Atmospheric tides and rotation of the Earth

The six-hourly values of the atmospheric angular momentum (AAM) functions computed by the U.S. National Meteorological Center (NMC) were used to estimate the effects of the atmospheric tides on the Earth's rotation. Variations of the equatorial components ₁ and ₂ of the AAM have periods close to gravitational tidesP ₁ andK ₁.The amplitudes of the detected variations in ₁ and ₂ functions have been found to be much larger than the theoretical ones, the reason of this amplification remains unexplained. According to theoretical formulations, these waves can be expressed only as retrograde motions. Because of frame effects, there is a correspondance between diurnal retrograde polar motion and precession-nutations and the atmospheric effect on polar motion cannot be detected from observations.The second part of this paper deals the effects of atmospheric tides in Earth rotation. High-frequency UT1 variations have been derived from VLBI and GPS techniques during the SEARCH'92 campaign (Study ofEarth-AtmosphereRapidCHanges) (Dickey et al. 1994). They have been compared to values derived by Ray et al. (1994) from global ocean tide model. The results obtained in the present paper show the existence of variations of thermal origin with an amplitude of about 1µs in Universal Time UT1. The agreement between observed and theoretical values is better when the determined thermal atmospheric tides are taken into account.Oceanic tidal signal explains a large part (60% of the signal variance) of the diurnal and sub-diurnal variations. Our results show that only a small part of the residuals (5%) accounts for the atmospheric tidal effects. The residual signal remains unexplained; it might be due to mismodelization of oceanic or atmospheric tides or effect of other geophysical phenomena.     

The equilibrium figure of the Earth,I

Based on the method of virial equations, the integro-differential equations governing the physical figure of the earth are derived. Volume forces of gravitational type and surface forces of stress type are assumed. Initial stress is represented by the H. TAKEUCHI (1951) model. Equilibrium figures for different earth models-elastic, elastic under initial stress, liquid-are studied. It is proved that non-liquid earth models allow ellipsoidal structures of MACLAURIN type.     

Lilliput and Blefuscu and the figure of the Earth

Is the intense controversy between French and English scientists of the late 1600 th and early 1700 th—relating to the figure of the Earth—reflected in the “most obstinate war” fought between “the two great empires of Lilliput and Blefuscu”—over the correct way of breaking eggs?     

“数字鸿沟”与地球信息科学的应对

2003年上半年连续出现的全球性突发事件,是对我国的严峻考验。面对严峻复杂的世界形势,地球信息科学可以大有作为,如建设各类型的地理信息系统,以增强应变能力,制定长远规划,加强基础研究和数据储备,将地球信息科学的先进技术和成果应用于国家应对突发事件和政府决策,提出强强联合,共同攻克难关。     

Angular momentum of Arctic Ocean tides

Oceanic tidal angular momentum (OTAM) is calculated for the four major tides of the Arctic Ocean, based on the tidal elevations and current velocities from a recent two-dimensional numerical hydrodynamic model. The presented OTAM tables are meant to be complementary to other modeling studies that use satellite altimetry (which cannot observe Arctic Ocean tides because of ice cover and limited satellite inclinations). Although the Arctic Ocean's influence on earth rotation is, as may be expected, relatively small, the rapid advancement of the subject now calls for such small contributions to be explicitly accounted for. Received: 22 January 1996; Accepted: 5 December 1996     

Shallow-water loading tides in Japan from superconducting gravimetry

Gravity observations from superconducting gravimeters are used to observe loading effects from shallow-water tides on the Japanese east and west coasts. Non-linear third-diurnal and higher-frequency shallow-water tides are identified in the tide-gauge observations from these coastal areas. The most energetic constituents in the tide gauge observations are also seen in the gravity observations due to their loading effects on the deformation of the Earth. Even though the shallow-water tides at the Japanese east coast have an amplitude of only a few millimetres, they are still able to generate a loading signal at gravity sites located several hundred kilometres inland. In particular, the S₃, S₄ and S₅ solar tides occur in both gravity and tide gauge observations. It is indicated that in other shelf regions with large shallow water tides, the shallow water loading signals account for a significant signal, which should be taken into account.Acknowledgement The authors would like to thank the Hydrographic and Oceanographic Department (Japan Coast Guard), Japan Meteorological Agency and Hokkaido Development Agency for access to the tide-gauge data. Also, the Global Geodynamic Project Information System and Data Center (GGP-ISDC) is acknowledged for providing the gravity data.     

南极国际GPS跟踪站的海潮位移改正

This paper describes the ocean loading tides corrections of GPS stations in Antarctica, such as the Great Wall station and Zhongshan station. Based on the theory of ocean loading tides, the displacement corrections of ocean loading tides on GPS stations in Antarctica are calculated by using the CRS4.0 ocean loading tides model. These corrections are also applied to GPS data processing. The GPS data are analyzed by the GAMIT software with and without these corrections. We compared and analyzed the GPS baseline components to get the differences. The results show that the ocean tidal displacement corrections have obvious effects upon GPS baseline components. Therefore, we should not ignore the ocean loading tides corrections of GPS stations in Antarctica to obtain precise and reliable results.     

The introduction of the Iau 1980 nutation theory in the computation of the Earth Rotation Parameters by the Bureau International de l'Heure

Summary The status of nutation theory in the computation of the Earth Rotation Parameters from the different observational techniques is reviewed. The impact on the combined solution of the Bureau International de l'Heure is evaluated. In view of the improvement brought by the IAU 1980 Nutation Theory, its introduction in the BIH publications, without waiting for the adoption by the astronomical ephemerides (1984 Jan. 1) is decided.     

Voronoi图增点构造算法研究

论述了一种由计算机自动生成Voronoi图的增点构造法。该方法以一个原始的Delaunay三角网和相应的Voronoi图为基础,针对构造过程中出现的不满足Delaunay三角形空圆特性的数据点,利用最大最小角度法则对三角网进行局部优化,根据优化后的三角网生成最终的Voronoi图。     

水准高差的日月潮汐改正

本文研究了日月潮汐对水准高差的影响 ,导出了水准高差的日月潮汐改正公式 ,从而验证了现行水准测量规范引用的公式 ,并发现其存在的个别错误 ,给出了计算潮汐改正需要的日月时角和赤纬的表达式     

On an Earth ellipsoid best-fitted to the Earth surface

Historically, the mean Earth ellipsoid is obtained by fitting an ellipsoid of revolution to the geoid. Such an ellipsoid, however, does not necessarily best fit the physical surface of the Earth due to the existence of topography outside the geoid. In this paper, we present a purely geometrically defined Earth ellipsoid that best fits the physical surface of the Earth so that the resulting ellipsoidal height attains minimum global mean square value. Using a global digital terrain model and a global geopotential model, the size, shape and position of such an Earth ellipsoid have been numerically estimated. Received: 6 September 1996 / Accepted: 1 April 1998     

固体潮对BDS精密单点定位的影响研究

针对在精密单点定位中固体潮引起的测站位移直接影响精密单点定位精度的问题,该文在全球范围内选取了66个IGS测站,对其2020年第245～274天连续30 d的观测数据进行了处理和计算,研究分析了固体潮对BDS-2、BDS-3和BDS-2+3精密单点定位精度的影响.结果 表明:固体潮对BDS-2、BDS-3和BDS-2+...     

Polar motion for an elastic Earth model with a homogeneous liquid core using a canonical theory

The rotational motion for an elastic Earth model with a homogeneous liquid core has been obtained using Hamilton's equations. From the canonical equations for the precessional and nutational motions in an inertial frame, the corresponding equations in an Earth fixed frame are deduced. The linearized equations obtained for polar motion and liquid core motion are equivalent to the Sasao-Okubo-Saito equations.