共查询到20条相似文献，搜索用时 31 毫秒
1.
M. Hayakawa K. Ohta V.M. Sorokin A.K. Yaschenko J. Izutsu Y. Hobara A.P. Nickolaenko 《Journal of Atmospheric and Solar》2010,72(17):1292-1298
The observation of ULF/ELF electromagnetic waves in the frequency range below 50 Hz has been continued at Nakatsugawa (in the Gifu prefecture), Japan since 1998. This paper summarizes anomalous Schumann resonance (SR) phenomena and SR-like line emissions observed at Nakatsugawa in possible association with recent nearby earthquakes (EQs) (the 2004 Mid-Niigata prefecture and the 2007 Noto-Hanto (peninsula) EQs), which have been already described in detail by Ohta et al. (2009). The intensity of particular modes of SR increased before these large EQs and the excitation of other anomalous SR-like line emissions also existed at the frequency shifted by about 2 Hz from the typical SR modes. Since temporal changes of the anomalous SR modes and line emissions are synchronous in time, there might be a possibility that the line emission is a consequence of the anomalous SR. In this paper we propose an interpretation of those anomalous phenomena in terms of excitation of gyrotropic waves due to input wave from below with a band from 15 to 20 Hz as an exciter. The theoretical computational results seem to be generally consistent with the observational finding. 相似文献
2.
Probing the lower ionospheric perturbations associated with earthquakes by means of subionospheric VLF/LF propagation 
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下载免费PDF全文 Masashi Hayakawa 《地震科学（英文版）》2011,24(6):609-637
There have been reports for many years that the ionosphere is very sensitive to seismic effects, and the detection of ionospheric perturbations associated with earthquakes (EQs) attracts a lot of attention as a very promising candidate for short-term EQ prediction. In this review we present a possible use of VLF/LF (very low frequency (3–30 kHz)/low frequency (30–300 kHz)) radio sounding of seismo-ionospheric perturbations. In order to avoid the overlapping with my own previous reviews, we first show some pioneering results for the Kobe EQ and we try to present the latest results including the statistical evidence on the correlation between the VLF/LF propagation anomalies (ionospheric perturbations) and EQs (especially with large magnitude and with shallow depth), medium-distance (6-8 Mm) propagation anomalies, the fluctuation spectra of subionospheric VLF/LF data (the effect of atmospheric gravity waves, the effect of Earth's tides, etc.), and the mechanism of lithosphere-atmosphere-ionosphere coupling. Finally, we indicate the present situation of this kind of VLF/LF activities going on in different parts of the globe and we suggest the importance of international collaboration in this seismo-electromagnetic study. 相似文献
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Geomagnetism and Aeronomy - The results of the study of simultaneous observations of midlatitude ultra low frequency (ULF) noise emissions in the frequency range of 0–7 Hz and disturbances in... 相似文献
5.
Sarita Sharma Swati Singh Raj Pal Pundhir Devbrat Singh Birbal 《Geomagnetism and Aeronomy》2021,61(4):619-631
Geomagnetism and Aeronomy - The data related to lithospheric electromagnetic emissions such as ultra low frequency (ULF, f = 0.01 Hz–10 Hz) and very low frequency (VLF, f =... 相似文献
6.
M. Hayakawa Y. Kasahara T. Nakamura Y. Hobara A. Rozhnoi M. Solovieva O.A. Molchanov 《Journal of Atmospheric and Solar》2010,72(13):982-987
The long-term data during seven years from January 2001 to December 2007, as observed by the Pacific VLF/LF network consisting of several Japanese stations and one station in Kamchatka, are extensively utilized to perform a statistical correlation study between the lower ionospheric perturbations as detected by subionospheric propagation and earthquakes (EQs). In this paper, we adopt a physical parameter, the maximum seismicity intensity observed (I) to define the strength of an EQ unlike the previously and conventionally used EQ magnitude and depth, which is a combined effect of EQ magnitude and depth, together with the Earth’s surface information and geological condition around the EQ epicenter. After considering EQs only take place on the land because of the use of seismicity and by using the superimposed epoch analysis, it is found for the larger EQs with I from 5 to 7 (we feel serious trembling and we expect serious damage) that the most important VLF/LF parameter, trend (nighttime average amplitude), shows a definite decrease about 10 days before the EQ by exceeding 2σ (σ: standard deviation) criterion; the dispersion shows a maximum about 10 days before the EQ but not exceeding 2σ line and finally the nighttime fluctuation shows an enhancement about 10 days before the EQ (with exceeding the 2σ level). A definite statistical correlation is confirmed between the ionospheric perturbations and I when I is strong enough in a range from 5 to 7. Whereas, there is no significant correlation between the two when I is in a range from 3 to 4. Finally, together with the corresponding results for EQs in the sea, but close to the land, these results are discussed in the light of lithosphere–ionosphere coupling mechanism. 相似文献
7.
Poleward-moving auroral forms, as observed by meridian-scanning photometers, in the vicinity of the cusp region are generally assumed to be the optical signature of flux transfer events. Another class of quasi-continuous, short period (1–2 min) wave-like auroral emission has been identified, closely co-located with the convection reversal boundary in the post-noon sector, which is similar in appearance to such cusp aurora. It is suggested that these short period wave-like auroral emissions, the optical signature of boundary plasma sheet precipitation in the region 1 field-aligned current system, are associated with ULF magnetohydrodynamic wave activity, which is observed simultaneously by ground magnetometer stations. This association with ULF wave activity is strengthened by the observation of several harmonic frequencies in the pulsation spectrum, each an overtone of the fundamental standing wave resonance frequency. 相似文献
8.
V.M. Sorokin Yu.Ya. Ruzhin A.K. Yaschenko M. Hayakawa 《Journal of Atmospheric and Solar》2011,73(5-6):664-670
Observational data of the seismic related VHF radio emissions at 41 and 53 MHz obtained at the four stations of Create Island are presented. The epicenter of EQs is located at the distance more than 300 km behind the horizon. It was shown that VHF radiation is generated at the altitudes 1–10 km in the atmosphere over the epicenter of EQs. The theory of generation of electromagnetic radiation by random electric discharges was developed. These discharges are excited by DC electric field enhanced up to the breakdown value in the atmosphere. The field is connected with the electric current flowing in the atmosphere–ionosphere circuit, whose source is generated by convective transport of charged aerosols, which are injected in the atmosphere by soil gases during the enhancement of seismicity. Calculations of the spectrum of electromagnetic radiation are derived, and the theoretical results are confirmed by observation data. 相似文献
9.
Summary Using methods of numerical modelling of the propagation of ULF waves through the ionosphere, the characteristics of the vertical flux of electromagnetic energy are analysed in the ULF range — at the outer boundary of the modelled ionosphere (altitude 1000 km) the reflexibility and penetrability of the energy, at the Earth's surface the transmissivity of the energy. The existence of two frequency bands is proved within the ULF range with different forms of ionospheric wave filtration: a) The band of extremely low frequencies, f<0.1–0.2 Hz (pc3–5 and Pc2 pulsation ranges) with a mirroring effect of the ionosphere-Earth system, but with small absorption; b) the band f>0.2 Hz (the Pc1 range) with increased absorption, but with resonance windows and wave emissions with a very well defined frequency structure. 相似文献
10.
基于法国DEMETER卫星观测的超低频(ULF)电场波形, 本文提出了更简单易实施的ULF电场扰动预处理方法. 利用该方法, 对文献中已报道的2010年2月27日智利MS8.8地震前的ULF电场扰动进行了更全面的分析. 结果表明: 已报道的20°S—40°S地磁纬度带内的ULF电场扰动并非仅出现在最靠近震中的半轨道, 而是出现在较大的经度范围内. 大范围ULF电场扰动的区域正好位于南大西洋异常区, 很可能受到该区域异常磁场的影响. 南大西洋异常中心区域的ULF电场扰动表现出共轭特征, 即在南北地磁纬度20°—40°范围内ULF电场均出现约5 mV/m的扰动, 北纬地区的ULF电场扰动幅度相比南纬地区更小. 而在南大西洋异常中心区域外的ULF电场扰动则仅在20°S—40°S地磁纬度带内出现, 在其共轭区并未观测到ULF电场扰动. 这可能是由于南大西洋异常中心区域外的ULF电场扰动幅度比中心区域更小所致, 在电离层中由于碰撞效应更易被衰减, 因此ULF电场扰动无法传播至其共轭区. 本文的方法和结果可为后续更全面地分析卫星在电离层高度记录的ULF电场扰动提供参考. 相似文献
11.
Ultra low frequeney electromagnetic wave anomaly and its spectrum characteristics before earthquakes
ＵｌｔｒａｌｏｗｆｒｅｑｕｅｎｅｙｅｌｅｃｔｒｏｍａｇｎｅｔｉｃｗａｖｅａｎｏｍａｌｙａｎｄｉｔｓｓｐｅｃｔｒｕｍｃｈａｒａｃｔｅｒｉｓｔｉｃｓｂｅｆｏｒｅｅａｒｔｈｑｕａｋｅｓＪｉａｎ－ＧｕｏＨＡＯ；Ｙｕｎ－ＦｕＺＨＡＮＧ；Ｈｕａｉ－ＷｅｎＰＡＮ；... 相似文献
12.
Recent satellite and ground-based observations prove that during the formative period of earthquakes VLF/LF and ULF electromagnetic emissions are observed in seismogenic areas. This work offers an original model of self-generated electromagnetic oscillations of local segments of the lithospheric origins of the emissions. In the paper, the seismogenic area is considered to be an oscillatory-distributed system. This model simplifies physical analyses of the nonlinear effects and qualitatively explains the mechanisms that generate very low frequency electromagnetic waves in the period prior to an earthquake. 相似文献
13.
Recent work suggests that the quasi-periodic (QP) modulation \sim10-50 s of naturally occurring ELF-VLF radio emissions (\sim0.5-5 kHz) is produced by the compressional action of Pc3 magnetic pulsations on the source of the emissions. Whilst it is generally accepted that these magnetic pulsations have an exogenic source, it is not clear what the mechanism of their generation is. A study of QP emissions observed during 1988 at Halley, Antarctica, in conjunction with IMP-8 satellite solar wind data, shows that the occurrence and modulation frequency of the emissions are strongly dependent upon the direction and strength of the IMF, respectively. The observed relationships are very similar to those previously reported for Pc3 pulsations associated with upstream ion-cyclotron resonance, involving proton beams reflected at the bowshock. In comparing the observed QP modulation frequencies with upstream wave theory, agreement was found by considering wave excitation exclusively associated with a proton beam reflected from a position on the bowshock at which the shock normal is parallel to the ambient IMF direction. Other geometries were found to be either impropitious or uncertain. The work indicates the useful diagnostic role QP emissions could play in the study of compressional ULF waves in the upstream solar wind and in monitoring the IMF conditions responsible for their generation. 相似文献
14.
1996年11月19日新疆和田地区发生了ML=7.1地震. 在这次地震发生前,观测到了地震的超低频（ULF）电磁辐射前兆. 电磁辐射前兆的特点是电位漂移、极化椭圆主轴的垂直方向指向震中和大幅度的电磁辐射. 本文根据电磁辐射特征建立了地震电磁辐射前兆垂直电偶极子模型,并且给出了观测结果的物理解释. 偶极子产生一个不稳定的静电场使水平分量的电位日均值发生明显漂移,震前电偶极子中电荷复合放电产生的随机弱电磁噪声造成在ULF频段上水平分量偏振主轴方向偏转. 喀什台站和安西台站观测到的电势比值与模型估计值相近,从水平分量判断出偶极子间电流方向向下,与垂直电偶极子模型一致. 相似文献
15.
A type of relatively low frequency ULF magnetic disturbance has been generally observed by the magnetic induction-meter since
it’s operation at Baijiatuan observatory in Beijing. As the amplitudes and frequencies of such disturbance signals change
with time and are different from the disturbances produced by some man-made magnetic sources, therefore they are usually taken
as a kind of earthquake precursors for ULF electro-magnetic emission. However, a comparative analysis with magnetic storms
on the magnetogram obtained by variometerat the same station indicates that such signals always occur in the period of magnetic
storm occurrence and so far we have not found the cases where such signals occur with no magnetic storms, therefore this kind
of ULF magnetic disturbances should not be taken as a ULF earthquake precursors of the electromagnetic emission at present.
The main features of such signals are as follows: the signals occur discontinuously during storms and the duration of each
time section with such signals and the occurrence rates of the sections and the disturbance amplitudes are usually related
to the types and intensities of storms. The wave form characteristics of the ULF disturbance are also related to the types
of storms. Generally, the amplitudes and durations for SC storms are stronger and longer respectively than those for GC stroms,
and if a storm is with largerK index, then relatively large amplitudes and higher rates and longer durations as well as variable frequencies will be observed
andvice versa. Most of the start time and the time section with strongest disturbance recorded by the ULF unit and by the variometer are
not consistent with each other, and the same one is only about 44%. The periods and intensities of such disturbance signals
are in the ranges of few to several seconds and 0.04–8 nT respectively. The predominant frequency is about 0.06 Hz and certain
energies are also distributed on the harmonic frequencies.
Contribution No. 95A0063, Institute of Geophysics, SSB, China. 相似文献
16.
Results of Russian experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere using the EISCAT facilities 总被引：1，自引：0，他引：1
N. F. Blagoveshchenskaya T. D. Borisova M. T. Rietveld T. K. Yeoman D. M. Wright M. Rother H. Lühr E. V. Mishin C. Roth 《Geomagnetism and Aeronomy》2011,51(8):1109-1120
We present the results of complex experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere
using the European Incoherent Scatter Scientific Association (EISCAT) facilities. During the ionospheric F-region heating by powerful extraordinary (X-mode) polarized HF radiowaves under the conditions of heating near the critical
f
H frequency f
H ≈ f
x
F2 of the extraordinary wave of the F2-layer, we were first to detect the excitation of intense artificial small-scale ionospheric irregularities (ASIs), accompanied
by electron temperature increases by approximately 50%. The results of coordinated satellite and ground-based observations
of the powerful HF radiowave impact on the high-latitude ionosphere are considered. During ionospheric F-region heating by powerful HF radiowaves of ordinary polarization (O-mode) during evening hours, the phenomenon of ion outflow
accompanied by electron temperature increases and thermal plasma expansion was revealed. Concurrent DMSP-F15 satellite measurements
at a height of about 850 km indicate an O+ ion density increase. The CHAMP satellite observations identified ULF emissions at the modulation frequency (3 Hz) of the
powerful HF radiowave, generated during modulated emissions of the powerful HF radiowave of O-polarization and accompanied
by a substantial increase in the electron temperature and ASI generation. 相似文献
17.
On the Generation of ULF Magnetic Variations by Conductivity Fluctuations in a Fault Zone 总被引：1，自引：0，他引：1
G. D. Egbert 《Pure and Applied Geophysics》2002,159(6):1205-1227
v--vPrior to the October 18, 1989 Loma Prieta Ms 7.1 earthquake, Fraser-Smith et al. (1990) recorded a 10-100 fold increase in ultra-low frequency (ULF) magnetic fields near the earthquake epicenter. Several mechanisms for generation of these ULF fields by fluid flow in the earth have been advanced, but all appear to require unrealistic fluid velocities or hydraulic permeabilities to match the observations. As an alternative explanation, Merzer and Klemperer (1998) proposed that the increase in ULF magnetic fields could result from induced electric currents flowing in a fault-zone made temporarily much more electrically conductive by stress-induced reorganization of pore geometry. Using a numerical model we show that while this mechanism could produce a significant increase in ULF variations, mutual induction between the fault zone and the surrounding crust would probably limit the amplitude increase to levels well below those observed at Loma Prieta. We consider a variant on this quasi-static conductive fault zone model in which low frequency telluric currents are modulated by small higher frequency variations of bulk fault zone conductivity. We show that because the spectrum of natural EM variations is red, substantially larger relative increases in ULF magnetic fields could be produced by this mechanism with even small conductivity fluctuations at these frequencies. These variations would be easy to detect with a well-designed experiment, if they occurred. In principle this mechanism could explain the Loma Prieta ULF observations, however the magnitude of conductivity fluctuations that would be required to match the very large reported amplification factors still appears to be too large to be physically plausible. 相似文献
18.
19.
K. Morrison M. J. Engebretson J. R. Beck J. E. Johnson R. L. Arnoldy L. J. Cahill Jr. D. L. Carpenter M. Gallani 《Annales Geophysicae》1994,12(2-3):139-146
The spatial extent and temporal behaviour of quasi-periodic (QP) intensity modulations of 0.5-2 kHz ELF-VLF signals were investigated in a comparative study of data collected at the Antarctic stations of South Pole (L=14), Halley (L=4), and Siple (L=4). Frequently, the waveforms of ELF-VLF signals simultaneously received at each site were identical. Although of similar frequency structure, the waveforms of the accompanying Pc3 magnetic pulsations did not show a one-to-one association. Whereas both are dayside phenomena, QP emissions occur over a smaller range of local times, and have a maximum of occurrence later in the day closer to local noon. QP emissions are identified with the periodic modulation of the electron pitch-angle distribution by the propagation of ULF compressional fast-mode waves through a region. However, contrary to previous ideas, rising-tone emissions do not represent the frequency-time signatures of such waves. In addition to generation close to the equatorial plane, we propose an additional high-latitude source of QP emissions. These emissions are associated with regions of minimum B produced by the dayside compression of the magnetosphere close to the magnetopause. Model magnetic field calculations of these minimum-B regions as a function of magnetic local time and invariant latitude are presented. 相似文献
20.
震前电磁场和大地自电位的异常是重要的地震前兆现象．在零磁空间对超低频段的磁场和自电位的变化进行了岩石破裂的实验研究，细致地揭示出电场、磁场出现异常变化的全过程，对深入认识超低频电磁信号的微观机理具有重要的意义．实验发现，岩石受力后应变、电位和磁场的缓慢变化在空间分布上是首先在近破裂源处出现，继而随裂纹的发展而改变位置；在时间序列上先出现自电位异常，然后是超低频磁场的变化；在异常形态上，超低频电磁信号呈现出早期、中期、晚期3个阶段的明显差异．研究表明，岩石微破裂引起裂隙尖端处的电荷分离. 静电荷在局部区域的积累和运移，导致了自电位的脉冲状变化；而在主破裂阶段，积累电荷的急速运动形成瞬间电流，激发了脉冲式的磁场异常．本文详细介绍了这一综合实验的技术步骤和观测结果，并对地震电磁前兆的微观机理进行了探讨． 相似文献