共查询到20条相似文献，搜索用时 31 毫秒
1.
S. V. Chalov 《Astronomy Letters》2012,38(3):191-200
The spectra of energetic protons measured on the Voyager-1 and Voyager-2 spacecraft in the inner heliospheric shock layer can be explained in terms of the classical theory of the shock drift acceleration
of interstellar pickup protons with allowancemade for theirmultiple reflection from the front. The spacecraft entered this
region after the heliospheric termination shock crossing in 2004 and 2007, respectively. The large-scale variations of the
magnetic field direction near the shock front associated with the passage of sector structures through it are the decisive
factor in explaining the measurements. 相似文献
2.
M. Koenig A. Ravasio A. Benuzzi-Mounaix B. Loupias N. Ozaki M. Borghesi C. Cecchetti D. Batani R. Dezulian S. Lepape P. Patel H. S. Park D. Hicks A. Mckinnon T. Boehly A. Schiavi E. Henry M. Notley R. Clark S. Bandyopadhyay 《Astrophysics and Space Science》2007,307(1-3):257-261
In this paper, experimental results on X-ray and proton radiography of shock compressed matter are presented. It has been
performed at the Rutherford Appleton Laboratory (RAL) using three long pulse beams to generate a shock wave in a multi-layer
foil and a short pulse beam to create either an X-ray or protons source for a transverse radiography. Depending on the probe
material (aluminium or carbon foam) a Molybdenum Kα source or a proton beam are used. Density data of the shocked aluminium,
in the multimagabar regime are presented. 相似文献
3.
N. J. Lehtinen S. Pohjolainen K. Huttunen-Heikinmaa R. Vainio E. Valtonen A. E. Hillaris 《Solar physics》2008,247(1):151-169
A high-speed, halo-type coronal mass ejection (CME), associated with a GOES M4.6 soft X-ray flare in NOAA AR 0180 at S12W29
and an EIT wave and dimming, occurred on 9 November 2002. A complex radio event was observed during the same period. It included
narrow-band fluctuations and frequency-drifting features in the metric wavelength range, type III burst groups at metric – hectometric
wavelengths, and an interplanetary type II radio burst, which was visible in the dynamic radio spectrum below 14 MHz. To study
the association of the recorded solar energetic particle (SEP) populations with the propagating CME and flaring, we perform
a multi-wavelength analysis using radio spectral and imaging observations combined with white-light, EUV, hard X-ray, and
magnetogram data. Velocity dispersion analysis of the particle distributions (SOHO and Wind
in situ observations) provides estimates for the release times of electrons and protons. Our analysis indicates that proton acceleration
was delayed compared to the electrons. The dynamics of the interplanetary type II burst identify the burst source as a bow
shock created by the fast CME. The type III burst groups, with start times close to the estimated electron-release times,
trace electron beams travelling along open field lines into the interplanetary space. The type III bursts seem to encounter
a steep density gradient as they overtake the type II shock front, resulting in an abrupt change in the frequency drift rate
of the type III burst emission. Our study presents evidence in support of a scenario in which electrons are accelerated low
in the corona behind the CME shock front, while protons are accelerated later, possibly at the CME bow shock high in the corona. 相似文献
4.
Kinetic theory is used to calculate the power dissipated by obliquely propagating Alfvén waves to heat the solar wind protons,
using the Generalized (r, q) distribution function. The evolution of power dissipation of protons with increasing heliocentric distance is subsequently
determined. Comparison between theoretical and observational results with data shows good agreement, especially for the slow
solar wind streams. Previous results where a Maxwellian distribution function was used to calculate the power dissipated did
not match well with observations. 相似文献
5.
A transient flow system containing several streams and shocks associated with the Bastille Day 2000 solar event was observed
by the WIND and ACE spacecraft at 1 AU. Voyager 2 (V2) at 63 AU observed this flow system after it moved through the interplanetary medium and into the distant heliosphere,
where the interstellar pickup protons strongly influence the MHD structures and flow dynamics. We discuss the Voyager 2 magnetic and plasma observations of this event. Increases in the magnetic field strength B, density N, temperature T and
speed V were observed at the front of a stream at V2, consistent with presence of a shock related to the Bastille Day shock
at 1 AU. However, the jumps occurred in a 16.9-hour data gap, so that the shock was not observed directly, and the properties
of the candidate shock cannot be determined precisely. The candidate shock was followed by a merged interaction region (MIR)
that moved past V2 for at least 10 days. The first part of this MIR contains a structure that might be a magnetic cloud. Just
ahead of the shock there was an abrupt increase in density associated with a decrease in temperature such that the solar wind
thermal pressure was constant across it. Just behind the shock there was an abrupt decrease in density associated with a net
increase in magnetic field strength. This appears to be a pressure balanced structure in which the interstellar pickup protons
make a significant contribution. 相似文献
6.
The initially supersonic flow of the solar wind passes through a magnetic shock front where its velocity is supposed to be reduced to subsonic values. The location of this shock front is primarily determined by the energy density of the external interstellar magnetic field and the momentum density of the solar wind plasma. Interstellar hydrogen penetrating into the heliosphere undergoes charge exchange processes with the solar wind protons and ionization processes by the solar EUV radiation. This results in an extraction of momentum from the solar wind plasma. Changes of the geometry and the location of the shock front due to this interaction are studied in detail and it is shown that the distance of the magnetic shock front from the Sun decreases from 200 to 80 AU for an increase of the interstellar hydrogen density from 0.1 to 1.0 cm−3. The geometry of the shock front is essentially spherical with a pronounced embayment in the direction opposite to the approach of interstellar matter which depends very much on the temperature of the interstellar gas. Due to the energy loss by the interaction with neutral matter the solar wind plasma reduces its velocity with increasing distance from the Sun. This modifies Parker's solution of a constant solar wind velocity. 相似文献
7.
Adi Nusser 《Monthly notices of the Royal Astronomical Society》2007,375(3):1106-1110
We present general relativistic solutions for self-similar spherical perturbations in an expanding cosmological background of cold pressure-less gas. We focus on solutions having shock discontinuities propagating in the surrounding cold gas. The pressure, p , and energy density, μ, in the shock-heated matter are assumed to obey p = w μ , where w is a positive constant. Consistent solutions are found for shocks propagating from the symmetry centre of a region of a positive density excess over the background. In these solutions, shocks exist outside the radius marking the event horizon of the black hole which would be present in a shock-less collapse. For large jumps in the energy density at the shock, a black hole is avoided altogether and the solutions are regular at the centre. The shock-heated gas does not contain any sonic points, provided the motion of the cold gas ahead of the shock deviates significantly from the Hubble flow. For shocks propagating in the uniform background, sonic points always appear for small jumps in the energy density. We also discuss self-similar solutions without shocks in fluids with w < −1/3 . 相似文献
8.
The Bastille Day (14 July) 2000 CME is a fast, halo coronal mass ejection event headed earthward. The ejection reached Earth
on 15 July 2000 and produced a very significant magnetic storm and widespread aurora. At 1 AU the Wind spacecraft recorded a strong forward shock with a speed jump from ∼ 600 to over 1000 km s−1. About 6 months later, this CME-driven shock arrived at Voyager 2 (∼ 63 AU) on 12 January 2001 with a speed jump of ∼ 60 km s−1. This provides a good opportunity to study the shock propagation in the outer heliosphere. In this study, we employ a 2.5-D
MHD numerical model, which takes the interaction of solar wind protons and interstellar neutrals into account, to investigate
the shock propagation in detail and compare the model predictions with the Voyager 2 observations. The Bastille Day CME shock undergoes a dramatic change in character from the inner to outer heliosphere. Its
strength and propagation speed decay significantly with distance. The model results at the location of Voyager 2 are in good agreement with in-situ observations.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014293527951 相似文献
9.
M. Yokosawa 《Astrophysics and Space Science》1984,107(1):109-123
The dynamical evolution of a relativistic explosion in a homogeneous medium is studied by means of a time-dependent, hydrodynamic code. When the expanding velocity of the shock front reduces to the sound velocity in the relativistic fluid, the reverse shock wave propagating inward through the expanding material is generated. The radius of the turning point of the reverse shock wave is proportional to the explosion energy and hardly depends on the mass of the explosion products. In the case of the non-relativistic explosion, the reverse shock wave is generated just after the free expansion stage. The radius of the turning point of the reverse shock wave is proportional to the mass of the explosion products and little depends on the explosion energy. In both cases of the non-relativistic and relativistic explosion, the reverse shock wave is strong in a spherical explosion and weak in a cylindrical one. The plane symmetric explosion does not generate the reverse shock wave. 相似文献
10.
11.
We use a one-dimensional, time-dependent adaptive grid MHD code to study the interaction between fast and slow shocks in the solar wind. Our results show that: (1) a forward slow shock (FSS) can be destroyed by a forward fast shock (FFS) that overtakes it from behind; (2) two propagating FSSs can merge into a stronger FSS; (3) a strong FSS can survive by following a strong forward fast shock; and (4) the strength of a FSS is decreased by following an FFS. These simulation results reproduce an important feature of the Helios observations (Richter, 1987) where transient fast shocks were more frequently followed within a few hours by slow shock ype discontinuities rather than by fast reverse shocks. 相似文献
12.
In high-speed solar wind, propagating Alfvén waves can be transferred into fast magnetosonic waves. When both the magnetic field strength and Alfvén wave velocity approach zero, fast magnetosonic waves will be transferred into ion-acoustic waves. As the phase velocity of ion-acoustic waves is slightly greater than the thermal velocity of protons, the turbulence energy of ion-acoustic waves can largely be absorbed by protons and can cause the mean temperature of protons to be greater than that of electrons by stochastic turbulence heating of ion-acoustic waves for protons. 相似文献
13.
Energetic protons haying ring type distributions are shown to generate low-frequency electrostatic waves, propagating nearly transverse to the geomagnetic field lines, in the ring current region by exciting Mode 1 arid Mode 2 nonresonant instabilities and a resonant instability. Mode 1 nonresonant instability has frequencies around ~4 Hz with transverse wavelengths of ~(8–80) km, and it is likely to occur in the region L = (7–8). Mode 2 nonresonant instability can generate frequencies ~(850–1450) Hz with transverse wavelengths ~(2–20) km. The typical frequencies and transverse wavelengths associated with the resonant instability are (950–1250) Hz and (30–65) km. Both the Mode 2 nonresonant instability and the resonant instability can occur in the ring current region with L = (4–6). The low-frequency modes driven by energetic protons could attain maximum saturation electric field amplitude varying from 0.8 mV/m to 70 mV/m. It is suggested that the turbulence produced by the low-frequency modes may cause pitch angle scattering of ring current protons in the region outside the plasmapause resulting in the ring current decay. 相似文献
14.
S. Masson K.-L. Klein R. Bütikofer E. Flückiger V. Kurt B. Yushkov S. Krucker 《Solar physics》2009,257(2):305-322
The origin of relativistic solar protons during large flare/CME events has not been uniquely identified so far. We perform
a detailed comparative analysis of the time profiles of relativistic protons detected by the worldwide network of neutron
monitors at Earth with electromagnetic signatures of particle acceleration in the solar corona during the large particle event
of 20 January 2005. The intensity – time profile of the relativistic protons derived from the neutron monitor data indicates
two successive peaks. We show that microwave, hard X-ray, and γ-ray emissions display several episodes of particle acceleration within the impulsive flare phase. The first relativistic
protons detected at Earth are accelerated together with relativistic electrons and with protons that produce pion-decay γ rays during the second episode. The second peak in the relativistic proton profile at Earth is accompanied by new signatures
of particle acceleration in the corona within ≈1R
⊙ above the photosphere, revealed by hard X-ray and microwave emissions of low intensity and by the renewed radio emission
of electron beams and of a coronal shock wave. We discuss the observations in terms of different scenarios of particle acceleration
in the corona. 相似文献
15.
As a possible mechanism for particle acceleration in the impulsive phase of solar flares, a new particle acceleration mechanism in shock waves is proposed; a collisionless fast magnetosonic shock wave can promptly accelerate protons and electrons to relativistic energies, which was found by theory and relativistic particle simulation. The simultaneous acceleration of protons and electrons takes place in a rather strong magnetic field such that
ce
pe
. For a weak magnetic field (
ce
pe
), strong acceleration occurs to protons only. Resonant protons gain relativistic energies within the order of the ion cyclotron period (much less than 1 s for solar plasma parameters). The electron acceleration time is shorter than the ion-cyclotron period. 相似文献
16.
Ten to 100 meV protons from the solar flare of March 24, 1966 were observed on the University of California scintillation counter on OGO-I. The short rise and decay times observed in the count rates of the 32 channels of pulse-height analysis show that scattering of the protons by the interplanetary field was much less important in this event than in previously observed proton flares. A diffusion theory in which D = M
r
is found to be inadequate to account for the time behavior of the count rates of this event. Small fluctuations of the otherwise smooth decay phase may be due to flare protons reflected from the back of a shock front, which passed the earth on March 23. 相似文献
17.
D. J. Ampleford S. V. Lebedev A. Ciardi S. N. Bland S. C. Bott J. P. Chittenden G. Hall C. A. Jennings J. Armitage G. Blyth S. Christie L. Rutland 《Astrophysics and Space Science》2005,298(1-2):241-246
Whilst observations provide many examples of collimated outflows or jets from astrophysical bodies, there remain unresolved
questions relating to their formation, propagation and stability. The ability to form scaled jets in the laboratory has provided
many useful insights. Experiments (Lebedev et al.: 2002, ApJ 564, 113) using conical arrays of fine metallic wires on the MAGPIE generator (1MA in 240 ns) have produced radiatively cooled
collimated jets in vacuum using the redirection of convergent flows by a conical shock. Here we present results of a jet produced
by this method propagating through a photo-ionized, quasi-stationary gas cloud. A working surface is observed at the head
of the jet. The velocity of this working surface is lower than the velocity of a jet tip in vacuum. 相似文献
18.
S. Hayakawa 《Astrophysics and Space Science》1975,34(1):73-79
Dust grains expelled by radiation pressure of stars are charged to potentials in the range 30–40 V in Hi clouds. These grains may be responsible for the following phenomena which are otherwise hardly explicable. (1) A considerable fraction of electrons knocked-out by charged grains of high speeds have energies around 15 eV and produce singly ionized ions but not doubly ionized ones in accord with an ultraviolet observation of interstellar atoms and ions. (2) Transverse momentum transferred to grains by Coulomb scattering of ambient electrons and protons is greater than that by multiple scattering of cosmic ray protons, thus the former being more effective for the grain alignment than the latter. (3) At a shock front charge separation due to a large inertial mass of grains produces an electric field, thus accelerating charged particles and causing a drift of interstellar matter. 相似文献
19.
Prasanta Chatterjee Deb Kumar Ghosh Biswajit Sahu 《Astrophysics and Space Science》2012,339(2):261-267
The nonlinear propagation of ion acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of nonthermal
electrons, nonthermal positrons, and singly charged adiabatically hot positive ions, whose dynamics is governed by the two
dimensional nonplanar Kadomstev-Petviashvili-Burgers (KPB) equation. The shock solution of the KPB equations is obtained numerically.
The effects of several parameters and ion kinematic viscosities on the properties of ion acoustic shock waves are discussed
in planar and nonplanar geometry. It is shown that the ion acoustic shock wave propagating in cylindrical/spherical geometry
with transverse perturbation will be deformed as time goes on. Also, it is seen that the strength and the steepness of the
IASWs increases with increasing β, the nonthermal parameter. 相似文献
20.
We report observations made from several interplanetary spacecraft, of the large low-energy particle event of 23–27 April, 1979 associated with solar filament activity. We discuss the intensity, spectral and directional evolution of the event as observed in the energy range 35–1600 keV on ISEE-3, located ～ 0.99 AU from the Sun upstream of the Earth. We demonstrate that the shock disturbance propagating through the interplanetary medium and observed at ISEE-3 on 24/25 April strongly controls the particle event. From a comparison of the ISEE-3 observations with those on other spacecraft, in particular on Helios-2, located at 0.41 AU heliocentric distance near the Sun-Earth line, we identify the solar filament erupting on late 22 April near central meridian as the trigger for the propagating shock disturbance. This disturbance which comprises a forward shock and a reverse shock at the orbit of ISEE-3 is found to be the main source of the energetic proton population observed. 相似文献