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H.-L. Chen A. R. Rao 《Stochastic Environmental Research and Risk Assessment (SERRA)》1998,12(4):205-222
Cohen and Sweeter (1975) found the 20 to 22-year Hale (double sunspot) cycle signal in the maximum entropy spectra of sunspot
and Atlantic tropical cyclone data. Currie (1996) corroborated and extended their analysis, but he argued that this signal
is the 18.6-year luni-solar tidal constituent. Currie maintains that Cohen and Sweeter mistakenly conjectured that this long
term periodicity was induced by the 20 to 22-year Hale cycle signal. However, no further investigation of periodicity in the
extracted wave forms corresponding to the 18.6-year luni-solar signal was conducted. In this study, we follow Currie's signal
processing procedures to extract the wave forms corresponding to the 18.6-year luni-solar signal. In order to investigate
the periodicity in the extracted wave forms, multi-taper method (MTM) is used for harmonic analysis. Band pass filters are
then designed to extract the wave forms corresponding to the individual components identified in the MTM harmonic analysis.
The investigation results of the monthly precipitation and Palmer's drought severity index (PDSI) data in three of the midwestern
states – Illinois, Indiana and Ohio – show that two periodic components, the 20 to 22-year Hale cycle signal and the other
component with periods between 16.9 and 13.5 years, are identified. The bistability phenomenon, which Currie found in these
wave forms, is more likely to result from the superposition of these two periodic components, rather than from a nonlinear
mechanism. Besides, a periodic component with an approximate period of 33 years is detected. 相似文献
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Paul Sava 《Geophysical Prospecting》2016,64(3):581-594
Reverse time migration backscattered events are produced by the cross‐correlation between waves reflected from sharp interfaces (e.g., salt bodies). These events, along with head waves and diving waves, produce the so‐called reverse time migration artefacts, which are visible as low wavenumber energy on migrated images. Commonly, these events are seen as a drawback for the reverse time migration method because they obstruct the image of the geologic structure, which is the real objective for the process. In this paper, we perform numeric and theoretical analysis to understand the reverse time migration backscattering energy in conventional and extended images. We show that the reverse time migration backscattering contains a measure of the synchronization and focusing information between the source and receiver wavefields. We show that this synchronization and focusing information is sensitive to velocity errors; this implies that a correct velocity model produces reverse time migration backscattering with maximum energy. Therefore, before filtering the reverse time migration backscattered energy, we should try to obtain a model that maximizes it. 相似文献
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IntroductionWith the time passing by and the environment changing, the characteristics of the components in a seismometer may change a little to some extent because of some certain reasons. Therefore the reliability of a sensor(s output may lower the reliability and a wrong result may also be produced if these changes are not realized and controlled or adjusted in time. Hence, the seismometers must be calibrated either before leaving factory or in use, so as to check the parameters and the cha… 相似文献
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This contribution comprises geological and magnetic results obtained in loess and paleosols profiles outcropped in the Pampean plain (Argentina). The sedimentary sequence exposed in Córdoba province is represented by four profiles Corralito I, Corralito II, Monte Ral815o and Lozada, 32°S 64°14'W (Argentina). These profiles were mineralogically described and magnetically analyzed. The sediments that compound the profiles contain volcanic glass between 20 and 90%. The results of two paleosols with different percentage of volcanic glass in the parent material (correlated to Marine Isotope Stage 5, MIS 5) exposed at Corralito I and Lozada, were compared; an important relationship between environmental magnetism signal and volcanic glass content was observed. All the results suggest that there are variations between different paleosols of the same area and age; such variations are attributed to content of volcanic glass in parent material; time of exposure of the parent material to pedogenic processes; and geomorphological place of each profile. At present, it is not possible to quantify certainly the paleo-precipitation index. Only qualitative interpretation can be done taking into account many variables of the geological system. 相似文献
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Introduction The automatic processing of continuous seismic data is important for monitoring earthquake, in which real data recorded by field stations located in different regions is transmitted to data cen- tre through internet or satellite communication systems. Automatic processing will run firstly on data, afterwards these automatic processing results will be reviewed and modified. The load of interactive analysis would be increase if there were more false events or missed events after run… 相似文献
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The brief theories of wavelet analysis and Hilbert-Huang transform (HHT) are introduced firstly in the present paper. Then several signal data were analyzed by using wavelet and HHT methods, respectively. The comparison shows that HHT is not only an effective method for analyzing non-stationary data, but also is a useful tool for examining detailed characters of time history signal. 相似文献
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The cloud amount summer nighttime data obtained from the 1994 to 2007 NASA satellite infrared and visible range measurements taken within the framework of the International Satellite Cloud Climatology Project (ISCCP) were analyzed, and the contribution by lunar signal to the cloud amount was extracted. Although the fact of lunar influence on cloudiness is known, this investigation has made it possible to separate the lunar-phase and lunar-declination effects on cloudiness. The relative cloud amount tends to grow with a change in lunar phase from a quadrature to the New Moon or Full Moon and with an increase in lunar declination by absolute value. Both the effects are statistically significant, the lunar-declination effect is a little stronger. The obtained results do not seem to contradict the theory of lunar tides. 相似文献
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Keshav Prasad Kandel Balaram Khadka Karan Bhatta Peter Wilhelm Schnoor Basu Dev Ghimire 《Acta Geophysica》2017,65(6):1269-1276
On August 24, 2016, an earthquake of magnitude 6.2 struck Central Italy (42.706°N and 13.223°E) at 1:36 UT. We present the results obtained from the US Navy VLF Transmitter’s NSY signal of 45.9 kHz transmitted from Niscemi, in the province of Sicily, Italy and received at the Kiel Longwave Monitor, Germany for 2016. We analysed the terminator times and their individual differences. We also analysed trends, dispersion and night time fluctuation which gave us a possible precursor the Italy earthquake. We found ionospheric perturbations in these parameters on 14th, 19th and 22nd of August, few days prior. Moreover, we filtered the possible effects due to lightning, storms and auroras if any. 相似文献
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Introduction EM technique of artificial SLF/ELF (Super low frequency/extremely low frequency, their frequency ranges from 0.1 to 300 Hz) can be used to investigate crustal conductivity structure. The SLF/ELF artificial signal is very stable and transmitte… 相似文献
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E. V. Pomozov 《Geomagnetism and Aeronomy》2014,54(1):127-134
In the used model, the quasistationary electric field in the atmosphere of the Earth is obtained by solving the conductivity equation. The penetration characteristics of the electric field from the Earth’s surface into the ionosphere depend on both atmospheric and ionosphere conductivity. The ionosphere is taken into account by setting a special condition on the upper boundary of the atmosphere. The influence of the atmospheric surface layer with a reduced conductivity on the penetration of the electric field from the surface of the Earth into the ionosphere is analyzed. 相似文献
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Water Resources - Aliphatic and polycyclic aromatic hydrocarbons have been studied in suspended matter and bottom sediments at the geochemical barrier the Northern Dvina–Dvina Bay during... 相似文献
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Geomagnetism and Aeronomy - Macroscopic discontinuous structures observed in the solar wind are considered in the framework of magnetic hydrodynamics. The interaction of strong discontinuities is... 相似文献
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The atmosphere is a kind of fluid surrounding therotating earth, and its state can be described by thevelocity vector v, the temperature T, the density ρ, andthe pressure p at each point. Its evolution process isessentially governed by the Navier-Stockes equationand the temperature equation. Due to the specialty andthe complexity of the atmospheric problem, althoughsome modified and simplified work have made onthese fluid mechanics and temperature equations, theyare still a very complex forc… 相似文献
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The suprabenthos comprises all bottom-dependent animals, mainly crustaceans (including decapods and peracarids), which perform--with varying amplitude, intensity and regularity--seasonal or daily vertical migrations above the sea floor. The presence of organisms in the Benthic Boundary Layer is determined by two general factors: (1) organism behaviour, which depends on the light penetration in the water column and (2) boundary-layer hydrodynamics. In the coastal zone of the eastern English Channel, during the spring Phaeocystis bloom, the presence of gelatinous colonies modifies the penetration of light in the water column, which may seriously affect the abundance and/or the behaviour of the suprabenthos community. To clarify this point, 19 suprabenthic hauls were taken with a modified Macer-GIROQ sledge both during the day and during the night, from March to June 2002 (i.e., before, during and after the bloom). Two sites, located in the coastal and offshore areas of the Ophelia medium sand macrobenthic community were investigated. The bloom had no effect on species richness and abundance in either site. However, the diel migrations of some dominant species--such as the cumaceans Pseudocuma longicornis and Pseudocuma similis, the mysid Gastrosaccus spinifer and the amphipod Stenothoe marina--were modified. During the bloom, diurnal and nocturnal suprabenthic abundances were similar, and in the absence of bloom, species remained benthic during the day. The permanent presence of suprabenthic species in the Benthic Boundary Layer could have a consequence on their predation by fish (mainly juveniles which preferentially consume small crustaceans in their diet), unless fish behaviour and predation efficiency--especially for visual predators--are also disturbed by changes in light intensity. 相似文献
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YIN Hongfu CHEN Guojin LI Chang抋n & WEI Yuan . School of Earth Sciences China University of Geosciences Wuhan China . Hydrogeological Team Hubei Bureau of Geology Mineral Resources Jingzhou China . Geological Survey of Jiangxi Province Nanchang China 《中国科学D辑(英文版)》2004,47(5)
1 Origin, process and method of the research Silt deposition created the fertile Dongting and Jianghan Plains of the middle Yangtze drainage, but has become a main cause of the deteriorating flooding along the middle Yangtze. The history of flood and waterlog of the Yangtze River in last century, esp. the disastrous 1998 flood, has proved that the key to the Yangtze flood control is its middle reach, especially the Jingjiang Segment. To study the silt deposition of the middle Yangtze and … 相似文献
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L. P. Imaeva B. M. Koz’min V. S . Imaev N. N. Grib S. V. Ashurkov 《Journal of Seismology》2017,21(2):385-410
The paper presents the modern structural-tectonic pattern and a tectonodynamic model of the zone of interaction of the most seismically active northeastern side of the Baikal rift zone (BRZ) and the conjugate system of seismogenic structures of the Aldan-Stanovoy block, where disastrous events with M ≥ 6.0 have been reported. Regularities in the structural formation of active faults and their kinematics are discussed. The faults form block structures accumulating significant tectonic strain. Motions between large tectonic blocks cause sudden release of the strain, which results in catastrophic events (M ≥ 6.0) with focal mechanisms of definite kinematic type. 相似文献