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 46 毫秒
1.
Eselevich  V.G.  Eselevich  M.V. 《Solar physics》2002,208(1):5-16
Based on analyzing corona images taken by the LASCO C1, C2, and C3 instruments, a study is made of the behavior of the streamer belt spanning one half of the 1996–2001 cycle of solar activity, from minimum to maximum activity, in the absence of coronal mass ejections. It is shown that: (1) The position of the streamer belt relative to the solar equator is generally characterized by two angles: o and E, where o is the latitudinal position (near the solar surface) of the middle of the base of the helmet, the top of which gradually transforms to a ray of the streamer belt with a further distance from the Sun, and E is the latitude of this ray for R>5–6 R from the Sun's center where the ray becomes radial. (2) Only rays lying at some of the selected latitudes o retain their radial orientation (oE) throughout their extent. Namely: o0° (equator), o±90° (north and south poles), and the angle o lying in the range ±(65°–75°) in the N- and S-hemispheres. (3) A deviation of rays from their radial orientation in the direction normal to the surface of the streamer belt occurs: for latitudes o<|65°–75°| toward the equator (>0°) reaching a maximum in the N and S hemispheres, respectively, when OM40°, and OM–42° for latitudes o>|65°–75°| toward the pole (<0°). The regularities obtained here are a numerical test which can be used to assess of the validity of the theory for describing the behavior of the Sun's quasi-stationary corona over a cycle of solar activity.  相似文献   

2.
Using the flux-transport equation in the absence of sources, we study the relation between a highly peaked polar magnetic field and the poleward meridional flow that concentrates it. If the maximum flow speed m greatly exceeds the effective diffusion speed /R, then the field has a quasi-equilibrium configuration in which the poleward convection of flux via meridional flow approximately balances the equatorward spreading via supergranular diffusion. In this case, the flow speed () and the magnetic field B() are related by the steady-state approximation () (/R)B()/B() over a wide range of colatitudes from the poles to midlatitudes. In particular, a general flow profile of the form sin p cos q which peaks near the equator (q p) will correspond to a cos n magnetic field at high latitudes only if p = 1 and m = n /R. Recent measurements of n 8 and 600 km2 s–1 would then give m 7 m s–1.  相似文献   

3.
Spherically symmetric, steady-state, optically thick accretion onto a nonrotating black hole with the mass of is studied. The gas accreting onto the black hole is assumed to be a fully ionized hydrogen plasma withn 0=108 cm–3 andT 0=104 K far from the black hole, and a new approximate expression for the Eddington factor is introduced. The luminosity is estimated to beL=1.875×1033 erg s–1, which primarily arises from the optical surface (1) ofT104 K. The accretion flow is characterized by 1 and (v/c)10. In the optically thin region, the flow remains isothermal, and the increase of temperature occurs at 1. The radiative equilibrium is strictly realized at (v/c)10.  相似文献   

4.
Exact corotations are equilibrium points in the phase space of the asteroidal elliptic restricted problem of three bodies averaged over the synodic period, at a mean-motions resonance. If the resonant critical angle is =(p+q) jup –p–q, exact corotations are double resonant motions defined by the conditionsd/dt=0 andd(– jup )/dt=0. The first condition is characteristic of the periods resonance(p + q) : p and the second one is a secular resonance equivalent to that usually known as thev 5-resonance. This paper presents the symmetric solutions =0 (mod ), = jup (mod ). Corotations have a coherence property which is unique in non-collisional Celestial Mechanics: An elementary calculation shows that, in the neighbourhood of these solutions, the motions cluster aroundp independent longitude values and are, in each cluster, as close together as and are close to the equilibrium values.  相似文献   

5.
An analysis of the effects of Hall current on hydromagnetic free-convective flow through a porous medium bounded by a vertical plate is theoretically investigated when a strong magnetic field is imposed in a direction which is perpendicular to the free stream and makes an angle to the vertical direction. The influence of Hall currents on the flow is studied for various values of .Nomenclature c p specific heat at constant pressure - e electrical charge - E Eckert number - E electrical field intensity - g acceleration due to gravity - G Grashof number - H 0 applied magnetic field - H magnetic field intensity - (j x , j y , j z ) components of current densityJ - J current density - K permeability of porous medium - M magnetic parameter - m Hall parameter - n e electron number density - P Prandtl number - q velocity vector - (T, T w , T ) temperature - t time - (u, v, w) components of the velocity vectorq - U 0 uniform velocity - v 0 suction velocity - (x, y, z) Cartesian coordinates Greek Symbols angle - coefficient of volume expansion - e cyclotron frequency - frequency - dimensionless temperature - thermal conductivity - coefficient of viscosity - magnetic permeability - kinematic viscosity - mass density of fluid - e charge density - electrical conductivity - e electron collision time  相似文献   

6.
A local geometric construction is proposed on thepartially ordered set of instantsI. A totally ordered subsetC(I)I is assumed to have 3-dimensional affine coordinate structure,without a specified metric, called the -space ofC(I). Guided by a strong analogy with analytical mechanics theT-configuration space (, ), a real parameter, is constructed where-upon the usual Hamilton-Jacobi theory establishes a simple geometrical construction, viz., the complete figure from the calculus of variations. The duration function, dur:C(I)R is associated withtemporally equidistant hypersurfaces through which pass a congruence of extremal curves to the fundamental integral.  相似文献   

7.
It has empirically been shown that, for a given value of the effective temperature, the correction in (B-V) due to line blanketing varies linearly with the metallicity parameter S. Next, on the basis of considerations different from those used to obtain a similar result by Sturch (1966), a relation between reciprocal effective temperature e (=5040/T e ) and intrinsic line-free colour index(B-V) o,c has been obtained based on the e and (B-V) values for five RR Lyr variables. Relations between e and intrinsic colour(B-V) o for different groups of stars having a S parameter in the range 0S11 have also been obtained.  相似文献   

8.
Multiple expansion of the tidal potential   总被引：1，自引：0，他引：1  
The Earth tidal deformation causes an additional gravitational potential. Its effect on the Moon orbital motion has been studied by several authors.In this contribution, we develop this additional potential without specifying the inertial frame chosen.For this purpose, we use the properties of the representation of rotation groups in 3 dimensions space. We finally obtain the interaction potential between the distorted Earth and the Moon which is a necessary preliminary to the study of the evolution of the Earth-Moon system.Nomenclature T.R.O Tide raising object - (, , ) Spherical coordinates of the T.R.O. - (J, E ) Earth spin axis orientation. E is the longitude of the ascending node of Earth's equator on thexy-plane - (a ,I ,e , , ,M ) Elliptics elements of the T.R.O  相似文献   

9.
As a consequence of the Taylor–Proudman balance, a balance between the pressure, Coriolis and buoyancy forces in the radial and latitudinal momentum equations (that is expected to be amply satisfied in the lower solar convection zone), the superadiabatic gradient is determined by the rotation law and by an unspecified function of r, say, S(r), where r is the radial coordinate. If the rotation law and S(r) are known, then the solution of the energy equation, performed in this paper in the framework of the ML formalism, leads to a knowledge of the Reynolds stresses, convective fluxes, and meridional motions. The ML-formalism is an extension of the mixing length theory to rotating convection zones, and the calculations also involve the azimuthal momentum equation, from which an expression for the meridional motions in terms of the Reynolds stresses can be derived. The meridional motions are expanded as U r(r,)=P 2(cos)2(r)/r 2+P 4(cos)4(r)/r 2 +..., and a corresponding equation for U (r,). Here is the polar angle, is the density, and P 2(cos), P 4(cos) are Legendre polynomials. A good approximation to the meridional motion is obtained by setting 4(r)=–H2(r) with H–1.6, a constant. The value of 2(r) is negative, i.e., the P 2 flow rises at the equator and sinks at the poles. For the value of H obtained in the numerical calculations, the meridional motions have a narrow countercell at the poles, and the convective flux has a relative maximum at the poles, a minimum at mid latitudes and a larger maximum at the equator. Both results are in agreement with the observations.  相似文献   

10.
In this paper, a technique of recursive analysis is developed for the integral transform A of the exponential integral functionsE n which is denoted as n (). The main result of this analysis enables us to establish a two-term recurrence formula for n (0) and a three-term recurrence formula for n (); 0. A computational algorithm based on these formulae is also constructed and its numerical results forn=2(1)25 are presented to 15-digit accuracy.  相似文献   

11.
P. A. Robinson 《Solar physics》1991,136(2):343-360
It is shown that small magnetic perturbations can significantly alter the rates of cyclotron growth, absorption, mode conversion, and refraction because of the sensitive dependence of these processes on the field strength in narrow layers. In particular, growth lengths are increased, absorption depths decreased, mode conversion becomes more effective, and turbulent refraction leads to isotropization of the emission. The criteria for significant effects to occur are derived and it is shown that they can be met by the few-percent field perturbations observed in coronal loops. Relative to the theory of cyclotron-maser emission in smoothly varying plasmas, perturbations enable fundamental o-mode (o1) and second-harmonic x-mode (x2) radiation to saturate more effectively, increase the chance of x1, o1, and x2 radiation escaping to infinity through absorption and mode-coupling windows, and partially isotropize radiation emitted near the x-mode cutoff. It is concluded that o1 and x1 emission are both likely to be present, and that x2 emission is possible under some circumstances. However, x1 radiation can escape only at near-parallel propagation ( 0) or via mode conversion to the o-mode at 90°, whereas o1 and x2 emission can escape for a wide range of angles around = 0 and, under many circumstances, near = 90°.  相似文献   

12.
Durney  Bernard R. 《Solar physics》2001,202(2):201-228
  相似文献   

13.
Following our series of works on anisotropic radiation, we analyze the erenkov condition in magnetized plasmas in this paper. We have discovered that the usual erenkov condition cos =1/n isnot satisfied at a far field point in anisotropic media, implying that when a charge is moving in a magnetized plasma, a linear shock wave front does not form. Thus we can calculate the power received at a far field per unit time in such a medium — this quantity could not be evaluated according to previous theory. Numerical examples are presented to show various relevant characteristics of erenkov radiation in model plasmas.  相似文献   

14.
Free convection effects on MHD flow past a semi infinite porous flat plate is studied when the time dependent suction velocity changes in step function form. The solution of the problem is obtained in closed form for the fluid with unit Prandtl number. It is observed that for both cooling and heating of the plate the suction velocity enhances the velocity field. The heat transfer is higher with increase in suction velocity.Notations B intensity of magnetic field - G Grashof number - H magnetic field parameter,H=(M+1/4) 1/2–1/2 - M magnetic field parameter - N u Nusselt number - P Prandtl number of the fluid - r suction parameter - T temperature of the fluid - T w temperature of the plate - T temperature of the fluid at infinity - t time - t non-dimensional time - u velocity of the fluid parallel to the plate - u non-dimensional velocity - U velocity of the free stream - suction velocity - 1 suction velocity att0 - 2 suction velocity att>0 - x,y coordinate axes parallel and normal to the plate, respectively - y non-dimensional distance normal to the plate - coefficient of volume expansion - thermal diffusivity - kinematic viscosity - electric conductivity of the fluid - density of the fluid - non-dimensional temperature of the fluid - shear stress at the plate - non dimensional shear stress - erf error function - erfc complementary error function  相似文献   

15.
Two-dimensional unsteady free convection and mass transfer, flow of an incompressible viscous dissipative and electrically conducting fluid, past an infinite, vertical porous plate, is considered, when the flow, is subjected in the action of uniform transverse magnetic field. The magnetic Reynolds number is taken to be small enough so that the induced magnetic field is negligible. The solution of the problem is obtained in the form of power series of Eckert numberE, which is very small for incompressible fluids. Analytical expressions for the velocity field and temperature field are given, as well as for the skin friction and the rate of heat transfer for the case of the mean steady flow and for the unsteady one. The influence of the magnetic parameter,M, modified Grashof numberG c , Schmidt numberS c and frequency , on the flow field, is discussed with the help of graphs, when the plate is being cooled, by the free convection currents (G r ,E>0), or heated (G r ,E<0). A comparative study with hydrodynamic case (M=0) and the hydromagnetic one (M0) is also made whenever necessary.List of symbols B0 applied magnetic field - |B| amplitude of the skin friction - C concentration inside the boundary layer - C concentration in the free stream - C w concentration at the porous plate - C p specific heat at constant pressure - D diffusion coefficient - E Eckert number - g x acceleration due to gravity - G c modified Grashof number - G r Grashof number - M magnetic parameter - N u Nusselt number - P Prandtl number - |Q| amplitude of the rate of heat transfer - S c Schmidt number - T temperature of the fluid - T w temperature of the plate - T temperature of the fluid in the free stream - T r ,T i fluctuating parts of the temperature profile - u, v velocity components in thex, y directions - u dimensionless velocity in thex direction - u 0 mean steady velocity - u 1 unsteady part of the velocity - u r ,u i fluctuating parts of the velocity profile - U dimensionless free stream volocity - U 0 mean free stream velocity - v 0 suction velocity - x, y co-rodinate system Greek Symbols phase angle of the skin-friction - coefficient of volume expansion - * coefficient of expansion with concentration - phase angle of the rate of heat transfer - dimensionless co-ordinate normal to the plate - dimensionless temperature - 0 mean steady temperature - 1 unsteady part of temperature - k thermal conductivity - v kinematic viscocity - density of fluid in the boundary layer - density of fluid in the free stream - electrical conductivity of the fluid - skin friction - 0 mean skin friction - frequency - dimensionless frequency  相似文献   

16.
The observations of the BATSE instrument on the Compton Gamma-Ray Observatory show that the spatial distribution of -ray burst sources is isotropic but radially non-uniform. As is well known, the spectral features, the time histories and the X-ray tails present in some -ray bursts suggest that they may arise from galactic neutron stars. But, low velocity neutron stars born in the Galactic disk would concentrate toward the galactic plane and center, and could not fit the BATSE results. However, the high velocity neutron stars with velocity 1000 km s–1 may escape from the Galactic gravitational field and form a nearly isotropic distribution. Here we calculate the three statistical values of V/V max, sin2 b and cos as functions of the intensitiesC max/C min and find that they could be fitted by the distribution of high velocity neutron stars under the assumption that the high velocity neutron stars should turn on as -ray burst sources only after some time (perhaps after they have ceased to be radio pulsars). Our calculation shows that the statistical value of cos is more sensitive than sin2 b to the angular distribution of high velocity neutron stars, i.e. the deviation of cos from 0 is more readily detected than the deviation of sin2 b from 1/3, so we expect that with the increasing sensitivity of instrument and the more exact value of cos , it is possible to determine whether this high velocity neutron star model is correct. Some results are discussed in the text.  相似文献   

17.
We consider the linear stability of the equilibrium points of the generic rotating potentials U(r), U(r, ), U(r, and U(r, , . The stability analysis is performed using the concept of Krein's signature. This signature is calculated for all eigenvalues of the above potentials. Thereby, the Lagrangian points of the restricted three-body problem and the synchronous satellites of oblate and prolate planets are also studied. We find also the new positions of the eigenvalues for perturbations of the original L 4 and L 5 points of Mars, Jupiter, Saturn, Uranus and Neptune. Finally, we study the problem with the mass ratio µ close to the critical value and the stability of geostationary satellites perturbed by the Moon.  相似文献   

18.
. - . . , . - . - , , , -. ., , .
The structure of rotating magnetic polytropes is considered in Roche approximation. Investigation of the influence of poloidal as well as toroidal magnetic fields on the conditions of the beginning of matter outflow due to rotational instability is carried out. The influence of the turbulent convection and twisting of magnetic force-lines on the time of smoothing of differential rotation is considered. The estimate of the magneto-turbulence energy generated by differential rotation is presented. Both maximum possible energy output and duration of the quasi-statical evolution phase up to the appearance of hydrodynamic instability due to the effects of general relativity are calculated for supermassive magnetic polytropes of index three with uniform or differential rotation. The radius-mass relation is obtained for supermassive differentially-rotating magnetic polytropes referring to the longest part of the quasi-statistical evolution stage; some consequences are pointed out, including the period-luminosity relation.The evolution of the considered models of supermassive rotating magnetic polytropes with different character of rotation and different geometry of a magnetic field is discussed.The results obtained are summarized in the last section.

English translation will appear in the next issue ofAstrophys. Space Sci.

Receipt delayed by postal strike in Great Britain  相似文献   

19.
In a previous paper (Paper I), we studied a dynamo model of the Babcock-Leighton type (i.e., the surface eruptions of toroidal magnetic field are the source for the poloidal field) that included a thin, deep seated, generating layer (GL) for the toroidal field, B. Meridional motions (of the order of 12 m s–1 at the surface), rising at the equator and sinking at the poles were essential for the dynamo action. The induction equation was solved by approximating the latitudinal dependence of the fields by Legendre polynomials. No solutions were found with p = f where p and f are the fluxes for the preceding and following spot, respectively. The solutions presented in Paper I, had p = –0.5 f , were oscillatory in time, and large radial fields, B, were present at the surface.Here, we resume the study of Paper I with a different numerical approach allowing for a much higher resolution in , the polar angle. The time dependent partial differential equations for the toroidal and poloidal field are solved with the help of a second order, time and space centered, finite difference scheme. Oscillatory solutions with p = f are found for various values of the meridional motions and diffusivity coefficients. The surface values of B, while considerably smaller than those of Paper I, are still unacceptably large, specially at the poles. The reason can be traced to the eruption of toroidal field at high latitudes. It appears that in order to obtain small values for the radial field in the polar regions, high latitude sources ( smaller than /4, say), must reach their maximum below the surface. Weaker meridional motions near the poles than in the equatorial region are also suggested.  相似文献   

20.
Moon  Y.-J.  Wang  Haimin  Spirock  Thomas J.  Goode  P.R.  Park  Y.D. 《Solar physics》2003,217(1):79-94
We present a new method to resolve the 180° ambiguity for solar vector magnetogram measurements. The basic assumption is that the magnetic shear angle (), which is defined as the difference between the azimuth components of observed and potential fields, approximately follows a normal distribution. The new method is composed of three steps. First, we apply the potential field method to determine the azimuthal components of the observed magnetic fields. Second, we resolve the ambiguity with a new criterion: –90°+mp lele90°+mp, where mp is the most probable value of magnetic shear angle from its number distribution. Finally, to remove some localized field discontinuities, we use the criterion B tB mt ge0, where B t and B mt are an observed transverse field and its mean value for a small surrounding region, respectively. For an illustration, we have applied the new ambiguity removal method (Uniform Shear Method) to a vector magnetogram which covers a highly sheared region near the polarity inversion line of NOAA AR 0039. As a result, we have found that the new ambiguity solution was successful and removed spatial discontinuities in the transverse vector fields produced in the magnetogram by the potential field method. It is also found that our solution to the ambiguity gives nearly the same results, for highly sheared vector magnetograms and vertical current density distributions, of NOAA AR 5747 and AR 6233 as those of other methods. The validity of the basic assumption for an approximate normal distribution is demonstrated by the number distributions of magnetic shear angle for the three active regions under consideration.  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