共查询到20条相似文献,搜索用时 31 毫秒
1.
Using a combined analytical and numerical Method we have treated the question of two-dimensional MHD equilibriam in an inviscid compressible, perfect conducting plasma with an embedded magnetic field in the spherically symmetric gravitational field of the sun. Two solutions are obtained. (1) A steady, self-consistent plasma flow in a magnetic field with both a closed and an open region. In the open region, beyond a few solar radii, the plasma velocity exceeds the local sound and Alfvén velocities. (2) The plasma velocity is everywhere smaller than the local sound and Alfvén velocities and tends to zero at large radial distances. 相似文献
2.
Cheng Jiu-heng 《Chinese Astronomy and Astrophysics》1994,18(4):374-382
Starting from the equations of motion of a thin magnetic tube, the characteristic curves and velocities and compatibility relations are derived as basis for investigating its motion and for correctly formulating the problem of stationary solution. It is shown that the characteristic velocity of transverse waves is related to the Alfvén Mach number of the flow in the tube. When the flow velocity exceeds the critical value for the Kelvin-Helmholtz instability, transverse waves cease to exist. 相似文献
3.
The evolution of Alfvén turbulence due to three-wave interactions is discussed using kinetic theory for a collisionless, thermal plasma. In particular, we consider decay of Alfvén waves through three-wave coupling with an ion sound mode in the random-phase approximation. Two decay processes are of particular interest: an Alfvén wave decays into a backward propagating Alfvén wave and a forward propagating ion sound wave, and an Alfvén wave decays into a backward propagating fast magnetoacoustic wave and a forward ion sound wave. The former was widely discussed in the literature, particularly under the coherent wave assumption. The latter was not well explored and is discussed here. 相似文献
4.
Tsutomu Tamao 《Planetary and Space Science》1978,26(12):1141-1148
Within a framework of the two-fluids approximation, basic modes constituting hydromagnetic coupling oscillations in non-uniform, finite-β plasmas are examined. It is shown that the oscillations consist of a coupling between a localized mode and a propagating one, and a strong peak appears at a resonance point. In the case of isothermal plasma (Te = Ti), there are two localized modes, the Alfvén (or drift Alfvén) and the ion drift modes, and a propagating mode being known as the fast magnetosonic wave. Coupling oscillations associated with the Alfvén mode exhibit a nearly incompressible character, whereas those with the ion drift mode are compressional and diamagnetic. Furthermore, the slow magnetosonic wave also couples with the localized mode in the case of Te > Ti. Based on characteristics of these oscillations, the origin of geomagnetic pulsations is discussed in connection with the distribution of plasma parameters in the outer magnetosphere. 相似文献
5.
Akio K. Inoue Akinori Oka Taishi Nakamoto 《Monthly notices of the Royal Astronomical Society》2009,393(4):1377-1390
The temperature in the optically thick interior of protoplanetary discs is essential for the interpretation of millimetre observations of the discs, for the vertical structure of the discs, for models of the disc evolution and the planet formation, and for the chemistry in the discs. Since large icy grains have a large albedo even in the infrared, the effect of scattering of the diffuse radiation in the discs on the interior temperature should be examined. We have performed a series of numerical radiation transfer simulations, including isotropic scattering by grains with various typical sizes for the diffuse radiation as well as for the incident stellar radiation. We also have developed an analytic model including isotropic scattering to understand the physics concealed in the numerical results. With the analytic model, we have shown that the standard two-layer approach is valid only for grey opacity (i.e. grain size ≳10 μm) even without scattering. A three-layer interpretation is required for grain size ≲10 μm. When the grain size is 0.1–10 μm, the numerical simulations show that the isotropic scattering reduces the temperature of the disc interior. This reduction is nicely explained by the analytic three-layer model as a result of the energy loss by scatterings of the incident stellar radiation and of the warm diffuse radiation in the disc atmosphere. For grain size ≳10 μm (i.e. grey scattering), the numerical simulations show that the isotropic scattering does not affect the interior temperature. This is nicely explained by the analytic two-layer model; the energy loss by scattering in the disc atmosphere is exactly offset by the 'green-house effect' due to the scattering of the cold diffuse radiation in the interior. 相似文献
6.
Gong-liang Zhang 《Chinese Astronomy and Astrophysics》1996,20(4):482-486
Observed instances are given in this paper to show that sub-Alfvénic flow can be formed in the quiet and recurrent low-speed solar wind streams. This kind of flow appears in regions with abnormal enhancement of Alfvénic speed and is associated with a specific type of magnetic configuration. 相似文献
7.
William M. Sinton 《Icarus》1973,20(3):284-296
An atmosphere containing 0.5 cm atm of ammonia is assumed on Io. Such an atmosphere will be frozen at the unilluminated pole during the solstices, but will evaporate at the equinoctial seasons. The ammonia atmosphere will explain: (1) the posteclipse brightenings and their observed times of occurrence and nonocurrence; (2) the observed departure from a two-layer model beating curve upon emergence from eclipse; (3) the discordant temperatures obtained at 10 and 20 μm; and (4) discordant temperatures obtained at 10 and 20 μm during the total phase of an eclipse by Jupiter.In order to explain items 3 and 4 above, a proton flux in Jupiter's magnetosphere of 1.1 × 109 cm?2s? at an energy of 0.5MeV at io's distance from Jupiter is assumed. This flux is 40 times the flux in Divine's (1972) “upper-limit” model of the Jovian radiation belts, while the proton energy is eight times less. The proton flux, plus the solar ultraviolet and infrared flux absorbed by the ammonia, will heat the atmosphere to 245 ± 10°K. At this temperature the occultation atmospheric upper limit allows the addition of 4 cmatm of nitrogen. 相似文献
8.
On the basis of the equivalent circuit model, we investigate two different mechanisms of extracting energy of rotation and angular momentum from a black hole by magnetic field, namely, the Blandford-Znajek (BZ) process and the magnetic coupling (MC) process. The contributions to the efficiency of energy release via pure accretion process, BZ process and MC process are compared in detail by studying the evolutionary characteristics of the spin parameter of the black hole at the center of the magnetized accretion disk. It is shown that the MC process is an important new mechanism of extracting energy from the rotating black hole and its efficiency of energy release is almost as high as that of the BZ process. The efficiency of energy release via pure accretion process is higher than those of BZ process and magnetic coupling process. However, when the rotation of a black hole approaches that of an extreme Kerr black hole,the efficiency of energy release is mainly due to the contributions of BZ process and MC process. 相似文献
9.
The principal features which distinguish the atmosphere on Venus from that of the Earth are the slow rotation of the planet, the large mass of the atmosphere, and the opacity of the atmosphere to long-wave radiation. The slow rotation of the planet gives rise, first of all, to nongeostrophuc dynamics (the atmosphere gas has a tendency to move along the pressure gradient), with the result that the region of the main influx of solar energy is located on one side of the planet, and the region of maximum cooling on the other. These considerations lead to a much simpler scheme of circulation than that in the Earth's atmosphere.The large mass of the atmosphere is the cause of a high thermal and mechanical inertia, which explains why the atmospheric circulation is asymmetrical relative to the solar-antisolar axis. The daily center of circulation is displaced to the second half of the Cytherean solar day, i.e., to the line of zero budget of thermal energy corresponding to a height of the Sun abobe the horizon of about 20°. The notions of cold and warm regions are very relative for Venus. While the horizontal temperature differences on the Earth may reach 100°, a mean horizontal temperature drop as small as 3° in the Cytherean atmosphere may be looked upon as an exceptional phenomenon. This high thermal homogeneity is due to a very large thermal inertia, with cooling at the poles never manifesting itself in the temperature fields obtained.The opacity of the Cytherean atmosphere to long-wave radiation results in vertical heat transfer by turbulence, mesoscale convection, and large-scale currents. This produces adiabatic stratification in the troposphere and a high temperature in the lower layers.These phenomena were studied in a general manner using two- and three-level models. Steps have recently been undertaken to investigate in greater detail the vertical structure of the troposphere on Venus using ten-level models. It appeared that the vertical dynamic structure of the troposphere is very much dependent on the distribution in height of the solar energy influx. In the greenhouse model, the entire atmosphere is affected by circulation. Pronounced velocity maxima are observed in the lower and upper layers. In a model with adsorption of solar radiation in the upper layer, the velocity is small in the lower layers, but it rapidly increases and changes its direction several times in the upper layers. The mean kinetic energy of the atmosphere proves to be two to three times smaller than in the greenhouse model.Attempts have been made in the calculations to find the principal modes of the statistical fluctuations. The results obtained show that atmospheric circulation may be represented by a global mean basic state following the rotation of the planet with deviations from that basic state which are indeterminate disturbances. The mean basic state exhibits a high degree of symmetry relative to the equator. On account of nonlinearity, the disturbances were observed in all the models independently of space and time resolution. This phenomenon appears to reflect the actual properties of the Cytherean atmosphere and has no bearing on the details of the numerical scheme. 相似文献
10.
J.F. Mcclay 《Planetary and Space Science》1973,21(12):2193-2211
This paper is based on the postulate that the natural electromagnetic radiation observed in the micropulsation band is accounted for by the eigenmodes of a resonant cavity in the Earth's outer atmosphere, just as the adjacent ELF part of the spectrum is explained by resonances in the Earth-ionosphere cavity. The inner edge of the plasma sheet (the Alfvén layer) forms an effective resonant cavity which we call the Alfvénsphere. Its complex medium is characterized by two parameters, effective conductivity, and effective Alfvén speed: its quasi-stationary states are specified by two state parameters, effective cavity size, and effective time scale for magnetospheric processes, and in principle, they can be evaluated from the power spectra of observed micropulsations. Because of the complex geometry of the cavity and the fact that the vector hydromagnetic wave equation for an asymmetric electric field is not simply separable in spherical and orthogonal dipole coordinates (and the spatial boundary value problem is virtually insoluble), a model is developed which contains the essential physics and admits of tractable equations. A coupling scheme is defined and discussed which permits one to study the eigenvalue equation under conditions of weak and strong coupling as well as the uncoupled case. Emphasis is placed on the most difficult weakly-coupled case because the results can be readily compared with the uncoupled case. The complex dispersion relation-ship is presented and complex eigenvalues are calculated. It is shown that for any mode (v, i, m), the fundamental (i = 1) appears at the highest latitude and the highest harmonic (i = imax) appears at the lowest latitude. Further it is shown that the fundamental and harmonics are split into multiplet frequency states, clustered at different latitudes, and ordered at a particular latitude by the asymmetric label m. This property is used to explain beating and atitudinal and longitudinal variations in pearl pulsations. It is demonstrated that the east-west magnetic component of the perturbed magnetic field (for any mode) has two spatial resonances (logarithmic and asymmetric) and this feature can be used to derive and interpret the T cos2Θ = const law. This in turn suggests a method for ordering the east-west component power spectra for a station at any latitude below 70° N mag. in terms of v, and evaluating the corresponding phenomenological state parameters. The inescapable conclusion appears to be that there is no intrinsic difference between the ‘different’ classes of pulsations; they are simply the excited eigenmodes of the Alfvénsphere for different quasi-stationary states. 相似文献
11.
AC Cnc is a nova-like, eclipsing binary of period 7h13m. I chose it for observation because its eclipses are rather symmetrical. A photometric solution gives inclination i = 74.5° ± 0.8°, mass of white dwarf M1 = 0.74 ± 0.07 M, mass of the late-type companion, M2 = 0.97 ± 0.8 M. Temperature of the accretion disk varies approximately as inverse half-power of the radial distance, the temperature at the edge of the disk is 7600 K. Rate of mass transfer from the late-type star to the white dwarf is 7(−9) M/yr. The distance of AC Cnc is 500 ± 100 pc. 相似文献
12.
A. A. Nusinov T. V. Kazachevskaya S. N. Kuznetsov I. N. Myagkova B. Yu. Yushkov 《Solar System Research》2006,40(4):282-285
The results of simultaneous measurements of variations of UV radiation (in a band near the hydrogen Lα line, 121.6 nm) and hard X-ray and gamma-ray radiation (50 keV-200 MeV) performed by the VUSS-L and SONG instruments, respectively, onboard the CORONAS-F spacecraft are presented for periods of solar flares. Variations in the Lα ultraviolet radiation during the impulsive phase of a flare are shown to be synchronous with those of hard X-ray radiation. Temporal variations of UV and X-ray fluxes correspond to the progressive heating of higher and higher regions of the solar atmosphere and the energy transfer from the lower layers of the solar atmosphere to the coronal areas of flare regions. The energy of electrons in beams arising during the impulsive phase of flares can be as high as 500 keV. The velocity of the energy propagation from the regions of its release to the upper layers of the solar atmosphere can reach several tens of kilometers per second. 相似文献
13.
V. I. Shematovich 《Solar System Research》2017,51(4):249-257
This is a study of the kinetics and transport of hot oxygen atoms in the transition region (from the thermosphere to the exosphere) of the Martian upper atmosphere. It is assumed that the source of the hot oxygen atoms is the transfer of momentum and energy in elastic collisions between thermal atmospheric oxygen atoms and the high-energy protons and hydrogen atoms precipitating onto the Martian upper atmosphere from the solar-wind plasma. The distribution functions of suprathermal oxygen atoms by the kinetic energy are calculated. It is shown that the exosphere is populated by a large number of suprathermal oxygen atoms with kinetic energies up to the escape energy 2 eV; i.e., a hot oxygen corona is formed around Mars. The transfer of energy from the precipitating solar-wind plasma protons and hydrogen atoms to the thermal oxygen atoms leads to the formation of an additional nonthermal escape flux of atomic oxygen from the Martian atmosphere. The precipitation-induced escape flux of hot oxygen atoms may become dominant under the conditions of extreme solar events, such as solar flares and coronal mass ejections, as shown by recent observations onboard NASA’s MAVEN spacecraft (Jakosky et al., 2015). 相似文献
14.
O. Bschorr 《Solar physics》1982,79(2):327-331
In addition to the heating the corona by sound waves, there exists a radiation pressure caused by the absorption of acoustic waves as well as plasma waves. Whereas in the hydrostatic balance of the solar atmosphere, the light pressure can be neglected, the radiation pressure due to acoustic waves and Alfvén waves is much higher and has to be taken into account.In the solar atmosphere, the acoustic radiation pressure is generated by (i) absorption of sound energy, (ii) reflection of sound energy, and (iii) change of the sound velocity.The radiation pressure caused by absorption is dominating within the solar corona. The radiation pressure caused by reflection and the wave velocity change probably produce a pressure inversion in the transition zone between chromosphere and corona. Furthermore, the spicule phenomena are due to instationary radiation pressure. 相似文献
15.
Coronal heating is one of the unresolved puzzles in solar physics from decades. In the present paper we have investigated the dynamics of vortices to apprehend coronal heating problem. A three dimensional (3d) model has been developed to study propagation of dispersive Alfvén waves (DAWs) in presence of ion acoustic waves which results in excitation of DAW and evolution of vortices. Taking ponderomotive nonlinearity into account, development of these vortices has been studied. There are observations of such vortices in the chromosphere, transition region and also in the lower solar corona. These structures may play an important role in transferring energy from lower solar atmosphere to corona and result in coronal heating. Nonlinear interaction of these waves is studied in view of recent simulation work and observations of giant magnetic tornadoes in solar corona and lower atmosphere of sun by solar dynamical observatory (SDO). 相似文献
16.
Solar variability is often cast in terms of radiative emission and the associated long-term climate response; however, growing
societal reliance on technology is creating more interest in day-to-day solar variability. This variability is associated with both solar radiative and solar wind emissions. In this paper we explore
the combined effects of radiative and solar wind fluctuations at Earth. The fluctuations in radiative and geomagnetic power
create an extended interval of solar maximum for the upper atmosphere. We use a trio of empirical models to estimate, over
the last three solar cycles, the relative contributions of solar extreme ultraviolet (UV) power, Joule power, and particle
kinetic power to the Earth’s upper atmosphere energy budget. Daily power values are derived from three source models. The
SOLAR2000 solar irradiance specification model provides estimates of the daily extreme and far UV solar power input. Geomagnetic
power is derived from a combination of satellite-estimated particle precipitation power and an empirical model of Joule power
from hemispherically integrated estimates of high-latitude energy deposition. During the interval 1975 to 2003, the average
daily contributions were: particles – 36 GW, Joule – 95 GW and solar – 464 GW for a total of 595 GW. Solar wind-driven geomagnetic
power provided 22% of the total global upper atmospheric energy. In the top 15 power events, geomagnetic power contributed
two-thirds of the total power budget. In each of these events, Joule power alone exceeded solar power. With rising activity,
Joule power becomes the most variable element of solar upper atmosphere interactions. 相似文献
17.
G. Siemieniec-Ozi
b
o 《Astroparticle Physics》2002,16(4):425-428
In the previous paper [Astropart. Phys. 10 (1999) 121] we showed that the opposite helicity circularly polarized Alfvén waves of finite amplitudes provide conditions to forward–backward asymmetry of particle scattering. In this letter we present an analytic solution of kinematic equation proving the enhancement of stochastic acceleration efficiency due to regular (asymmetry) term. The process is controlled by the ratio of the regular and the ordinary diffusion term. 相似文献
18.
In 1988, Uchida and Shibata proposed a model for compact loop flares as due to the collision of two large amplitude torsional Alfvén wave packets coming up along a coronal magnetic loop, leaking out from the subphotospheric convective layers of the solar atmosphere. We investigate the possibility that active region transient brightenings occur when a single torsional Alfvén wave packet transits a coronal loop. Assuming this related origin for flares and transient brightenings, the statistics of the two phenomena must also be closely related. It is shown that the observed power-law frequency-energy distributions of flares and transient brightenings may be accounted for in a natural way if the energy distribution of the underlying torsional Alfvén wave packets is itself a power law. 相似文献
19.
《Icarus》1986,67(3):484-514
Most of the solar energy absorbed by Venus is deposited in the atmosphere, at levels more than 60 km above the surface. This unusual flux distribution should have important consequences for the thermal structure and dynamical state of that atmosphere. Because there are few measurements of the solar flux at levels above 60 km, a radiative transfer model was used to derive the structure and amplitude of the solar fluxes and heating rates in the Venus mesosphere (60–100 km). This model accounts for all sources of extinction known to be important there, including absorption and scattering by CO2, H2O, SO2, H2SO4 aerosols and an unidentified UV absorber. The distributions of these substances in our model atmosphere were constrained by a broad range of spacecraft and ground-based observations. Above the cloud tops, (71 km), near-infrared CO2 bands absorb enough sunlight to produce globally averaged heating rates ranging from 4° K/day (24-hr period) at 71 km to more than 50° K/day at 100 km. The sulfuric acid aerosols that compose the Venus clouds are primarily scattering agents at solar wavelengths. These aerosols reflect about 75% of the incident solar flux before it can be absorbed by the atmosphere or surface. The unknown substance that causes the observed cloud-top ultraviolet contrasts is responsible for most of the absorption of sunlight within the upper cloud deck (57.5−71 km). This substance absorbs almost half of the sunlight deposited on Venus and contributes to solar heating rates as large as 6° K/day at levels near 65 km. With the exception of CO2, all of the important sources of solar extinction have concentrations that vary with position, and, in general, these concentrations are not well known. To determine the sensitivity of the model results to these uncertainties, the concentrations of these opacity sources were varied in the model atmosphere and solar fluxes were computed for each case. These tests indicate that CO2 dominates the solar absorption at levels above the cloud tops and that heating rates are relatively insensitive to the distribution of other sources of extinction there. Within the upper cloud deck, uncertainties in the distribution of the UV absorber and the H2SO4 aerosols can produce heating rate errors as large as 50% at some levels. Diurnally averaged solar heating rates for the nominal opacity distribution were computed as a function of latitude at altitudes between 55 and 100 km, where most of the solar flux is deposited. The zonal wavenumber 1 (diurnal) and zonal wavenumber 2 (semidiurnal) components of the diurnally varying solar heating rates were also computed in this domain. These results should be sufficiently reliable for use in numerical dynamical models of the Venus atmosphere. 相似文献
20.
The origin of the solar wind is a long-standing issue in both observational and theoretical studies. To understand how and
where in the solar atmosphere the mass and energy of the solar wind are supplied is very important. Previous observation suggests
a scenario in which the fast solar wind originates at heights above 5 Mm in the magnetically open funnel, a process that is
accompanied by downward flow below 5 Mm, whereby the mass and energy are supplied through reconnection between the open funnel
and adjacent closed loops. Based on this scenario, we develop a fluid model to study the solar wind generation under the assumption
that mass and energy are deposited in the open funnel at 5 Mm. The mass supply rate is estimated from the mass loss rate as
given by the emptying of the side loops as a result of their assumed reconnection with the open funnel. Similarly, the energy
input rate is consistent with the energy release rate as estimated from the energy flux associated with the reconnection between
the open magnetic funnel and the closed magnetic loops. Following the observations, we not only simulate the plasma flowing
upward to form the solar wind but also calculate the downward flow back to the lower atmosphere. This model is a first attempt
to study physically the proposed scenario of solar wind origin and gives a new physical illustration of the possible initial
deposition and consequent transportation of mass and energy in the coronal funnel. 相似文献