18.
The ESA/NASA spacecraft Ulysses is making, for the first time, direct measurements in the solar wind originating from virtually all places where the corona expands. Since the initial two polar passes of Ulysses occur during relatively quiet solar conditions, we discuss here the three main regimes of quasi-stationary solar wind flow: the high speed streams (HSSTs) coming out of the polar coronal holes, the slow solar wind surrounding the HSSTs, and the streamers which occur at B-field reversals. Comparisons between H- maps and data taken by Ulysses demonstrate that as a result of super-radial expansion, the HSSTs occupy a much larger solid angle than that derived from radial projections of coronal holes. Data obtained with SWICS-Ulysses confirm that the strength of the FIP effect is much reduced in the HSSTs. The systematics in the variations of elemental abundances becomes particularly clear, if these are plotted against the time of ionisation (at the solar surface) rather than against the first ionisation potential (FIP). We have used a superposed-epoch method to investigate the changes in solar wind speed and composition measured during the 9-month period in 1992/93 when Ulysses regularly passed into and out of the southern HSST. We find that the patterns in the variations of the Mg/O and O7+/O6+ ratios are virtually identical and that their transition from high to low values is very steep. Since the Mg/O ratio is controlled by the FIP effect and the O7+/O6+ ratio reflects the coronal temperature, this finding points to a connection between chromospheric and coronal conditions.  相似文献   

19.
The solar wind emanating from coronal holes (CH) constitutes a quasi-stationary flow whose properties change only slowly with the evolution of the hole itself. Some of the properties of the wind from coronal holes depend on whether the source is a large polar coronal hole or a small near-equatorial hole. The speed of polar CH flows is usually between 700 and 800 km/s, whereas the speed from the small equatorial CH flows is generally lower and can be <400 km/s. At 1 AU, the average particle and energy fluxes from polar CH are 2.5×108 cm–2 sec–1 and 2.0 erg cm–2 s–1. This particle flux is significantly less than the 4×108 cm–2 sec–1 observed in the slow, interstream wind, but the energy fluxes are approximately the same. Both the particle and energy fluxes from small equatorial holes are somewhat smaller than the fluxes from the large polar coronal holes.Many of the properties of the wind from coronal holes can be explained, at least qualitatively, as being the result of the effect of the large flux of outward-propagating Alfvén waves observed in CH flows. The different ion species have roughly equal thermal speeds which are also close to the Alfvén speed. The velocity of heavy ions exceeds the proton velocity by the Alfvén speed, as if the heavy ions were surfing on the waves carried by the proton fluid.The elemental composition of the CH wind is less fractionated, having a smaller enhancement of elements with low first-ionization potentials than the interstream wind, the wind from coronal mass ejections, or solar energetic particles. There is also evidence of fine-structure in the ratio of the gas and magnetic pressures which maps back to a scale size of roughly 1° at the Sun, similar to some of the fine structures in coronal holes such as plumes, macrospicules, and the supergranulation.  相似文献   

20.
Until the ULYSSES spacecraft reached the polar regions of the solar wind, the only high-latitude measurements available were from indirect techniques. The most productive observations in regions of the solar wind between 5R and 200R have been the family of radio scattering techniques loosely referred to as Interplanetary Scintillation (IPS) (Coles, 1978). Useful observations can be obtained using a variety of radio sources, for example spacecraft beacons, planetary radar echoes and compact cosmic sources (quasars, active galactic nuclei, pulsars, galactic masers, etc.). However for measurement of the high-latitude solar wind cosmic sources provide the widest coverage and this review will be confined to such observations. IPS observations played a very important role in establishing that polar coronal holes (first observed in soft x-ray emission) were sources of fast solar wind streams which occasionally extend down to the equatorial region and are observed by spacecraft. Here I will review the IPS technique and show the variation of both the velocity and the turbulence level with latitude over the last solar cycle. I will also outline recent work and discuss comparisons that we hope to make between IPS and ULYSSES observations.  相似文献   

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