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991.
Based on the Bayesian principle and the fact that GPS carrier-phase ambiguities are integers, the posterior distribution
of the ambiguities and the position parameters is derived. This is then used to derive the maximum posterior likelihood solution
of the ambiguities. The accuracy of the integer ambiguity solution and the position parameters is also studied according to
the posterior distribution. It is found that the accuracy of the integer solution depends not only on the variance of the
corresponding float ambiguity solution but also on its values.
Received: 27 July 1999 / Accepted: 22 November 2000 相似文献
992.
Geoid, topography, and the Bouguer plate or shell 总被引:1,自引:1,他引:1
Topography plays an important role in solving many geodetic and geophysical problems. In the evaluation of a topographical
effect, a planar model, a spherical model or an even more sophisticated model can be used. In most applications, the planar
model is considered appropriate: recall the evaluation of gravity reductions of the free-air, Poincaré–Prey or Bouguer kind.
For some applications, such as the evaluation of topographical effects in gravimetric geoid computations, it is preferable
or even necessary to use at least the spherical model of topography. In modelling the topographical effect, the bulk of the
effect comes from the Bouguer plate, in the case of the planar model, or from the Bouguer shell, in the case of the spherical
model. The difference between the effects of the Bouguer plate and the Bouguer shell is studied, while the effect of the rest
of topography, the terrain, is discussed elsewhere. It is argued that the classical Bouguer plate gravity reduction should
be considered as a mathematical construction with unclear physical meaning. It is shown that if the reduction is understood
to be reducing observed gravity onto the geoid through the Bouguer plate/shell then both models give practically identical
answers, as associated with Poincaré's and Prey's work. It is shown why only the spherical model should be used in the evaluation
of topographical effects in the Stokes–Helmert solution of Stokes' boundary-value problem. The reason for this is that the
Bouguer plate model does not allow for a physically acceptable condensation scheme for the topography.
Received: 24 December 1999 / Accepted: 11 December 2000 相似文献
993.
994.
995.
Effects of the spherical terrain on gravity and the geoid 总被引:3,自引:0,他引:3
996.
Condensation heating of the Asian summer monsoon and the subtropical anticyclone in the Eastern Hemisphere 总被引:27,自引:0,他引:27
The effects of condensation heating on the formation of the subtropical anticyclone in the Eastern Hemisphere (EH) are studied
by means of theoretical analysis and numerical simulation. The complete vorticity equation is employed for the analysis. It
is found that, due to the vertical gradient of strong condensation heating, the distribution of cyclone and anticyclone in
the upper troposphere is out of phase with that in the middle and lower troposphere. This is confirmed by a series of numerical
experiments. The horizontal gradient of the condensation heating also affects the configuration of the subtropical anticyclone.
It is concluded that condensation heating is a key factor for the formation and location of the summer subtropical anticyclone
in the EH. The latent heating released by the Asian monsoon rainfall contributes to the formation of the 200 hPa South Asian
anticyclone on the western side of the heating center and the 500 hPa western Pacific subtropical anticyclone on the eastern
side of the center. Such configurations are modified to some extent by surface sensible heating and orography. The circulation
in mid-latitudes is also affected by the latent heating in the subtropical area through the propagation of Rossby waves.
Received: 10 September 1999 / Accepted: 5 June 2000 相似文献
997.
Y. Shao M. Sogalla M. Kerschgens W. Brücher 《Meteorology and Atmospheric Physics》2001,78(3-4):157-181
Summary
In this paper, we examine the effects of land-surface heterogeneity on the calculation of surface-energy and momentum fluxes
in a meso-scale atmospheric model. A series of numerical experiments has been carried out with a combination of different
resolutions for the atmosphere and the land surface, which allows an examination of the aggregation and dynamic effects associated
with land-surface heterogeneity. The numerical results show that for a given atmospheric model resolution, increased land-surface
resolution leads to better estimates of surface-energy and momentum fluxes, and for a given land-surface resolution, increased
atmospheric model resolution also improves the estimates of these fluxes. This latter result contradicts the prevailing view
that subgrid variation in atmospheric data plays only a minor role in estimating the fluxes. It is also shown that subgrid
land-surface heterogeneity leads to increased turbulent fluctuations. The responsible mechanisms of this effect are both the
subgrid variation of surface-energy fluxes and their impact upon the development of convective cells. It is suggested that
subgrid atmospheric motions induced by surface heterogeneity may be an important factor which needs to be considered in subgrid
closure schemes for atmospheric models.
Received August 28, 2000/Revised June 1, 2001 相似文献
998.
999.
A study of NAO variability and its possible non-linear influences on European surface temperature 总被引:2,自引:0,他引:2
D. Pozo-Vázquez M. J. Esteban-Parra F. S. Rodrigo Y. Castro-Díez 《Climate Dynamics》2001,17(9):701-715
The relationship between European winter temperature spatial and temporal modes of variability and the North Atlantic Oscillation
(NAO) has been studied during the period 1852–1997. Temporal modes of variability of the NAO and temperatures are analysed
using wavelet transform. Results show that the NAO presents a strong non-stationary behaviour. The most important feature
is the existence of a quasi-periodic oscillation, with a period between 6–10 years and maximum amplitude of eight years, during
the periods 1842–1868 and 1964–1994. Between 1875 and 1939 the spectra of the NAO is almost white. The possible relationship
between the occurrence of extreme events of the NAO and its spectral behaviour has been analysed. The results indicate that
quasi-periodic oscillations in the NAO do not lead to more extreme episodes, but rather that an extreme value of the oscillation
is more likely to persist for few years. Particularly energetic modes of coherent variability between temperature and NAO
are found between 2–6 years for 1857–1879 and 1978–1984, and between 6–10 years from 1961 to 1991. The relationship between
the NAO and temperatures as a function of the state of the oscillation has been studied using composites. Empirical evidence
has been found suggesting that winter temperatures, in a great part of the study area, do not vary in a linear manner with
respect to phase and intensity of the NAO. Regions in the study area differ in sensitivity to changes in the NAO. The spatial
patterns of variability of the temperatures are found to be independent of the NAO spectra.
Received: 8 April 1999 / Accepted: 19 September 2000 相似文献
1000.
天津及邻区1999~2000年地震震源机制研究 总被引:2,自引:0,他引:2
文中使用的是天津市、河北省地震台的 P,Pn波初动方向资料 ,研究了 1 999~ 2 0 0 0年发生在天津及邻区的 4个地震的震源机制。其中 1 999年 8月 1 1日河北省大城县 ML 3.1地震发生在大城断裂上 ,震源机制解的节面 (走向 2 0 8°,倾角 54°,滑动角 1 2°)与大城断裂的走向一致。2 0 0 0年 1月 2 6日蓟县 ML 3.3地震发生在蓟县 -邦均断裂上 ,震源机制解的节面 (走向 2 85°,倾角 77°,滑动角 1 38°)与蓟县 -邦均断裂的走向一致。表明这两个断层在活动 ,这两个地震发生在多年来 (有感 )地震不多的地区 ,并且是发生在首都圈中部 ,应该引起注意 相似文献