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1.
The electron distribution functions from the solar corona to the solar wind are determined in this paper by considering the
effects of the external forces, of Coulomb collisions and of the wave – particle resonant interactions in the plasma wave
turbulence. The electrons are assumed to be interacting with right-handed polarized waves in the whistler regime. The acceleration
of electrons in the solar wind seems to be mainly due to the electrostatic potential. Wave turbulence determines the electron
pitch-angle diffusion and some characteristics of the velocity distribution function (VDF) such as suprathermal tails. The
role of parallel whistlers can also be extended to small altitudes in the solar wind (the acceleration region of the outer
corona), where they may explain the energization and the presence of suprathermal electrons. 相似文献
2.
F. R. Allum R. A. R. Palmeira U. R. Rao K. G. McCracken J. R. Harries I. Palmer 《Solar physics》1971,17(1):241-268
Data obtained by the Explorer 34 satellite regarding the degree of anisotropy of ≳ 70 keV electrons of solar origin are reported.
It is shown that the anisotropies are initially field aligned, and that they decay to ≲ 10% in a time of the order of 1 hr.
The decays of the concurrent ionic and electronic anisotropies for one well observed event are in good agreement with the
diffusive propagation model of Fisk and Axford. The data suggest parallel diffusion coefficients for both ions and electrons
that are rigidity independent. From considerations of a long lived electron event, it is shown that the electronic fluxes
exhibit ‘equilibrium’ anositropies at late times. These are interpreted as indicating that convective removal at the solar
wind velocity is the dominant mechanism whereby solar cosmic ray electrons (∼- 70 keV) leave the solar system. They also indicate
that there is a positive density gradient at late times in a solar electron event. The data suggest that this was established
prior to the establishment of a similar gradient for the cosmic ray ions.
This research was supported by the National Aeronautics and Space Administration under contracts NASr-198 and NAS5-9075. The
research in India was supported by funds from the Department of Atomic Energy, Government of India and funds from the grant
NAS-1492 from the National Academy of Sciences, U.S.A. Support in data analysis was also provided by Air Force Cambridge Research
Laboratories, and by the Australian Research Grants Committee. 相似文献
3.
The probability of the interstellar wind atoms (H and He) to survive ionization by solar wind electrons is presented. For the first time a dual temperature electron distribution is used to model the effects of “core” (10 eV) and “halo” (60 eV) solar electrons on the probabilities. Survival probability distributions as a function of helicocentric distance were calculated for variations in the electron temperature, solar radiation force, and the interstellar wind flow velocity. These probabilities are important in determining the radial density distributions of the interstellar atoms. It has been found that the interstellar wind has a distinctively higher probability of surviving “halo” rather than “core” electron ionization only at heliocentric distances, ρ, smaller than about 0.5 a.u. For distances larger than 0.5 a.u., the probabilities of surviving “halo” electrons are close to the probabilities of surviving “core” electrons. Also, the probabilities for both “core” and “halo” electrons are relatively insensitive to changes in u∞ (interstellar wind velocity at infinity), μ (the solar ratio of radiation to gravitational force) and α (a model parameter for solar electron temperature) for ρ > 0.5. For distances smaller than that, the sensitivity increases significantly. 相似文献
4.
《Chinese Astronomy and Astrophysics》1982,6(3):192-198
We investigate the possibility of an additional acceleration of the high speed solar wind by whistler waves propagating outward from a coronal hole. We consider a stationary, spherically symmetric model and assume a radial wind flow as well as a radial magnetic field. The energy equation consists of (a) energy transfer of the electron beam which excites the whistler waves, and (b) energy transfer of the whistler waves described by conservation of wave action density. The momentum conservation equation includes the momentum transfer of two gases (a thermal gas and an electron beam). The variation of the temperature is described by a polytropic law. The variation of solar wind velocity with the radial distance is calculated for different values of energy density of the whistler waves. It is shown that the acceleration of high speed solar wind in the coronal hole due to the whistler waves is very important. We have calculated that the solar wind velocity at the earth's orbit is about equal to 670 km/sec (for wave energy density about 10?4 erg cm?3 at 1.1R⊙). It is in approximate agreement with the observed values. 相似文献
5.
Interfacing MHD Single Fluid and Kinetic Exospheric Solar Wind Models and Comparing Their Energetics
An exospheric kinetic solar wind model is interfaced with an observation-driven single-fluid magnetohydrodynamic (MHD) model. Initially, a photospheric magnetogram serves as observational input in the fluid approach to extrapolate the heliospheric magnetic field. Then semi-empirical coronal models are used for estimating the plasma characteristics up to a heliocentric distance of 0.1 AU. From there on, a full MHD model that computes the three-dimensional time-dependent evolution of the solar wind macroscopic variables up to the orbit of Earth is used. After interfacing the density and velocity at the inner MHD boundary, we compare our results with those of a kinetic exospheric solar wind model based on the assumption of Maxwell and Kappa velocity distribution functions for protons and electrons, respectively, as well as with in situ observations at 1 AU. This provides insight into more physically detailed processes, such as coronal heating and solar wind acceleration, which naturally arise from including suprathermal electrons in the model. We are interested in the profile of the solar wind speed and density at 1 AU, in characterizing the slow and fast source regions of the wind, and in comparing MHD with exospheric models in similar conditions. We calculate the energetics of both models from low to high heliocentric distances. 相似文献
6.
In the present paper, the proton velocity distribution function (VDF) in the solar wind is determined by numerically solving the kinetic evolution equation. We compare the results obtained when considering the effects of external forces and Coulomb collisions with those obtained by adding effects of Alfvén wave turbulence. We use Fokker–Planck diffusion terms to calculate the Alfvénic turbulence, which take into account observed turbulence spectra and kinetic effects of the finite proton gyroradius. Assuming a displaced Maxwellian for the proton VDF at the simulation boundary at 14 solar radii, we show that the turbulence leads to a fast (within several solar radii) development of the anti-sunward tail in the proton VDF. Our results provide a natural explanation for the nonthermal tails in the proton VDFs, which are often observed in-situ in the solar wind beyond 0.3 AU. 相似文献
7.
Richard Woo 《Solar physics》2005,231(1-2):71-85
The solar magnetic field is key to a detailed understanding of the Sun's atmosphere and its transition to the solar wind.
However, the lack of detailed magnetic field measurements everywhere except at the photosphere has made it challenging to
determine its topology and to understand how it produces the observed plasma properties of the corona and solar wind. Recent
progress based on the synthesis of diversified observations has shown that the corona is highly filamentary, that the coronal
magnetic field is predominantly radial, and that the ability of closed fields to trap plasma at the base of the corona is
a manifestation of how the solar field controls the solar wind. In this paper, we explain how these results are consistent
with the relationship between density structure of white-light images and fields and flow. We point out that the ‘shape’ of
the corona observed in white-light images is a consequence of the steep fall-off in density with radial distance, coupled
with the inherent limitation in the sensitivity of the observing instrument. We discuss how the significant variation in radial
density fall-off with latitude leads to a coronal shape that is more precisely revealed when a radial gradient filter is used,
but which also gives a false impression of the tracing of highly non-radial fields. Instead, the coronal field is predominantly
radial, and the two magnetic features that influence the shape of the corona are the closed fields at the base of the corona,
and the polarity reversal forming the heliospheric current sheet in the outer corona.
An erratum to this article is available at . 相似文献
8.
Assuming a stationary, radial, spherically symmetric solar wind and a radial magnetic field direction in the vicinity of the
sun, an equation of motion for ions heavier than protons in the solar wind is derived. The general properties of this equation
are discussed and the results of numerical integrations are given. These results are based on the assumption of maxwellian
velocity distribution functions for electrons, protons and ions, but the effects of first order deviations from such distributions
are also presented and discussed. It is shown that dynamical friction, i.e. momentum transfer from protons to heavier ions
accounts for the observed fact that heavier ions - if accelerated at all - normally reach the same velocity as the protons
in the solar wind. Because of the non-linear relation between dynamical friction and proton-ion velocity difference a minimum
proton flux is required to carry a certain ion species in the solar wind. Formulae comparing the minimum fluxes for different
ions are given. It is shown that elements up to and beyond iron will be carried along in the solar wind as long as helium
is carried along. Substantial isotopic fractionation is possible, in particular in the case of helium. The effects of ion
motion and escape on abundances in the corona and in the outer convective zone of the sun are discussed. 相似文献
9.
The comparison of the brightness and area of coronal holes (CH) to the solar wind speed, which was started by Obridko et al. (Solar Phys.
260, 191, 2009a) has been continued. While the previous work was dealing with a relatively short time interval 2000 – 2006, here we have
analyzed the data on coronal holes observed in the Sun throughout activity Cycle 23. A catalog of equatorial coronal holes
has been compiled, and their brightness and area variations during the cycle have been analyzed. It is shown that CH is not
merely an undisturbed zone between the active regions. The corona heating mechanism in CH seems to be essentially the same
as in the regions of higher activity. The reduced brightness is the result of a specific structure with the magnetic field
being quasi-radial at as low an altitude as 1.1R
⊙ or a bit higher. The plasma outflow decreases the measure of emission from CH. With an adequate choice of the photometric
boundaries, the CH area and brightness indices display a fairly high correlation (0.6 – 0.8) with the solar wind velocity
throughout the cycle, except for two years, which deviate dramatically – 2001 and 2007, i.e., the maximum and the minimum of the cycle. The mean brightness of the darkest part of CH, where the field lines are nearly
radial at low altitudes, is of the order of 18 – 20% of the solar brightness, while the brightness of the other parts of the
CH is 30 – 40%. The solar wind streams originate at the base of the coronal hole, which acts as an ejecting nozzle. The solar
wind parameters in CH are determined at the level where the field lines are radial. 相似文献
10.
The plasma particle velocity distributions observed in the solar wind generally show enhanced (non-Maxwellian) suprathermal
tails, decreasing as a power law of the velocity and well described by the family of Kappa distribution functions. The presence
of non-thermal populations at different altitudes in space plasmas suggests a universal mechanism for their creation and important
consequences concerning plasma fluctuations, the resonant and nonresonant wave – particle acceleration and plasma heating.
These effects are well described by the kinetic approaches where no closure requires the distributions to be nearly Maxwellian.
This paper summarizes and analyzes the various theories proposed for the Kappa distributions and their valuable applications
in coronal and space plasmas. 相似文献
11.
David R. Criswell 《Earth, Moon, and Planets》1973,7(1-2):202-238
It is suggested that boundary conditions for solar wind/lunar limb interactions are active. The whole-Moon limb does not evoke a shock cone because warm (13 eV/electron) solar wind electrons are replaced by cool (2 eV/electron) photoelectrons that are ejected from the generally smooth areas of the lunar terminator illuminated at glazing angles by the Sun. A localized volume of low thermal pressure is created in the solar wind by these cool photoelectrons. The solar wind expands into this turbulence-suppressive volume without shock production. Conversely, directly illuminated highland areas exchange hot photoelectrons (> 20 eV/electron) for warm solar wind electrons. The hot electrons generate a localized pressure increase (p) in the adjacent solar wind flow which evokes a shock streamer in the solar wind. Shock streamers are identifiable by a coincident increase in the magnitude (B p) of the solar wind magnetic field immediately external to the lunar wake. Shock occurrence is controlled by lunar topography, solar activity in the hard ultraviolet (> 20 eV), solar wind electron density and thermal velocity, and the intensity of the solar wind magnetic field.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973.The Lunar Science Institute is operated by the Universities Space Research Association under Contract No. NSR 09-051-001 with the National Aeronautics and Space Administration. 相似文献
12.
C. C. Harvey 《Solar physics》1975,40(1):193-216
In an earlier paper (Harvey and Aubier, 1973) the large scale radial electron density gradient in the corona and solar wind was shown to cause the phase velocity of plasma waves to decrease as they propagate away from the Sun, thus leading to appreciable Landau damping of the plasma waves. It is proposed here that this same phase velocity decrease creates conditions which facilitate the stabilisation of a beam of exciter electrons of finite duration, provided that three conditions are fulfilled. Two of these conditions concern the velocity-time distribution of the exciter electrons at their point of ejection from the Sun, while the third is simply that, above a certain altitude, the coronal electron density decreases with altitude r faster than r ?2. The plasma wave source is then associated with the leading edge of the electron stream. The spatial density of the power converted into plasma waves is calculated as a function of position and time, and is shown to be independent of the nature of the stabilisation mechanism. The maximum of this power density is found to move outwards from the Sun at a uniform speed when a simple electron injection model with a Maxwellian velocity distribution is introduced. 相似文献
13.
In the present work the cosmic ray data of three different neutron monitoring stations, Deep River, Inuvik, and Tokyo, located
at different geomagnetic cutoff rigidities and altitudes have been harmonically analyzed for the period 1980–95 for a comparative
study of diurnal semi-diurnal and tri-diurnal anisotropies in cosmic ray intensity in connection with the change in interplanetary
magnetic field Bz component and solar wind velocity on 60 quietest days. It is observed that the amplitudes of all the three
harmonics increase during the period 1982–84 at all the stations during the high speed solar wind stream epoch and remain
low during the declining phase of the stream. The amplitudes of the three harmonics have no obvious characteristics associated
with the time variation of magnitude of the Bz component. The phases of all the three harmonics have no time variation characteristics
associated with solar wind velocity and Bz.
Published in Astrofizika, Vol. 49, No. 4, pp. 651–664 (August 2006). 相似文献
14.
IMP-6 spacecraft observations of low frequency radio emission, fast electrons, and solar wind plasma are used to examine the dynamics of the fast electron streams which generate solar type-III radio bursts. Of twenty solar electron events observed between April, 1971 and August, 1972, four were found to be amenable to detailed analysis. Observations of the direction of arrival of the radio emission at different frequencies were combined with the solar wind density and velocity measurements at 1 AU to define an Archimedean spiral trajectory for the radio burst exciter. The propagation characteristics of the exciter and of the fast electrons observed at 1 AU were then conpared. We find that: (1) the fast electrons excite the radio emission at the second harmonic; (2) the total distance travelled by the electrons was between 30 and 70% longer than the length of the smooth spiral defined by the radio observations; (3) this additional distance travelled is the result of scattering of the electrons in the interplanetary medium; (4) the observations are consistent with negligible true energy loss by the fast electrons. 相似文献
15.
Ko Yuan-Kuen Fisk Lennard A. Geiss Johannes Gloeckler George Guhathakurta Madhulika 《Solar physics》1997,171(2):345-361
The solar wind ions flowing outward through the solar corona generally have their ionic fractions freeze-in within 5 solar radii. The altitude where the freeze-in occurs depends on the competition between two time scales: the time over which the wind flows through a density scale height, and the time over which the ions achieve ionization equilibrium. Therefore, electron temperature, electron density, and the velocity of the ions are the three main physical quantities which determine the freeze-in process, and thus the solar wind ionic charge states. These physical quantities are determined by the heating and acceleration of the solar wind, as well as the geometry of the expansion. In this work, we present a parametric study of the electron temperature profile and velocities of the heavy ions in the inner solar corona. We use the ionic charge composition data observed by the SWICS experiment on Ulysses during the south polar pass to derive empirically the electron temperature profile in the south polar coronal hole. We find that the electron temperature profile in the solar inner corona is well constrained by the solar wind charge composition data. The data also indicate that the electron temperature profile must have a maximum within 2 solar radii. We also find that the velocities of heavy ions in their freeze-in regions are small (<100 km s-1) and different elements must flow at different velocities in the inner corona. 相似文献
16.
In late October and early November 2003, a series of space weather hazard events erupted in solar-terrestrial space. Aiming
at two intense storm (shock) events on 28 and 29 October, this paper presents a Two-Step method, which combines synoptic analysis
of space weather–`observing’ and quantitative prediction – ‘palpating’, and uses it to test predictions. In the first step,
‘observing’, on the basis of observations of the source surface magnetic field, interplanetary scintillation (IPS) and ACE
spacecraft, we find that the propagation of the shock waves is asymmetric and northward relative to the normal direction of
their solar sources due to the large-scale configuration of the coronal magnetic fields, and the Earth is located near the
direction of the fastest speed and greatest energy of the shocks. Being two fast ejection shock events, the fast explosion
of extremely high temperature and strong magnetic field, and background solar wind velocity as high as 600 and 1000 km s−1, are also helpful to their rapid propagation. According to the synoptic analysis, the shock travel times can be estimated
as 21 and 20 h, which are close to the observational results of 19.97 and 19.63 h, respectively. In the second step, ‘palpating’,
we adopt a new membership function of the fast shock events for the ISF method. The predicted results here show that for the
onset time of the geomagnetic disturbance, the relative errors between the observational and the predicted results are 1.8
and 6.7%, which are consistent with the estimated results of the first step; and for the magnetic disturbance magnitude, the
relative errors between the observational and the predicted results are 4.1 and 3.1%, respectively. Furthermore, the comparison
among the predicted results of our Two-Step method with those of five other prevailing methods shows that the Two-Step method
is advantageous in predicting such strong shock event. It can predict not only shock arrival time, but also the magnitude
of magnetic disturbance. The results of the present paper tell us that understanding the physical features of shock propagation
thoroughly is of great importance in improving the prediction efficiency. 相似文献
17.
An extensive study of the IMP-6 and IMP-8 plasma and radio wave data has been performed to try to find electron plasma oscillations associated with type III radio noise bursts and low-energy solar electrons. This study shows that electron plasma oscillations are seldom observed in association with solar electron events and type III radio bursts at 1.0 AU. In nearly four years of observations only one event was found in which electron plasma oscillations are clearly associated with solar electrons. For this event the plasma oscillations appeared coincident with the development of a secondary maximum in the electron velocity distribution functions due to solar electrons streaming outwards from the Sun. Numerous cases were found in which no electron plasma oscillations with field strengths greater than 1 μV m?1 could be detected even though electrons from the solar flare were clearly detected at the spacecraft. For the one case in which electron plasma oscillations are definitely produced by the electrons ejected by the solar flare the electric field strength is relatively small, only about 100 μV m?1. This field strength is about a factor of ten smaller than the amplitude of electron plasma oscillations generated by electrons streaming into the solar wind from the bow shock. Electromagnetic radiation, believed to be similar to the type III radio emission, is also observed coming from the region of the more intense electron plasma oscillations upstream of the bow shock. Quantitative calculations of the rate of conversion of the plasma oscillation energy to electromagnetic radiation are presented for plasma oscillations excited by both solar electrons and electrons from the bow shock. These calculations show that neither the type III radio emissions nor the radiation from upstream of the bow shock can be adequately explained by a current theory for the coupling of electron plasma oscillations to electromagnetic radiation. Possible ways of resolving these difficulties are discussed. 相似文献
18.
We present a kinetic theory for boundary layers associated with MHD tangential discontinuities in a collisionless magnetized plasma such as those observed in the solar wind. The theory consists of finding self-consistent solutions of Vlasov's equation and Maxwell's equation for stationary, one-dimensional boundary layers separating two Maxwellian plasma states. Layers in which the current is carried by electrons are found to have a thickness of the order of a few electron gyroradii, but the drift speed of the current-carrying electrons is found to exceed the Alfvén speed, and accordingly such layers are not stable. Several types of layers, in which the current is carried by protons are discussed; in particular, we considered cases in which the magnetic field intensity and/or direction changed across the layer. In every case, the thickness was of the order of a few proton gyroradii and the field changed smoothly, although the characteristics depended somewhat on the boundary conditions. The drift speed was always less than the Alfvén speed, consistent with stability of such structures. Our results are consistent with the observations of boundary layers in the solar wind near 1 AU. 相似文献
19.
V. S. Geroyannis 《Astrophysics and Space Science》1985,114(1):175-189
In this paper the ‘class of near homoaxial rotations’ is defined, being suitable for treatment of problems of nonuniform rotation
of stars. This class is represented by a proper form of the so-called ‘velocity tensor’, the latter describing efficiently
the motion of a deformable finite material continuum in the common frame. The ‘class of particular near homoaxial rotations’
is then defined, characterized by simple transformation equations of the velocity tensor in two noninertial frames; namely,
in a ‘frame rotating uniformly’ relative to the common frame, and in a ‘frame rotating nonuniformly’ relative to it. A sufficient
condition is also derived so that a near homoaxial rotation be reducible to a particular one. ‘Preferred frames’ are then
defined in the sense that they preserve a near homoaxial rotation in its class when referring thismotion; that is, such frames
keep invariant the intertial class of the motion. Finally, a method is proposed for constructing a nonuniformly rotating preferred
frame, to which a near homoaxial rotation is referred simply as ‘radial distortion’. 相似文献
20.
Hakamada Kazuyuki Kojima Masayoshi Tokumaru Munetoshi Ohmi Tomoaki Yokobe Atsushi Fujiki Ken'ichi 《Solar physics》2002,207(1):173-185
Relationships between solar wind speed and expansion rate of the coronal magnetic field have been studied mainly by in-ecliptic observations of artificial satellites and some off-ecliptic data by Ulysses. In this paper, we use the solar wind speed estimated by interplanetary scintillation (IPS) observations in the whole heliosphere. Two synoptic maps of SWS estimated by IPS observations are constructed for two Carrington rotations CR 1830 and 1901; CR 1830 starting on the 11th of June, 1990 is in the maximum phase of solar activity cycle and CR 1901 starting on the 29th of September, 1995 is in the minimum phase. Each of the maps consist of 64800 (360×180) data points. Similar synoptic maps of expansion rate of the coronal magnetic field (RBR) calculated by the so-called potential model are also constructed under a radial field assumption for CR 1830 and CR1901. Highly significant correlation (r=–0.66) is found between the SWS and the RBR during CR1901 in the solar minimum phase; that is, high-speed winds emanate from photospheric areas corresponding to low expansion rate of the coronal magnetic field and low speed winds emanate from photospheric areas of high expansion rate. A similar result is found during CR 1830 in solar maximum phase, though the correlation is relatively low (r=–0.29). The correlation is improved when both the data during CR 1830 and CR 1901 are used together; the correlation coefficient becomes –0.67 in this case. These results suggest that the correlation analysis between the SWS and the RBR can be applied to estimate the solar wind speed from the expansion rate of the coronal magnetic field, though the correlation between them may depend on the solar activity cycle. We need further study of correlation analysis for the entire solar cycle to get an accurate empirical equation for the estimation of solar wind speed. If the solar wind speed is estimated successfully by an empirical equation, it can be used as an initial condition of a solar wind model for space weather forecasts. 相似文献