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571.
Can electromagnetic disturbances related to the recent great earthquakes be detected by satellite magnetometers? 总被引:1,自引:0,他引:1
On December 26, 2004 the world's fourth largest earthquake since 1900 and the largest since the 1964 Prince William Sound, Alaska earthquake, occurred off the west coast of northern Sumatra with a magnitude of 9.3. On March 28, 2005 another event of magnitude 8.7 took place in the same region. The December 26, 2004 earthquake has prompted scientists to investigate possible electromagnetic signatures of this event, using ground magnetic observations. Iyemori et al. [Iyemori, T. et al., 2005. Geomagnetic pulsations caused by the Sumatra earthquake on December 26, 2004. Geophys. Res. Lett., 32, L20807, doi:10.1029/2005GL024083.] have suggested that a 3.6 min long geomagnetic pulsation, observed shortly after this event, was generated by the earthquake. They have speculated that a 30 s magnetic pulsation was also caused by the earthquake. Here for the first time, CHAMP satellite magnetic and electron density data are examined to find out if electromagnetic signatures which are possibly related to these recent megathrust earthquakes are observed in satellite magnetic data. We have shown that some specific features are observed after the two earthquakes, with periods of about 16 and 30 s. Our results favor an external source origin for the 30 s pulsation. Moreover, after more than 1 h, CHAMP magnetic data indicate the existence of a feature characterized by the same parameters (duration, amplitude, and frequency content), which could be associated with each earthquake, respectively. Further investigations are required in order to answer the question of whether these signals can be associated with earthquakes and to assign their possible usefulness with respect to earthquake development. 相似文献
572.
《Astroparticle Physics》2012,35(6):346-353
The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth’s magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between ∼6 and ∼13 GeV with an estimated uncertainty of ∼2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars. 相似文献
573.
利用SNOE卫星1998年3月11日至2000年9月30日共计935天观测的NO密度和太阳软X射线数据,分析了低热层NO的时空分布特征及其对太阳和地磁活动的响应,得出了以下结论:NO密度从96.67 km开始增加,大约在105~110 km高度达到最大,随后开始减小;同一高度处一般夏季期间最大,冬季次之,春秋分季最小;密度峰值大小变化范围约为(0.5~1.5)×108 mol/cm3,峰值高度基本分布在107 km和113 km高度处,且不随太阳活动变化,平均值约为107 km;NO密度与太阳软X射线及地磁Ap指数的相关系数在不同高度存在0、1和2天的最佳延迟时间,而同太阳软X射线的统计关系在不同高度和季节存在"线性"、"放大"和"饱和"现象;从统计和事件分析结果来看,太阳活动对磁赤道地区低热层NO密度的气候尺度变化的影响远大于地磁活动,但地磁活动对NO短期变化贡献非常明显. 相似文献
574.
J. Ndiritu 《水文科学杂志》2013,58(8):1704-1717
AbstractRaingauge measurements are commonly used to estimate daily areal rainfall for catchment modelling. The variation of rainfall between the gauges is usually inadequately captured and areal rainfall estimates are therefore very uncertain. A method of quantifying these uncertainties and incorporating them into ensembles of areal rainfall is demonstrated and tested. The uncertainties are imposed as perturbations based on the differences in areal rainfall that result when half of the raingauges are alternately omitted. Also included is a method of: (a) estimating the proportion rainfall that falls on areas where no gauges are located that are consequently computed as having zero rain, and (b) replacing them with plausible non-zero rainfalls. The model is tested using daily rainfall from two South African catchments and is found to exhibit the expected behaviour. One of the two parameters of the model is obtained from the rainfall data, while the other has direct physical interpretation.Editor D. Koutsoyiannis; Associate editor C. OnofCitation Ndiritu, J., 2013. Using data-derived perturbations to incorporate uncertainty in generating stochastic areal rainfall from point rainfall. Hydrological Sciences Journal, 58 (8), 1704–1717. 相似文献
575.
In this paper, we use the daily ranges of the vertical magnetic intensity of approximately 76 geomagnetic stations from January 1, 2008 to December 31, 2010 to analyze the spatial and temporal characteristics of Z ranges. The results are summarized as follows: (1) Temporally, we use regressive analysis and FFT analysis to analyze the data. The results show that the Z component daily ranges of all stations have an obvious cyclical variation, the computed Fourier spectra of all data sets have clearly resolved the required periodicities in the data, in the form of distinct peaks at days 365, 183, 22, and 73, and the power spectra of day 365 is the highest in all periods. (2) In terms of spatial variation, the daily ranges show nonlinear variation with latitude in China. The results show the existence of a point of inflexion (maximal value point) nearby at about 25°N, the daily ranges of Z rise from 15°~25°N and have a good linear decrease variation along with 25°~50°N. (3) Compared with the spatial and temporal variations of Z daily ranges with the Sq current inversion, we found that the spatial and temporal characteristics of Z ranges are decided mainly by the spatio-temporal evolution of the Sq current system. (4) If the latitudes of the maximum amplitudes of variation of the vertical component in the geomagnetic quiet days are roughly taken as the latitudes corresponding to the foci of Sq overhead current system, we can see that these latitudes of foci become higher in summer, are lowest in winter and highest during Equinoxes, displaying conspicuous monthly and daily variations. For two successive geomagnetic quiet days, the latitudes of foci may vary ten degrees. 相似文献
576.
577.
578.
陈协珍 《中国天文和天体物理学报》1996,(2)
本文采用天体力学方法,考虑太阳系九大行星对太阳表面局部区域的摄动力,建立了太阳表面受行星起潮力的数值计算模型.利用此模型,针对历史上发生的100个大太阳耀斑事件,计算各耀斑区耀斑发生前后所受行星起潮力的变化.从耀斑发生的时间分布统计得到:在100个耀斑中,有75个耀斑发生在行星综合起潮力合力极大前后三天内.证明行星摄动对太阳活动有调制作用.最后,本文还对太阳活动起源、活动周期等问题进行了简要的讨论. 相似文献