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The relationship between the directions of polar acoustic gravity waves and a wind at 250–350 km altitudes has been studied based on an analysis of the Dynamics Explorer 2 satellite measurements. A method, which makes it possible to determine the direction of these waves relative to the satellite velocity vector based on one-point measurements of different neutral atmosphere parameters, is presented. It has been established that acoustic gravity waves observed over the polar caps systematically propagate upwind, which argues for their spatial wind filtering. In the polar regions, waves mainly propagate in two directions: toward magnetic noon and 15–16 MLT. Waves tend to move counterclockwise and clockwise over the northern and southern polar caps, respectively. 相似文献
3.
This paper reviews how the study of the surface gravity changes is able to provide useful information on the Earth's structure and global dynamics. The spectral range which is observable with superconducting gravimeters is broad and goes from the seismic frequency band to periods longer than one year. We first investigate the seismic and sub-seismic bands with a special attention paid to the gravity detection of core modes in the liquid core and to the Slichter mode of translation of the solid inner core. In the tidal bands, we show how accurate measurements allow us to infer constraints on various phenomena such as mantle (an-)elasticity, as well as ocean and atmospheric loading. The observation of the Free Core Nutation resonance in the diurnal frequency band is reviewed and indirectly suggests an increase in the ellipticity of the core-mantle boundary with respect to its hydrostatic value. A similar resonance is also theoretically predicted in the diurnal band for the rotation of the solid inner core (Free Inner Core Nutation) but we show that its detection is much more difficult because of the small amplitude and lack of a nearby tidal frequency. Oceanic and atmospheric loading mechanisms induce gravity changes over a wide spectral range and we present some recent progress in this field. Finally, because superconducting gravimeters have high calibration stability and small long-term instrumental drift, they can easily measure longperiod gravity variations due to polar motion and hydrogeology. 相似文献
4.
Summary When correcting precise gravity measurements for polar motion, the Earth's rotational deformation must be considered, as this will increase the correction based on a rigid Earth by about 15%. Conversely the gravity observations can be used to estimate the Love numbers h2 and k2 at the Chandler frequency. 相似文献
5.
《Journal of Atmospheric and Solar》2007,69(16):2071-2080
Multimoment fluid simulation frameworks, which effectively account for anomalous transport due to microprocesses, combine best features of small-scale kinetic and global-scale MHD models. The most practical models of this type, 1D flux tube models, have been successfully used for realistic simulations of space plasmas including polar wind and magnetosphere–ionosphere coupling processes characterized by a wide range of temporal and spatial scales. Our earlier flux tube models with field-aligned current and microprocesses have been formulated for spatially stationary flux tubes. However, horizontal convection due to electric fields is an important aspect of the high-latitude ionosphere–polar wind system and typical time scales of the polar wind upflow are comparable to the transit time across the polar cap. To take into account this important feature we have added flux tube convection to our earlier model. Using typical convecting flux tube that starts outside auroral oval, then enters and leaves downward current region, it has been shown that anomalous transport effects due to current-driven microinstabilities significantly alter dynamics of several plasma moments and should be taken into account for an accurate interpretation and prediction of the observed data. Future applications of our new model have also been discussed. 相似文献
6.
In this study we compared contributions to polar motion excitation determined separately from each of three kinds of geophysical
data: atmospheric pressure, equivalent water height estimated from hydrological models, and harmonic coefficients of the Earth
gravity field obtained from Gravity Recovery and Climate Experiment (GRACE). Hydrological excitation function (Hydrological
Angular Momentum — HAM) has been estimated from models of global hydrology, based on the observed distribution of surfacewater,
snow, ice, and soil moisture. In our considerationwe used several global models of land hydrosphere and models ofAtmospheric
Angular Momentum (AAM) and Oceanic Angular Momentum (OAM). All of themwere compared with observed Geodetic Angular Momentum
(GAM). The spectra of the following excitation functions of polar motion: GAM, AAM+OAM, AAM+OAM+HAM, GAM-AAM-OAM residual
geodetic excitation function, and HAM were computed too. The time variable spectra of geodetic, gravimetric, and the sum of
atmospheric, oceanic, and hydrological excitation functions are also presented. Phasor diagrams of the seasonal components
of polar motion excitation functions of all HAM excitation functions as well as of two GRACE solutions: Center for Space Research
(CSR), Centre National d’Etudes Spatiales/Groupe de Recherche en Geodesie Spatiale (CNES/GRGS) were determined and discussed. 相似文献
7.
The development of studies on estimating the accuracy of the Earth’s modern global gravity models in terms of the spherical harmonics of the geopotential in the problematic regions of the world is discussed. The comparative analysis of the results of reconstructing quasi-geoid heights and gravity anomalies from the different models is carried out for two polar regions selected within a radius of 1000 km from the North and South poles. The analysis covers nine recently developed models, including six high-resolution models and three lower order models, including the Russian GAOP2012 model. It is shown that the modern models determine the quasi-geoid heights and gravity anomalies in the polar regions with errors of 5 to 10 to a few dozen cm and from 3 to 5 to a few dozen mGal, respectively, depending on the resolution. The accuracy of the models in the Arctic is several times higher than in the Antarctic. This is associated with the peculiarities of gravity anomalies in every particular region and with the fact that the polar part of the Antarctic has been comparatively less explored by the gravity methods than the polar Arctic. 相似文献
8.
A gravity field model is computed from the four accurate gravitational gradient components of GOCE (Gravity field and steady-state Ocean Circulation Explorer), combined with the analysis of the kinematic orbits, and some moderate constraint (or stabilization) in the polar areas where no observation from GOCE is available due to the orbit geometry. The normal matrix of each component is computed individually in order to study its contribution to the combined solution. The results show that the contribution of Vzz is the largest, with an average value of 32.74% of the total solution; the second and the third largest are Vzz and Vyy, with average values of 28.04% and 26.08%, respectively; the component Vxz contributes 11.81%. Validation with external data shows that each component has its characteristic value and that the information content of the component Vxz is not negligible and should be included for gravity field recovery. The orbit part as derived from high-low satellite-to-satellite tracking (SST-hl) to the GPS contributes mostly to the coefficients below degree and order (d/o) 20, and to non-zonal coefficients from d/o 20 to 80. The mean value of the contribution of the polar stabilization is the smallest with a value of 0.22%, nevertheless it is important. In addition to the contribution analysis in terms of the normal matrices, each individual component of the gradiometer has been combined with SST and polar stabilization, to give a set of single component gravity field models. These partially combined solutions are compared to the fully combined solution in terms of geoid differences. They show that the partially combined solution with Vzz is closest to the complete solution. Even closer is a combination with Vxx and Vyy. In addition to the GOCE-only solution, a GOCE-GRACE (Gravity Recovery And Climate Experiment) combined gravity field model is derived and the information content of GOCE and an available set of normal equations of GRACE are investigated. Results show that, as expected, GRACE dominates the solution below degree 90 and GOCE above degree 140. 相似文献
9.
重、磁勘探具有效率高、成本低、工作范围广等优点,已在地球物理勘探中得到了广泛应用.前人大多在不考虑重、磁勘探观测精度的条件下进行了垂向识别能力的研究,但在考虑重、磁观测精度条件下,重力（重力异常、重力张量）与磁力（磁力异常、磁力三分量、磁力张量）对孤立异常的垂向识别能力如何则需要进行深入的理论研究.本文从重、磁场正演理论出发,以球体（点源模型）和无限延伸水平圆柱体（线源模型）为例,考虑给定观测精度条件下,以重力和磁力幅值大小与观测精度的关系来研究垂向识别能力,从而消除了背景场的影响,提高了研究结果的可靠度.通过研究表明,对于孤立异常,重力张量在浅部一定深度内比重力异常的垂向识别能力强,该深度与重力异常和重力张量观测精度的比值成正比;垂直磁化磁力张量在浅部一定深度内比化极磁力异常的垂向识别能力强,该深度与磁力异常与磁力张量观测精度的比值成正比;磁力在浅部一定深度内比重力的垂向识别能力强,该深度与地质体的磁化强度和剩余密度比值、重力观测精度和磁力观测精度比值成正比.通过重力和磁力垂向识别能力的研究将为重、磁勘探的实际应用起到指导作用. 相似文献
10.
M. K. Paul 《Pure and Applied Geophysics》1971,85(1):20-37
Summary A method of computation of the vertical gradients of gravity, at different elevations, from the residual gravity profile due to a localised two dimensional causative body is presented. The vertical gradient at an elevation above a station has been expressed as a weighted summation of the gravity values at equally spaced stations along a profile. These weights (coefficients) depend only upon the positions of the individual stations, relative to the station of computation, and upon the ratio of the elevation at which the vertical gradient value is sought to the separation of the stations. Functional forms of these coefficients have been derived analytically and they have been computed for different relative positions of the individual stations and for different values for the ratio of elevation to separation.An analytical expression has been derived for the remainder term which is necessary when the above summation is performed over a finite length of the profile only. As this expression involves the parameters, (i) total mass per unit length and (ii) the positions of the centre of gravity of the causative body, a method has been developed separately for their accurate determination from the anomaly profile of finite length.The efficacy of the method has been assessed by applying it to an arbitrary theoretical model. 相似文献
11.
The European Gravity Field and Steady-State Ocean Circulation Explorer Satellite Mission Its Impact on Geophysics 总被引：1，自引：0，他引：1
J. A. Johannessen G. Balmino C. Le Provost R. Rummel R. Sabadini H. Sünkel C.C. Tscherning P. Visser P. Woodworth C. Hughes P. Legrand N. Sneeuw F. Perosanz M. Aguirre-Martinez H. Rebhan M. Drinkwater 《Surveys in Geophysics》2003,24(4):339-386
Current knowledge of the Earth's gravity field and its geoid, as derived from various observing techniques and sources, is incomplete. Within a reasonable time, substantial improvement will come by exploiting new approaches based on spaceborne gravity observation. Among these, the European Space Agency (ESA) Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite mission concept has been conceived and designed taking into account multi-disciplinary research objectives in solid Earth physics, oceanography and geodesy. Based on the unique capability of a gravity gradiometer combined with satellite-to-satellite high-low tracking techniques, an accurate and detailed global model of the Earth's gravity field and its corresponding geoid will be recovered. The importance of this is demonstrated by a series of realistic simulation experiments. In particular, the quantitative impact of the new and accurate gravity field and geoid is examined in studies of tectonic composition and motion, Glaciological Isostatic Adjustment, ocean mesoscale variability, water mass transport, and unification of height systems. Improved knowledge in each of these fields will also ensure the accumulation of new understanding of past and present sea-level changes. 相似文献
12.
We discuss how the geophysical fluids affect the Earth orientation parameters (EOP) and in particular polar motion and nutation. We show that the Earth orientation modeling is a perfect example of the integrated approach recommended by GGOS. GGOS considers the Earth system as a whole, including the solid Earth as well as the fluid components; geodesy observes and models the dynamics inside this system through the static and time-varying gravity field, the station displacements, and the Earth orientation parameters and the associated length-of-day variation, nutation and polar motion. Global-scale transfer in the Earth system and its geodetic consequences is proposed to be the central theme of GGOS. We show that the Earth orientation parameters perfectly fit this theme. 相似文献
13.
《Journal of Geodynamics》2006,41(4-5):394-399
We discuss how the geophysical fluids affect the Earth orientation parameters (EOP) and in particular polar motion and nutation. We show that the Earth orientation modeling is a perfect example of the integrated approach recommended by GGOS. GGOS considers the Earth system as a whole, including the solid Earth as well as the fluid components; geodesy observes and models the dynamics inside this system through the static and time-varying gravity field, the station displacements, and the Earth orientation parameters and the associated length-of-day variation, nutation and polar motion. Global-scale transfer in the Earth system and its geodetic consequences is proposed to be the central theme of GGOS. We show that the Earth orientation parameters perfectly fit this theme. 相似文献
14.
Hasan Yildiz Rene Forsberg Carl Christian Tscherning Daniel Steinhage Graeme Eagles Johannes Bouman 《Studia Geophysica et Geodaetica》2017,61(1):53-68
An airborne gravity campaign was carried out at the Dome-C survey area in East Antarctica between the 17th and 22nd of January 2013, in order to provide data for an experiment to validate GOCE satellite gravity gradients. After typical filtering for airborne gravity data, the cross-over error statistics for the few crossing points are 11.3 mGal root mean square (rms) error, corresponding to an rms line error of 8.0 mGal. This number is relatively large due to the rough flight conditions, short lines and field handling procedures used. Comparison of the airborne gravity data with GOCE RL4 spherical harmonic models confirmed the quality of the airborne data and that they contain more high-frequency signal than the global models. First, the airborne gravity data were upward continued to GOCE altitude to predict gravity gradients in the local North-East-Up reference frame. In this step, the least squares collocation using the ITGGRACE2010S field to degree and order 90 as reference field, which is subtracted from both the airborne gravity and GOCE gravity gradients, was applied. Then, the predicted gradients were rotated to the gradiometer reference frame using level 1 attitude quaternion data. The validation with the airborne gravity data was limited to the accurate gradient anomalies (TXX, TYY, TZZ and TXZ) where the long-wavelength information of the GOCE gradients has been replaced with GOCO03s signal to avoid contamination with GOCE gradient errors at these wavelengths. The comparison shows standard deviations between the predicted and GOCE gradient anomalies TXX, TYY, TZZ and TXZ of 9.9, 11.5, 11.6 and 10.4 mE, respectively. A more precise airborne gravity survey of the southern polar gap which is not observed by GOCE would thus provide gradient predictions at a better accuracy, complementing the GOCE coverage in this region. 相似文献
15.
《Journal of Geodynamics》2010,49(3-5):340-347
Gravity data stored in the GGP database (GGP-ISDC) are used to study the small gravity variations caused by polar motion. In a first step the dominant tidal signal and the instrumental drift have to be eliminated from the gravity data. In most cases it is sufficient to model the instrumental drift by polynomials of low degree. The resulting non-tidal gravity variations are split up into their main constituents by fitting two sinusoidal waves with periods of 365.25 days (annual wobble) and 432 days (Chandler wobble). In a similar way the gravity effect of the observed polar motion (IERS-Data) is processed. The ratio between the correspondent amplitudes gives the amplitude factors δ of both wobbles.In a more sophisticated model an additional annual wave was included, destined to absorb disturbing influences with annual period (e.g. environmental influences of different origin). The amount of these influences and the success of their elimination are very different at the individual stations.Besides the comparison of the amplitude factors it also was tried to compare the gravity residuals itself. For that purpose the data series recorded at the different stations were transferred to a common reference point (0°E, 45°N). The graph of the stacked data series gives a first impression of the accordance of the data series recorded at the different stations. Since randomly distributed disturbing influences are reduced by the averaging the amplitude factors derived from the mean of the stacked data series are more reliable than the values derived from the data at the individual stations.In the end 12 data series were included in a common processing. Amplitude factors of 1.183 for the annual and 1.168 for the Chandler wobble result with mean errors less than ±0.010 (roughly estimated). Although corrections for environmental influences were not included directly, the additionally fitted annual wave reduced the scatter of the amplitude factors in the annual range considerably. In contrast to that the amplitude factor of the Chandler wobble remains nearly unaffected, confirming the assumption that the disturbing environmental influences do not extend into the period range of the Chandler wobble. 相似文献
16.
为了对感兴趣区域运动信息进行估计,首先扩展中心切片定理并推导微分约束条件,然后用有限Hilbert变换算法求出方位角与径向图像导函数,最后用改进的光流方程求解极坐标系下的运动场。与一般运动估计算法相比,该算法不使用图像域差分运算计算导函数,因此具有更高精度,并且极坐标系下的运动估计更加适合医学诊断需要。数值仿真也验证了... 相似文献
17.
Summary It has been proved that the formulae for determining the horizontal co-ordinates of the centre of gravity, derived by Gamburtsev in 1938 and adopted in many textbooks of gravimetry and other works, are not accurate. A method of estimating the co-ordinates of the centre of gravity of a disturbing body has been elaborated under the assumption that just the values of the vertical gradient of the disturbing gravitational potential in the xOy-plane are known. 相似文献
18.
《Journal of Geodynamics》2006,41(4-5):414-431
Towards the end of the 19th century, geodetic observation techniques allowed it to create geodetic networks of continental size. The insight that big networks can only be set up through international collaboration led to the establishment of an international collaboration called “Central European Arc Measurement”, the predecessor of the International Association of Geodesy (IAG), in 1864. The scope of IAG activities was extended already in the 19th century to include gravity.At the same time, astrometric observations could be made with an accuracy of a few tenths of an arcsecond. The accuracy stayed roughly on this level, till the space age opened the door for milliarcsecond (mas) astrometry. Astrometric observations allowed it at the end of the 19th century to prove the existence of polar motion. The insight that polar motion is almost unpredictable led to the establishment of the International Latitude Service (ILS) in 1899.The IAG and the ILS were the tools (a) to establish and maintain the terrestrial and the celestial reference systems, including the transformation parameters between the two systems, and (b) to determine the Earth's gravity field.Satellite-geodetic techniques and astrometric radio-interferometric techniques revolutionized geodesy in the second half of the 20th century. Satellite Laser Ranging (SLR) and methods based on the interferometric exploitation of microwave signals (stemming from Quasars and/or from satellites) allow it to realize the celestial reference frame with (sub-)mas accuracy, the global terrestrial reference frame with (sub-)cm accuracy, and to monitor the transformation between the systems with a high time resolution and (sub-)mas accuracy. This development led to the replacement of the ILS through the IERS, the International Earth Rotation Service in 1989.In the pre-space era, the Earth's gravity field could “only” be established by terrestrial methods. The determination of the Earth's gravitational field was revolutionized twice in the space era, first by observing geodetic satellites with optical, Laser, and Doppler techniques, secondly by implementing a continuous tracking with spaceborne GPS receivers in connection with satellite gradiometry. The sequence of the satellite gravity missions CHAMP, GRACE, and GOCE allow it to name the first decade of the 21st century the “decade of gravity field determination”.The techniques to establish and monitor the geometric and gravimetric reference frames are about to reach a mature state and will be the prevailing geodetic tools of the following decades. It is our duty to work in the spirit of our forefathers by creating similarly stable organizations within IAG with the declared goal to produce the geometric and gravimetric reference frames (including their time evolution) with the best available techniques and to make accurate and consistent products available to wider Earth sciences community as a basis for meaningful research in global change. IGGOS, the Integrated Global Geodetic Observing System, is IAG's attempt to achieve these goals. It is based on the well-functioning and well-established network of IAG services. 相似文献
19.
Changes in polar ice could cause vertical crustal motion of up to several mm yr-1 along the edge of the Greenland and Antarctic ice caps. Measurements of the uplift could help constrain the changing ice volumes. The problem is complicated by the Earth's visco-elastic response to past loading, including the Late Pleistocene deglaciation. A method is described for removing these visco-elastic effects, by using simultaneous measurements of vertical motion and surface gravity. A linear combination of these two measurement types can be formed which is relatively independent of visco-elastic effects, and which can be interpreted in terms of present-day fluctuations in ice. 相似文献
20.
A. K. Fedorenko 《Geomagnetism and Aeronomy》2010,50(1):107-118
Wave disturbances of the Neutral Atmosphere above the polar caps are studied based on the Dynamic Explorer 2 satellite measurements.
The characteristic spatial scales of these disturbances are 500— 600 km. Based on an analysis of the synchronous variations
in different parameters, these disturbances were interpreted as propagating acoustic gravity waves (AGWs). The mass-spectrometer
measurements of concentrations of individual atmospheric gases made it possible to determine the following AGW components:
density of the acoustic compression, thermobaric, and average kinetic energies. It has been found out that the average (during
the period) densities of the acoustic and thermobaric energies are approximately equal for polar AGWs. The results indicate
that the contribution of these waves to the energy of the polar upper atmosphere is considerable. 相似文献