排序方式： 共有46条查询结果，搜索用时 250 毫秒
1.
L. L. Kitchatinov 《Astronomy Reports》2004,48(2):153-160
Although the theory of differential rotation is in satisfactory agreement with helioseismological data for the deep convection zone, there are considerable discrepancies near the solar surface. This disagreement can be eliminated if the anisotropy of turbulent convection is taken into account together with the effects of nonuniformity of the medium, on which the most recent models for differential rotation are based. The model for the differential rotation of the convection envelope is supplemented by computations for the transition layer between nonuniform and rigid-body rotation in the upper layers of the solar radiative zone. These are the first computations of differential rotation for the entire volume of the Sun. 相似文献
2.
L. L. Kitchatinov 《Astronomy Reports》2001,45(10):816-823
Differential-rotation and dynamo models are computed for a young, solar-mass star at the initial stage of the formation of its radiative core. It is argued that the global magnetic fields in the radiative zones of the contemporary Sun and similar stars are due to the action of a hydromagnetic dynamo at early evolutionary stages. Our computations suggest that this field should be nonaxisymmetric. Physical reasons for departures from axial symmetry are discussed in detail. It is suggested that nonaxisymmetric relic fields are responsible for the phenomenon of active longitudes. 相似文献
3.
A nonlinear dynamo model that allows for the dependence of the turbulent diffusivity on the magnetic field shows the phenomenon
of a hysteresis. In a certain range of dynamo numbers, two types of solutions are possible: decaying oscillations of weak
fields and magnetic cycles with a constant and large amplitude, which are settled depending on the initial conditions. Fluctuations
in α-parameter cause transitions between these two regimes and calculations show the intermittency of magnetic cycles with a relatively
large amplitude and epochs of weak magnetic fields. This behavior can serve as a model of grand minima of solar activity like
the well-known Maunder minimum. 相似文献
4.
The components of the total stress tensor (Reynolds stress plus Maxwell stress) are computed within the quasilinear approximation for a driven turbulence influenced by a large‐scale magnetic background field. The conducting fluid has an arbitrary magnetic Prandtl number and the turbulence without the background field is assumed as homogeneous and isotropic with a free Strouhal number St. The total large‐scale magnetic tension is always reduced by the turbulence with the possibility of a ‘catastrophic quenching’ for large magnetic Reynolds number Rm so that even its sign is reversed. The total magnetic pressure is enhanced by turbulence in the high‐conductivity limit but it is reduced in the low‐conductivity limit. Also in this case the sign of the total pressure may reverse but only for special turbulences with sufficiently large St > 1. The turbulence‐induced terms of the stress tensor are suppressed by strong magnetic fields. For the tension term this quenching grows with the square of the Hartmann number of the magnetic field. For microscopic (i.e. small) diffusivity values the magnetic tension term becomes thus highly quenched even for field amplitudes much smaller than their equipartition value. In the opposite case of large‐eddy simulations the magnetic quenching is only mild but then also the turbulence‐induced Maxwell tensor components for weak fields remain rather small (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
Some consequences of a nonlinear coupling between magnetic field and rotation are studied within a solar type 2D dynamo model for a spherical convective shell. The magnetic feedback on the rotation law produces two main effects. First, the torsional oscillations are excited. Second, a long-term amplitude modulation of the dynamo cycles is produced. The latter may be identified with the grand cycle of solar activity. The dynamo model seems to be in accord with the phase relations between the torsional and magnetic activity oscillations observed in the 11-year cycle as well as in the 55-year grand cycle. It, however, fails to reproduce the observationally suggested global decreasing trend in the equatorial rotation rate. 相似文献
6.
7.
The stability of a self‐gravitating infinitesimally thin gaseous disk rotating around a central mass is studied. Our global linear analysis concerns marginal stability, i.e. it yields the critical temperature for the onset of instability for any given ratio of the disk mass to the central mass. Both axisymmetric and low‐m nonaxisymmetric excitations are analysed. When the fractional disk mass increases, the symmetry character of the instability changes from rings (m = 0) to one‐armed trailing spirals (m = 1). The distribution of the surface density along the spiral arms is not uniform, but describes a sequence of maxima that might be identified with forming planets. The number of the mass concentrations decreases with increasing fractional disk mass. We also obtain solutions in the form of global nonaxisymmetric vortices, which are, however, never excited. 相似文献
8.
L. L. Kitchatinov 《Geomagnetism and Aeronomy》2016,56(8):945-951
Mean-field hydrodynamics advanced to clear explanations for the origin and properties of the global meridional flow in stellar convection zones. Qualitative arguments and analysis of basic equations both show that the meridional circulation is driven by non-conservative centrifugal and buoyancy forces and results from a slight disbalance between these two drivers. The deviations from the thermal wind balance are relatively large near the boundaries of convection zones. Accordingly, the meridional flow attains its largest velocities in the boundary layers and decreases inside the convection zone. This picture, however, is neither supported nor dismissed by the conflicting results of recent helioseismic soundings or 3D numerical experiments. The relevant physics of the differential temperature and its possible relation to the solar oblateness are briefly discussed. 相似文献
9.
The αΩ-dynamo model with casual fluctuations of parameter α reproduces all main indications of solar grand minimums and maximums.
If we take the dependence of turbulent diffusivity on the magnetic field into account, we obtain the phenomenon of hysteresis,
when two solutions are possible in a certain interval of dynamo number values: decaying oscillations of weak fields and magnetic
cycles with a constant and a large amplitude, which are formed depending on initial conditions. Fluctuations in parameter
α result in transitions between these regimes, and the computations indicate that magnetic cycles with a relative large amplitude
alternate with epochs of weak magnetic fields. Such behavior can be used as a model of grand minimums and maximums of solar
activity. 相似文献
10.
L. L. Kitchatinov 《Astronomy Letters》2013,39(8):561-569
A linear analysis of baroclinic instability in a stellar radiation zone with radial differential rotation is performed. The instability sets in at a very small rotation inhomogeneity, ΔΩ ～ 10?3Ω. There are two families of unstable disturbances corresponding to Rossby waves and internal gravity waves. The instability is dynamical: its growth time is several thousand rotation periods but is short compared to the stellar evolution time. A decrease in thermal conductivity amplifies the instability. Unstable disturbances possess kinetic helicity. Magnetic field generation by the turbulence resulting from the instability is possible. 相似文献