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11.
By using an image-dipole magnetic field model for a variety of plasma density profiles we have studied the latitude effect of the 0.1–1.0-Hz hydromagnetic wave propagation in the Earth's magnetosphere. On comparing the results of signal group delay time calculations for dipole and model magnetic fields with ground and satellite observations we obtain some propagation characteristics of Pc1s and localize the regions of their generation. Our results show that most high-latitude Pc1 events are generated in the outer magnetosphere in accordance with ground and satellite observations and theoretical considerations. The non-dipole geometry of the geomagnetic field in the outer magnetosphere (at geomagnetic latitudes φ0 > 66°, L > 6) has a significant effect on the hydromagnetic wave propagation. 相似文献
12.
The solar wind quasi-invariant (QI) has been defined by Osherovich, Fainberg, and Stone (Geophys. Res. Lett.
26, 2597, 1999) as the ratio of magnetic energy density and the energy density of the solar wind flow. In the regular solar wind QI is a
rather small number, since the energy of the flow is almost two orders of magnitude greater than the magnetic energy. However,
in magnetic clouds, QI is the order of unity (less than 1) and thus magnetic clouds can be viewed as a great anomaly in comparison
with its value in the background solar wind. We study the duration, extent, and amplitude of this anomaly for two groups of
isolated magnetic clouds: slow clouds (360<v<450 km s−1) and fast clouds (450≤v<720 km s−1). By applying the technique of superposition of epochs to 12 slow and 12 fast clouds from the catalog of Richardson and Cane
(Solar Phys. 264, 189, 2010), we create an average slow cloud and an average fast cloud observed at 1 AU. From our analysis of these average clouds,
we obtain cloud boundaries in both time and space as well as differences in QI amplitude and other parameters characterizing
the solar wind state. Interplanetary magnetic clouds are known to cause major magnetic storms at the Earth, especially those
clouds which travel from the sun to the Earth at high speeds. Characterizing each magnetic cloud by its QI value and extent
may help in understanding the role of those disturbances in producing geomagnetic activity. 相似文献
13.
ABSTRACT Several commonly-used nonparametric change-point detection methods are analysed in terms of power, ability and accuracy of the estimated change-point location. The analysis is performed with synthetic data for different sample sizes, two types of change and different magnitudes of change. The methods studied are the Pettitt method, a method based on the Cramér von Mises (CvM) two-sample test statistic and a variant of the CUSUM method. The methods differ considerably in behaviour. For all methods the spread of estimated change-point location increases significantly for points near one of the ends of the sample. Series of annual maximum runoff for four stations on the Yangtze River in China are used to examine the performance of the methods on real data. It was found that the CvM-based test gave the best results, but all three methods suffer from bias and low detection rates for change points near the ends of the series. 相似文献
14.
Kosakowski Paweł Kotarba Maciej J. Piestrzyński Adam Shogenova Alla Więcław Dariusz 《International Journal of Earth Sciences》2017,106(2):743-761
International Journal of Earth Sciences - We present geochemical characteristics of the Lower Palaeozoic shales deposited in the Baltic Basin and Podlasie Depression. In the study area, this strata... 相似文献
15.
Alla V. Silina 《Ocean Science Journal》2006,41(4):211-219
A comparison was made of population of the economically important cockleAnadara (=Scapharca)broughtoni (Bivalvia, Arcidae) inhabiting different areas of the Razdolnaya River estuary at the head of Amurskii Bay (Peter the Great
Gulf, East Sea). Also, changes in cockle population density and structure, as well as in cockle growth rates during the last
20 years were studied. In all years of investigation, the morphometrical parameters and growth rates of cockles were smaller
at the sites located close to the River mouth than farther down-estuary. The differences can be attributed to higher concentration
of suspended particulate matter, decreased salinity and water temperature, as well as a longer exposure to these unfavorable
environmental factors at sites located close to the River mouth, compared to farther sites. For two decades, cockle population
density had decreased by almost 30 times at some sites in the River estuary. The main reason for this population decline is
commercial over-fishing of the cockle. Besides, for the last 20 years, linear parameters of the cockles in the population
decreased approximately by 30% and weight parameters, almost two times. Cockle growth rates also decreased for this period.
Evidently, these facts are due to the damaging effect of dredging. 相似文献
16.
The sedimentary record of the Issyk Kul basin,Kyrgyzstan: climatic and tectonic inferences 
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下载免费PDF全文 Euan A. Macaulay Edward R. Sobel Alexander Mikolaichuk Michael Wack Stuart A. Gilder Andreas Mulch Alla B. Fortuna Scott Hynek Farid Apayarov 《Basin Research》2016,28(1):57-80
A broad array of new provenance and stable isotope data are presented from two magnetostratigraphically dated sections in the south‐eastern Issyk Kul basin of the Central Kyrgyz Tien Shan. The results presented here are discussed and interpreted for two plausible magnetostratigraphic age models. A combination of zircon U‐Pb provenance, paleocurrent and conglomerate clast count analyses is used to determine sediment provenance. This analysis reveals that the first coarse‐grained, syn‐tectonic sediments (Dzhety Oguz formation) were sourced from the nearby Terskey Range, supporting previous thermochronology‐based estimates of a ca. 25–20 Ma onset of deformation in the range. Climate variations are inferred using carbonate stable isotope (δ18O and δ13C) data from 53 samples collected in the two sections and are compared with the oxygen isotope compositions of modern water from 128 samples. Two key features are identified in the stable isotope data set derived from the sediments: (1) isotope values, in particular δ13C, decrease between ca. 26.0 and 23.6 or 25.6 and 21.0 Ma, and (2) the scatter of δ18O values increased significantly after ca. 22.6 or 16.9 Ma. The first feature is interpreted to reflect progressively wetter conditions. Because this feature slightly post‐dates the onset of deformation in the Terskey Range, we suggest that it has been caused by orographically enhanced precipitation, implying that surface uplift accompanied late Cenozoic deformation and rock uplift in the Terskey Range. The increased scatter could reflect variable moisture source or availability caused by global climate change following the onset of Miocene glaciations at ca. 22.6 Ma, or enhanced evaporation during the Mid‐Miocene climatic optimum at ca. 17–15 Ma. 相似文献
17.
Laws of formation and criteria for predicting nickel content in weathering crusts of east Kazakhstan
Boris A. Dyachkov Bakytzhan B. Amralinova Indira E. Mataybaeva Alla V. Dolgopolova Arkady I. Mizerny Anastassiya P. Miroshnikova 《Journal of the Geological Society of India》2017,89(5):605-609
The article considers from the theoretical point of new global tectonics the geological conditions of formation, peculiar features of material composition, and criteria for predicting deposits of nickeliferous weathering crusts of east Kazakhstan. According to geotectonic zoning, this territory includes geological structures of the Big Altai (BA), which is part of the central Asian mobile belt. The ore-controlling role is assigned to the area of global interaction of the Kazakhstan and Siberian paleocontinents during the stage of the Hercynian collision (Ñ1-Ñ3) followed by the formation of the Zaisan suture zone, the structure of which is represented by the Charsky-Gornostaevsky ophiolite belt (suture stitch). During the Hercynian cycle of tectogenesis, main gold fields of the regions appeared in the Zaisan suture (gold-quartz, gold-sulphide, gold-listvenite, etc.) in a collision situation, controlled by a system of deep faults of the crust and mantle type. In similar tectonic environment, large stockwork gold deposits were formed in Rudny Altai, north Kazakhstan, and other regions. During the Cimmerian cycle, the residual weathering crust deposits of Au, Ti-Zr, Ni-Co were formed in the region of continental rifting. The article emphasizes the spatial association of silicate cobalt-nickel deposits to the outputs of serpentinized ultrabasites of the Charsky-Gornostaevsky belt and provides a characteristic of the geological structure and material composition of nickel content in ores of the Belogorskoye and Gornostaevskoye standard deposits. Expansion of prospects depends on the possibility of growth of reserves of cobalt and nickel ores on the flanks and deep horizons of the known ore fields and search for buried deposits in prospective areas determined by geological and geophysical studies. 相似文献
18.
Bernd R.T. Simoneit Alla Yu. Lein G.A. Osipov 《Geochimica et cosmochimica acta》2004,68(10):2275-2294
The lipid components in hydrothermal sulfide deposits from the Rainbow vent field (Mid-Atlantic Ridge at 36°N) were studied by gas chromatography/mass spectrometry. The Rainbow vent field is one of two known active hydrothermal systems related to abyssal circulation, where high-temperature fluids are formed during serpentinization of ultrabasic crustal rocks. The major amount of the extractable organic matter from the sulfides consists of normal and branched alkanes, UCM, PAHs, terpenoids, and fatty acids. The branched alkanes are comprised of unique gem-diethylalkane series, possibly from sulfide oxidizing bacteria, and biphytanes from archaea. The characteristic lipid and biomarker compounds found in the hydrothermal samples support a predominantly biological origin of the bitumens from the thermal transformation of the biomass of microorganisms (bacteria and archea) and minor macrofauna of this vent field. A search for molecular evidence for abiogenic thermocatalytic synthesis of organic compounds was negative. However, methane in the hydrothermal fluids and possibly a minor amount of the alkanes in the sulfides may be of an abiogenic origin in the Rainbow vent field. 相似文献
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20.
Stable isotope composition of syngenetic and epigenetic ice wedges, radiocarbon age, and pollen spectra of the surrounding deposits were studied during long term investigations at the "Belyi Klyuch" site on the first(6-8 m height) terrace of the Chara River(720 m.a.s.l.) in northern Transbaikalia to assess climatic conditions during ice-wedge formation. It was revealed that Holocene ice wedges had been formed from 10 to 7.5 ka 14 C BP. The isotope composition(δ~(18)O, δ~2 H) of relict ice wedges is the lightest and amounts-23‰ and-185‰, correspondingly. The isotopic compositions of ice lenses from sandy loam above ice wedges are-15.7‰, and-133‰; of small ice wedge in peat and sand are-15.3‰ and-117.9‰, accordingly.Interpretation of the ice wedge isotope composition has yielded that mean winter temperatures during cold stages of Holocene optimum were lower than today, during warm stages they were close to modern ones. During the coldest stages of Holocene optimum the total annual freezing index varied from-5100 to-5700 ℃ degree days, i.e. 300-600 ℃ degree days colder than during extremely severe modern winters. The total annual thawing index varied from 1300 to 1800 ℃ degree days, which was slightly higher than modern ones. 相似文献