共查询到20条相似文献，搜索用时 31 毫秒
1.
A model is presented which describes the 3-dimensional non-radial solar wind expansion between the Sun and the Earth in a specified magnetic field configuration subject to synoptically observed plasma properties at the coronal base. In this paper, the field is taken to be potential in the inner corona based upon the Mt. Wilson magnetograph observations and radial beyond a certain chosen surface. For plasma boundary conditions at the Sun, we use deconvoluted density profiles obtained from synopticK-coronameter brightness observations. The temperature is taken to be 2 × 106 K at the base of closed field lines and 1.6 x 106K at the base of open field lines. For a sample calculation, we employ data taken during the period of the 12 November 1966 eclipse. Although qualitative agreement with observations at 1 AU is obtained, important discrepancies emerge which are not apparent from spherically symmetric models or those models which do not incorporate actual observations in the lower corona. These discrepancies appear to be due to two primary difficulties - the rapid geometric divergence of the open field lines in the inner corona as well as the breakdown in the validity of the Spitzer heat conduction formula even closer to the Sun than predicted by radial flow models. These two effects combine to produce conductively dominated solutions and lower velocities, densities, and field strengths at the Earth than those observed. The traditional difficulty in solar wind theory in that unrealistically small densities must be assumed at the coronal base in order to obtain observed densities at 1 AU is more than compensated for here by the rapid divergence of field lines in the inner corona. For these base conditions, the value ofβ(ratio of gas pressure to magnetic pressure) is shown to be significantly greater than one over most of the lower corona - suggesting that, for the coronal boundary conditions used here, the use of a potential or force-free magnetic field configuration may not be justified. The calculations of this paper point to the directions where future research on solar-interplanetary modelling should receive priority:
- better models for the coronal magnetic field structure
- improved understanding of the thermal conductivity relevant for the solar wind plasma.
2.
A. Geranios 《Astrophysics and Space Science》1981,77(1):167-178
Plasma temperature observations in the solar wind at 1 AU show that very low temperatures of electrons and protons appear not only after interplanetary shock waves, but also after solar wind streams. It is generally believed that the region embedded by a fast preceding and a slower following solar wind is expanding. In this way, the plasma inside may become cooler. In this analysis, we use plasma measurements made aboard the VELA and IMP satellites. Due to the limitations of data, we only give a qualitative picture of the possibility that low temperature regions may be given to local expansions of the plasma. In addition, we assume that these regions are not magnetically closed and therefore not thermically isolated, but are open and connected with the hot corona along the interplanetary magnetic field lines. Therefore, these regions are heated from the corona due to the thermal conduction. In this analysis both the theoretically predicted and the experimentally measured conducted electron heat fluxes are considered. 相似文献
3.
4.
Fine time resolution observations of the angular distributions of the intensities of energetic electrons (220 ≤ E e ≤ 500 keV) by the IMP-7 and 8 spacecraft during the onsets of solar electron events and the technique of mapping the solar wind to the solar corona have been incorporated in this work in order to obtain the large-angle scattering distance of these particles under different configurations of the large scale structure of the interplanetary medium. It is found that in the presence of stream-stream interaction regions with compressed magnetic fields beyong 1 AU, the large-angle scattering is determined by the distance along the streamlines from the spacecraft to their intersection by a faster solar wind stream. In cases of diverging magnetic fields the estimated large-angle scattering distance exceeds 1 AU. 相似文献
5.
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
6.
The study of the solar corona has been strewn with great discoveries, surprises and controversies. The major steps since van
de Hulst's (1953)and Chapman's (1957) early hydrostatic models of the extended corona, until the most recent generations of
kinetic models of the coronal expansion and of the supersonic solar wind flows, are presented. These models are compared to
in-situ observations. Progress in polar wind models went through a somewhat similar evolution that is outlined also. The advantages
and limitations of the successive brands of solar wind and polar wind models are considered.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
A global numerical 3-D MHD model of the solar wind 总被引：2，自引：0，他引：2
A. V. Usmanov 《Solar physics》1993,146(2):377-396
A fully three-dimensional, steady-state global model of the solar corona and the solar wind is developed. A numerical, self-consistent solution for 3-D MHD equations is constructed for the region between the solar photosphere and the Earth's orbit. Boundary conditions are provided by the solar magnetic field observations. A steady-state solution is sought as a temporal relaxation to the dynamic equilibrium in the region of transonic flow near the Sun and then traced to the orbit of the Earth in supersonic flow region. The unique features of the proposed model are: (a) uniform coverage and self-consistent treatment of the regions of subsonic/sub-Alfvénic and supersonic/super-Alfvénic flows, (b) inferring the global structure of the interplanetary medium between the solar photosphere and 1 AU based on large-scale solar magnetic field data. As an experimental test for the proposed technique, photospheric magnetic field data for CR 1682 are used to prescribe boundary condition near the Sun and results of a simulation are compared with spacecraft measurements at 1 AU. The comparison demonstrates a qualitative agreement between computed and observed parameters. While the difference in densities is still significant, the 3-D model better reproduces variations of the solar wind velocity than does the 2-D model presented earlier (Usmanov, 1993). 相似文献
8.
C. Dougados S. Cabrit J. Ferreira N. Pesenti P. Garcia D. O'Brien 《Astrophysics and Space Science》2004,292(1-4):643-650
We discuss in this contribution constraints on the origin of mass-loss from young stars brought by recent observations at high angular resolution (0.1″ = 14 AU) of the inner regions of winds from T Tauri stars. Jet widths and collimation scales, the large extent of the velocity profile as well as the detection of rotation signatures agree with predictions from magneto-centrifugal disk wind ejection models. However dynamically cold disk wind solutions predict too large terminal velocities and too low jet densities and ionisation fractions, suggesting that thermal gradients (originating in an accretion heated disk corona for example) may play an important role in accelerating the flow. 相似文献
9.
Due to their different mass and varying charge states, heavy solar ions provide invaluable information on the physical mechanisms
responsible for the heating of the corona and the solar wind acceleration. It is shown in the present work that some key characteristics
observed in the corona are straightforward features predicted by the velocity filtration effect. This mechanism originally
proposed by Scudder (1992a,b) accounts for the heating of the corona by just assuming that the velocity distribution functions
have enhanced supra-thermal tails. The apparent `heating' is then a natural consequence of the increasing ratio of supra thermal
over thermal particles as a function of altitude. Applied to the minor ions, it offers a natural explanation for the high
temperatures of the heavy ions compared to the protons. The kinetic filtration theory predicts temperatures more than proportional
to the mass of the ions, with a small correction for the charge state. With sufficiently high temperatures, the ions flow
faster than the protons. These characteristics are in good agreement with the most recent spectroscopic and in-situ solar wind observations. 相似文献
10.
C. O. Lee J. G. Luhmann D. Odstrcil P. J. MacNeice I. de Pater P. Riley C. N. Arge 《Solar physics》2009,254(1):155-183
We present results of solar-wind parameters generated by 3D MHD models. The ENLIL inner-heliosphere solar-wind model together
with the MAS or Wang – Sheeley – Arge (WSA) coronal models, describe the steady solar-wind stream structure and its origins
in the solar corona. The MAS/ENLIL and WSA/ENLIL models have been tuned to provide a simulation of plasma moments as well
as interplanetary magnetic-field magnitude and polarity in the absence of disturbances from coronal transients. To investigate
how well the models describe the ambient solar wind structure from the Sun out to 1 AU, the model results are compared to
solar-wind measurements from the ACE spacecraft. We find that there is an overall agreement between the observations and the
model results for the general large-scale solar-wind structures and trends, such as the timing of the high-density structures
and the low- and high-speed winds, as well as the magnetic sector structures. The time period of our study is the declining
phase of Solar Cycle 23 when the solar activity involves well-defined stream structure, which is ideal for testing a quasi-steady-state
solar-wind model. 相似文献
11.
Flux ropes are twisted magnetic structures that can be detected by in-situ measurements in the solar wind. However, different properties of detected flux ropes suggest different types of flux-rope populations. As such, are there different populations of flux ropes? The answer is positive and is the result of the analysis of four lists of flux ropes, including magnetic clouds (MCs), observed at 1 AU. The in-situ data for the four lists were fitted with the same cylindrical force-free field model, which provides an estimate of the local flux-rope parameters such as its radius and orientation. Since the flux-rope distributions have a broad dynamic range, we went beyond a simple histogram analysis by developing a partition technique that uniformly distributes the statistical fluctuations across the radius range. By doing so, we found that small flux ropes with radius R<0.1 AU have a steep power-law distribution in contrast to the larger flux ropes (identified as MCs), which have a Gaussian-like distribution. Next, from four CME catalogs, we estimated the expected flux-rope frequency per year at 1 AU. We found that the predicted numbers are similar to the frequencies of MCs observed in-situ. However, we also found that small flux ropes are at least ten times too abundant to correspond to CMEs, even to narrow ones. Investigating the different possible scenarios for the origin of these small flux ropes, we conclude that these twisted structures can be formed by blowout jets in the low corona or in coronal streamers. 相似文献
12.
Proton heating at stream interaction regions in the solar wind is investigated based on the solar wind data obtained by Suisei spacecraft between 0.68 and 1.01 AU from the Sun. The deflection angle of the solar wind flow in the ecliptic plane is used to identify the interaction region. In the solar wind flows coming from east of the Sun in low-speed streams and coming from west in high-speed streams, the radial gradient of proton temperature is flattened owing to heating in the interaction region. From comparison of the best-fitted power law dependence of proton temperature on the radial distance in the deflected flow with that in the non-deflected flow, it is suggested that heating in the interaction regions starts around 0.6–0.7 AU from the Sun. 相似文献
13.
In coronal holes the electron (proton) density is low, and heating of the proton gas produces a rapidly increasing proton temperature in the inner corona. In models with a reasonable electron density in the upper transition region the proton gas becomes collisionless some 0.2 to 0.3 solar radii into the corona. In the collisionless region the proton heat flux is outwards, along the temperature gradient. The thermal coupling to electrons is weak in coronal holes, so the heat flux into the transition region is too small to supply the energy needed to heat the solar wind plasma to coronal temperatures. Our model studies indicate that in models with proton heating the inward heat conduction may be so inefficient that some of the energy flux must be deposited in the transition region to produce the proton fluxes that are observed in the solar wind. If we allow for coronal electron heating, the energy that is needed in the transition region to heat the solar wind to coronal temperatures, may be supplied by heat conduction from the corona. 相似文献
14.
We present recent observations of the plasma parameters in coronal holes at the origin of the fast solar wind and in the interplanetary
medium. A model based on the heat conductivity law in a dilute plasma shows the coherency of the electron and proton temperature
observations from coronal holes to the interplanetary medium. These new observations are severe constraints for any model
of the expansion of the fast solar wind. We discuss why and how non-equilibrium multispecies Fokker-Planck approach must be
developed and present a generalized Grad's solution.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
The effect of an interplanetary atomic hydrogen gas on solar wind proton, electron and α-particle temperatures beyond 1 AU
is considered. It is shown that the proton temperature (and probably also the α-particle temperature) reaches a minimum between
2 AU and 4 AU, depending on values chosen for solar wind and interstellar gas parameters. Heating of the electron gas depends
primarily on the thermal coupling of the protons and electrons. For strong coupling (whenT
p
≳T
e
), the electron temperature reaches a minimum between 4 AU and 8 AU, but for weak coupling (Coulomb collisions only), the
electron temperature continues to decrease throughout the inner solar system. A spacecraft travelling to Jupiter should be
able to observe the heating effect of the solar wind-interplanetary hydrogen interaction, and from such observations it may
be possible of infer some properties of the interstellar neutral gas.
Currently a National Research Council Resident Research Associate. 相似文献
16.
Y. C. Whang 《Solar physics》1983,88(1-2):343-358
A one-fluid model is employed to study the global expansion of the solar wind from a two-hole corona, under the assumptions that the holes are confined to polar caps within 30° of heliographic colatitude, the flow is steady and axisymmetric, and the geometry of streamlines is prescribed. The boundary conditions are adjusted in such a way that the calculated solar wind properties at 1 AU are in a reasonable agreement with observational results. A series of numerical solutions are obtained, the series produces a maximum terminal speed of 829 km s?1 at the pole. The calculated solar wind speeds are strongly latitude dependent and are positively correlated with local divergence factor of a stream tube. The solutions imply that most plasma properties are highly inhomogeneous at the polar caps. The flow velocity, the temperature, the proton number flux and the conduction heat flux all increase towards the hole center. 相似文献
17.
The influence of latitudinally dependent boundary conditions on the large radius values of meridional flow in the distant solar wind is examined through a double perturbation expansion of the magnetohydrodynamic equations. A general result is derived for the meridional velocity which allows arbitrary specification of radial velocity, radial magnetic field, and mass flux, as a function of colatitude at some coronal reference surface. Three specific examples are treated, including the model of Pneuman and Kopp (1971). The latter example indicates that there may be flow toward the equator at large radii, as opposed to the pure equatorial divergence of internally generated motion due to a flow which is latitudinally uniform at the reference radius. A solar cycle effect most probably averages the boundary conditions so that only the equatorial divergence from an average spherically symmetric corona is seen in comet-tail observations. This may also explain the off-and-on-again nature of the meridional gradient in the radial velocity of the solar wind as seen in radio scintillation observations. 相似文献
18.
The required electron density to excite a type III solar burst can be predicted from different theories, using the low frequency radio observations of the RAE-1 satellite. Electron flux measurements by satellite in the vicinity of 1 AU then give an independent means of comparing these predicted exciter electron densities to the measured density. On this basis, one theory predicts the electron density in closest agreement with the measured values.NAS/NRC Postdoctoral Resident Research Associate. 相似文献
19.
M. P. Nakada 《Solar physics》1977,51(2):327-343
Average solar wind properties at 1 AU either alone or together with the electron density distribution are used to obtain or review some results that relate coronal temperatures, temperature gradients, and compositions. Measured values of the temperature (T) and the temperature gradient parameter ( = -d ln T/d ln r) are used to find compositions that satisfy the equations used to obtain the results. The total energy equation may be satisfied if the thermal conductivity is reduced by considerable depletions of H+ in the corona. The electron energy equation only gives information on coronal compositions that are coupled with d/d ln r. The hydrostatic approximation (momentum equation) for the electron density distribution also appears to require considerable depletions of H+ in the corona. Results from the integrated momentum equation for the solar wind support the hydrostatic results; together, they give some information on the minimum value of in the outer corona. Some changes in assumptions or values of parameters that may modify these interpretations are discussed. 相似文献
20.
B. A. Lindblad 《Solar physics》1981,74(1):187-196
An analysis of 346 high-speed solar wind streams observed at 1 AU during 1964–75 is presented. The analysis shows that a two-sector structure was the dominant feature of the interplanetary magnetic field associated with the high-speed solar wind plasma. The high-speed streams occurred at preferred Bartels days: Positive polarity streams were most frequent near Bartels day 4, negative polarity streams were most frequent near Bartels day 17. Since the solar wind carries with it the photospheric magnetic polarity of the solar source region, the observed distribution of Bartels days must indicate a fundamental property of the distribution of the solar sources of high-speed plasma streams. The observations are explained in terms of a tilted dipole model of the solar-interplanetary field.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献