共查询到20条相似文献，搜索用时 140 毫秒
1.
I.A. Barghouthi V. Pierrard A.R. Barakat J. Lemaire 《Astrophysics and Space Science》2001,277(3):427-436
A Monte Carlo simulation is used to study the effects of Kappa H+distributions in the polar wind. We consider the gravity, the polarization electric field, the divergence of geomagnetic field
lines and Coulomb collisions of H+ in a background of O+ ions. The aim is to study the consequences of a velocity distribution function with an enhanced high energy tail instead
of a Maxwellian distribution as assumed in earlier Monte Carlo simulations. The transformation of the velocity distribution
function of H+ ions as a function of the altitude is presented. Effects resulting from the acceleration of the particles by the polarization
electric field and from Coulomb collisions depend on the energy of the particles. Coulomb collisions mainly affect low energy
particles while high energy particles are more efficiently accelerated by the upward directed ambipolar electric field. The
combination of both effects results in double-hump velocity distribution functions developing in the transition region. We
study consequences of suprathermal tails distributions on the shape of the double-hump and on the moments of the velocity
distribution function.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
The energization of charged particles, due to interaction with the ambient electromagnetic turbulence, has a significant influence
on the plasma transport in space. The effect of wave-particle interactions on the outflow characteristics of polar wind plasma
was investigated. The theoretical model included gravitational acceleration (g), polarization electrostatic field (Ep), and divergence of the geomagnetic field. Within the simulation region (1.7 to 10
earth radii, Re) the ions were assume to be collisionless and the electrons to obey a Boltzmann relation. Profiles of altitude-dependent
diffusion coefficients [D⊥ (O+) and D⊥ (H+)] were computed from the wave spectral density (S) observed by the Plasma Wave
Instrument (PWI) on board DE-1. The effects of WPI were introduced via a Monte Carlo technique, and an iterative approach
was used in order to converge to self-consistent results. The main conclusions of this study were the following. As a result
of perpendicular heating, the temperature anisotropy (T| /T⊥) was reduced and even reversed (T| < T⊥) at high altitudes. The
O+ velocity distribution function developed a conic shape at high altitudes. The altitudes above which the WPI influences
the O+ ions were lower than those for the H+ ions. The escape flux of O+ could be enhanced by more than an order of magnitude
while the H+ flux remains constant. The O+ ions are heated more efficiently than the H+ ions, especially at low altitudes
due to the 'pressure cooker' effect. As the ions are heated and move to higher altitudes, the ion's Larmor radius a
L
may become comparable to the perpendicular wavelength λ⊥. As the ratio aL /λ⊥ becomes > 1, the heating rate becomes self-limited
and the ion distribution displays toroidal features. This result is consistent with the observation of O+ toroidal distribution
in the high altitude ionosphere. Finally, the large variability in the wave spectral density S was studied. This variability
was found to change our results only in a quantitative manner, while our conclusions remained qualitatively unchanged.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
E. Martínez-Gómez H. J. Durand-Manterola H. Pérez de Tejada 《Astrophysics and Space Science》2007,310(3-4):211-230
A model is presented to describe the energization of charged particles in planetary magnetospheres. The model is based on
the stochastic acceleration produced by a random electric field that is induced by the magnetic field fluctuations measured
within the magnetospheres. The stochastic behavior of the electric field is simulated through a Monte Carlo method. We solve
the equation of motion for a single charged particle—which comprises the stochastic acceleration due to the stochastic electric
field, the Lorentz acceleration (containing the local magnetic field and the corotational electric field) and the gravitational
planetary acceleration of the particle—under several initial conditions. The initial conditions include the ion species and
the velocity distribution of the particles which depends on the sources they come from (solar wind, ionospheres, rings and
satellites). We applied this model to Saturn’s inner magnetosphere using a sample of particles (H+, H2O+, N+, O+ and OH+) initially located on Saturn’s north pole, above the C-Ring, on the south pole of Enceladus, in the north pole of Dione and
above the E-Ring. The results show that the particles tend to increase the value of their energy with time reaching several
eV in a few seconds and the large energization is observed far from the planet. We can distinguish three main energization
regions within Saturn’s inner magnetosphere: minimum (Saturn’s ionosphere), intermediate (Dione) and high-energy (Enceladus
and the E-ring). The resulting energy spectrum follows a power-law distribution (>1 keV), a logistic, an exponential decay
or an asymmetric sigmoidal (<1 keV). 相似文献
4.
Bernie D. Shizgal 《Astrophysics and Space Science》2007,312(3-4):227-237
The energization of a charged test-particle of mass m in contact with a large ensemble of charged particles of mass M at equilibrium is studied with the Fokker-Planck equation for Coulomb collisions and a quasi-linear diffusion operator for
wave-particle interactions. The features of the nonequilibrium steady state velocity distribution of the test-particle system
is studied as a function of the mass ratio m/M, and the relative strengths of the wave-particle interactions and Coulomb collisions. It is shown that the steady distribution
function is not necessarily a Kappa distribution. The temperature of heavy minor ions given by the model is shown to vary
linearly with the mass ratio as observed in the solar wind. The time evolution of the distribution function with and without
the energization by wave-particle interactions is calculated and it is demonstrated that the Kullback relative entropy rather
than the Tsallis nonextensive entropy rationalizes the results obtained. 相似文献
5.
W. Köhnlein 《Earth, Moon, and Planets》1989,45(1):53-100
An empirical model of atomic ion densities (H+, He+, N+, O+) is presented up to 4000 km altitude as a function of time (diurnal, annual), space (position, altitude) and solar flux (F10.7) — using observations of satellites (AE-B, AE-C, AE-D, AE-E, ISIS-2, OGO-6) and rockets during quiet geophysical conditions (K
p 3). The numerical treatment is based upon harmonic functions for the horizontal pattern and cubic splines for the vertical structure.The ion densities increase with increasing height up to a maximum (depending roughly on the ion mass) and decrease beyond that with increasing altitude. Above 200 km, O+ is the main ionic constituent being replaced at approximately 800 km (depending on latitude, local time, etc.) by H+. Around polar regions the light ions, H+ and He+, are depleted (polar wind) and the heavier ones enhanced. During local summer conditions the ion densities increase around polar latitudes and correspondingly decrease during local winter, except He+ which reflects the opposite pattern. Diurnal variations are intrinsically coupled to the individual plasma layers: N+ and O+ peak, in general, during daytime, while the amplitudes and phases of H+ and He+ change strongly with altitude and latitude.
Earth, Moon and Planets Review article. 相似文献
6.
Using particle aspect approach, the effect of multi-ions densities on the dispersion relation, growth rate, perpendicular resonant energy and growth length of electromagnetic ion cyclotron wave with general loss-cone distribution function in hot anisotropic multi-ion plasma is presented for auroral acceleration region. It is observed that higher He+ and O+ ions densities enhance the wave frequency closer to the H+ ion cyclotron frequency and growth rate of the wave. The differential heating of He+ ions perpendicular to the magnetic field is enhanced at higher densities of He+ ions. The waves require longer distances to achieve observable amplitude by wave-particle interactions mechanism as predicted by growth length. It is also found that electron thermal anisotropy of the background plasma enhances the growth rate and reduces the growth length of multi-ions plasma. These results are determined for auroral acceleration region. 相似文献
7.
N.‐E. Raouafi 《Astronomische Nachrichten》2003,324(4):341-343
The present work is about the interpretation of the linear polarization of the O VI D2 (λ1032) coronal line observed by SUMER/SoHO. We take into account the effect of the Doppler redistribution due to the scattering ions motion. We consider the cases of isotropic and anisotropic velocity field distributions. The latter can be interpreted by the ioncyclotron effect that affects heavy ions in the solar corona. The comparison of the numerical results with the observations yields constraints on the solar wind outflow speed and on the velocity field distribution of the O5+ ions at low coronal altitudes in the polar holes. 相似文献
8.
9.
Roman M. Häberli Michael R. Combi Tamas I. Gombosi Darren L. De Zeeuw Kenneth G. Powell 《Icarus》1997,130(2):373-386
The observation of ions created by ionization of cometary gas, either by ground-based observations or byin situmeasurements can give us useful information about the gas production and composition of comets. However, due to the interaction of ions with the magnetized solar wind and their high chemical reactivity, it is not possible to relate measured ion densities (or column densities) directly to the parent gas densities. In order to quantitatively analyze measured ion abundances in cometary comae it is necessary to understand their dynamics and chemistry. We have developed a detailed ion–chemical network of cometary atmospheres. We include production of ions by photo- and electron impact-ionization of a background neutral atmosphere, charge exchange of solar wind ions with cometary atoms/molecules, reactions between ions and molecules, and dissociative recombination of molecular ions with thermal electrons. By combining the ion–chemical network with the three-dimensional plasma flow as computed by a new fully three-dimensional MHD model of cometary plasma environments (Gombosiet al.1996) we are able to compute the density of the major cometary ions everywhere in the coma. The input parameters for our model are the solar wind conditions (density, speed, temperature, magnetic field) and the composition and production rate of the gas. We applied our model to Comet P/Halley in early March 1986, for which the input parameters are reasonably well known. We compare the resulting column density of H2O+with ground-based observations of H2O+from DiSantiet al.(1990). The results of our model are in good agreement with both the spatial distribution and the absolute abundance of H2O+and with their variations with the changing overall water production rate between two days. The results are encouraging that it will be possible to obtain production rates of neutral cometary constituents from observations of their ion products. 相似文献
10.
We present the results of a study of solar wind velocity and magnetic field correlation lengths over the last 35 years. The
correlation length of the magnetic field magnitude λ
|B| increases on average by a factor of two at solar maxima compared to solar minima. The correlation lengths of the components
of the magnetic field lBXYZ\lambda_{B_{XYZ}} and of the velocity lVYZ\lambda_{V_{YZ}} do not show this change and have similar values, indicating a continual turbulent correlation length of around 1.4×106 km. We conclude that a linear relation between λ
|B|, VB
2, and Kp suggests that the former is related to the total magnetic energy in the solar wind and an estimate of the average
size of geoeffective structures, which is, in turn, proportional to VB
2. By looking at the distribution of daily correlation lengths we show that the solar minimum values of λ
|B| correspond to the turbulent outer scale. A tail of larger λ
|B| values is present at solar maximum causing the increase in mean value. 相似文献
11.
We have theoretically studied the influence of a far-infrared radiation (FIR) field from Hπ region on the cooling by C and O atoms, C+ ion and CO molecule in a photodissociation region, and a molecular cloud associated with Hπ region (hereinafter referred as HI region) at low temperatures (T
k≤200 K). Comparisons have been made for cooling with and without FIR for two extreme abundances (10−4 and 10−7) of the mentioned species for temperatures ranging between 10 and 200K and an hydrogen particle density range 10 cm−3≤n
o≤ 107 cm3.
The cooling by the species with low line-splitting (CI, Cπ and CO) is significantly influenced by the radiation field for temperaturesT
k < 100 K while the effect of radiation field on cooling by OI is significant even at higher temperatures (T
k > 100 K). The effect of FIR field on the cooling of CO from low rotational transitions is negligibly small, whereas it is
considerable for higher transitions. In general, the cooling terms related to the short-wavelength transitions are more affected
by FIR than those related to longer wavelengths.
It is also demonstrated here that in the determination of thermal structure of an HI region the dust grains play an important role in the heating of gas only through photoelectron emission following irradiation
by far-ultraviolet (FUV) radiation, as the infrared radiation from the dust is too small to have substantial effect on the
cooling. It is found that in the Hπ /HI interface the FIR field from grains in the Hπ region is not capable of modifying the temperature of the warmest regions but does so in the inner part where the temperature
is low enough. 相似文献
12.
Numerical integration of particle trajectories is performed to evaluate the statistical acceleration coefficients D
TT for 1 to 100 MeV protons in a solar wind corotating interaction region (CIR) seen at 2.5 and 5.0 AU. Acceleration is followed in the solar wind reference frame and is due to random wave-particle interactions and to random drift motion in moderate scale field gradients. D
TT due to the first effect reaches a peak value of 4 × 10 –7 MeV2 s–1 post shock at 10 MeV at 2.5 AU consistent with estimates based both upon cyclotron resonance and transit time damping theory. D
TT from the second effect is less well established but is of the order of 10–7 MeV2 s–1 at 10 MeV, 5 AU. A comparison is made between the time constant for statistical acceleration within this CIR and estimates for diffuse shock acceleration and adiabatic deceleration. All three time constants are of the same order, but deceleration is faster than shock acceleration which in turn is faster than statistical acceleration. 相似文献
13.
G.H. Jones 《Earth, Moon, and Planets》1997,77(3):281
The Isaac Newton Group’s CoCam instrument obtained wide-field (10°X 20°) CCD images of the H2O+ tail of Hale-Bopp on March 12–15, 19, 20, 25, 28, 29, 31, April1, 7, 9–13, 21, 23–29 and May 4, 1997. A 6185? filter recorded
the distribution of H2O+; 6250?-centered continuum images were also obtained. Initial analysis has revealed the CoCam dataset to be an invaluable
record of the large-scale structure of the comet's ion tail. Several images show evidence of upstream parabolic envelopes
of ions reminiscent of those reported in C/1908 R1 Morehouse (Eddington A. S., Mon. Not. Roy. Astron. Soc. 70, 442–458, 1910).
Studies of these features may help towards a better understanding of the tail ray phenomenon. During most of March and early
April, the tail had a largely consistent quiescent appearance, with numerous rays exhibited, but no major disturbances; most
probably as a result of being in the stream of fast polar solar wind. A significant kink propagated down the tail around April
9/10. Towards the end of April, as the comet entered more variable solar wind at near-equatorial heliographic latitudes, the
tail's morphology became significantly more structured. Striking tail disturbances were recorded in late April and early May,
when the comet was in the vicinity of the heliospheric current sheet. Analysis of the dataset continues.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
The thermal structure of the plasma in the polar wind is examined. With O+H+ Joule heating as the mechanism for heating the plasma, it is found that O+ and H+ temperatures are significantly greater than the electron temperature. With the adopted input parameters the O+H+ temperature difference is relatively small. 相似文献
15.
A comparative study of the viscous transport of solar wind momentum to the upper layers of the Venus ionosphere with that occurring within the trans-terminator flow leads to estimates of the ratio of the viscosity coefficients that are applicable to both cases. Support for viscous forces between the solar wind and the ionospheric plasma in the trans-terminator flow derives from the momentum flux balance between the momentum flux in the latter flow and the deficiency of solar wind momentum along the flanks of the ionosheath. By comparing the relative width of the viscous boundary layer in the Venus ionosheath and the width of the trans-terminator flow we find that the transport of momentum within the upper ionosphere proceeds at a rate similar to that at which momentum is delivered to the upper ionosphere from the solar wind. Comparable values are obtained for the viscosity coefficient of the solar wind that streams over the ionosphere and that implied from momentum transport within the ionospheric trans-terminator flow. It is further suggested that despite the different nature of the processes that give place to the viscous transport of the solar wind momentum to the upper ionosphere (wave-particle interactions) and those responsible for its distribution within the ionosphere (through coulombian collisions) there is a similar response in the behavior of both plasmas to momentum transport. Calculations show that with comparable values of the viscosity coefficient in the ionosheath and in the upper ionospheric plasma the mean free path suitable to wave-particle interactions in the ionosheath is of the same order of magnitude as the mean free path of the planetary O+ ions that interact through coulombian collisions in the upper ionosphere. The effects of this similarity are considered in the discussion. 相似文献
16.
Synoptic maps of white-light coronal brightness from SOHO/LASCO C2 and distributions of solar wind velocity obtained from
interplanetary scintillation are studied. Regions with velocity V≈300 – 450 km s−1 and increased density N>10 cm−3, typical of the “slow” solar wind originating from the belt and chains of streamers, are shown to exist at Earth’s orbit,
between the fast solar wind flows (with a maximum velocity V
max ≈450 – 800 km s−1). The belt and chains of streamers are the main sources of the “slow” solar wind. As the sources of “slow” solar wind, the
contribution from the chains of streamers may be comparable to that from the streamer belt. 相似文献
17.
We present profiles of the line-of-sight (l.o.s.) ionospheric wind velocities in the southern auroral/polar region of Saturn. Our velocities are derived from the measurement of Doppler shifting of the H3+ν2Q(1,0−) line at 3.953 microns. The data for this study were obtained using the facility high-resolution spectrometer CSHELL on the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii, during the night of February 6, 2003 (UT). The l.o.s. velocity profiles finally derived are consistent with an extended region of the upper atmosphere sub-corotating with the planet: the ion velocities in the inertial reference are only 1/3 of those expected for full planetary corotation. We discuss the results in the light of recent proposals for the kronian magnetosphere, and suggest that, in this region, Saturn's ion winds may be under solar wind control. 相似文献
18.
Gombosi Tamas I. Hansen Kenneth C. DeZeeuw Darren L. Combi Michael R. Powell Kenneth G. 《Earth, Moon, and Planets》1997,79(1-3):179-207
MHD simulation results of the interaction of the expanding atmosphere of comet Hale-Bopp with the magnetized solar wind are
presented. At the upstream boundary a supersonic and superalfvénic solar wind enters into the simulation box 25 million km
upstream of the nucleus. The solar wind is continuously mass loaded with cometary ions originating from the nucleus. The effects
of photoionization, recombination and ion-neutral frictional drag are taken into account in the model. The governing equations
are solved on an adaptively refined unstructured Cartesian grid using our MUSCL-type upwind numerical technique, MAUS-MHD
(Multiscale Adaptive Upwind Scheme for MHD). The combination of the adaptive refinement with the MUSCL-scheme allows the entire
cometary atmosphere to be modeled, while still resolving both the shock and the diamagnetic cavity of the comet.
Detailed simulation results for the plasma environment of comet Hale-Bopp for slow and fast solar wind conditions are presented.
We also calculate synthetic H2O+, CO+ and soft x-ray images for observing conditions on April 11, 1997.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
High‐resolution mass spectrometry (HRMS) imaging by desorption electrospray ionization (DESI) coupled with Orbitrap MS using methanol (MeOH) spray was performed on a fragment of the Murchison (CM2) meteorite in this study. Homologues of CnH2n–1N2+ (n = 7–9) and CnH2nNO+ (n = 9–14) were detected on the sample surface by the imaging. A high‐performance liquid chromatography (HPLC)/HRMS analysis of MeOH extracts from the sample surface after DESI/HRMS imaging indicated that the CnH2n–1N2+ homologues corresponds to alkylimidazole, and that a few isomers of the CnH2nNO+ homologues present in the sample. The alkylimidazoles and CnH2nNO+ homologues displayed different spatial distributions on the surface of the Murchison fragment, indicating chromatographic separation effects during aqueous alteration. Moreover, the distribution pattern of compounds is also different among homologues. This is probably also resulting from the separation of isomers by similar chromatographic effects, or different synthetic pathways. Alkylimidazoles and the CnH2nNO+ homologues are mainly distributed in the matrix region of the Murchison by mineralogical observations, which is consistent with previous reports. Altered minerals (e.g., Fe‐oxide, Fe‐sulfide, and carbonates) occurred in this region. However, no clear relationship was found between these minerals and the organic compounds detected by DESI/HRMS imaging. Although this result might be due to scale differences between the spatial resolution of DESI/HRMS imaging and the grain size in the matrix of the Murchison, our results would indicate that alkylimidazoles and the CnH2nNO+ homologues in the Murchison fragment were mainly synthesized by different processes from hydrothermal alteration on the parent body. 相似文献
20.
We have studied the H+ velocity distribution function at Mars and Venus near the bow shock both in the solar wind and in the magnetosheath by a simple analytical one-dimensional model. We found that over half of the ions in the ring velocity distribution which moved towards the magnetosheath were scattered back into the bow shock. The original ring distribution is destroyed in less than an ion gyro period. Ions contained in the magnetosphere which hit the bow shock bounce back into the solar wind with a maximum energy exceeding twice the energy of solar wind protons. The ions finite gyroradius causes an asymmetric flow in the magnetosheath with respect to the direction of the convective electric field, which can be observed already a few ion gyroradius downstream of the bow shock. 相似文献