共查询到20条相似文献，搜索用时 906 毫秒
1.
Using analytical approximations we study the effects of different external magnetic configurations on the half-width, mass, and internal magnetic structure of a quiescent solar prominence, modelled as a thin vertical sheet of cool plasma. Firstly, we build up a zeroth-order model and analyse the effects produced by a potential coronal field or a constant- force-free field. This model allows us to obtain the half-width and mass of the prominence for different values of the external field, pressure and shear angle. Secondly, the effects of these external magnetic configurations on a two-dimensional model proposed by Ballester and Priest (1987) are studied. The main effects are a change of the half-width with height, an increase of the mass, a decrease of the magnetic field strength with height and a change in the shape of the magnetic field lines. 相似文献
2.
The effects of the orientation of the interplanetary magnetic field (IMF) on the structure of the distant magnetotail are studied by superposing a uniform magnetic field on a magnetospheric model. It is shown that a southward component of the IMF alone can reduce the closed field region in the magnetotail, while a northward turning of the IMF can produce a new closed field region. It is suggested that these two effects can explain thinning and thickening, respectively, of the plasma sheet during magnetospheric substorms without invoking internal instabilities. 相似文献
3.
The analysis procedure proposed by Auer et al. (1977) for deducing magnetic field vectors from Stokes profiles has been tested to investigate the influence of magneto-optical effects on the deduced field parameters. The quality of the fit between synthetic profiles generated with the inclusion of magneto-optical effects and the profiles returned by the inversion routine is also investigated. The results show that magneto-optical effects should be included in the inversion routine especially to increase the accuracy of the deduced, azimuth of the magnetic field. 相似文献
4.
Paul S. Cally 《Monthly notices of the Royal Astronomical Society》2009,395(3):1309-1318
Phase perturbations due to inclined surface magnetic field of active region strength are calculated numerically in quiet Sun and simple sunspot models in order to estimate and compare the direct and indirect (thermal) effects of the fields on helioseismic waves. It is found that the largest direct effects occur in highly inclined field characteristic of penumbrae, and scale roughly linearly with magnetic field strength. The combined effects of sunspot magnetic and thermal anomalies typically yield negative travel-time perturbations in penumbrae. Travel-time shifts in umbrae depend on details of how the thermal and density structure differs from the quiet Sun. The combined shifts are generally not well approximated by the sum of the thermal and magnetic effects applied separately, except at low field strengths of around 1 kG or less, or if the thermal shift is small. A useful rule-of-thumb appears to be that travel-time perturbations in umbrae are predominantly thermal, whereas in penumbrae they are mostly magnetic. 相似文献
5.
Alejandra Kandus 《Monthly notices of the Royal Astronomical Society》2007,378(4):1356-1364
We study semi-analytically and in a consistent manner the generation of a mean velocity field by helical magnetohydrodynamical (MHD) turbulence, and the effect that this field can have on a mean field dynamo. Assuming a prescribed, maximally helical small-scale velocity field, we show that large-scale flows can be generated in MHD turbulent flows via small-scale Lorentz force. These flows back-react on the mean electromotive force of a mean field dynamo through new terms, leaving the original α and β terms explicitly unmodified. Cross-helicity plays the key role in interconnecting all the effects. In the minimal τ closure that we chose to work with, the effects are stronger for large relaxation times. 相似文献
6.
Bhimsen K. Shivamoggi 《Astrophysics and Space Science》1982,84(1):255-258
The effect of the electron-streaming along the applied magnetic field on the electromagnetic circularly-polarised modes in a Vlasov plasma propagating along the applied magnetic field is studied. It is found that the growth or decay of the circularly-polarised modes is affected by the electron-streaming in the presence of the thermal effects, unlike the case with the thermal effects absent. 相似文献
7.
Atmospheric models of He-peculiar stars: synthetic He I line profiles and absolute visual magnitudes
Rodolfo Vallverdú Lydia Cidale René Rohrmann Adela Ringuelet 《Astrophysics and Space Science》2014,352(1):95-102
We analyze the influence of magnetic pressure effects on the atmospheric structure of B peculiar type stars, as well as, on the emergent He?I line profiles and absolute visual magnitudes. We consider a photosphere in local thermodynamic and hydrostatic equilibrium. The hydrostatic equilibrium equation is modified to include the Lorentz force. Atomic occupational numbers are computed in LTE considering non-ideal effects in the gas equation of state. We depict the influence of a magnetic field on local He?I line profiles and discuss the effects of the helium abundance in magnetic B-type stars. The Lorentz force might explain local variations up to 7 % in the equivalent width of helium lines, while local enhancements of He chemical abundances would produce larger changes. To analyze the line variations in real stars we computed the net contribution of a bipolar magnetic field over the stellar disk. The resulting disk-averaged magnetic field predicts variations with the rotation phase up to 2–3 % in the line EWs for a dipolar magnetic field of 1000 G. 相似文献
8.
The growth of weak MHD discontinuities have been studied in a radiation induced flow field at very high temperature. Growth and decay properties of weak MHD discontinuities have been discussed under the influences of time-dependent gasdynamic field, the radiation field and the magnetic field with finite electrical conductivity. The effects of thermal radiation and conduction of the global behaviour of weak MHD discontinuities have been studied under a quasi-equilibrium and quasi-isotropic hypothesis of the differential approximation to the radiative heat transfer equation. It is shown that the existence of the time-dependent radiation field gives rise to a radiation induced wave which has a negligibly small effect on the non-relativistic flow properties of the gasdynamic field. It is also shown that the radiation stresses resist the steepening tendency of a compressive weak wave and help in stabilizing it whereas the thermal conduction effects counteracts to destabilize it. It is found that under radiation effects the shock formation is either disallowed or delayed. The two cases of diverging waves and converging waves have been studied separately to answer a particular question as to when a shock discontinuity or a coustic will be formed or disallowed under curvature effects. 相似文献
9.
The first aim of the present work is to compute a more accurate and recent model for the Earth’s magnetic field. The second
aim is to determine the effects of the Earth’s magnetic field on the motion of a charged artificial satellite to evaluate
the variations of the orbital elements of the satellite due to these effects. The magnetic field and its variation with time
have been studied at different heights, longitudes and latitudes. The geomagnetic field is considered as a multiple potential
field and the electrical charge of the satellite is assumed to be constant. A new computer code has been constructed to follow
the components of the magnetic field in spherical harmonic models. The Gauss equations are solved numerically. The results
concentrate on the computation of the numerical values of orbital perturbation for the case of a low Earth satellite. RS-1
satellite and space craft gravity probe B (GPB) are chosen as cases of studies for a detailed numerical analysis. 相似文献
10.
The gravitational instability of an infinite homogeneous self-gravitating and finitely conducting, rotating gas-particle medium, in the presence of a uniform vertical magnetic field, is studied to include finite Larmor radius and suspended particles effects. The particular cases of the effects of rotation, finite conductivity, finite Larmor radius and suspended particles on the waves propagated along and perpendicular to magnetic field have been discussed. Jeans's criterion determines the gravitational instability. 相似文献
11.
S. Webb 《Planetary and Space Science》1974,22(12):1719-1723
A self-consistent computation of the interplanetary magnetic field is presented which takes into account the effects of interstellar particles newly ionised on entering the solar cavity. The resulting field differs infinitesimally from the Parker spiral for all reasonable parameters and is in agreement with recent observations on board Pioneer 10. 相似文献
12.
13.
J. B. Singh 《Astrophysics and Space Science》1988,150(1):43-52
Using a well-known similarity method, different aspects of cylindrical shock waves in magnetogasdynamics are investigated. Weak and strong shocks have been discussed in strong magnetic field. Combined effects of both the components of magnetic field on flow variables are studied. 相似文献
14.
In this paper we apply the so-called complex-plane iterative technique (CIT) to the computation of classical white dwarf models
distorted by rotation (either rigid, or differential) and toroidal magnetic field. We give emphasis on computing critical
rotations and rotations with effects that, combined with the effects of the toroidal magnetic field, give configurations with
almost spherical shape.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
An analytical study is performed to examine the heat source characteristics on the free-convection and mass transfer flow past an impulsively started infinite non-conducting vertical plate of a viscous, incompressible electrically-conducting fluid under the action of a uniform magnetic field through porous medium. The effects of various parameters on the velocity field are extensively discussed. 相似文献
16.
A comparative study has been made between the effects of transverse and axial components of the magnetic field on the self-similar flow variables of the field behind the cylindrical shock waves propagating into a non-uniform atmosphere at rest. The total energy of the wave is constant. 相似文献
17.
戴子高 《中国天文和天体物理学报》1997,(2)
本文研究了中子星的热演化、自转演化和磁场演化的相互影响．考虑了一个自洽模型：中子星因磁偶极辐射而自转减慢，在内部产生某些加热过程，中子星磁场通过壳层的欧姆耗散来衰减．结果表明，磁场衰减提高了加热过程的重要性；相反，加热效应减慢了磁衰减．因此可以得出，中子星的热、自转和磁场也许不是独立演化的．不仅如此，这些演化与初始条件有关，因此，人们也许可以从射电和Ｘ射线观测对脉冲星年龄、初始磁场和周期给出某些限制． 相似文献
18.
R. C. Sharma 《Astrophysics and Space Science》1974,29(1):L1-L4
The gravitational instability of an infinite homogeneous self-gravitating rotating plasma in the presence of a uniform vertical magnetic field has been studied to include the FLR effects. It has been found that the Jeans' criterion of instability remains unaffected even if rotation and FLR effects are included. The effect of rotation is to decrease the Larmor radius by an amount-depending upon the wavenumber of perturbation. The particular cases of the effect of FLR and rotation on the waves propagated along and perpendicular to the magnetic field have been discussed. 相似文献
19.
Thermosolutal-convective instability of a stellar atmosphere is considered. The criteria for monotonic instability are derived. The effects of a variable horizontal magnetic field and the simultaneous presence of a uniform rotation and a uniform horizontal magnetic field have been considered on the thermosolutal-convective instability. The criteria derived for monotonic instability are found to hold good in the presence of a variable horizontal magnetic field as well as in the presence of a uniform rotation and a uniform horizontal magnetic field. 相似文献
20.
The effects of both density stratification and magnetic field expansion on torsional Alfvén waves in magnetic flux tubes are
studied. The frequencies, the period ratio P
1/P
2 of the fundamental and its first-overtone, and eigenfunctions of torsional Alfvén modes are obtained. Our numerical results
show that the density stratification and magnetic field expansion have opposite effects on the oscillating properties of torsional
Alfvén waves. 相似文献