Fairweather atmospheric electricity at Antarctica during local summer as observed from Indian station,Maitri     

C. Panneerselvam  C. Selvaraj  K. Jeeva  K. U. Nair  C. P. Anilkumar  S. Gurubaran 《Journal of Earth System Science》2007,116(3):179-186

Surface measurements of the atmospheric electrical parameters like Maxwell current, electric field and conductivity studied at the Indian station, Maitri (70.75° S, 11.75° E, 117 m above mean sea level), Antarctica, during austral summer have been analyzed for the years 2001 to 2004. A total of 69 days were selected which satisfied the ‘fairweather’ conditions, i.e., days with absence of high winds, drifting or falling snow, clouds, and fog effects. The diurnal variation curve of electric field and vertical current averaged for 69 fairweather days is a single periodic with a minimum at 03:00 UT and a maximum near 19:00 UT, which is very similar to the Carnegie curve. The correlation coefficient between these measured parameters has a high value (more than 0.9) for all the days. During fairweather days the measured current and field variations are similar and hence it is clear that the conductivity is more or less stable. During magnetically disturbed days, the dawn-dusk potential drop has clear influences on the diurnal variation and it modifies the conductivity. Apart from the day-to-day variation in low latitude thunderstorm activity, there are diurnal, seasonal, inter-annual variations in the electric potential and the currents, as well as solar influences on the measured parameters. This study will help us to examine the impact of solar and geophysical phenomena like solar flares, geomagnetic storms and substorms on the global electric circuit.  相似文献   

河西走廊风能时空特征   总被引：3，自引：0，他引：3  

王毅荣 《干旱区地理》2007,30(3):43-350

利用河西走廊地区1970-2004年风速气候资料和2004年9月-2005年8月周年风塔精细资料,采用气候订正和即时风速订正,得到接近自然的风速,依此研究了该区域近地面70 m层内风能分布。结果表明:河西走廊区域风速变幅较小、气候变化趋势较稳定;有效风速(≥3 m/s)时数在6 000 h/a,10 m高度风能大多在150 w/m2以上,风能随高度线形增长(在70 m高度层内),平均每升高10 m风能增加28 w/m2;10~70 m层内总风能年储量相当丰富,普遍在1.5×1016kWh/m2(千瓦时/平方米)以上,潜在年产值达千万亿元。河西走廊风能存在明显周日和月季变化,风能和有效风速时数存在空间差异,其时空差异与河西走廊独特的戈壁下垫面关系密切。  相似文献   

威连滩冲沟砂黄土的风蚀与降雨侵蚀模拟实验   总被引：3，自引：0，他引：3  

宋阳  严平  刘连友  杨恒华  朱孟郡  杜建会  马玉凤 《中国沙漠》2007,27(5):814-819

 通过风洞与模拟降雨实验，研究了风力与降雨对青海省贵南县威连滩冲沟砂黄土的复合侵蚀作用。实验得出：①风蚀后的降雨使砂黄土表面在风干过程中形成了一层较为坚硬的结壳，增大了土壤的抗蚀性，降低了第二次风洞实验后期的风蚀率;②土壤水分与人为扰动是影响土壤风蚀的两个重要因素。当土壤水分较小时，风蚀率受人为扰动影响巨大;当土壤水分较大时，人为扰动对土壤风蚀的影响较小;③在持续降雨的实验条件下，砂黄土的产流、产沙量随着雨强的变化而改变。这种变化与表土的侵蚀率、可蚀性物质的多少、土壤水分以及土壤的入渗率等都有很大的关系。  相似文献   

Exploring the influence of the non-dipole field on magnetic records for field reversals and excursions     

Maxwell C. Brown  Richard Holme  Alistair Bargery 《Geophysical Journal International》2007,168(2):541-550

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Three-dimensional modelling of streaming potential     

M. R. Sheffer  D. W. Oldenburg 《Geophysical Journal International》2007,169(3):839-848

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Bootstrapped discrete scale invariance analysis of geomagnetic dipole intensity     

Art R. T. Jonkers 《Geophysical Journal International》2007,169(2):646-658

The technique of bootstrapped discrete scale invariance allows multiple time-series of different observables to be normalized in terms of observed and predicted characteristic timescales. A case study is presented using the SINT2000 time-series of virtual axial dipole moment, which spans the past 2 Myr. It is shown that this sequence not only bears a clear signature of a preferred timescale of about 55.6 Ka, but additionally predicts similar features (of shorter and longer duration) that are actually observed on the timescales of historical secular variation and dipole reversals, respectively. In turn, the latter two empirical sources both predict the characteristic timescale found in the dipole intensity sequence. These communal scaling characteristics suggest that a single underlying process could be driving dynamo fluctuations across all three observed timescales, from years to millions of years.  相似文献   

王艳，廖明生，李德仁等.利用长时间序列相干目标获取地面沉降场.地球物理学报，2007          下载免费PDF全文

王艳  廖明生  李德仁  魏子新  方正 《地球物理学报》2007,50(2)

方法，相干目标分析是利用时间序列多景影像获取地表稳定反射体——高相干点目标的新方法.实验区选择上海市主城区约100 km2 区域，InSAR的实验数据采用覆盖1992～2000年间的25景ERS-1/2的单视复影像.在无先验沉降场模型的情况下，实验结果显示该实验区的地面沉降场在时间范围上跨越8年，平均观测时间采样率约为4个月，垂直形变精度优于5 mm，满足我国对城市地面沉降形变观测的要求.研究结果表明该方法可以用于今后大时间/空间尺度上的高精度地表形变观测.  相似文献   

Automatic Interpretation of Magnetic Data Using Euler Deconvolution with Nonlinear Background   总被引：1，自引：0，他引：1  

Pawan Dewangan  T. Ramprasad  M. V. Ramana  M. Desa  B. Shailaja 《Pure and Applied Geophysics》2007,164(11):2359-2372

The voluminous gravity and magnetic data sets demand automatic interpretation techniques like Naudy, Euler and Werner deconvolution. Of these techniques, the Euler deconvolution has become a popular choice because the method assumes no particular geological model. However, the conventional approach to solving Euler equation requires tentative values of the structural index preventing it from being fully automatic and assumes a constant background that can be easily violated if the singular points are close to each other. We propose a possible solution to these problems by simultaneously estimating the source location, depth and structural index assuming nonlinear background. The Euler equation is solved in a nonlinear fashion using the optimization technique like conjugate gradient. This technique is applied to a published synthetic data set where the magnetic anomalies were modeled for a complex assemblage of simple magnetic bodies. The results for close by singular points are superior to those obtained by assuming linear background. We also applied the technique to a magnetic data set collected along the western continental margin of India. The results are in agreement with the regional magnetic interpretation and the bathymetric expressions.  相似文献   

Effect of surface stress on magneto-elastic surface waves in finitely conducting media     

Debi Pada Acharya  Chaitali Maji 《Acta Geophysica》2007,55(4):554-576

This paper deals with the investigation of the effect of surface stress and conductivity on the propagation of surface wave in isotropic, homogeneous, elastic media under the action of a primary magnetic field. Formulation of the general surface wave propagation problem has been made, and the corresponding frequency equation has been derived. Frequency equations for Rayleigh wave, surface shear wave and Stoneley wave have been deduced from that of general surface wave as special cases. The effects of surface stress and magnetic field on the wave velocities and attenuation factors of Rayleigh wave and surface shear wave are shown by numerical calculations and graphs. Some important wave velocity equations, as obtained by other authors, have been deduced as special cases from the wave velocity equation for Stoneley wave. It is found that the combined effect of surface stress and magnetic field modulates the wave velocity ratios and attenuation factors of Rayleigh wave and surface shear wave to a considerable extent.  相似文献   

Use of variograms for field magnetometry analysis in Upper Silesia Industrial Region     

J. Zawadzki  P. Fabijańczyk 《Studia Geophysica et Geodaetica》2007,51(4):535-550

Measurements of topsoil magnetic susceptibility are often used for quick assessment of soil contamination of anthropogenic origin, with heavy metals or other pollutants. However, because of complicated correlations between low-field magnetic susceptibility (shortened to magnetic susceptibility) of topsoil and soil pollution, the outcome of a field magnetometry survey can not be related directly to soil pollution. For each case study, the results should be interpreted on their own taking into account not only the type of pollution but also pedogenic, biogenic and environmental factors. In practice, it is very difficult to measure and consider all these factors. Here we illustrate the merit of geostatistical methods, which are focused on the spatial variability of a phenomenon, in the interpretation of soil magnetometry results. This article presents the analysis of spatial variability of top soil layers magnetic susceptibility-within the Upper Silesia Industrial Region (USIR)-using semivariance analysis. It also explains how to adjust the sampling density of field magnetometry measurements to spatial variability of the soil pollution as well as to the spatial scale of the investigated area. For this purpose, the values of magnetic susceptibility have been measured by using various sampling densities at areas of different size located within USIR. This enabled to determine the main scales of magnetic susceptibility spatial variability of soils within USIR using semivariance. A few distinct scales of variability were found from the site scale to a more regional scale. Variability ranges of 30 km, 12 km, and 5 km refer to the large regional scale, whereas smaller ranges of few hundreds down to a few tens of meters, can be attributed to the local (site) scale. In addition, the precision of the measuring campaigns, performed within USIR with different sampling densities, was compared through the analysis of the spatial variability of the soil magnetic susceptibility signal by using ordinary kriging. jarek97@yahoo.com, piotr.fabijanczyk@is.pw.edu.pl  相似文献