Anomalous curvature of equipotential surfaces due to variations in the Earth's rotation

Summary The anomalies of the Gaussian curvature of geopotential equipotential surfaces due to variations in the Earth's rotation vector have been derived theoretically.

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am mmuu ¶rt; aau a uu nmunmuaa, a auauu ma au u.

     

A note on secular variation of gravity due to non-tidal geodynamic phenomena

Summary Secular non-tidal variations of geopotential and gravity are estimated due to secular decrease of the second zonal geopotential harmonic, secular polar motion and deceleration of the Earth's rotation.

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am a nuu uunmuaa u u u mmu, a u m aauunmuaa, ¶rt;uu n u u mu au u.

     

Secular variation of seismo-volcanic phenomena in the azores

By studying the past behaviour of Azorean volcanoes, sunspot and Earth tide correlations have been discovered, and may certainly help in prediction. Some evidence has also been found that buckling of the thin roof of magma chambers may be the mechanism responsible for the eruptions, including the accompanying seismic swarms. If this is the case, geodetic control of the adjacent regions will probably be decisive in forecasting future activity.     

利用重力梯度张量等位面曲率的地质体定位

针对重力梯度张量曲率的研究, 前人的工作主要集中在重力张量曲率的解释及边缘检测中, 几乎没有涉及到地下密度异常体的定位.本文结合重力矢量和重力梯度张量提出了一套基于重力梯度张量等位面曲率的地下密度异常体位置估计策略.首先, 从重力梯度张量等位面曲率的基本定义出发, 计算重力梯度张量等位面曲率.然后, 通过寻找球面或圆形等位面的重力梯度张量曲率, 提出了利用最大主曲率定位地下密度异常体位置的源参数估计方法, 并详细推导了估计3D球体(质点)和2D水平线源位置信息的解析表达式.再者, 针对噪声和多源存在的情况, 提出了一套利用重力梯度张量等位面曲率获得密度异常体位置信息的稳健估计流程, 并利用模糊C均值聚类算法进一步确定地下密度异常体的中心位置.最后, 通过理论模型测试和文顿盐丘实测航空重力梯度数据测试, 验证了本文算法的可行性和可靠性.结果表明: 在满足曲率半径定义条件的情况下, 本文所提出的源参数估计方法可以定位单个或多个地下3D和2D密度异常体的空间位置, 具有较好的稳健性和抗噪能力.该方法拓展了重力梯度张量曲率的应用范围, 可为重力梯度张量的三维反演工作提供先验的空间位置信息.

     

Secular tidal and nontidal variations in the Earth's rotation

Summary On the basis of the angular momentum balance in the Earth — Moon — Sun system and with the use of the observed secular variation in the Moon's mean motion and the variation in the second zonal geopotential harmonic, the tidal and nontidal variations in the angular velocity of the Earth's rotation are computed and different values describing the field of tidal forces estimated.

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¶rt; u au m uma ¶rt;uu um —a—, um n a¶rt;u uu ¶rt; ¶rt;uu u m aauunmuaa nuu u nuu auauu mu au u u ¶rt;am ua a ¶rt;a uu, nuau n u nuu mu.

     

Secular trends in variations of Spitsbergen ice resources

A relationship is established between many-year variations of the total budget of Spitsbergen glacier mass and variations of the solar radiation reaching the upper atmospheric boundary in the Northern Hemisphere per year. A regression equation was used to evaluate the total mass budget of glaciers Austre Broggebreen and Midre Lovenbreen over period from 1850 to 2050. The trend in the decrease of ice resources in Spitsbergen is show to be related with an increase in the internlatitudinal heat exchange and the greenhouse effect because of the accumulation of heat from incoming solar radiation.     

The mean curvature of the external equipotential surface and the vertical gravity gradient as functions of stokes's constants

Summary The mean curvature of the equipotential surface and the vertical gradient of gravity are expressed in terms of a development into a series of spherical harmonics [1, 2, 4], neglecting terms of the order of 10^–8. The curvature anomalies have been computed using the satellite data [3]. The symbols used are the same as in [5].Dedicated to 90th Birthday of Professor Frantiek Fiala     

Secular non-random variations of cosmogenic carbon-14 in the terrestrial atmosphere

The time dependence of the¹⁴C content of bristlecone pine wood samples dated by their tree rings and grown during the last 8000 years was examined. The¹⁴C values as measured by the La Jolla Radiocarbon Laboratory were used for the investigation.Two different smoothing techniques were used for constructing values for equal time intervals. In this manner the introduction of regularities, that could have resulted from applied mathematical techniques, could be excluded.There is good evidence for non-random features in the power spectrum, in particular for a 200-year periodicity.The regularities in the power spectrum are further indications supporting the assumption that the¹⁴C variations reflect a property of the sun.     

Acoustic emission phenomena due to plasticity of rocks

Acoustic emission patterns arising at the stage of plastic deformation (creep and relaxation) of plastic and brittle rocks are discussed. It is suggested that these patterns are related to the spatial localization of plastic deformation and strain hardening of rocks under loads exceeding the yield strength.     

Secular geomagnetic variations and volcanic pulses in the Permian-Triassic traps of the Norilsk and Maimecha-Kotui provinces

Detailed paleomagnetic studies have shown that the effusive Permian-Triassic traps in the Kotui River valley were formed as the result of volcanic activity, which occurred in the form of volcanic pulses and individual eruptions with net duration of at most 7000–8000 years, excluding the periods of volcanic quiescence. According to the analysis of the paleomagnetic data earlier obtained by Heunemann and his coauthors [2004b] on the Abagalakh and Listvyanka sections in the Norilsk region, those geological units were formed during 25 volcanic pulses and separate eruptions, which all lasted up to 8000 years altogether, whereas the total time of formation (including the periods of volcanic quiescence) exceeded 10000–100000 years for the Norilsk section and was probably a bit shorter for the Kotui section. Comparison of the positions of virtual geomagnetic poles calculated for the Norilsk and the Kotui sections provides no grounds to suggest that these sections were formed at different geological times. The scatter in the positions of the virtual geomagnetic poles (VGP) for the directional groups and individual directions (58 altogether) jointly for the two sections (more than 160 lava flows) indicates that the secular geomagnetic variations at the Permian-Triassic boundary had similar amplitudes to those that occurred in the past 5 Ma.     

Tidal friction. Secular variations of the inclination and eccentricity of the Moon's orbit

Summary The computation of the secular variation of the inclination and eccentricity of the Moon's orbit due to tidal forces is revised. Also the effect of the Earth's ellipticity, which amounts to 10^–6 to 10^–5 of the value for the spherical earth, is estimated and found to be negligible. The results agree well with the computations of Kaula [7], as opposed to MacDonald's results [8] which display an order-of-magnitude difference in the variation of the eccentricity, apparently due to a printing error. Finally, solutions are presented for various values of the dissipation factor.

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amuam uu uu aa u muumma um, a nuuu uau. m n¶rt;a a uu amu u; m uu mam m 10^–5 ¶rt; 10^–6 au ¶rt; aa u u ¶rt;am nu. mam am uuu aa [7], muu m mam aa¶rt;a [8],¶rt; aua a n¶rt; uuu muumma u¶rt; aa nam. a ¶rt;a u ¶rt; a au ama ¶rt;uunauu.

     

Secular variations ing 1 0 component of geomagnetic field and its origin

The secular variations (SV) ing ₁ ⁰ of geomagnetic field, caused by the interaction between the geomagnetic field and the radial fluid-flow of the outer-core, are discussed with both statistical and analytic methods. When the value ofg ₁ ⁰ s ₂ ⁰ is relatively high compared with other terms, SV ing ₁ ⁰ is characterized by exponential change. When the effect of non-dipole field is notable, SV ing ₁ ⁰ shows complex features. Especially when the value of g ₁ ⁰ is close to zero, SV ing ₁ ⁰ is completely determined by the random process of non-dipole fields. Project supported by the National Natural Science Foundation of China (Grant No. 49429405) and by the Chinese Academy of Sciences.     

Secular variations of carbon and helium isotopes at Izu-Oshima Volcano, Japan

Secular variations in ¹³C/¹²C ratios and chemical compositions of gas samples from October 1986 to July 1992 are reported from a 92–95 °C steam well located about 3 km north of Mt. Mihara, an active volcano on Izu-Oshima Island, Japan. The δ¹³C value steeply increased from −2.97‰ (relative to PDB carbonate) in December 1986 to −1.15‰ in March 1988 and then gradually decreased to −1.75‰ in July 1992. Over the same period, the CO₂ content changed similarly with time, even though the experimental error is relatively large. These variations are consistent with helium isotope changes. Initially rapid and then slow enhancements of ³He/⁴He ratio, δ¹³C value and CO₂ content are invoked by violent eruptions of Izu-Oshima volcano from 15 November to 18 December 1986. After the eruptive activity, depletion of magmatic gas emission and subsequent mixing with crustal fluids in the hydrothermal system may produce the gradual decreases of ³He/⁴He ratio, δ¹³C value and CO₂ content. Taking into account the rates of these decreases, we suggest that helium and carbon isotope ratios will return to the situation of before the magmatic eruption within 15 years.     

Secular variations in the main geomagnetic field within the scope of the dynamic model of field sources

The effect of different-level sources on the spatial structure of the secular variations has been considered based on the dynamic model of sources of the main geomagnetic field developed by us. It has been obtained that the development of 13 most powerful dipoles only roughly characterizes global anomalies of the secular variations, and each anomaly results from the superposition of the dynamics of several sources. The model secular variations have been compared with the data from the observatories. It has been obtained that it is impossible to describe local anomalies of the observed secular variations ignoring sources of the third order of smallness as compared to the main dipole. It has been assumed that topographic vortices, originating around inhomogeneities of the core-mantle boundary, can be physical sources responsible for dipoles of the third order.     

Secular variation in numerical geodynamo models with lateral variations of boundary heat flow

We study magnetic field variations in numerical models of the geodynamo, with convection driven by nonuniform heat flow imposed at the outer boundary. We concentrate on cases with a boundary heat flow pattern derived from seismic anomalies in the lower mantle. At a Rayleigh number of about 100 times critical with respect to the onset of convection, the magnetic field is dominated by the axial dipole component and has a similar spectral distribution as Earth’s historical magnetic field on the core-mantle boundary (CMB). The time scales of variation of the low-order Gauss coefficients in the model agree within a factor of two with observed values. We have determined the averaging time interval needed to delineate deviations from the axial dipole field caused by the boundary heterogeneity. An average over 2000 years (the archeomagnetic time scale) is barely sufficient to reveal the long-term nondipole field. The model shows reduced scatter in virtual geomagnetic pole positions (VGPs) in the central Pacific, consistent with the weak secular variation observed in the historical field. Longitudinal drift of magnetic field structures is episodic and differs between regions. Westward magnetic drift is most pronounced beneath the Atlantic in our model. Although frozen flux advection by the large-scale flow is generally insufficient to explain the magnetic drift rates, there are some exceptions. In particular, equatorial flux spot pairs produced by expulsion of toroidal magnetic field are rapidly advected westward in localized equatorial jets which we interpret as thermal winds.