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1.
The Earth’s free oscillations are recorded for the first time in variations of the geomagnetic field measured at the Earth’s surface. The Earth’s free oscillations in the frequency range from 0.3 to 4 mHz manifest in the spectra of geomagnetic variations in the form of clearly expressed quasi-harmonic peaks. It is shown that the spectral amplitudes of the main modes of the Earth’s free oscillations are not constant and change with a periodicity corresponding to a lunar (sideral) month. The data obtained indicate the influence of oscillations in the internal geospheres on variations in the terrestrial magnetic field. The results provide new opportunities to study the Earth’s free oscillations and to specify their multiplet components. In addition, they also have certain implications for further research into the internal structure of the Earth and geodynamic processes in internal geospheres, on the basis of magnetometric data.  相似文献   

2.
Anisotropy of electrical conductivity in the lower mantle, presumably caused by phase change of dielectric magnesiowustite, can be estimated from geomagnetic records of the globally distributed geomagnetic array. The components of the conductivity tensor corresponding to the tangential components of the geomagnetic field are obtained from the magnetic mode alone recorded on the surface. Inversion by the perturbation method is applied to monthly means of geomagnetic variations along the X, Y, and Z components for the period from 1920 to 2009, borrowed from the World Monthly Means Database. The anisotropy contribution is expressed as corrections to the conductivity tensor components. The contribution of anisotropy to induction responses becomes notable for geomagnetic variations with at least decadal periods and increases with the period length.  相似文献   

3.
During the analysis of archived VLF data from Indian low latitude ground stations, some discrete VLF emissions recorded at the low latitude ground station Gulmarg (geomagnetic latitude 24°26′N; geomagnetic longitude 147°09′E, L = 1.28) during moderate magnetic storm activity (Σ K P − = 32, K P index varies from 4 to 6 during the observation period) on 6/7 March, 1986 are presented in this paper. The dynamic spectra of these discrete VLF emissions were observed along with tweeks and its harmonics, which is interesting and complex to explain. In most of the events the harmonic frequency of tweeks correlates with the starting frequency of harmonics of discrete emissions. In order to explain the observed features of discrete VLF emissions, we propose cyclotron resonance interaction between whistler mode wave and energetic electrons of inner radiation belt as possible generation mechanism. An attempt is also made to determine parallel energy, anisotropy and wave growth relevant to the generation process of VLF emissions.  相似文献   

4.
This study provides a compilation of the paleointensity records for the Cretaceous period derived from sediments of the Russian Plate and adjacent areas. The paleoinetensity values were calibrated using the laboratory redeposition experiments. Remarkable differences in the relative paleointensity variations were detected at the Berriasian–Early Barremian, Late Barremian–Santonian and Early–Late Maastrichtian boundaries. In the Berriasian–Early Barremian interval, the paleointensity varied stochastically, with the amplitude of about 1Ho and the mean value of 0.63Ho (Ho is the present-day geomagnetic field intensity assumed to be 40 μT). The records for the Barremian–Santonian give a picture of the geomagnetic field with alternating high- and low-amplitude features. The mean paleointensities remain constantly high (being on average 0.87Ho), and intervals of low-amplitude variation alternate with the pronounced bursts (3.5Ho). The Late Maastrichtian interval is characterized by high-amplitude paleointensity variations (4Ho) and a sharp drop towards the end of the interval. All records show remarkable similarities near the boundaries between geological time intervals, which are an increase in the amplitude and mean values of intensity at the end of intervals followed by a decrease towards the beginning of the subsequent interval.  相似文献   

5.

2070 unique, homogeneous photometric and polarization observations of the microquasar in a binary system with a black hole V404 Cyg/GS2023+338 obtained in 2015 with the MASTER global network of robotic telescopes (16 robotic telescopes located at eight points on the Earth in Russia, Spain, South Africa, and Argentina) are presented. MASTER was the first telescope network to obtain optical observations of the microquasar after its gamma-ray outburst in 2015. Observations were carried out from 18:34:09 UT on June 15, 2015 until December 2015 in four polarizations and in the four standard BV RI filters. The paper presents the results of these observations and a comparative analysis of optical and X-ray data. The observations confirm the previously discovered super-long delays of the optical radiation relative to the X-ray outbursts. Possible mechanisms causing the delay in the optical variations relative to the X-ray variations are discussed. Variability of the optical polarization discovered earlier is confirmed another similar episode reported.

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6.
We observed a direct reaction of metallic iron with water to form iron hydride and iron oxide, 3Fe + H2O–>2FeHx + FeO, at pressures from 6 GPa to 84 GPa and temperatures above 1,000 K in diamond anvil cell (DAC). Iron hydride is dhcpFeHx or -FeHx, and iron oxide has the rhombohedral or B1 structure at pressures at least up to 37 GPa. The formation of an assembly composed of dhcpFeHx and FeO with the B8 structure was observed at 84 GPa. In primordial Earth, water formed by dehydration of the low temperature primitive materials reacts with metallic iron in the high temperature component to form iron hydride FeHx and iron oxide FeO. The former would be incorporated in the iron forming the core. Thus hydrogen could be an important element of the Earths core. This reaction would be essential for transport of hydrogen into the core in the accretion stage of the Earth.  相似文献   

7.
Mead axisymmetric distortions in the geomagnetic field and uniform electrostatic field parallel to geomagnetic field have been assumed to derive an expression for the inhomogeneity parameter, αd. Consequent change in the pitch angle diffusion of charged particles has been obtained. Using these parameters, the variations in the precipitating electron influx with varying stand-off distances and parallel electrostatic fields have been computed.  相似文献   

8.
Spivak  A. A.  Loktev  D. N.  Tikhonova  A. V.  Kharlamov  V. A. 《Doklady Earth Sciences》2023,507(3):S442-S445
Doklady Earth Sciences - Based on the results of instrumental observations of geomagnetic variations at the Mikhnevo Observatory of the Institute of Geosphere Dynamics, Russian Academy of Sciences,...  相似文献   

9.
Spivak  A. A.  Riabova  S. A. 《Doklady Earth Sciences》2022,501(1):S22-S26
Doklady Earth Sciences - Results from instrumental observations of geomagnetic variations and variations in the electrical characteristics of the surface atmosphere (electric field, atmospheric...  相似文献   

10.
Discontinuity and periodicity of tectonic processes, eustatic fluctuations of the ocean level, volcanic and metallogenic activity, and some other global processes in the Earth’s history are indicative of the pulsatory nature of the Earth’s evolution. Correlation of geomagnetic field variations with global geological processes shows the geomagnetic field polarity to be an indicator of pulsations. The phases of the Earth’s expansion correspond to normal (present-day) polarity, and the planet’s contraction to epochs of reversed polarity. In terms of the concept of geopulsations, the diversity of basic geodynamic regimes of continents is determined by the combination of three factors: the phases of the Earth’s evolution (contraction-expansion), the effects of deep fluid and heat flows (plumes), and the state of the asthenosphere (its depth, thickness, and degree of heating). The general evolution of Phanerozoic ore deposition and the specific metallogenic features of tectonomagmatic cycles may be considered in a new light in view of the Earth’s pulsatory history.  相似文献   

11.
The asymmetry of the magnetic field of the Sun and its manifestation in the interplanetary magnetic field (IMF) are studied. The dominant magnetic polarity of the radial component of the IMF alternates from cycle to cycle, but with an overall systematic dominance of polarity directed toward the Sun. The global asymmetry is also manifest in the component of the IMF perpendicular to the plane of the solar equator. The dominance of positive values of B z together with an appreciable linear trend in the cumulative sum of this quantity is interpreted as a manifestation of a relic solar magnetic field. The strength of this relic magnetic field near the Earth is estimated to be 0.048 ± 0.015 nT, based on the growth of the linear component of the cumulative sum of B z . Time intervals, in which negative values of the B z component of the IMF dominate and enhanced geomagnetic activity is observed, are identified. Our analysis of solar and heliospheric magnetic fields in an integrated representation has enabled us to compare various types of measurements and estimate their stability.  相似文献   

12.
Chromite mineralization in metamorphosed dunites from the southern Klyuchevskoy dunite-harzburgite ultramafic complex (Central Urals) has been investigated using geomagnetic surveys along with laboratory studies of ore-forming and accessory spinels of the same genetic type. Magnetization in the study area is carried mainly by accessory Fe-Cr-spinel of a variable Fe2 +(Cr2 -xFex3 +)O4 composition. Metamorphism caused changes in element contents and in both crystal and magnetic structure of the primary nonmagnetic accessory spinel, unlike the almost fresh ore-forming spinel. Thus, ore bodies stand against their host rocks, which is a prerequisite for the use of geomagnetic surveys for exploration of podiform chromite deposits in dunite-harzburgite complexes. Ground magnetic surveys at a test site composed of faulted rocks bearing disseminated chromite mineralization in metamorphosed dunites resolved a chromite ore zone and a fault block boundary showing up as geomagnetic anomalies. Laboratory studies using high technologies (thermomagnetic analysis at 4 to 1000 K, as well as magnetic resonance and magnetic force spectroscopy) revealed, for the first time, magnetic clusters (superparamagnetic phases) in primary nonmagnetic accessory spinel, which are responsible for the magnetic properties of the host rocks. Microscale variations in Cr-spinel correlate with the geomagnetic anomalies recorded by field surveys at the test site.© 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.  相似文献   

13.
Analysis of experimental observations of the Earth’s magnetic field variations recorded by the scientific instruments at the Northern Caucasus Geophysical Observatory of the Institute of Physics of the Earth, Russian Academy of Sciences, in the period 2007–2009 was performed. It was found that the characteristic ultra-low-frequency (ULF) waveforms of the geomagnetic disturbances were distinguished in the structure of the observed variations that reflect the process of preparation and development of a tsunamigenic earthquake.  相似文献   

14.

A numerical–analytical approach is used to investigate irregular effects in oscillations of the Earth’s pole related to variations in the Chandler and annual components. An approach to studying oscillations in the motion of the Earth’s pole based on a joint analysis of the Chandler and annual components of this motion is proposed. A transformation to a new coordinate system in which the motion of the pole is synchronous with the precession of the lunar orbit can be found in this approach. Estimates of the precision of predictions of the coordinates of the Earth’s pole taking into account additional terms due to lunar perturbations are presented.

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15.
We have analyzed polarization observations of the subdwarf Bal 09, which is one of a group of hybrid sdB stars that display simultaneously both short- and long-period pulsations. Certain properties previously unknown for subdwarfs have been established for Bal 09, such as variations of the pulsation amplitude of the main oscillation mode, rotational splitting of multiplets, and variations of this splitting. Information about the stellar magnetic field must be considered if we wish to explain these properties. New observational data enabling estimation of the longitudinal magnetic field of Bal 09 have been obtained on the main stellar spectrograph of the 6-m telescope of the Special Astrophysical Observatory. Studies of the longitudinal component of the magnetic field 〈B z 〉 were carried out using a regression analysis. This method simultaneously yields estimates of the uncertainty in 〈B z 〉. Test measurements of 〈B z 〉 were carried out using the same method. For the star HD 158974, which has zero total magnetic field, the estimated longitudinal magnetic field is 〈B z 〉 = −4 ± 5 G. The standard magnetic field for the Ap star α 2CVn was measured to be −363 ± 17 G, in very good agreement with measurements in the literature. The estimated longitudinal magnetic field for Bal 09 is 34 ± 63G—appreciably lower than values established earlier for six subdwarfs, ≈1.5 kG. The results of the regression analysis for both individual spectral subranges and for intervals containing characteristic spectral features did not indicate reliable detections of a magnetic field exceeding the uncertainties in 〈B z 〉. The uncertainty in 〈B z 〉, which was 60–80 G for the entire spectral range and 140–200 G for selected spectral intervals, leads to an estimated upper limit on the longitudinal magnetic field 〈B z 〉 for Bal 09. This estimate for 〈B z 〉 can place observational constraints on theoretical explanations for the amplitude variations of the pulsations, rotational splitting of multiplets, and possible variations of the internal structure of the star.  相似文献   

16.
The premonitory variations of seismic-wave velocities before earthquakes originate from various cracking processes before the fracture. It can be shown that these variations are comparable with wave-velocity variations in porous model samples with defined pore sizes. Furthermore, it is possible to describe analytically the variation of wave velocities as a function of the parameter K0, which describes the fracturing process, and a material/depth parameter AP. On the basis of the wave velocity vs. pressure curves of rocks, it is possible to determine K0 and A. Using the material/depth parameter AP sediments in covering strata and eruptive rocks in regions of earthquakes of shallow to medium depth can be descirbed. A relationship between ΔυD and ΔK0 can be established. For acid to ultrabasic rocks, a variation of up to 2 km/s indicates a variation of K0 of 0.1–1.0.Moreover, it is possible to establish a relationship between K0 and the number as well as the mean length of cracks in the rock. The solutions differ depending on the cracks being closed or open. For closed cracks a wave-velocity minimum of 6% results. For oper cracks the variations of the number and mean length of cracks are taken into account by means of a stochastic process; the resulting variations of K0 and the wave velocity car adequately explain the variations in seismic-wave velocity. Variations of the pore pressure have an influence on K0and the wave velocity only under most favourable geologica conditions; generally they are insignificant. Also for S-wavc velocities and for the ratio υp/υs the wave velocity vs. pressure equations are valid; it is possible to state K0 and A-values.  相似文献   

17.
Mantle circulation in planets with strongly temperature‐dependent viscosity results in stagnant‐lid convection. It is fundamental to understand how this stagnant‐lid regime can change into a plate‐like convection regime as on the present‐day Earth. Here, we use 2D numerical models to study subduction initiation from an initial stagnant lid with laboratory‐consistent parameters and without pre‐existing weak zones or kinematic boundary conditions. Our results show that subduction can be initiated dynamically as a result of a thermal localization instability. The lithosphere may deform in a stagnant‐lid mode, an un‐necking mode, a symmetric‐subduction mode or an asymmetric‐subduction mode. The asymmetric‐subduction mode occurs only for relatively large friction angles and moderate thermal ages, and the presence of heterogeneities increases the parameter space of this mode. The limited parameter space might explain why only the present‐day Earth has plate tectonics, and suggests that the initiation of plate tectonics is more difficult than previously anticipated.  相似文献   

18.
Rybnov  Yu. S.  Riabova  S. A.  Spivak  A. A. 《Doklady Earth Sciences》2022,504(2):385-389
Doklady Earth Sciences - The results of instrumental observations of acoustic oscillations and geomagnetic variations during the fall of the bolide on November 17, 2021, near the town of Izhevsk...  相似文献   

19.
The assemblage clinopyroxene + magnesite was observed in Earth’s high-pressure metamorphic samples, and its stability in subducting slabs was confirmed by experiments. Recent studies also suggested that the fO2 variations observed in SNC meteorites can be explained by polybaric graphite-CO-CO2 equilibria in the Martian mantle. Although there is no direct evidence for the stability of the cpx + mc assemblage in Mars mantle, its high-pressure–high-temperature decomposition to cpx + fo + CO2 makes it a good analogue for the source of carbon metasomatism, in particular, to study nakhlites formation. Iron, which is present in the Earth’s and Martian mantles, may, however, influence the speciation of carbon. We performed experiments on a clinopyroxene + magnesite assemblage at 1.8 and 3.0 GPa and temperatures corresponding to the Earth’s and Martian mantles. The role of iron and of fO2 was investigated by (1) replacing all or part of the magnesite by siderite FeCO3, (2) adding Fe0 and (3) using graphite C capsules. A carbonate-silicate melt forms at both Earth and Mars conditions. Clinopyroxene and olivine are the main solid phases in the iron-free experiments. Fe2+ and Fe0 decrease their melting temperatures and increase the silicate fraction in the melt. The produced carbonate-silicate melts may be involved in the formation of some carbon-rich lavas on Earth (e.g., carbonatites, ultramafic lamprophyres, or kamafugites). Our results may also be used to interpret ophiolite samples or inclusions. In particular, we show that wüstite may form in equilibrium with carbonate-silicate melt in opx-(and silica-) poor regions of the mantle below 3 GPa. Our results also confirm the hypothesis of carbon metasomatism in the Martian nakhlites source. Immiscibility or reduction could explain the absence or rarity of C in Martian lavas.  相似文献   

20.
He  Haibo  Liu  Zaihua  Chen  Chongying  Wei  Yu  Bao  Qian  Sun  Hailong  Hu  Yundi  Yan  Hao 《中国地球化学学报》2019,38(5):613-626

Biological carbon pumping (BCP) is a key process in which dissolved inorganic carbon in terrestrial aquatic ecosystems is utilized by aquatic autotrophs for photosynthesis and transformed into autochthonous organic matter (AOC). However, the mechanisms underlying BCP and the amount of generated AOC deposited effectively, are still poorly understood. Therefore, we conducted a systematic study combining modern hydrochemical monitoring and a sediment trap experiment in Fuxian Lake (Yunnan, SW China), the second-deepest plateau, oligotrophic freshwater lake in China. Temperature, pH, EC (electrical conductivity), DO (dissolved O2), [HCO3−], [Ca2+], SIc, partial CO2 (pCO2) pressure, and carbon isotopic compositions of HCO3− (δ13CDIC) in water from Fuxian Lake all displayed distinct seasonal and vertical variations. This was especially apparent in an inverse correlation between pCO2 and DO, indicating that variations of hydrochemistry in the lake water were mainly controlled by the metabolism of the aquatic phototrophs. Furthermore, the lowest C/N ratios and highest δ13Corg were recorded in the trap sediments. Analyses of the C/N ratio demonstrated that the proportions of AOC ranged from 30% to 100% of all OC, indicating that AOC was an important contributor to sedimentary organic matter (OC). It was calculated that the AOC flux in Fuxian Lake was 20.43 t C km−2 in 2017. Therefore, AOC produced by carbonate weathering and aquatic photosynthesis could potentially be a significant carbon sink and may have an important contribution to solving the lack of carbon sinks in the global carbon cycle.

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