共查询到10条相似文献，搜索用时 78 毫秒
1.
M. V. Samokhin 《Earth, Moon, and Planets》1993,61(1):29-37
Using the well-known equation for the normal component of the current which exist near the tangential discontinuity in the plasma in the case of the frozen-in magnetic field, and supposing that the current closes in the ionosphere in the auroral oval in the region 1, one calculates and compares with the data of observations the dependence of the density of the field-aligned current at the level of the ionosphere on the local time. 相似文献
2.
In this paper we first emphasize why it is important to know the successive zonal harmonics of the Sun's figure with high
accuracy: mainly fundamental astrometry, helioseismology, planetary motions and relativistic effects. Then we briefly comment
why the Sun appears oblate, going back to primitive definitions in order to underline some discrepancies in theories and to
emphasize again the relevant hypotheses. We propose a new theoretical approach entirely based on an expansion in terms of
Legendre's functions, including the differential rotation of the Sun at the surface. This permits linking the two first spherical
harmonic coefficients (J
2 and J
4) with the geometric parameters that can be measured on the Sun (equatorial and polar radii). We emphasize the difficulties
in inferring gravitational oblateness from visual measurements of the geometric oblateness, and more generally a dynamical
flattening. Results are given for different observed rotational laws. It is shown that the surface oblateness is surely upper
bounded by 11 milliarcsecond. As a consequence of the observed surface and sub-surface differential rotation laws, we deduce
a measure of the two first gravitational harmonics, the quadrupole and the octopole moment of the Sun: J
2=−(6.13±2.52)×10−7 if all observed data are taken into account, and respectively, J
2=−(6.84±3.75)×10−7 if only sunspot data are considered, and J
2=−(3.49±1.86)×10−7 in the case of helioseismic data alone. The value deduced from all available data for the octopole is: J
4=(2.8±2.1)×10−12. These values are compared to some others found in the literature.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005238718479 相似文献
3.
Yoshio Kubo 《Celestial Mechanics and Dynamical Astronomy》2009,105(4):261-274
We calculate the so-called convective term, which shows up in the expression for the angular velocity of the elastic Earth,
within the Andoyer formalism. The term emerges due to the fact that the elasticity-caused perturbation depends not only on
the instantaneous orientation of the Earth but also on its instantaneous angular velocity. We demonstrate that this term makes
a considerable contribution into the overall angular velocity. At the same time the convective term turns out to be automatically
included into the correction to the nutation series due to the elasticity, if the series is defined by the perturbation of
the figure axis (and not of the rotational axis) in accordance with the current IAU resolution. Hence it is not necessary
to take the effect of the convective term into consideration in the perturbation of the elastic Earth as far as the nutation
is related to the motion of the figure axis. 相似文献
4.
介绍和论述了在后牛顿引力理论(PPN形式)中在优越参考系和非优越参考系中经过参数化后引力常数变化对地球自转产生的效应,其中特别重点介绍了年周期变化的效应。此外也将理论结果同观测结果相对比。 相似文献
5.
B. P. Kondratyev 《Solar System Research》2013,47(1):1-10
A two-component theoretical model of the physical libration of the Moon in longitude is constructed with account taken of the viscosity of the core. In the new version, a hydrodynamic problem of motion of a fluid filling a solid rotating shell is solved. It is found that surfaces of equal angular velocity are spherical, and a velocity field of the fluid core of the Moon is described by elementary functions. A distribution of the internal pressure in the core is found. An angular momentum exchange between the fluid core and solid mantle is described by a third-order differential equation with a right-hand side. The roots of a characteristic equation are studied and the stability of rotation is proved. A libration angle as a function of time is found using the derived solution of the differential equation. Limiting cases of infinitely large and infinitely small viscosity are considered and an effect of lag of a libration phase from a phase of action of an external moment of forces is ascertained. This makes it possible to estimate the viscosity and sizes of the lunar fluid core from data of observations. 相似文献
6.
L. Györi 《Solar physics》1989,120(2):421-430
For a perfectly aligned Coudé heliograph the north direction of Sun's image in the image plane of the heliograph changes linearly with the hour angle of the Sun or in a common heliograph it is constant. But if the alignment is not perfect and there are instrumental errors the angle between the north direction of the Sun's image and a direction fixed in the image plane is a complicated function of the hour angle of the Sun. In this paper we derive this dependence. 相似文献
7.
Near-infrared brightness temperature contrasts observed on the night side of Venus indicate variations in the size and distribution of particles in the lower and middle cloud decks. McGouldrick and Toon [McGouldrick, K., Toon, O.B., 2007. Icarus 191, 1-24] have shown that these changes can be explained by large-scale dynamics; in particular, that downdrafts may produce optical depth “holes” in the clouds. The lifetimes of these holes are observed to be moderately short, on the order of ten days. Here, we explore a simple model to better understand this lifetime. We have coupled a microphysical model of the Venus clouds with a simple, two-dimensional (zonal, vertical) kinematical transport model to study the effects of the zonal flow on the lifetime of the holes in the clouds. We find that although wind shear may be negligible within the cloud itself, the shear that is present near the top and the bottom of the statically unstable cloud region can lead to changes in the radiative-dynamical feedback which ultimately lead to the dissipation of the holes. 相似文献
8.
A. G. W. Cameron 《Earth, Moon, and Planets》1973,7(3-4):377-383
The basic geochemical model of the structure of the Moon proposed by Anderson, in which the Moon is formed by differentiation of the calcium, aluminium, titanium-rich inclusions in the Allende meteorite, is accepted, and the conditions for formation of this Moon within the solar nebula models of Cameron and Pine are discussed. The basic material condenses while iron remains in the gaseous phase, which places the formation of the Moon slightly inside the orbit of Mercury. Some condensed metallic iron is likely to enter the Moon in this position, and since the Moon is assembled at a very high temperature, it is likely to have been fully molten, so that the iron can remove the iridium from the silicate material and carry it down to form a small core. Interactions between the Moon and Mercury lead to the present rather eccentric Mercury orbit and to a much more eccentric orbit for the Moon, reaching past the orbit of the Earth, establishing conditions which are necessary for capture of the Moon by the Earth. In this orbit the Moon, no longer fully molten, will sweep up additional material containing iron oxide. This history accounts in principle for the two major ways in which the bulk composition of the Moon differs from that of the Allende inclusions.Paper dedicated to Professor Harold C. Urey on the occasion of his 80th birthday on 29 April 1973. 相似文献
9.
The spiral waves in a model galaxy consisting of differentially rotating and non-rotating subsystems are considered on the basis of participating phenomena. The subsystems involved represent the Populations I and II of normal spirals, respectively. The spiral waves in such a systems are unstable in the Landau sense. Due to this instability they grow up to attain finite amplitude. This growth is stopped by a non-linear effect (the quasilinear effect), the steady state with waves of finite amplitude being established. The hypothesis is proposed that these waves should be identified with the spiral structure of the galaxies. 相似文献
10.
Bernard Shizgal 《Planetary and Space Science》1977,25(2):203-204
The validity of the Chapman-Enskog method in the calculation of the heat conductivity of the solar wind is studied. The predictions of the Chapman-Enskog theory are compared with known results of rarefied gas kinetic theory. The results suggest that the use of the Chapman-Enskog theory to describe the transport processes in the solar wind is not strictly justified. 相似文献