首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
A model is proposed in which a mixture of hot solar wind and cold atmospheric plasma flowing in the dayside equatorial boundary layer towards the dawn-dusk plane generates hydromagnetic waves near the frequency ω = ωBi¦1 ? T∥¦T⊥¦ where ωBi is the ion gyrofrequency and T∥, T⊥ are the temperatures of the solar wind plasma, parallel and perpendicular respectively to the magnetic field B. The model accounts for the properties of IPRP events, i.e. intervals of geomagnetic pulsations of periods rising on average from about 2 s to about 7 s over an interval of about 5 min. The diagnostic potential of this phenomenon for study of the boundary layer is indicated.  相似文献   

2.
The particle aspect approach is adopted to investigate the trajectories of charged particles in the electromagnetic field of kinetic Alfven wave. Expressions are found for the dispersion relation, damping rate and associated currents in homogenous plasma. Kinetic effects of electrons and ions are included to study kinetic Alfven wave because both are important in the transition region. It is found that the ratio β of electron thermal energy density to magnetic field energy density and the ratio of ion to electron thermal temperature (Ti/Te) affect the dispersion relation, damping-rate and associated currents in both cases (warm and cold electron limits). The treatment of kinetic Alfven wave instability is based on the assumption that the plasma consists of resonant and non-resonant particles. The resonant particles participate in an energy exchange process, whereas the non-resonant particles support the oscillatory motion of the wave.  相似文献   

3.
Using the Main Stellar Spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a polametric analyzer, we measured the longitudinal magnetic field component B∥ for the T Tauri stars T Tau and AS 507 on January 16 and 18 and February 15, 2003. For both stars, we determined only the upper limits on B∥ from photospheric lines: +15±30 G for T Tau and ?70±90 G for AS 507. The magnetic field of AS 507 was not measured previously, while B∥ for T Tau is lower than its values that we obtained in 1996 and 2002 (B∥?150±50G), suggesting that the longitudinal magnetic field component in the photosphere of T Tau is variable. We also measured the longitudinal magnetic field component for T Tau in the formation region of the He I 5876 Å emission line. We found B∥ in this region to be ?+650, ?+350, and ?+1100 G on January 16, 18, and February 15, 2003, respectively. Our observations on January 18 and February 15 correspond to virtually the same phase of the star's rotation period, but the profiles of the He I 5876 Å line differ markedly on these two nights. Therefore, we believe that the threefold difference between the B∥ values on these nights does not result from observational errors. We discuss the possible causes of the B∥ variability in the photosphere and the magnetosphere of T Tau.  相似文献   

4.
Two solar flares of 25 July 1981 and 5 November 2004 of importance 2N and M4.1/1B, respectively, were investigated using observational data obtained with the Echelle spectrograph of the Kyiv University Astronomical Observatory. Stokes I and V profiles of the FeI lines 5233, 5247.1, 5250.2, 5250.6, 5576.1 and of CrI 5247.6 Å have been analyzed. We found several evidences for the existence of spatially unresolved magnetic field structures with kG strengths. In particular, the values of the measured average longitudinal field B ∥ depend on the Lande factors g of the lines: in general, B ∥ increases with increasing factor g. Analogously, the observed line ratio B ∥(5250.2)/B ∥(5247.1) is increasing with increasing distance Δλ from the line center. The observed Stokes V profiles show some deviations from that of an assumed homogeneous field, presented by the Stokes I gradient, dI/dλ. A comparison with the non-split line FeI 5576.1 Å shows that some of these deviations are real and indicate the presence of subtelescopic magnetic elements with discrete field strengths of several kG. The lines with large Lande factors have considerable broadenings of the Stokes I profiles, indicating a strong background magnetic field of mixed polarity. On the basis of all these data we conclude that a four-component magnetic field structure is a possible explanation. The field strengths are about ±1.05 kG in the background field, and 1.3?1.5, 3.9?4.0, and 7.4?7.8 kG at level of middle photosphere (h ≈ 300 km) in the spatially unresolved, small-scale magnetic elements.  相似文献   

5.
We calculate the kinetic coefficients and the transport mean free paths of high-energy particles parallel to the regular magnetic field in the approximation of a large-scale anisotropic random magnetic field by using a nonlinear collision integral, i.e., by taking into account the processes of strong random scattering. We consider the diffusion of solar and Galactic cosmic rays by two-dimensional turbulence. Strong random scattering by two-dimensional turbulence is shown to reduce the parallel transport mean free path several fold. The momentum dependence of the parallel mean free path does not change, Λ∥ ∝ p2?v. In the case of strong random scattering by turbulence formed by several modes, the parallel transport mean free path is Λ∥ ∝ p. We show that two-dimensional turbulence can make a major contribution to the parallel transport mean free paths of cosmic rays in the heliosphere and the interstellar medium.  相似文献   

6.
Concurrent interplanetary magnetic field and 0.7–7.6 MeV proton cosmic-ray anisotropy data obtained from instrumentation on Explorers 34 and 41 are examined for five cosmic-ray events in which we observe a persistent eastern-anisotropy phase late in the event (t ? 4 days). The direction of the anisotropy at such times shows remarkable invariance with respect to the direction of the magnetic field (which generally varies throughout the event) and it is also independent of particle species (electrons and protons) and particle speed over the range 0.06 ? β ? 0.56. The anisotropy is from the direction 38.3° ± 2.4° E of the solar radius vector, and is inferred to be orthogonal to the long term, mean interplanetary field direction. Both the amplitude of the anisotropy and the decay time constant show a strong dependence on the magnetic field azimuth. Detailed comparison of the anisotropy and the magnetic field data shows that the simple model of convection plus diffusion parallel to the magnetic field is applicable for this phase of the flare effect. It is demonstrated that contemporary theories do not predict the invariance of the direction as observed, even when the magnetic field is steady; these theories need extension to take into account the magnetic field direction ψ varying from its mean direction ψ o. It is shown that the late phase anisotropy vector is not expected to be everywhere perpendicular to the mean magnetic field. The suggestion that we are observing kinks in the magnetic field moving radially outwards from the Sun leads to the conclusion that the parallel diffusion coefficient varies as 1/cos2 (ψ ? ψ o). Density gradients in the late decay phase are estimated to be ≈ 700%∣AU for 0.7–7.6 MeV protons. A simple theory reproduces the dependence of the decay time constant on anisotropy; it also leads to a radial density gradient of about 1000%∣AU and diffusion coefficient of 1.3 × 1020 cm2 s?1.  相似文献   

7.
Jun-Ichi Sakai 《Solar physics》1983,84(1-2):109-118
Transverse amplitude modulations of fast magnetosonic waves propagating perpendicular to the background magnetic field are shown to be unstable on a time scale τ ～- λ∥/V aφ, if the wave amplitude φ exceeds a critical value, φ c = C s/V a. The slow modes generated by the modulational instability under gravity can propagate along the magnetic field with the characteristic velocity, V ph = g/2k ∥ V aφ. The applications of this modulational instability and slow-mode generation mechanism to a solar plasma are discussed.  相似文献   

8.
Equations for parallel motion for a particle trapped in a magnetic field have been considered and improved solutions of differential equations have been derived. The expressions for the change in energy of the particle (Δw) and diffusion coefficient (Dww) have been presented in a simple form using the improved solution.  相似文献   

9.
Crank-Nicholson solutions are obtained to the time-dependent Fokker-Planck equation for propagation in the interplanetary medium following a point in time injection of energetic solar particles and including the acceleration terms $$\frac{\partial }{{\partial T}}\left( {D_{TT} \frac{{\partial U}}{{\partial T}}} \right) - \frac{\partial }{{\partial T}}\left( {\frac{{D_{TT} U}}{{2T}}} \right)$$ . The diffusion coefficient in kinetic energyD TT is allowed to be either independent of radial distance,R(AU), or follow the lawD TT=D0T2R 0 2 /(A2+R2) in either case with the 1 AU value ofD TT at 10 MeV ranging between 10?4 (MeV)2 s?1 and zero. The spatial diffusion mean free path at the Earth's orbit is fixed at λ‖ AU at 10 MeV according to numerical estimates made by Moussas and Quenby. However, a variety ofR dependences are allowed. Reasonable agreement with experimental data out to 4 AU is obtained with the above values ofD TT and the spatial diffusion coefficientK r=K0R?2 forR«1 andK r=K0R0.4 forR»1 AU. It is only in the decay phases of prompt events as seen at 2–4 AU that significant differences in the temporal behaviour of the events can be distinguished, depending on the value ofD TT chosen within the above range. Experimental determination of the decay constant is difficult.  相似文献   

10.
The diffusion of electrons through interstellar space, and the energy dependence of the diffusion coefficient are considered. Apart from the caseD=const the spectral index for electrons with spectral index γ0 changes according to γ0+μ→γ0+½μ+½→γ0+1 (D(E)=D0(E/E0)μ) for μ<1; for μ>1 to γ0+1→γ0+½μ+½→γ0+μ. We consider the radio emission spectrum in such a case. From a comparison with observations the limit μ≤0.4 is obtained.  相似文献   

11.
The present paper reports a class of new solutions of charged fluid spheres expressed by a space time with its hypersurfaces t=const. as spheroid for the case 0<K<1 with surface density 2×1014 gm/cm3. When the Buchdahl’s type fluid spheres are electrified with generalized charged intensity and it is utilized to construct a super-dense star and found that star satisfies all reality conditions except the casual condition for 0<K≤0.05. The maximum mass occupied and the corresponding radius have been obtained 8.130871 M Θ and 24.60916 km respectively. Further, the redshift at the centre and on the surface are noted by z 0=0.933729 and z a =0.383808 respectively.  相似文献   

12.
  相似文献   

13.
We discuss certain properties of the external field of a rotating and charged body in the frame of the vector graviton metric field theory. We find: 1) a black hole cannot have angular momentum or charge, that is, a rotating body whether charged or not, cannot be a black hole. The Kerr black hole and the Kerr-Newman black hole do not exist. 2) For a rotating and charged axisymmetric body, there exists a latitude-dependent critical distance rk(θ), such that the radial force acting on a test particle is attractive or repulsive according as the particle is outside or inside the critical distance. The repulsive force means that a massive object cannot collapse indefinitely. Maximum redshift in this case comes from sources on the equator. 3) A test particle also experiences a force along the meridian.  相似文献   

14.
Assuming a certain horizontal distribution of the convection field at a certain altitude above the ionosphere, the associated electric field and current distributions in a vertical plane are calculated using a model with finite current-dependent conductivity along the magnetic field lines. It is seen that given the kind of horizontal distribution of E6 commonly observed by polar-orbiting satellites at inverted-V electron precipitation events, the calculated distribution of E∥ is able to reproduce the basic spatial structure of the precipitation. It is also seen that the combined effect of a locally increased ionization within auroral forms and a large potential difference (ΔV)∥ along the magnetic field lines at higher altitudes is a strong reduction of E6 within the auroral forms. From the basic features of the electric field, it is concluded that an interpretation of auroral precipitation in terms of a static E∥ may require a mechanism that can support a large (ΔV)∥ even at relatively weak current densities and at the same time allow local enhancements of the parallel conductivity within the region of non-zero E∥. It is suggested that the magnetic mirroring combined with gyro-resonant wave-particle interactions may be a suitable mechanism.  相似文献   

15.
We consider the behavior of charged particles with an anisotropic initial velocity distribution in a magnetic trap with approaching mirrors in connection with the problem of particle acceleration in solar flares. We show that, irrespective of the charge sign, the efficiency of confinement and acceleration increases with increasing anisotropy factor of the initial distribution α = (T⊥/T∥)1/2. For a positive electric potential of the trap plasma relative to the mirrors, the emerging additional effect of ion expulsion form the trap increases with αi. The derived estimate of the electric potential suggests an amplification of the initial perturbation and the development of instability.  相似文献   

16.
The influence of low-frequency electrostatic turbulence on the flux of precipitating magnetospheric electrons is analyzed in the framework of the quasilinear kinetic equation. It is shown that an electron population in a turbulent region, with an electric field parallel to the ambient magnetic field, can be separated into two parts by introducing a pitch angle dependent runaway velocity vr(θ). Lower energy electrons with parallel velocity v∥ < vr are effectively scattered by plasma waves, so that they remain in the main population and are subjected to an anomalous transport equation. A distribution function f ∞ v?4 (or the particle flux vs energy J ∞ E?1) is established in this velocity range. Faster electrons with v∥ ? vr are freely accelerated by a parallel electric field, so that they contribute directly to hot electron fluxes which are observed at ionospheric altitudes. New expressions are derived for the magnetic-field aligned current and the electron energy flux implied by this model. These expressions agree well with empirical relations observed in auroral inverted-V structures.  相似文献   

17.
Density profiles for CO, O, and O2 in the Cytherean atmosphere above 90 km are plotted with eddy diffusion coefficient (K) as a parameter, subject to the constraint that the mixing ratios of CO and O2 approach their observed value or values under the observed upper limit at the lower boundary. It is then shown that the value of K puts upper limits on the amount of hydrogen (in the form of H2O, HCl, and H2) the atmosphere near 90km can contain. This value is a function of the density and temperature of hydrogen at the critical level and the magnitude of the total escape flux, where unspecified flux mechanisms other than thermal are postulated ad hoc. In general these constraints call for large values of K to accomodate the atomic hydrogen produced by measured mixing ratios of HCl and H2O. Hence they constrain thee amount of O in the upper atmosphere to values well under 1% at 130 km unless there are very large hydrogen escape fluxes, 107 cm?2sec?1 or larger. The freedom to assume arbitrary amounts of H2 in the atmosphere is also restricted. We suggest either very effective escape mechanisms—despite low exospheric hydrogen densities—or novel excitation mechanisms for O(33S) and O(35S) in the upper atmosphere.  相似文献   

18.
The distribution of By in the geomagnetic tail associated with a net cross-tail magnetic flux, recently experimentally discovered, is here investigated within the framework of two-dimensional but non-planar field adiabatic time-independent equilbria. It is found that the flux distribution is controlled by the pressure anisotropy of the plasma, By being enhanced at the current sheet centre relative to that in the lobes for P∥>P⊥ and vice-versa for P⊥>P∥. For P⊥>P∥ a broad region of depressed field strength is found across the centre plane of the current sheet, terminated at its outer boundaries by spikes in the perpendicular current, across which By and Bx are “switched on” and rapidly increase towards their values in the low-β lobes. For P∥>P⊥ a thin high-current density layer forms at the sheet centre if the marginal firehose condition is approached, across which the Bx field reverses by rotation at nearly constant magnitude about the z-axis. The field magnitude in this thin layer depends upon the pressure anisotropy, such that the plasma remains just firehose stable within it, and may approach an appreciable fraction of the lobe field strength even for moderate anisotropies. Such structures have been observed in the geomagnetic tail, but do not appear to be a common feature of the quiet-time plasmasheet, where the field strength at the centre plane can reach small values with little obvious enhancement of By. In terms of the present model these observations require that either P⊥>P∥ in the quiet-time tail or that the plasma is within one or two per cent of isotropy if P∥>P⊥. These results then indicate that the production of plasma pressure anisotropy during adiabatic inward transport towards the Earth, which is generally expected to lead to P∥>P⊥ and its destruction by either macroscopic or microscopic processes, requires further study.  相似文献   

19.
In the present paper, we have obtained a class of charged super dense star models, starting with a static spherically symmetric metric in isotropic coordinates for perfect fluid by considering Hajj-Boutros (in J. Math. Phys. 27:1363, 1986) type metric potential and a specific choice of electrical intensity which involves a parameter K. The resulting solutions represent charged fluid spheres joining smoothly with the Reissner-Nordstrom metric at the pressure free interface. The solutions so obtained are utilized to construct the models for super-dense star like neutron stars (ρ b =2 and 2.7×1014 g/cm3) and Quark stars (ρ b =4.6888×1014 g/cm3). Our solution is well behaved for all values of n satisfying the inequalities \(4 < n \le4(4 + \sqrt{2} )\) and K satisfying the inequalities 0≤K≤0.24988, depending upon the value of n. Corresponding to n=4.001 and K=0.24988, we observe that the maximum mass of quark star M=2.335M ⊙ and radius R=10.04 km. Further, this maximum mass limit of quark star is in the order of maximum mass of stable Strange Quark Star established by Dong et al. (in arXiv:1207.0429v3, 2013). The robustness of our results is that the models are alike with the recent discoveries.  相似文献   

20.
The diffusion of charged particles in a stochastic magnetic field (strengthB) which is superimposed on a uniform magnetic fieldB 0 k is studied. A slab model of the stochastic magnetic field is used. Many particles were released into different realizations of the magnetic field and their subsequent displacements z in the direction of the uniform magnetic field numerically computed. The particle trajectories were calculated over periods of many particle scattering times. The ensemble average was then used to find the parallel diffusion coefficient . The simulations were performed for several types of stochastic magnetic fields and for a wide range of particle gyro-radius and the parameterB/B 0. The calculations have shown that the theory of charged particle diffusion is a good approximation even when the stochastic magnetic field is of the same strength as the uniform magnetic field.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号