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Numerical simulation of Martian historical dynamo:Impact of the Rayleigh number on the dynamo state

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Science China Earth Sciences 2009年第3期52卷 402-410页

作者： WANG TianYuan KUANG WeiJia MA ShiZhuang laboratory for Computational geodynamics Graduate University of Chinese Academy of SciencesBeijing 100049China Planetary geodynamics laboratory NASA Goddard Space Flight CenterGreenbeltMD 20771USA

The observed Mars remnant magnetism suggests that there was an active dynamo in the Martian core. We use the MoSST core dynamics model to simulate the Martian historical dynamo, focusing on the variation of the dynamo states with the Rayleigh number Ra (a non-dimensional parameter describing the buoyancy force in the core). Our numerical results show that the mean field length scale does not vary monotonically with the Rayleigh number, and the field morphology at the core mantle boundary changes with Rayleigh number. In particular, it drifts westward with a speed decreasing with Rayleigh number.

关键词： Mars magnetic field Rayleigh number dynamo

Degree One Loading by Pressure Variations at the CMB

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Journal of Earth Science 2013年第5期24卷 736-749页

作者： Ming Fang Bradford H Hager Weijia Kuang Department of Earth Atmospheric & Planetary Sciences Massachusetts Institute of Technology Planetary geodynamics laboratory NASA Goddard Space Flight Center

Hemispherical asymmetry in core dynamics induces degree-1 pressure variations at the core mantle boundary （CMB）, which in turn deforms the overlaying elastic mantle, at the same time keeps center of mass of the whole Earth stationary in space. We develop a systematic procedure to deal with the degree-1 CMB pressure loading. We find by direct calculation a surprisingly negative load Love number h1=-1.425 for vertical displacement. Further analysis indicates that the negative hi corre- sponds to thickening above the positive load that defies intuition that pressure inflation pushes over- laying material up and thins the enveloping shell. We also redefine the pressure load Love numbers in general to enable comparison between the surface mass load and the CMB pressure load for the whole spectrum of harmonic degrees. We find that the gravitational perturbations from the two kinds of loads at degrees n〉l are very similar in amplitude but opposite in sign. In particular, if the CMB pressure variation at degree 2 is at the level of -1 hpa/yr （1 cm water height per year）, it would perturb the variation of Earth＇s oblateness, known as the J2, at the observed level.

关键词： Degree One Loading by Pressure Variations at the CMB MRSP

Modeling seismic wave propagation in heterogeneous medium using overlap domain pseudospectral method

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Earthquake Science 2008年第1期21卷 46-57+108页

作者：严九鹏王彦宾 Beijing 100871 China laboratory of Computational geodynamics Department of Geophysics School of Earth and space Sciences Pe-king University laboratory of Computational geodynamics Department of Geophysics School of Earth and space Sciences Pe-king University

Pseudospectral method is an efficient and high accuracy numerical method for simulating seismic wave propaga- tion in heterogeneous earth medium. Since its derivative operator is global, this method is commonly considered not suitable for parallel computation. In this paper, we introduce the parallel overlap domain decomposition scheme and give a parallel pseudospectral method implemented on distributed memory PC cluster system for modeling seismic wave propagation in heterogeneous medium. In this parallel method, the medium is decomposed into several subdomains and the wave equations are solved in each subdomain simultaneously. The solutions in each subdomain are connected through the transferring at the overlapped region. Using 2D models, we compared the parallel and traditional pseudospectral method, analyzed the accuracy of the parallel method. The results show that the parallel method can efficiently reduce computation time for the same accuracy as the traditional method. This method could be applied to large scale modeling of seismic wave propagation in 3D heterogeneous medium.

关键词： overlap domain decomposition scheme Fourier pseudospectral method parallel computation seismic wavefield

Carbon isotopes in eclogite and apatite separate from Huangzhen and Shima in SE Dabie

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Science China Earth Sciences 2000年第5期43卷 449-457页

作者：李一良郑永飞龚冰傅斌 laboratory for Chemical geodynamics Department of Earth and Space Sciences University of Science and Technology of China Hefei 230026 China

The carbon isotope compositions of high- and ultrahigh-pressure eclogite and apatite separate from Huangzhen and Shima in SE Dabie Mountains were analyzed by EA-MS online technique. The δ13C values of the eclogites cover a wide range of -30.7‰ - +1.5‰, whereasthose of apatites only have a small range of -28.1‰- -21.0‰. Some of the eclogites with thehigh δ13C values suffered retrogressive alteration by CO2-bearing fluids. The low δ13C values of the apatites indicate that the eclogites contain surficial carbon of organic origin. It is concluded that protoliths of the eclogites were exposed to the surface of the Earth, and that the carbon-bearing fluid was depleted in 13C during the eclogite-facies metamorphism.

关键词： organic carbon carbon isotopes apatite eclogite Dabie Mountains.

Controlled analogue experiments on propagation of seismic electromagnetic signals

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Chinese Science Bulletin 2005年第17期50卷 1956-1961页

作者： HUANG Qinghua Computational geodynamics laboratory Department of GeophysicsSchool of Earth and Space Sciences Peking University Beijing 100871China

This study presented a method of laboratory analogue experiments based on a geographical scaling model and a waveguide model to investigate the characteristics of the propagation of seismic electromagnetic signals in the crust and the atmosphere. Some controlled experiments were done to evaluate the possible influence on the experimental results from the background electromagnetic field, geo-graphical conditions, boundary effects, the source of elec-tromagnetic signals (position, magnitude, and frequency), and media conductivity. The reliability and the extensibility of the above analogue experimental method were also inves-tigated. This study indicated that such kind of analogue ex-perimental method provided an intuitionistic way of studying the propagation of seismic electromagnetic signals, which is one of the most difficult research topics in seismo-electro- magnetism.

关键词：地震电磁信号传播方式波导模式震源

Preprocessing photospheric vector magnetograms for nonlinear force-free field extrapolation of the global corona

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Research in Astronomy and Astrophysics 2018年第7期18卷 113-124页

作者： Ai-Ying Duan Huai Zhang Key laboratory of Computational geodynamics University of Chinese Academy of Sciences SIGMA Weather Group State Key Laboratory for Space Weather National Space Science Center Chinese Academy of Sciences laboratory for Marine Mineral Resources Qingdao National Laboratory for Marine Science and Technology

Nonlinear force-free magnetic field （NLFFF） extrapolation based on the observed photo- spheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric magnetograms contain magnetic forces and small-scale noises, and fail to be consistent with the force-free assumption of NLFFF models. The procedure for removing the forces and noises in observed data is called preprocessing. In this paper, we extend the preprocessing code of Jiang ＆ Feng to spherical coordinates for a full sphere. We first smooth the observed data with Gaussian smoothing, and then split the smoothed magnetic field into a potential field and a non-potential field. The potential part is computed by a numerical potential field model, and the non-potential part is prepro- cessed using an optimization method to minimize the magnetic forces and magnetic torques. Applying the code to synoptic charts of the vector magnetic field from SDO/HMI, we find it can effectively reduce the noises and forces, and improve the quality of data for a better input which will be used for NLFFF extrapolations applied to the global corona.

关键词： magnetic fields - magnetohydrodynamics (MHD) - methods numerical - Sun corona

Assessment of the performance of the TOPGNSS and ANN-MB antennas for ionospheric measurements using low-cost u-blox GNSS receivers

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Geodesy and geodynamics 2024年第3期15卷 291-301页

作者： Daniel Okoh Aderonke Obafaye Oluwakemi Dare-Idowu Babatunde Rabiu Anton Kashcheyev Claudio Cesaroni John Bosco Habarulema Bruno Nava United Nations African Regional Centre for space Science and Technology Education-English(UN-ARCSSTE-E) Obafemi Awolowo University CampusIle IfeNigeria National Institute for Geophysics and Volcanology(INGV) 00143 RomeItaly Institute for space Science and Engineering African University of Science and TechnologyAbujaNigeria University of New Brunswick FrederictonCanada South African National space Agency(SANSA) P.O Box 32Hermanus 7200South Africa Department of Physics and Electronics Rhodes University6140 MakhandaSouth Africa The Abdus Salam International Centre for Theoretical Physics Strada Costiera11I-34151 TriesteItaly

Low-cost GNSS receivers have recently been gaining reliability as good candidates for ionospheric studies. In line with these gains are genuine concerns about improving the performance of these receivers. In this work, we present a comprehensive investigation of the performances of two antennas(the u-blox ANN-MB and the TOPGNSS TOP-106) used on a low-cost GNSS receiver known as the u-blox ZED-F9P. The two antennas were installed on two identical and co-located u-blox receivers. Data used from both receivers cover the period from January to June 2022. Results from the study indicate that the signal strengths are dominantly greater for the receiver with the TOPGNSS antenna than for the receiver with the ANN-MB antenna, implying that the TOPGNSS antenna is better than the ANN-MB antenna in terms of providing greater signal strengths. Summarily, the TOPGNSS antenna also performed better in minimizing the occurrence of cycle slips on phase TEC measurements. There are no conspicuous differences between the variances(computed as 5-min standard deviations) of phase TEC measurements for the two antennas, except for a period around May-June when the TOPGNSS gave a better performance in terms of minimizing the variances in phase TEC. Remarkably, the ANN-MB antenna gave a better performance than the TOPGNSS antenna in terms of minimizing the variances in pseudorange TEC for some satellite observations. For precise horizontal(North and East) positioning, the receiver with the TOPGNSS antenna gave better results, while the receiver with the ANN-MB antenna gave better vertical(Up) positioning. The errors for the receivers of both antennas are typically within about 5 m(the monthly mean was usually smaller than 1 m) in the horizontal direction and within about 10 m(the monthly mean was usually smaller than 4 m) in the vertical direction.

关键词： GNSS Ionosphere Low-cost Antenna TOPGNSS U-blox

Deformation Localization-A Review on the Maximum-Effective-Moment(MEM) Criterion

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Acta Geologica Sinica(English Edition) 2015年第4期89卷 1133-1152页

作者： ZHENG Yadong ZHANG Qing HOU Quanlin School of Earth and space Sciences Peking University Institute of Geolomechanics Chinese Academy of Geological Sciences Key laboratory of Computational geodynamics Chinese Academy of Sciences

The essential difference in the formation of conjugate shear zones in brittle and ductile deformation is that the intersection angle between brittle conjugate faults in the contractional quadrants is acute （usually ～60°） whereas the angle between conjugate ductile shear zones is obtuse （usually 110°）. The Mohr-Coulomb failure criterion, an experimentally validated empirical relationship, is commonly applied for interpreting the stress directions based on the orientation of the brittle shear fractures. However, the Mohr-Coulomb failure criterion fails to explain the formation of the low-angle normal fault, high-angle reverse fault, and the conjugate strike-slip fault with an obtuse angle in the ~1 direction. Although it is ten years since the Maximum-Effective-Moment （MEM） criterion was first proposed, and increasingly solid evidence in support of it has been obtained from both observed examples in nature and laboratory experiments, it is not yet a commonly accepted model to use to interpret these anti- Mohr-Coulomb features that are widely observed in the natural world. The deformational behavior of rock depends on its intrinsic mechanical properties and external factors such as applied stresses, strain rates, and temperature conditions related to crustal depths. The occurrence of conjugate shear features with obtuse angles of -110~ in the contractional direction on different scales and at different crustal levels are consistent with the prediction of the MEM criterion, therefore -110° is a reliable indicator for deformation localization that occurred at medium-low strain rates at any crustal levels. Since the strain-rate is variable through time in nature, brittle, ductile, and plastic features may appear within the same rock.

关键词： anti-Mohr-Coulomb criterion features von Mises Criterion MEM-Criterion,homogeneous deformation deformation localization strain rate

A review of geophysical studies on the Mongolian Plateau

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Earthquake Science 2024年第3期37卷 224-240页

作者： Lei Zhang Zhouchuan Huang Xiaodong Song Qingju Wu SinoProbe laboratory School of Earth and Space SciencesPeking UniversityBeijing 100871China Hebei Hongshan National Observatory on Thick Sediments and Seismic Hazards Peking UniversityBeijing 100871China School of Earth Sciences and Engineering Nanjing UniversityNanjing 210023China Institute of Geophysics China Earthquake AdministrationBeijing 100081China

The Mongolian Plateau in Central Asia is an intracontinental tectonic system far from active plate *** its distance from these boundaries,the plateau is characterized by intense crustal deformation accompanied by voluminous Cenozoic volcanism and active modern ***,the intraplate deformation mechanism has long been debated owing to the scarcity of observations and contradictions between different *** recent years,growing geophysical studies have been conducted on the Mongolian Plateau,providing constraints on its lithospheric structure and ***,we review the geophysical research on the Mongolian Plateau over the last decade,including seismological,geodetic,gravity,magnetotelluric,and geodynamic *** review aims to(a)describe crustal and mantle structures based on multiscale seismic images;(b)describe deformation patterns based on seismic anisotropy,focal mechanisms,and global positioning system(GPS)observations;and(c)discuss the mechanisms behind intraplate deformation,volcanism,and seismic activity across the Mongolian *** images show that the crustal structure of the plateau has significant east-west *** blocks in the western Mongolian Plateau have thick crusts,including the Altai Mountains,Hovsgol Rift,and Hangay *** lithospheric deformation across the Mongolian Plateau has strong lateral variation,with NE-SW shortening in the Altai Mountains and W-E or NW-SE shear deformation in the Hangay Dome region and the eastern *** varied deformation may result from the superposition of multiple mechanisms,including far-field stress in the Altai Mountains,mantle upwelling,and mantle flow in the Hangay Dome ***,it is difficult to identify the geodynamics of the formation of the entire Mongolian Plateau because the deformation is too complicated,and the present models are not sufficient and are always ***,this review encompasses recent advances in seismic observa

关键词： Mongolian Plateau Central Asia seismic tomography crust-mantle structure intraplate deformation