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1.
Observations carried out from the coronagraphs on board space missions (LASCO/SOHO, Solar Maximum and Skylab) and ground-based facilities (HAO/Mauna Loa Observatory) show that coronal mass ejections
(CMEs) can be classified into two classes based on their kinematics evolution. These two classes of CMEs are so-called fast
and slow CMEs. The fast CME starts with a high initial speed that remains more or less constant; it is also called the constant-speed CME. On the other hand, the slow CME starts with a low initial speed, but shows a gradual acceleration; it is also called
the accelerated and slow CME. Low and Zhang [Astrophys. J. 564, L53–L56, 2002] suggested that these two classes of CMEs could be a result of a difference in the initial topology of the
magnetic fields associated with the underlying quiescent prominences. A normal prominence magnetic field topology will lead
to a fast CME, while an inverse quiescent prominence results in a slow CME, because of the nature of the magnetic reconnection
processes. In a recent study given by Wu et al. [Solar Phys. 225, 157–175, 2004], it was shown that an inverse quiescent prominence magnetic topology also could produce a fast CME. In this
study, we perform a numerical MHD simulation for CMEs occurring in both normal and inverse quiescent prominence magnetic topology.
This study demonstrates three major physical processes responsible for destabilization of these two types of prominence magnetic
field topologies that can launch CMEs. These three initiation processes are identical to those used by Wu et al. [Solar Phys. 225, 157–175, 2004]. The simulations show that both fast and slow CMEs can be initiated from these two different types of magnetic
topologies. However, the normal quiescent prominence magnetic topology does show the possibility for launching a reconnection island (or secondary O-line) that might be thought of as a “CME’’. 相似文献
2.
Pekka Janhunen Annika Olsson Christopher T. Russell Harri Laakso 《Space Science Reviews》2006,122(1-4):89-95
Auroral emission caused by electron precipitation (Hardy et al., 1987, J. Geophys. Res. 92, 12275–12294) is powered by magnetospheric driving processes. It is not yet fully understood how the energy transfer mechanisms
are responsible for the electron precipitation. It has been proposed (Hasegawa, 1976, J. Geophys. Res. 81, 5083–5090) that Alfvén waves coming from the magnetosphere play some role in powering the aurora (Wygant et al., 2000, J. Geophys. Res. 105, 18675–18692, Keiling et al., 2003, Science
299, 383–386). Alfvén-wave-induced electron acceleration is shown to be confined in a rather narrow radial distance range of
4–5 R
E
(Earth radii) and its importance, relative to other electron acceleration mechanisms, depends strongly on the magnetic disturbance
level so that it represents 10% of all electron precipitation power during quiet conditions and increased to 40% during disturbed
conditions. Our observations suggest that an electron Landau resonance mechanism operating in the “Alfvén resonosphere” is
responsible for the energy transfer. 相似文献
3.
Takeru K. Suzuki 《Space Science Reviews》2011,158(2-4):339-363
We review our recent results of Alfvén wave-driven winds. First, we present the result of self-consistent 1D MHD simulations for solar winds from the photosphere to interplanetary region. Here, we emphasize the importance of the reflection of Alfvén waves in the density stratified corona and solar winds. We also introduce the recent Hinode observation that might detect the reflection signature of transverse (Alfvénic) waves by Fujimura and Tsuneta (Astrophys. J. 702:1443, 2009). Then, we show the results of Alfvén wave-driven winds from red giant stars. As a star evolves to the red giant branch, the properties of stellar winds drastically change from steady coronal winds to intermittent chromospheric winds. We also discuss how the stellar evolution affects the wave reflection in the stellar atmosphere and similarities and differences of accretion disk winds by MHD turbulence. 相似文献
4.
5.
Hans Goedbloed 《Space Science Reviews》2006,122(1-4):239-246
Transonically rotating toroidal plasmas occur at all scales in the plasma universe and, recently, also in laboratory tokamak plasmas. This offers great opportunities for new insights of the effects of transonic transitions on the background equilibrium flows, and on the waves and instabilities excited. Transfer of knowledge and computational methods on MHD and two-fluid waves and instabilities in magnetically confined laboratory fusion plasmas to space and astrophysical plasmas is seriously hampered though by two related difficulties:
- in contrast to laboratory plasmas, astrophysical plasmas always have sizeable plasma flows so that they can never be described as a static equilibrium;
- these flows are usually ‘transonic’, i.e., surpass one of the critical speeds related to the different flow regimes with quite different physical characteristics.
6.
Vytenis M. Vasyliunas 《Space Science Reviews》1979,24(4):609-634
A wide class of galactic X-ray sources are believed to be binary systems where mass is flowing from a normal star to a companion that is a compact object, such as a neutron star. The strong magnetic fields of the compact object create a magnetosphere around it. We review the theoretical models developed to describe the properties of magnetospheres in such accreting binary systems. The size of the magnetosphere can be estimated from pressure balance arguments and is found to be small compared to the over-all size of the accretion region but large compared to the compact object if the latter is a neutron star. In the early models the magnetosphere was assumed to have open funnels in the polar regions, through which accreting plasma could pour in. Later, magnetically closed models were developed, with plasma entry made possible by instabilities at the magnetosphere boundary. The theory of plasma flow inside the magnetosphere has been formulated in analogy to a stellar wind with reversed flow; a complicating factor is the instability of the Alfvén critical point for inflow. In the case of accretion via a well-defined disk, new problems of magnetospheric structure appear, in particular the question to what extent and by what process the magnetic fields from the compact object can penetrate into the accretion disk. Since the X-ray emission is powered by the gravitational energy released in the accretion process, mass transfer into the magnetosphere is of fundamental importance; the various proposed mechanisms are critically examined.Proceedings of the NASA/JPL Workshop on the Physics of Planetary and Astrophysical Magnetospheres. 相似文献
7.
A fundamental reality throughout the space plasma is the existence of magnetic field-aligned flows. It is usually believed
that the spatial transverse shear in the parallel flow destabilizes many low frequency oscillations and this may be the origin
of low frequency oscillations in the ionosphere (V. V. Gavrishchaka et al., 1998, Phys. Rev. Lett., 80, 728 and Phys. Rev. Lett.: 2000, 85, 4285). Here we show that this notion of destabilizing influence of the shear in the parallel flow can be changed altogether
if one takes the effect of the flow curvature (second spatial derivative) into account. The transverse curvature in the parallel
flow can overcome the destabilizing influence of the shear and can render the low frequency modes stable. It is shown that
unlike flow shear the effect of flow curvature is sign- and mode-dependent.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
Yann Alibert Christoph Mordasini Olivier Mousis Willy Benz 《Space Science Reviews》2005,116(1-2):77-95
We present models of giant planet formation, taking into account migration and disk viscous evolution. We show that migration
can significantly reduce the formation timescale bringing it in good agreement with typical observed disk lifetimes. We then
present a model that produces a planet whose current location, core mass and total mass are comparable with the one of Jupiter.
For this model, we calculate the enrichments in volatiles and compare them with the one measured by the Galileo probe. We
show that our models can reproduce both the measured atmosphere enrichments and the constraints derived by Guillot et al. (2004), if we assume the accretion of planetesimals with ices/rocks ratio equal to 4, and that a substantial amount of CO2 was present in vapor phase in the solar nebula, in agreement with ISM measurements. 相似文献
9.
We study instabilities driven by a sheared plasma flow in the low-frequency domain. Two unstable branches are found: the ion-sound
mode and the kinetic Alfvén mode. Both instabilities are aperiodic. The ion-sound instability does not depend on the plasma
β (gas/magnetic pressure ratio) and has a maximum growth rate of about 0.1 of the velocity gradient dV
0/dx. On the other hand, the kinetic Alfvén instability is stronger for larger β and dominates the ion-sound instability for β
> 0.05. Possible applications for space plasmas are shortly discussed. 相似文献
10.
Solar Nebula Magnetohydrodynamics 总被引:1,自引:0,他引:1
The dynamical state of the solar nebula depends critically upon whether or not the gas is magnetically coupled. The presence
of a subthermal field will cause laminar flow to break down into turbulence. Magnetic coupling, in turn, depends upon the
ionization fraction of the gas. The inner most region of the nebula (≲0.1 AU) is magnetically well-coupled, as is the outermost
region (≳10 AU). The magnetic status of intermediate scales (∼1 AU) is less certain. It is plausible that there is a zone
adjacent to the inner disk in which turbulent heating self-consistently maintains the requisite ionization levels. But the
region adjacent to the active outer disk is likely to be magnetically ``dead.' Hall currents play a significant role in nebular
magnetohydrodynamics.
Though still occasionally argued in the literature, there is simply no evidence to support the once standard claim that differential
rotation in a Keplerian disk is prone to break down into shear turbulence by nonlinear instabilities. There is abundant evidence—numerical,
experimental, and analytic—in support of the stabilizing role of Coriolis forces. Hydrodynamical turbulence is almost certainly
not a source of enhanced turbulence in the solar nebula, or in any other astrophysical accretion disk.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
C. K. Goertz 《Space Science Reviews》1979,23(2):319-343
Magnetic field measurements made by the vector helium magnetometers on board Pioneers-10 and 11 reveal the existence of a current sheet (thickness 2R
J) carrying an eastward current. Self-consistent studies of the current sheet show that the magnitude of the current is of the order of 10+2 Am+1 and that the current is carried by a hot (T>1 keV) plasma, the density of which varies between 1 cm+3 at 30R
J to 10+2 cm+3 at 80R
J. The current sheet is warped azimuthally and parallel to the magnetic dipole equator.The existence of an azimuthal field component indicates a poloidal plasma flow transporting some 1029 ions per second from Jupiter into the outer magnetosphere. It is shown that, if the outer magnetosphere is in a steady state, this plasma must be transported outward within the current sheet by a diffusion process which is faster than the one responsible for particle transport in the inner magnetosphere but slower than Bohm diffusion. It is suggested that the diffusion is due to the observed mhd turbulence in the current sheet. Such a model requires the existence of open field lines along which particles can escape freely into interplanetary space.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978. 相似文献
12.
This chapter gives a brief review on the theory of gamma-ray bursts (GRBs), including the models of multi-messengers (e.g., prompt multiwavelength electromagnetic emissions, high-energy neutrinos, ultra-high-energy cosmic rays, and gravitational waves) and central engines (in particular, mergers of binary neutron stars for short GRBs). For detailed reviews, please see (Piran in Phys. Rep. 314:575, 1999; Rev. Mod. Phys. 76:1143, 2004; Mészáros in Annu. Rev. Astron. Astrophys. 40:137, 2002; Rep. Prog. Phys. 69:2259, 2006; Zhang and Mészáros in Int. J. Mod. Phys. A 19:2385, 2004; Zhang in Chin. J. Astron. Astrophys. 7:1, 2007; Nakar in Phys. Rep. 442:166, 2007; Kumar and Zhang in Phys. Rep. 561:1, 2015). 相似文献
13.
M. Goossens 《Space Science Reviews》1994,68(1-4):51-62
This review discusses Alfvén wave heating in non-uniform plasmas as a possible means for explaining the heating of the solar corona. It focusses on recent analytical results that enable us to understand the basic physics of Alfvén wave heating and help us with the interpretation of results of numerical simulations. First we consider the singular wave solutions that are found in linear ideal MHD at the resonant magnetic surface where the frequency of the wave equals the local Alfvén frequency. Next, we use linear resistive MHD for describing the waves in the dissipative region and explain how dissipation modifies the singular solutions found in linear ideal MHD. 相似文献
14.
It has been suggested that a surge can be modelled as a jet travelling in a sheared magnetic field, and that the transition to turbulence of this MHD tearing jet can explain several key observed features. In this paper we present our preliminary results of the transition to turbulencevia secondary instabilities of the MHD tearing jet. Our results confirm that turbulent transition can decelerate the surge, with decay times which compare well with surge data. Furthermore, we find that the turbulent MHD tearing jet forms magnetic field-aligned velocity filaments similar to those often observed in the surge flow field. 相似文献
15.
The composition of planetesimals depends upon the epoch and the location of their formation in the solar nebula. Meteorites
produced in the hot inner nebula contain refractory compounds. Volatiles were present in icy planetesimals and cometesimals
produced in the cold outer nebula. However, the mechanism responsible for their trapping is still controversial. We argue
for a general scenario valid in all regions of the turbulent nebula where water condensed as a crystalline ice (Hersant et al., 2004). Volatiles were trapped in the form of clathrate hydrates in the continuously cooling nebula. The epoch of clathration
of a given species depends upon the temperature and the pressure required for the stability of the clathrate hydrate. The
efficiency of the mechanism depends upon the local amount of ice available. This scenario is the only one so far which proposes
a quantitative interpretation of the non detection of N2 in several comets of the Oort cloud (Iro et al., 2003). It may explain the large variation of the CO abundance observed in comets and predicts an Ar/O ratio much less than
the upper limit of 0.1 times the solar ratio estimated on C/2001 A2 (Weaver et al., 2002). Under the assumption that the amount of water ice present at 5 AU was higher than the value corresponding to the
solar O/H ratio by a factor 2.2 at least, the clathration scenario reproduces the quasi uniform enrichment with respect to
solar of the Ar, Kr, Xe, C, N and S elements measured in Jupiter by the Galileo probe. The interpretation of the non-uniform
enrichment in C, N and S in Saturn requires that ice was less abundant at 10 AU than at 5 AU so that CO and N2 were not clathrated in the feeding zone of the planet while CH4, NH3 and H2S were. As a result, the 14N/15N ratio in Saturn should be intermediate between that in Jupiter and the terrestrial ratio.
Ar and Kr should be solar while Xe should be enriched by a factor 17. The enrichments in C, N and S in Uranus and Neptune
suggest that available ice was able to form clathrates of CH4, CO and the NH3 hydrate, but not the clathrate of N2. The enrichment of oxygen by a factor 440 in Neptune inferred by Lodders and Fegley (1994) from the detection of CO in the
troposphere of the planet is higher by at least a factor 2.5 than the lower limit of O/H required for the clathration of CO
and CH4 and for the hydration of NH3. If CO detected by Encrenaz et al. (2004) in Uranus originates from the interior of the planet, the O/H ratio in the envelope must be around of order of 260
times the solar ratio, then also consistent with the trapping of detected volatiles by clathration. It is predicted that Ar
and Kr are solar in the two planets while Xe would be enriched by a factor 30 to 70. Observational tests of the validity of
the clathration scenario are proposed. 相似文献
16.
17.
Stasiewicz K. Bellan P. Chaston C. Kletzing C. Lysak R. Maggs J. Pokhotelov O. Seyler C. Shukla P. Stenflo L. Streltsov A. Wahlund J.-E. 《Space Science Reviews》2000,92(3-4):423-533
This paper presents a comprehensive review of dispersive Alfvén waves in space and laboratory plasmas. We start with linear properties of Alfvén waves and show how the inclusion of ion gyroradius, parallel electron inertia, and finite frequency effects modify the Alfvén wave properties. Detailed discussions of inertial and kinetic Alfvén waves and their polarizations as well as their relations to drift Alfvén waves are presented. Up to date observations of waves and field parameters deduced from the measurements by Freja, Fast, and other spacecraft are summarized. We also present laboratory measurements of dispersive Alfvén waves, that are of most interest to auroral physics. Electron acceleration by Alfvén waves and possible connections of dispersive Alfvén waves with ionospheric-magnetospheric resonator and global field-line resonances are also reviewed. Theoretical efforts are directed on studies of Alfvén resonance cones, generation of dispersive Alfvén waves, as well their nonlinear interactions with the background plasma and self-interaction. Such topics as the dispersive Alfvén wave ponderomotive force, density cavitation, wave modulation/filamentation, and Alfvén wave self-focusing are reviewed. The nonlinear dispersive Alfvén wave studies also include the formation of vortices and their dynamics as well as chaos in Alfvén wave turbulence. Finally, we present a rigorous evaluation of theoretical and experimental investigations and point out applications and future perspectives of auroral Alfvén wave physics. 相似文献
18.
Two fractionation models are applied to the problem of generating the widely distributed “Q-component” noble gases in meteorites
from the solar-like isotopic and elemental compositions that presumably characterized the early solar accretion disk. Noble
gas fractionation by mass-dependent dissipation of the solar nebula, as suggested by Ozima et al. (1998), is examined in the context of a model developed by Johnstone et al. (1998) for accretion disk photoevaporation driven by intense UV radiation from a neighboring giant star. Hydrodynamic escape
of heavier species entrained in hydrogen outflow from the UV-heated outer regions of the disk can generate substantial noble
gas fractionations, but they do not match the observed Q-component isotopic pattern and moreover require the physically unrealistic
assumption that the fractionated gases are confined to the heated disk boundary zone, without mixing with the interior nebula,
for long periods of time. It seems more likely that hydrodynamic outflow is actually established below this zone, in the body
of the disk. In this case fractionations are governed by Rayleigh distillation of the entire remaining nebula, and are negligible
at the time when disk erosion is halted by the gravitational potential of the young sun embedded in the disk.
A “local” model of noble gas fractionation by hydrodynamic blowoff of transient, methane-rich atmospheres outgassed from the
interiors of large primitive planetesimals (Pepin, 1991) is updated and assessed against current data. Degassed atmospheres
are assumed to contain isotopically solar noble gases except for an additional nucleogenic Xe component that contributes primarily
to the two heaviest isotopes; there is evidence that this same component is present at varying levels in other solar-system
volatile reservoirs, possibly reflecting a compositional change with time in the solar nebula. Single fixed values for the
two free parameters in the blowoff modeling equations can generate fractionated Xe, Kr, Ar and Ne compositions in the residual
atmosphere that closely match observed meteoritic isotopic distributions, and Q-gas elemental ratios are approximated by adsorption
of fractionated gases on planetesimal surface grains using plausible values of relative Henry Law constants. Additional requirements
for adsorption of sufficient absolute amounts of Q-gases on carrier grains, and their subsequent ejection to space, mixing
in the nebula, and dispersal into meteorite bodies, are examined in the context of current models for body sizes and dynamical
evolution in an early mass-rich asteroid belt (Chambers and Wetherill, 2001). Despite its ability to replicate isotopic compositions,
uncertainties about the environments in which the blowoff model can successfully operate suggest that there is, as yet, no
entirely satisfactory understanding of how the Q-component noble gases might have evolved from solar-like precursor compositions.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
The properties of magnetohydrodynamic waves and instabilities of laboratory and space plasmas are determined by the overall
magnetic confinement geometry and by the detailed distributions of the density, pressure, magnetic field, and background velocity
of the plasma. Consequently, measurement of the spectrum of MHD waves (MHD spectroscopy) gives direct information on the internal
state of the plasma, provided a theoretical model is available to solve the forward as well as the inverse spectral problems.
This terminology entails a program, viz. to improve the accuracy of our knowledge of plasmas, both in the laboratory and in
space. Here, helioseismology (which could be considered as one of the forms of MHD spectroscopy) may serve as a luminous example.
The required study of magnetohydrodynamic waves and instabilities of both laboratory and space plasmas has been conducted
for many years starting from the assumption of static equilibrium. Recently, there is a outburst of interest for plasma states
where this assumption is violated. In fusion research, this interest is due to the importance of neutral beam heating and
pumped divertor action for the extraction of heat and exhaust needed in future tokamak reactors. Both result in rotation of
the plasma with speeds that do not permit the assumption of static equilibrium anymore. In astrophysics, observations in the
full range of electromagnetic radiation has revealed the primary importance of plasma flows in such diverse situations as
coronal flux tubes, stellar winds, rotating accretion disks, and jets emitted from radio galaxies. These flows have speeds
which substantially influence the background stationary equilibrium state, if such a state exists at all. Consequently, it
is important to study both the stationary states of magnetized plasmas with flow and the waves and instabilities they exhibit.
We will present new results along these lines, extending from the discovery of gaps in the continuous spectrum and low-frequency
Alfvén waves driven by rotation to the nonlinear flow patterns that occur when the background speed traverses the full range
from sub-slow to super-fast.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献