The adaptability of recent ocean tidal models and Earth tidal models is investigated comprehensively by means of 22 high precision tidal gravity observation series at 20 stations of the Global Geodynamics Project. Car...The adaptability of recent ocean tidal models and Earth tidal models is investigated comprehensively by means of 22 high precision tidal gravity observation series at 20 stations of the Global Geodynamics Project. Careful preprocessing of the original observations was carried out using international standard algorithms and the tidal gravity parameters were computed. The gravity load vectors of 8 main constituents are obtained based on loading computation theory and various global ocean models. The loading corrections of 14 secondary constituents are obtained based on a two-dimensional interpolation technique. Considering different characteristics of the wave amplitude, a method of “non-identical weighted mean” is developed for computing the av-eraged observed residual and remaining residual vectors at each station. The efficiency of the loading correction and the discrepancy between corrected amplitude factors and theoretical ones are analyzed. Meanwhile the calibration problem of the instruments is also discussed. After loading correction, the averaged tidal gravity parameters for all stations are obtained. The results show that the discrepancies between the global mean amplitude factors and theoretical values are less than 0.3%, the largest calibration error of the instruments is less than 0.5%. On the other hand, there are indications that the slight phase advance of K1 with respect to O1 in Mathews’ theory could be verified by ground based tidal gravity observations.展开更多
The long-term continuous gravity observations obtained by the superconducting gravimeters (SG) at seven globally-distributed stations are comprehensively analyzed. After removing the signals related to the Earth's...The long-term continuous gravity observations obtained by the superconducting gravimeters (SG) at seven globally-distributed stations are comprehensively analyzed. After removing the signals related to the Earth's tides and variations in the Earth's rotation, the gravity residuals are used to describe the seasonal fluctuations in gravity field. Meanwhile, the gravity changes due to the air pressure loading are theoretically modeled from the measurements of the local air pressure, and those due to land water and nontidal ocean loading are also calculated according to the corresponding numerical models. The numerical results show that the gravity changes due to both the air pressure and land water loading are as large as 100×10-9 m s-2 in magnitude, and about 10×10-9 m s-2 for those due to the nontidal ocean loading in the coastal area. On the other hand, the monthly-averaged gravity variations over the area surrounding the stations are derived from the spherical harmonic coefficients of the GRACE-recovered gravity fields, by using Gaussian smoothing technique in which the radius is set to be 600 km. Com-pared the land water induced gravity variations, the SG observations after removal of tides, polar mo-tion effects, air pressure and nontidal ocean loading effects and the GRACE-derived gravity variations with each other, it is inferred that both the ground- and space-based gravity observations can effec-tively detect the seasonal gravity variations with a magnitude of 100×10-9 m s-2 induced by the land water loading. This implies that high precision gravimetry is an effective technique to validate the re-liabilities of the hydrological models.展开更多
The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation...The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation and ellipticity. In this study, according to the splitting pattern of Slichter mode, an attempt has been made to detect the possibility of Slichter triplet’s existence by using the product spectra of the long-term continuous gravity measurements from the superconducting gravimeters (SG) at 6 glob- ally-distributed permanent stations in the Global Geodynamics Projects network. The results indicate that the background noise level of the global SG observations is 0.0158 nm s–2 and the magnitude threshold of any global harmonic signals, which may be detected by the global SG, is 0.0152 nm s–2 in the subtidal frequency band from 0.162 to 0.285 cph in which Slichter triplet may occur. it implies that the signatures, related to the triplet, may be identified in the global SG observations, if they exist. It is found that there is a group of global harmonic signatures with the periods of 5.310, 4.995 and 4.344 h emerging significantly from the background noise in the global SG observations. They are in good agreement with the splitting pattern of Slichter mode. It implies that this group of signatures may be related to the inner core translational oscillations. The associated density contrast across the inner core boundary may be deduced as between the values provided in the Earth models of the PREM and 1066 A.展开更多
基金supported jointly by the Knowledge Innovation Project(Grant No.KZCX3-SW-131)the Hundred Talents Program,the Chinese Academy of Sciences,the National Natural Science Foundation of China(Grant No.40374029)the Key International Scientific Cooperation Project via the Ministry of Sciences and Technology of China(Grant No.2002CB713904).
文摘The adaptability of recent ocean tidal models and Earth tidal models is investigated comprehensively by means of 22 high precision tidal gravity observation series at 20 stations of the Global Geodynamics Project. Careful preprocessing of the original observations was carried out using international standard algorithms and the tidal gravity parameters were computed. The gravity load vectors of 8 main constituents are obtained based on loading computation theory and various global ocean models. The loading corrections of 14 secondary constituents are obtained based on a two-dimensional interpolation technique. Considering different characteristics of the wave amplitude, a method of “non-identical weighted mean” is developed for computing the av-eraged observed residual and remaining residual vectors at each station. The efficiency of the loading correction and the discrepancy between corrected amplitude factors and theoretical ones are analyzed. Meanwhile the calibration problem of the instruments is also discussed. After loading correction, the averaged tidal gravity parameters for all stations are obtained. The results show that the discrepancies between the global mean amplitude factors and theoretical values are less than 0.3%, the largest calibration error of the instruments is less than 0.5%. On the other hand, there are indications that the slight phase advance of K1 with respect to O1 in Mathews’ theory could be verified by ground based tidal gravity observations.
基金Supported by Knowledge Innovation of Chinese Academy of Sciences (Grant No. KZCX2-YW-133)National Natural Science Foundation of China (Grant Nos. 40730316 and 40574034)Frontier Domain Item of Chinese Academy of Sciences
文摘The long-term continuous gravity observations obtained by the superconducting gravimeters (SG) at seven globally-distributed stations are comprehensively analyzed. After removing the signals related to the Earth's tides and variations in the Earth's rotation, the gravity residuals are used to describe the seasonal fluctuations in gravity field. Meanwhile, the gravity changes due to the air pressure loading are theoretically modeled from the measurements of the local air pressure, and those due to land water and nontidal ocean loading are also calculated according to the corresponding numerical models. The numerical results show that the gravity changes due to both the air pressure and land water loading are as large as 100×10-9 m s-2 in magnitude, and about 10×10-9 m s-2 for those due to the nontidal ocean loading in the coastal area. On the other hand, the monthly-averaged gravity variations over the area surrounding the stations are derived from the spherical harmonic coefficients of the GRACE-recovered gravity fields, by using Gaussian smoothing technique in which the radius is set to be 600 km. Com-pared the land water induced gravity variations, the SG observations after removal of tides, polar mo-tion effects, air pressure and nontidal ocean loading effects and the GRACE-derived gravity variations with each other, it is inferred that both the ground- and space-based gravity observations can effec-tively detect the seasonal gravity variations with a magnitude of 100×10-9 m s-2 induced by the land water loading. This implies that high precision gravimetry is an effective technique to validate the re-liabilities of the hydrological models.
基金supported by the National Natural Science Founda-tion of China (Grant Nos. 40574034 and 40730316)Key Project of the Knowledge Innovation of Chinese Academy of Sciences (Grant No. KZCX2 -YW-133)
文摘The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation and ellipticity. In this study, according to the splitting pattern of Slichter mode, an attempt has been made to detect the possibility of Slichter triplet’s existence by using the product spectra of the long-term continuous gravity measurements from the superconducting gravimeters (SG) at 6 glob- ally-distributed permanent stations in the Global Geodynamics Projects network. The results indicate that the background noise level of the global SG observations is 0.0158 nm s–2 and the magnitude threshold of any global harmonic signals, which may be detected by the global SG, is 0.0152 nm s–2 in the subtidal frequency band from 0.162 to 0.285 cph in which Slichter triplet may occur. it implies that the signatures, related to the triplet, may be identified in the global SG observations, if they exist. It is found that there is a group of global harmonic signatures with the periods of 5.310, 4.995 and 4.344 h emerging significantly from the background noise in the global SG observations. They are in good agreement with the splitting pattern of Slichter mode. It implies that this group of signatures may be related to the inner core translational oscillations. The associated density contrast across the inner core boundary may be deduced as between the values provided in the Earth models of the PREM and 1066 A.
