共查询到20条相似文献，搜索用时 31 毫秒
1.
Variability of short period oscillations of polar motion with periods ranging from 20 to 150 days were investigated in the period 1979–1991. The new computation method of time variable band pass filter spectra and the Wavelet Transform method were applied. These oscillations are elliptical with variable amplitudes. Modulation periods of amplitude variations of these oscillations of about two and three years were found. Correlations of short period oscillations of polar motion and of effective atmospheric angular momentum (EAAM) excitation functions show annual variations and connections of their increases with El Niño phenomena. 相似文献
2.
J. Höpfner 《Journal of Geodesy》2001,75(2-3):137-150
The annual and semiannual residuals derived in the axial angular momentum budget of the solid Earth–atmosphere system reflect
significant signals. They must be caused by further excitation sources. Since, in particular, the contribution for the wind
term from the atmospheric layer between the 10 and 0.3 hPa levels to the seasonal variations in length of day (LOD) is still
missing, it is necessary to extend the top level into the upper stratosphere up to 0.3 hPa. Under the conservation of the
total angular momentum of the entire Earth, variations in the oceanic angular momentum (OAM) and the hydrological angular
momentum (HAM) are further significant excitation sources at seasonal time scales. Focusing on other contributions to the
Earth's axial angular momentum budget, the following data are used in this study: axial atmospheric angular momentum (AAM)
data derived for the 10–0.3 hPa layer from 1991 to 1997 for computing the missing wind effects; axial OAM functions as generated
by oceanic general circulation models (GCMs), namely for the ECHAM3 and the MICOM models, available from 1975 to 1994 and
from 1992 to 1994, respectively, for computing the oceanic contributions to LOD changes, and, concerning the HAM variations,
the seasonal estimates of the hydrological contribution as derived by Chao and O'Connor [(1988) Geophys J 94: 263–270]. Using
vector representation, it is shown that the vectors achieve a close balance in the global axial angular momentum budget within
the estimated uncertainties of the momentum quantities on seasonal time scales.
Received: 6 April 2000 / Accepted: 13 December 2000 相似文献
3.
By exchanging angular momentum with the solid earth, tidal variations in ocean currents and sea level cause the rotation of
the solid earth to change. Observations of earth rotation variations can therefore be used to evaluate ocean tide models.
The rotational predictions of a spherical harmonic ocean tide model that is not constrained by any type of data are compared
here to the predictions of numerical ocean tide models and to earth rotation observations from which atmospheric and non-tidal
oceanic effects have been removed. The spherical harmonic ocean tide model is shown to account for the observed variations
at the fortnightly tidal period in polar motion excitation but not in length-of-day. Overall, its long-period polar motion
excitation predictions fit the observed tidal signals better than do the predictions of the numerical ocean tide models studied
here. It may be possible to improve its agreement with length-of-day observations by tuning certain model parameters, as was
done to obtain the close agreement reported here between the modeled and observed polar motion excitation; alternatively,
the discrepancy in length-of-day may point to the need to revise current models of mantle anelasticity and/or models of the
oceanic response to atmospheric pressure variations. 相似文献
4.
This research aims to study the influences of the atmospheric and oceanic excitations on polar motion.Power spectrum density analyses show that the efficiencies of the atmospheric and oceanic excitations differ not only at different frequencies but also in the retrograde and prograde components,but the sum of atmospheric and oceanic excitations shows the best agreement with the observed excitation. 相似文献
5.
Possible improvement of Earth orientation forecast using autocovariance prediction procedures 总被引：3，自引：2，他引：1
Autocovariance prediction has been applied to attempt to improve polar motion and UT1-UTC predictions. The predicted polar
motion is the sum of the least-squares extrapolation model based on the Chandler circle, annual and semiannual ellipses, and
a bias fit to the past 3 years of observations and the autocovariance prediction of these extrapolation residuals computed
after subtraction of this model from pole coordinate data. This prediction method has been applied also to the UT1-UTC data,
from which all known predictable effects were removed, but the prediction error has not been reduced with respect to the error
of the current prediction model. However, the results show the possibility of decreasing polar motion prediction errors by
about 50 for different prediction lengths from 50 to 200 days with respect to the errors of the current prediction model.
Because of irregular variations in polar motion and UT1-UTC, the accuracy of the autocovariance prediction does depend on
the epoch of the prediction. To explain irregular variations in x, y pole coordinate data, time-variable spectra of the equatorial components of the effective atmospheric angular momentum, determined
by the National Center for Environmental Prediction, were computed. These time-variable spectra maxima for oscillations with
periods of 100–140 days, which occurred in 1985, 1988, and 1990 could be responsible for excitation of the irregular short-period
variations in pole coordinate data. Additionally, time-variable coherence between geodetic and atmospheric excitation function
was computed, and the coherence maxima coincide also with the greatest irregular variations in polar motion extrapolation
residuals.
Received: 22 October 1996 / Accepted: 16 September 1997 相似文献
6.
We examine several digital filter methods designed to accurately estimate excitation axis variations from observed polar motion at frequencies exceeding 1 cycle per day. These methods are developed from a discrete time series filter equation originally presented in 1940 by Harold Jeffreys, and subsequently revised over the past two decades. The filters derived here provide improved amplitude accuracy at the highest frequencies now observable in space geodetic polar motion data. 相似文献
7.
An improved empirical model for the effect of long-period ocean tides on polar motion 总被引：2，自引：1，他引：1
Richard S. Gross 《Journal of Geodesy》2009,83(7):635-644
Because the tide-raising potential is symmetric about the Earth’s polar axis it can excite polar motion only by acting upon
non-axisymmetric features of the Earth like the oceans. In fact, after removing atmospheric and non-tidal oceanic effects,
polar motion excitation observations show a strong fortnightly tidal signal that is not completely explained by existing dynamical
and empirical ocean tide models. So a new empirical model for the effect of the termensual (Mtm and mtm), fortnightly (Mf and mf), and monthly (Mm) tides on polar motion is derived here by fitting periodic terms at these tidal frequencies to polar motion excitation observations
that span 2 January 1980 to 8 September 2006 and from which atmospheric and non-tidal oceanic effects have been removed. While
this new empirical tide model can fully explain the observed fortnightly polar motion excitation signal during this time interval
it would still be desirable to have a model for the effect of long-period ocean tides on polar motion that is determined from
a dynamical ocean tide model and that is therefore independent of polar motion observations. 相似文献
8.
Comparison of polar motion with oceanic and atmospheric angular momentum time series for 2-day to Chandler periods 总被引：2，自引：0，他引：2
J. Kouba 《Journal of Geodesy》2005,79(1-3):33-42
During a 4-year period starting in July 1996 and using intervals ranging from 3 days to 4 years, four precise polar motion (PM) series have been compared to excitation by atmospheric angular momentum (AAM) augmented with oceanic angular momentum (OAM) data. The first three series (C03, C04 and Bulletin A) are multi-technique combinations generated by the International Earth Rotation and Reference Systems Service (IERS) and the fourth combined series (IGS00P02) is produced by the International GPS Service (IGS) using only GPS data. The IGS PM compared the best with the combined excitations of atmosphere and oceans (AAM+OAM) at all intervals, showing high overall correlation of 0.8–0.9. Even for the interval of only three days, the IGS PM gave a significant correlation of about 0.6. Moreover, during the interval of February 1999 – July 2000, which should be representative of the current precision of the IGS PM, a significant correlation (>0.4) extended to periods as short as 2.2 days and 2.5 days for the xp and yp PM components, respectively. When using the IERS Bulletin B (C04) PM and an interval of almost 6 years, starting in November 1994, the combined OAM+AAM accounted for practically all the annual, semi-annual and Chandler wobble (CW) PM signals. When only AAM was used, either the US National Centers for Environment Prediction reanalysis data, which were used throughout this study, or the Japanese Meteorological Agency data, two large and well-resolved amplitude peaks of about 0.1 mas/day, remained at the retrograde annual and CW periods. 相似文献
9.
Y. H. Zhou X. H. Yan X. L. Ding X. H. Liao D. W. Zheng W. T. Liu J. Y. Pan M. Q. Fang M. X. He 《Journal of Geodesy》2004,78(1-2):109-113
Changes in the annual variation of the Earths polar motion are found to be largely caused by the variation of the atmospheric angular momentum (AAM). Recent simulation results of oceanic general circulation models further suggest global oceanic effects on the annual polar motion in addition to the atmosphere. In comparison with previous model studies of global oceanic effects, this research particularly singles out a large-scale ocean anomaly and investigates its effect on the annual polar motion, determined from satellite observations of the movement of the Western Pacific Warm Pool (WPWP). Although the scale of the warm pool is much smaller than that of the solid Earth, analysis of the non-atmospheric polar motion excitation has shown that the WPWP contributes non-negligibly to the annual polar motion. The analysis consists of over 30 years of WPWP data (1970–2000) and shows values of polar motion excitation for the x-component of (2.5 mas, –79°) and for the y-component of (0.6 mas, 173°). Comparison of this result with the total geodetic non-atmospheric polar motion excitation of (10.3 mas, 59°) for the x-component and (10.6 mas, 62°) for the y-component shows the significance of the WPWP. Changes in the Earths polar motion have attracted significant attention, not only because it is an important geodetic issue, but also because it has significant value as a global measure of variations within the hydrosphere, atmosphere, cryosphere, and solid Earth, and hence global changes.Tel: 86–21–64386191 Fax: 86–21–64384618Acknowledgments. The authors are grateful to Dr. R. Gross (JPL) and two anonymous reviewers for providing invaluable comments. They also thank Dr. J.L. Chen (CSR) for helpful discussions. Y. Zhou, D. Zheng and X. Liao were supported by the National Natural Science Foundation of China (10273018, 10133010) and Key Project of Chinese Academy of Sciences (KJCX2-SW-T1). X-H. Yan was supported by the National Aeronautics and Space Administration (NASA) through Grant NAG5–12745, and by the National Science Foundation (NSF) through the Presidential Faculty Fellow award to X-H. Yan (OCE-9453499). W.T. Liu was supported by the NASA Physical Oceanography Program. 相似文献
10.
GUO Junyi 《地球空间信息科学学报》2001,4(3):6-8
1 ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｍｏｄｅｒｎＥａｒｔｈｒｏｔａｔｉｏｎｔｈｅｏｒｙ ,ｔｈｒｅｅｒｅｆｅｒｅｎｃｅｆｒａｍｅｓａｒｅｕｓｕａｌｌｙｕｓｅｄ ,ｉ.ｅ .,ｔｈｅｓｐａｔｉａｌ (ｉｎｅｒｔｉａｌ)ｆｒａｍｅＯξ1 ξ2 ξ3,ｔｈｅｔｅｒｒｅｓｔｒｉａｌｆｒａｍｅＯｘ1 ｘ2 ｘ3ａｎｄｔｈｅｎｕｔａｔｉｏｎｆｒａｍｅＯｘ01 ｘ02 ｘ03.Ｔｈｅｎｕｔａｔｉｏｎｆｒａｍｅｄｅｆｉｎｅｓａｃｅｌｅｓｔｉａｌｅｐｈｅｍｅｒｉｓｐｏｌｅ .Ｔｈｅｍｏｔｉｏｎｏｆｔｈｉｓｃｅｌｅｓｔｉａｌｅｐｈｅｍｅｒｉｓｐｏｌｅｗ… 相似文献
11.
The polar motion excited by the fluctuation of global atmospheric angular momentum (AAM) is investigated. Based on the global AAM data, numerical results demonstrate that the fluctuation of AAM can excite the seasonal wobbles (e.g., the 18-month wobble) and the Chandler wobble, which agree well with previous studies. In addition, by filtering the dominant low frequency components, some distinct polar wobbles corresponding to some great diurnal and semi-diurnal atmospheric tides are found. 相似文献
12.
The polar motion excited by the fluctuation of global atmospheric angular momentum (AAM) is investigated. Based on the global
AAM data, numerical results demonstrate that the fluctuation of AAM can excite the seasonal wobbles (e.g., the 18-month wobble)
and the Chandler wobble, which agree well with previous studies. In addition, by filtering the dominant low frequency components,
some distinct polar wobbles corresponding to some great diurnal and semi-diurnal atmospheric tides are found. 相似文献
13.
地表质量的重分布会引起固体地球的弹性形变,GPS连续运行观测站能够精确测定地表负荷引起的地壳形变。本文通过模拟数据对利用云南省及其周边47个中国大陆构造环境监测网（陆态网）台站反演云南地区陆地水储量的可行性进行分析：以水文模型周年振幅为真值,计算47个台站点的负荷形变,同时加入随机误差构成模拟观测数据,最后采用模型反演陆地水储量变化;1000次的随机模拟试验表明利用当前GPS台站数据可有效地反演云南地区陆地水储量变化。基于上述结论,笔者反演了云南省2010—2014年陆地水储量变化,GPS反演结果表明：云南省陆地水变化呈现明显的地域分布特征,西南部高山地区的水储量周年变化高于东部平原地区;在时间尺度上,云南省大部分地区水储量在10月（夏季末）达到最大值,在4月（冬季末）达到最小值;云南省2010—2014年陆地水呈缓慢增长趋势,约为20 mm/a。通过GPS陆地水储量反演结果与GRACE、GLDAS以及TRMM数据综合对比分析,表明利用云南地区当前GPS台站可以作为独立观测量用于GRACE与GRACE Follow-on衔接期间的陆地水储量变化监测。 相似文献
14.
Angular momentum forecasts for up to 10 days into the future, modeled from predicted states of the atmosphere, ocean and continental hydrosphere, are combined with the operational IERS EOP prediction bulletin A to reduce the prediction error in the very first day and to improve the subsequent 90-day prediction by exploitation of the revised initial state and trend information. EAM functions derived from ECMWF short-range forecasts and corresponding LSDM and OMCT simulations can account for high-frequency mass variations within the geophysical fluids for up to 7 days into the future primarily limited by the accuracy of the forecasted atmospheric wind fields. Including these wide-band stochastic signals into the first days of the 90-day statistical IERS predictions reduces the mean absolute prediction error even for predictions beyond day 10, especially for polar motion, where the presently used prediction approach does not include geophysical fluids data directly. In a hindcast experiment using 1 year of daily predictions from May 2011 till July 2012, the mean prediction error in polar motion, compared to bulletin A, is reduced by 32, 12, and 3 % for prediction days 10, 30, and 90, respectively. In average, the prediction error for medium-range forecasts (30–90 days) is reduced by 1.3–1.7 mas. Even for UT1-UTC, where AAM forecasts are already included in IERS bulletin A, we obtain slight improvements of up to 5 % (up to 0.5 ms) after day 10 due to the additional consideration of oceanic angular momentum forecasts. The improved 90-day predictions can be generated operationally on a daily basis directly after the publication of the related IERS bulletin A product finals2000A.daily. 相似文献
15.
利用2002—2012年的GLDAS和WGHM模型模拟水文产品,以及重力恢复与气候试验卫星（Gravity Recovery and Climate Experiment,GRACE）观测数据,计算了全球范围内30个主要流域的水储量变化时间序列,从模拟数据与观测数据的年周期振幅、长期趋势项及时空分布一致性等几个方面,对GLDAS和WGHM进行了评估。结果表明,GLDAS的4个子模型都表现出了明显的季节性变化,CLM年周期振幅输出最小,MOSAIC和VIC最大,NOAH居中,且最接近4个子模型的平均值。与GRACE结果相比,约80%流域的GLDAS与WGHM模型年周期振幅输出呈明显低估现象,且GLDAS的低估程度大于WGHM,但靠近北极高纬度地区的流域有相反的情况出现。在长期趋势项方面,三者结果差异较大,尤其是对于面积较小且人类活动影响较大的流域,GLDAS与WGHM模型不能充分反映人类活动的影响,模型输出表现较差,GRACE结果更接近实际情况。此外,还研究了流域水储量长期变化趋势与灌溉率的关系,发现呈现明显下降趋势的流域主要集中在高灌溉率（>10%）地区,而灌溉率是影响流域水储量变化的重要因素之一。 相似文献
16.
利用GRACE时变重力场反演黑河流域水储量变化 总被引：5，自引：0，他引：5
黑河流域水储量变化对该区域的生态环境和经济建设等具有重要影响。本文利用2002年8月至2011年6月GRACE（Gravity Recovery and Climate Experiment）时变重力场模型GRGS-EIGEN-GL04,采用去相关滤波P3M6与300km高斯滤波相结合的滤波方法反演了黑河流域陆地水储量变化,扣除GLDAS（Global Land Data Assimilation System）水文模型计算的土壤水和冰雪变化,给出了黑河流域地下水储量的时空变化,并利用张掖地区23口地下水测井数据对地下水反演结果进行了初步验证。研究结果表明：（1）黑河流域陆地水储量整体上呈现减少趋势,与该流域气候变化和CPC水文模型的计算结果具有较好的一致性,其减少速率为2.3cm/a等效水高;（2）黑河流域地下水储量呈现长期减少趋势,其减少速率为2.5cm/a等效水高,上、中游区域地下水储量减少速率相当,下游区域地下水储量减少速率明显小于中上游区域。 相似文献
17.
The rapid polar motion for periods below 20 days is revisited in light of the most recent and accurate geodetic and geophysical
data. Although its amplitude is smaller than 2 mas, it is excited mostly by powerful atmospheric processes, as large as the
seasonal ones. The residual amplitude, representing about 20% of the total excitation, stems from the oceans. Rapid polar
motion has an irregular nature that is well explained by the combined influence of the atmosphere and the oceans. An overall
spectrum reveals cycles principally at 20, 13.6 (fortnightly tidal period) and 10 days (corresponding to the normal atmospheric
mode Y31{\Psi_3^1}), but this is only an averaged feature hiding its strong variability over seasonal time scales. This explains why it is so
delicate to determine an empirical model of the tidal effect on polar motion. The variability in both amplitude and phase
of the 13.6-day term is probably caused by a lunar barometric effect, modulated by some sub-seasonal thermal processes. The
irregularities of the prominent cycles of the short-term polar motion are well explained by the atmospheric and oceanic excitations.
The oceanic variability reinforces the atmospheric one, as they were triggered by the same agent, maybe seasonal and inter-annual
thermal variations. 相似文献
18.
王文均 《武汉大学学报(信息科学版)》2001,26(2):150-154
从滞弹性阻尼形变摄动造成CW频率调制假设出发，对CW的共振激发模型加上参数的时变调制，变成了参数共振模型。经正演计算发现，参数共振模型完全符合CW的实际，表明滞弹性阻尼形变摄动造成频率的3％调制，进一步使得CW振幅调制可达70％以上。这一参数共振模型是一个非线性动力系统，在非线性情况下，运动将发生分岔，即多解。 相似文献
19.
研究了反演区域陆地水储量变化的点质量模型方法,采用Tikhonov正则化方法解决了反演过程中参数估计病态问题。利用GRACE（gravity recovery and climate experiment）时变重力场模型数据,用点质量模型方法反演了中国大陆及其周边地区陆地水储量变化,将点质量模型反演结果与球谐系数法反演结果、GLDAS（global land data assimilation）水文模型数据进行了验证分析,并选取了4个特征点计算了陆地水储量变化时间序列。实验结果表明,由于点质量模型方法将研究区域内不同网格质量变化对地球重力场的影响分离开来,所得区域陆地水储量变化局部信号更明显,并且点质量模型方法反演结果与GLDAS水文模型数据相关性更强。 相似文献