The excitation of the Chandler wobble

The cause- or causes-of the excitation of the Chandler wobble is one of the most intriguing problems in geophysics. As a result of one of the most valuable examples of an international programme, the positions of the pole have been determined since the late 19th century with remarkable accuracy. These data have always been accepted as of great importance in the study of the atmosphere, oceans and solid Earth. Recently, new techniques have greatly improved the accuracy with which the polar motion can be determined. Interpretation of the older data was made much more difficult because of their errors-for example the interesting suggestion that earthquakes were a cause of the excitation (by D. E. Smylie and L. Manshinha) could not be tested because their effects, if any, were lost in the noise. With the great improvement in the data it is now possible to suppose that comparable advances will be made in the theoretical interpretation. A discussion meeting at the Royal Astronomical Society on 8 May, 1987 on this topic was held and the following gives a short survey of this topic, consisting of brief summaries given by the speakers. This review is therefore a collective one which it is hoped will make more widely known these great technical advances and to fundamental interest of the phenomena of thepolar motion.     

Variations in the amplitude of the chandler wobble

It is shown that within the framework of the Kolmogorov model the “energy” of the pole E(t) = x ₁² + x ₂² can be interpreted as a Markovian process. The exact analytical expression has been obtained for the density of the conditional probability of the quantity E(t) and the problem of the first passage time of the process E(t) has been analyzed. It was shown that the available data on the swing of the function E(t) are not at variance with the Kolmogorov model and a short-period drop of the amplitude of the Chandler wobble in the early 20th century fits this model at Q = 50–200 too; values of Q > 350 are less reasonable.     

Seismic physical modeling and quality factor

Accurate Q parameter is hard to be obtained, but there is great difference between Q measurements from different measurement methods in seismic physical modelling. The influence factors, stability and accuracy of different methods are analyzed through standard sample experiment and the seismic physical modelling. Based on this, we proposed an improved method for improving accuracy of pulse transmission method, in which the samples with similar acoustic properties to the test sample are selected as the reference samples. We assess the stability and accuracy of the pulse transmission, pulse transmission insertion, and reflection wave methods for obtaining the quality factor Q using standard and reference samples and seismic physical modeling. The results suggest that the Q-values obtained by the pulse transmission method are strongly affected by diffraction and the error is 50% or greater, whereas the relative error of the improved pulse transmission method is about 10%. By using a theoretical diffraction correction method and the improved measurement method, the differences among the Q-measuring methods can be limited to within 10%.     

The Chandler annual resonance and its possible geophysical significance

The secular decrease of the earth's rotation rate has caused the Chandler and annual modes of the earth's wobble to resonate in the past. The physics of the resonance is discussed as well as its thermal impact on the mantle. Energy of the order of 10²⁶ erg/year were dissipated in the upper mantle during the resonance. Estimates of the epoch and duration of the resonance place them at about 185 m.y. ago and about 10 m.y., respectively. The possibility of a causal connection between the resonance and the onset of continental drift is suggested.     

历史时期射阳湖的变迁及其成因探讨

射阳湖古时曾是苏北平原上最大的湖泊,湖深且阔,“承受扬州、兴化、高邮、宝应、泰州、盐城诸州邑水,东流入海.”自春秋至北宋,一直是江淮间南北运输通道.1128年黄河夺淮河故道入海后,黄河泛滥,决溢频仍,泥沙大量南下堆积在里下河地区.射阳湖于明崇祯、清乾隆年间被淤积几成平陆,现仅存湖身残迹马家荡和入海河流射阳河.据地学者们从微地貌、钻孔资料、岩性岩相、孢粉、海相生物和微体古生物化石等资料的综合分析,确认射阳湖由全新世高海面时苏北平原上的泻湖演化而成淡水湖泊.     

Measurements of recent geomagnetic secular variation in southeastern Australia and the question of dipole wobble

Archaeomagnetic and radiocarbon measurements on a series of ancient Aboriginal fireplaces and burnt tree-stump sites in southeastern Australia are presented, and an outline of changes in the local direction of the earth's magnetic field over the last 1500 years is offered.An analysis of these new data from the southern hemisphere and published data for the northern hemisphere indicates that a large change occurred in the orientation of the geomagnetic dipolar axis between about 1400 and 1650 A.D.     

On low period sub-oceanic Rayleigh waves and their attenuation

Summary In most cases it is found that Rayleigh waves in the period range I to 12 secs fail to cross appreciable oceanic paths. Several explanations have been given, but none seem very much satisfactory. Here an attempt has been made to show that the attenuation of the Rayleigh waves in the low period range is due to their passage through a non-uniform earth's crust, the non-uniformity arising due to the ocean. The ocean has been taken to be an indentation in a flat earth's crust, with horizontal bottom and slant sides. Approximate numerical calculations hint that the vertical component of displacement is attenuated more than the horizontal component.     

On short period signals obtained from explosions within the earth

Summary Propagation of dilational waves in radial directions from a spherical cavity in a medium with velocity varying periodically with distance has been considered. It has been shown that when the wave-length of the propagating wave is twice the wave-length of variation of the velocity in the medium the displacement even at a large distance is very great.     

Estimation of the quality factor in shallow soil using surface waves

IntroductionVelocityanditsattenuationinformationiscloselylinkedwiththeoreticalstudiesonthegroundmovementsduringearthquake.Therecentstudy(Malagnini,1996)showedthatthevelocitystructureofshearwaveinshallowsoilabove30mplaysanimpoftantroletoestimatestfonggroundmotionofsite.However,itishardtopreciselymeasurethesoilstructuresanddynamiccharacteristics.First,theloosesoilabsorbstheseismicwaveswithhighfrequencies;Second,theeffectsoffocusinganddispersioncausedbylocallyinhomogeneoussitecannotbeneglectedin…     

On Ps6 and longer period geomagnetic pulsations in the Indian equatorial region

Adopting an appropriate procedure suitable for processing the amplitude-time records based on the two-component spectral analysis technique, the statistical information on Ps6 and other longer periods are worked out on the geomagnetic field registrations in the Indian longitudinal regions at and away from the equatorial electrojet influence. The storm interval during 21 and 22 September 1982 has been chosen for the analysis, as violent and regular cyclic variations of the geomagnetic field were recorded in all the three components of the field at the Indian observatories. The procedure, when applied to two intervals of afternoon and night conditions of equatorial ionosphere, showed practically the same polarisation characteristics in the H-D plane at all the frequencies under the equatorial electrojet. At far away places from this influence, the ellipticities are found to be relatively to the west during the afternoon. These, along with the other results, are discussed.     

雄安新区白洋淀冰封期水体污染特征及水质评价

为明确白洋淀冬季冰封期水污染特征,于2019年1月对白洋淀原始区、旅游区、生活区、养殖区和入淀区5个特征区域25个代表性采样点进行水样采集,选取温度、溶解氧(DO)、氨氮(NH_3-N)、亚硝态氮(NO_2--N)、硝态氮(NO_3--N)、总氮(TN)、总磷(TP)、高锰酸盐指数作为评价因子,采用单因子评价法、综合污染指数(K)法和主成分分析法对水质进行综合评价.结果表明:白洋淀冰封期不同功能区水体温差波动较小、DO浓度变化幅度大,TN和TP浓度较高.单因子评价表明,TN参与评价时,25个采样点中,Ⅲ类水体占28%,其余为Ⅳ类、Ⅴ类和劣Ⅴ类; TP参与评价时,Ⅲ类水体占16%,其余为Ⅳ类、Ⅴ类和劣Ⅴ类,综合看,白洋淀水质整体状况较差;综合污染指数法表明,生活区水质最好,入淀区河流水质最差,其中白沟引河、府河和瀑河3条入淀口河流水质状况最差,为重度污染,主要污染物为TN、TP;主成分分析法表明,入淀区的6条河流彼此间偏差较大,所受污染的影响因子存在较大差异,与主成分1和主成分2高度相关的理化指标是TN、TP.通过3种评价方法定性定量的有机结合,得出白洋淀冬季冰封期水质限制因子为TN、TP且该时期水体污染较严重,冰封期作为湖泊水体的重要时期,探明污染源并治理可显著改善湖泊水质,不仅为白洋淀水体治理提供最佳时机,也为治理和修复淀区水体污染提供指导意义.     

地震波品质因子Q研究进展综述

研究地震波的衰减可以了解岩石的微构造及变化,以及岩石在地下所遇到的环境条件.衰减主要由岩石的微观性质-诸如岩石内部裂纹的密度、分布、构造以及所含流体的相互作用决定的,所以测量地震波的衰减对于了解岩石的物理状态非常重要.本文主要从岩石物理方面阐述了各种衰减机制、品质因子Q的主要影响因素及测量方法;说明了Q作为各种参量(频率、孔隙度、流体含量等)的函数是很有意义的观测量,对Q的测量在实际探测油气中有着重要意义.     

[专稿]太湖2007-2016十年水环境演变及“以渔改水”策略探讨

太湖水环境是国内外关注的焦点,其生态环境质量影响到流域经济社会发展.2007年太湖水危机事件,催生了对太湖的综合整治.本文基于2007-2016十年对太湖水质与蓝藻水华面积等的监测,分析了太湖水环境的演变趋势.太湖十年水质变化阶段性明显,2008-2012年各项水质指标下降明显,而后趋于平缓,近3年个别指标如总磷、叶绿素a浓度等呈现快速上升的反弹趋势;另外,水质指标在空间上的差异性逐步缩小,原来污染严重的西北部水域水质改善效果较为显著,其正从"污水湖"向"自然湖"状态过渡,而原来水质相对较好的东南部水域水质却逐步下降.本文也综述分析了太湖鱼类群落结构变化与水质环境变化的相关性,基于太湖局部水域的鱼类调控实践,提出了太湖现阶段"以渔改水"的鲢鳙控藻非经典生物操纵与鱼类结构调控的经典生物操纵结合的渔业途径.湖泊富营养化治理需要充分关注到鱼类对湖泊浮游生物和水质变化的重要驱动效应,需要充分考虑到鱼类群落结构优化和食物网调控对环境的改善作用.     

利用叠前CMP资料估计介质品质因子

本文提出了一种利用叠前CMP道集资料估计介质品质因子的方法,同时提出利用地震道间有效信号的相干性估计层位信息的方法.首先采用具有4个待定系数的函数去逼近震源子波,利用黏弹介质中单程波传播理论推导出地震子波包络峰值处的瞬时频率(EPIF)与不同偏移距处走时的关系;其次利用该关系,外推出该同相轴零偏移距处的EPIF,用小波域包络峰值处瞬时频率法(WEPIF)结合层位信息估计Q值.合成数据的结果表明,EPIFVO法(子波包络峰值瞬时频率随偏移距变化)无边界效应,计算精度相对较高;将该方法用于实际资料算例,结果表明,衰减强弱与储层的吸收有较好的对应关系.     

On the influence of the horizontal component of the earth's rotation on long period waves

Abstract

A general linearized wave equation for a stratified rotating fluid is derived and applied to obtain a dispersion relation for waves of short latitudinal extent in a thin shell of fluid. Long period wave solutions in three ocean models are compared: (1) for a stratified ocean with both components of the rotation vector; (2) for a stratified ocean without the horizontal component of rotation, and finally, (3) for a homogeneous ocean without horizontal rotation. The inclusion of the horizontal component of the Earth's rotation is found to have no noticeable effect on the dispersion relation of long period waves; its only influence is the introduction of a vertical phase shift in the motions. The origin of this phase shift is found in the tendency of the motions to satisfy the Taylor-Proudman theorem. The phase shift is of possible oceanographic relevance only for bottom-trapped buoyancy waves in a relatively weak stratification. The differences between the three ocean models are also discussed with the help of graphs of the numerically integrated dispersion relations. The relative influences of shell thinness and stratification in inhibiting the influence of the horizontal component of the earth's rotation are also briefly discussed.     

On the Aerosol factor in the twilight method)

Summary It is proved by means of measuring series for skylight polarization during twilight carried out at different places that the zenith polarization is affected by the tropospheric turbidity still during the middle phase of twilight. This result is important for the inverse problem of the twilight theory. 3 approaches which explain this effect are examined. — Aerosol in the mesopause region is the cause for the well-known dip in the polarization curve during the middle phase of twilight. This interpretation can be supported by the distinct spectral differences.

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Zusammenfassung An Meßreihen der Himmelslicht-Polarisation in der Dämmerung von verschiedenen Meßorten wird nachgewiesen, daß die Zenitpolarisation von der troposphärischen Trübung noch in der mittleren Dämmerungsphase beeinflußt wird. Dieses Ergebnis ist für die inverse Aufgabe der Dämmerungstheorie wichtig. 3 Möglichkeiten der Erklärung dieses Effekts werden untersucht. —Aerosol im Mesopausenbereich ist die Ursache für die bekannte Stufe in der Polarisationskurve während der mittleren Dämmerungsphase. Diese Deutung kann durch die deutlichen spektralen Unterschiede gestützt werden.

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This work has been presented at the IUGG/WMO Symposium on Radiation including Satellite Techniques (Bergen/Norway, August 22–28, 1968).     

Low-Frequency Variations, Chandler and Annual Wobbles of Polar Motion as Observed Over One Century

Polar motion data are available from the mid-19th century to the present. Basedon time series with a variety of sampling intervals (monthly, 0.05-year, 5-day anddaily), we have separated the low-frequency terms by low-pass filtering and theChandler and annual terms by recursive band-pass filtering of the pole coordinates.Using a simple unweighted least-squares fit to the filtered low-frequency terms, thelinear trends of the rotation pole were estimated. Assessing the estimates based onintercomparisons, the most reliable trend estimate was found. Using a Fast FourierTransform, we have computed the prograde, retrograde and total amplitude spectraof the low-frequency part of polar motion in order to reveal the long-periodic signals.The characteristics and time evolution of the Chandler and annual wobbles aredescribed by changes in their parameters (radii, directions and period lengths) overone century.