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1.
Experimental observations of the daytime variations of VLF phase and amplitude over a variety of long subionospheric paths have been found to be satisfactorily modelled with a D-region ionosphere, described by the two traditional parameters, H′ and β (being measures of the ionospheric height and the rate of increase of electron density with height, respectively). This VLF radio modelling uses the NOSC Earth–ionosphere waveguide programs but with an experimentally deduced dependence of these two ionospheric parameters on solar zenith angle. Phase and amplitude measurements from several VLF Omega and MSK stations were compared with calculations from the programs LWPC and Modefinder using values of H′ and β determined previously from amplitude only data. This led to refined curves for the diurnal variations of H′ and β which, when used in these programs, give not only calculated amplitudes but also, for the first time, calculated phase variations that agree well with a series of observations at Dunedin, New Zealand, of VLF signals from Omega Japan, Omega Hawaii, NPM (Hawaii) and NLK (Seattle) covering a frequency range of 10–25 kHz.  相似文献   

2.
Two methods for diagnosing ionospheric disturbances using VLF signals received on the DEMETER satellite are considered in connection with two cases of high seismic activity: the method for analyzing a signal reception zone in order to find large-scale spatial variations and the residual signal method used to reveal time variations. Based on an analysis of the VLF signal reception zone, performed in connection with the catastrophic earthquake near Sumatra, it has been found out that the signal amplitude decreased during a month before the earthquake. As a result, it has been concluded that the zone of ionospheric disturbances extends for several thousand kilometers. It has been indicated that the residual signal method showed good agreement between the ground and satellite data when high seismic activity near Japan was analyzed.  相似文献   

3.
Geomagnetism and Aeronomy - Changes in the state of the D and E ionospheric regions lead to variations in the amplitude-phase characteristics of VLF radio signals. The existing theoretical and...  相似文献   

4.
电离层声重波扰动的高频无线电诊断   总被引：1，自引：1，他引：1  
为了充分发挥现代数字式电离层探测仪在电离层结构与优动研究中的潜力,必须在传统的频高图真高换算的基础上,发展新的反演理论和算法.本文介绍了随时空缓变的各向异性电离层介质中无线电波包传播的广义射线方程组,讨论了计算波包射线几何路径以及计算波包参数,如频移、波矢、群时延等沿射线路径变化的传播正问题,并详细讨论了根据波包参量的测定值反演介质结构和扰动伏态的传播反问题.文中若干实验实例表明,这种反演理论和算法可用于数字式电离层探测仪记录的分析,它使高频无线电波探测技术成为研究全球电离层声重波一类扰动的有力工具。  相似文献   

5.
The storm period of 8–12 November 2004 offers an opportunity for insight into the phenomena of low-latitude ionospheric structure during geomagnetically disturbed times because of the strength of the disturbances, the timing of the storms, and the instrumentation that was operating during the interval. We will take advantage of these factors to model the ambient ionosphere and the plasma turbulence responsible for radio scintillation within it, using the AFRL low-latitude ambient/turbulent ionospheric model and the storm-time model features described in the companion paper [Retterer, J.M., Kelley, M.C., 2009. Solar-wind drivers for low-latitude ionospheric models during geomagnetic storms. J. Atmos. Solar-Terr. Phys., this issue]. The model plasma densities show very good agreement with the densities measured by the Jicamarca ISR as well as with the total electron content (TEC) measured by the Boston College South American chain of GPS receivers. The detection by the radar of coherent returns from plasma turbulence match well the times of predicted ionospheric instability. The predicted geographic extent of the occurrence of equatorial plasma bubbles was matched by DMSP satellite observations and our forecasts of scintillation strength were validated with measurements of S4 at Ancon and Antofagasta by stations of the AFRL SCINDA network.  相似文献   

6.
Using vertical and oblique radio-sounding data, we analyze the ionospheric and thermospheric disturbances during the magnetic storm that occurred in northeastern Russia on March 17–19, 2015. We consider the heliospheric sources that induced the magnetic storm. During the main and early recovery phases, the midlatitude stations are characterized by extremely low values of electron density at the F2 layer maximum. Using oblique sounding data, we recorded signals that propagated outside the great circle arc. In evening and night hours, no radio signals were found to pass along the Norilsk–Irkutsk and Magadan–Irkutsk paths. The observed ionospheric effects are shown to be caused by a sharp shift of the boundaries of the main ionospheric trough to the invariant latitude 46° N during the main phase of the magnetic storm. The negative ionospheric disturbance during the recovery phase of the storm, which was associated with significant variations in the composition of the neutral atmosphere, led to a change in the mode composition of received radio signals and a decline in observed maximal frequencies in daytime hours of March 18, 2015 by more than 2 times.  相似文献   

7.
基于LWPC和IRI模型的NWC台站信号传播幅度建模分析   总被引：2，自引：0，他引：2       下载免费PDF全文
频率为3~30 kHz的甚低频（VLF,Very Low Frequency）电磁波具有波长长、传播距离远的特点,能够沿地面-低电离层波导进行传播,在通信、导航等许多领域都被广泛应用.基于波导模理论的长波传播模型（LWPC,Long-Wavelength Propagation Capability）能够用于计算甚低频波的传播路径及幅度,进而研究耀斑、磁暴、地震等事件对电离层的扰动.本文利用国际电离层参考模型（IRI,International Reference Ionosphere）对LWPC中电子密度和碰撞频率进行改进,并将模拟结果与武汉大学VLF接收机实际观测到的NWC （North West Cape）台站信号幅度进行比较分析,结果表明改进后LWPC模型得到的幅度及变化趋势与实际值更加接近.LWPC模型给出的电子密度与IRI模型得到的电子密度在日间基本一致,但是在夜间存在差异,造成夜间部分区域NWC台站信号幅度的差异性,验证了电离层电子密度对于VLF信号传播具有的重要影响.传播路径上的晨昏变化也可以引起VLF信号幅度分布的突变,在日出和日落时间段内存在明显的过渡区域.基于IRI模型的LWPC,改善了VLF电波传播过程的预测分析效果,提供了一种长波导航通信质量的评估方法.  相似文献   

8.
Results of the spectral measurements of ionospheric noise in the meter band are presented. The events lasting several milliseconds (the emission maximum of which drifts upward (in frequency), is reflected (stops), and drifts downward) have been distinguished. Moreover, multiple harmonics are observed. The frequency-time structure of such events have been considered from the viewpoint of registration of the electron beam synchrotron emission harmonics at ionospheric altitudes in the geomagnetic field. The model calculations of the frequency-time structure of ionospheric radio noise bursts drifting in frequency have been performed taking into account the measurement conditions. It has been indicated that the model electron radio noise bursts agree with the measured bursts reflecting from the ionosphere at altitudes of 100–180 km. The model of the monoenergetic beam of electrons precipitating from the radiation belt (L ～ 2.0–2.8) into the ionosphere has been proposed.  相似文献   

9.
The paper discusses how the trajectory calculation method can be used to solve the problem of locality determination of shortwave (SW) emission sources. The dependence of the electron concentration on the coordinates is specified using the SPIM model; it is corrected using the ionospheric solar activity index, which is specified with the help of maps of total electron content. We suggested a variant of how a regional map of the total electron content can be plotted according to measurements of signals from GLONASS/GPS navigation systems. It is shown that the trajectory calculation method, coupled with an adjustable ionospheric model, allows for a more exact locality determination of SW radio emission sources.  相似文献   

10.
We present the results of studies of the subauroral and mid-latitude ionosphere variations in the north-eastern region of Asia. We used the data from network of vertical and oblique-incidence sounding ionosondes and optical measurements. Long-term experiments on the radio paths Magadan–Irkutsk and Norilsk–Irkutsk were carried out within the period 2005–2007. Vertical sounding stations operated in standard regime. Observation of airglow near Irkutsk was provided by the zenith photometer that measured intensities of 557.7 and 630.0 nm atomic oxygen emissions. The results may be summarized as follows. (1) Large daytime negative disturbances are observed during the main and recovery phases mainly at high latitudes, whereas the positive disturbances observed during the main phase at mid latitudes. The disturbances changed their sign between Yakutsk and Irkutsk. (2) During the main and recovery storm phases the fall of foF2 associated with the equatorward wall of the main ionospheric trough is observed in the afternoon and evening. (3) Fluctuations of the electron density more intensive at mid latitudes during the storm main phase are observed during all considered periods. They are classed as traveling ionospheric disturbances (TID). Such sharp gradients of electron density are responsible for the strong changes in the characteristics of the radio wave propagation, particularity MOF. (4) A large-scale ionospheric disturbance is noted at the meridional chain of ionosonds in December 2006 as the sharp increase of foF2. It appears in the evening in the minimum of Dst at high latitude and propagate to equator. (5) A maximum of 630 nm emission above Irkutsk corresponds to the foF2 increase. (6) The obtained experimental data on the net of vertical and oblique-incidence sounding with high time resolution show that such net is the effective facility to study the conditions of the radio wave propagation and can be used for the diagnostic of the ionosphere.  相似文献   

11.
This work investigates the occurrence of disturbances across a wide range of VLF and LF frequencies received prior to a seismic event (Mw = 4), that took place on May 12th 2012, the epicenter of which was very close (14 km) to the VLF/LF station. The signals analyzed were emitted from five VLF and five LF European transmitters. This seismic event produced precursory ionospheric disturbances, identified as spectral distortion, three days before its occurrence, providing a distinct pattern open to further investigation. Although the basis of the ionosphere interaction with seismic phenomena has been well documented in previous studies, the close proximity of the receiver to the seismic event provides a new perspective to this study. The monitored signals have undergone normalization and then they have been processed by means of the Hilbert-Huang Transform. Diagrams of the signals relevant to the phenomena are presented and the disturbances that are present in the raw data are accentuated through further processing.  相似文献   

12.
This paper reports on the detailed spatial structure and temporal dynamics of the ionospheric perturbations associated with the huge 2004 Mid-Niigata earthquake in Japan. The terminator time method in VLF/LF subionospheric propagation has been used to deduce the presence and dynamics of the seismo-ionospheric perturbations by making full use of our Japanese VLF/LF network observations. It is found that significant shifts were observed in terminator time for some selected paths, a few to several days before the earthquake, and we obtained the anisotropic shape of the inferred ionospheric perturbation likely elongated along the fault lines there. The temporal dynamics of inhomogeneity of the perturbations is suggested on the basis of a comparison of the observed terminator time shift and theoretical full-wave computations (2D FDTD and 3D full-wave scattering).  相似文献   

13.
通过大功率ELF/VLF调幅高频波能有效地扰动低电离层,形成等效的ELF/VLF电离层虚拟天线,用来辐射ELF/VLF波,所辐射出的低频信号可以进入中性大气层形成地球-电离层波导.本文基于调制加热模型,采用全波有限元算法计算由人工调制电离层所形成的电偶极矩所辐射出的ELF波在水平分层电离层中的波场,计算结果将与地面观测结果进行比较.模拟结果表明,所辐射出的ELF波在电离层中形成一个窄的准直波束,海面所能接收到的ELF信号强度为pT量级,并且频率越低,海面所接收到的场强就越小,与HAARP实验数据一致.结果还表明,低纬电离层对低频信号的传播衰减较大,并且所能透射出电离层的角度小,因此高纬地区更适合地球-电离层波导的激发.  相似文献   

14.
Transient amplitude and phase perturbations on subionospheric VLF signals, known as the Trimpi effect, are caused by the scattering of VLF radiation from localized ionization enhancements in the nighttime D-region. The patches of ionization are due to precipitation from the radiation belts of keV electrons, that is induced by lightning-generated whistlers.This work is concerned with the numerical simulation of such VLF perturbations, termed LEP (lightning-induced electron precipitation) or classic Trimpis. Two different codes are used to compute the VLF propagation in the Earth-ionosphere waveguide in the presence of a D-region inhomogeneity. The first is based on mode theory, and the second on the FDTD (finite-difference time-domain) method. Both codes are two-dimensional and, therefore, relevant only to LEP events lying on the transmitter-receiver great circle path (TRGCP). A method of simulation is proposed to interpret quantitatively VLF amplitude and phase changes in terms of the approximate location and size of the associated ionospheric perturbation along the TRGCP. The method is applied to LEP Trimpis observed at Poitiers (L = 2) on signals from the NAA and GQD transmitters. Results are discussed in the light of the information that may be deduced from the high-resolution analysis of VLF temporal signatures. A sequence of simultaneous LEP Trimpis observed at Poitiers on three widely separated transmission paths is studied; two alternative interpretations are proposed.  相似文献   

15.
低纬地区电离层电流的人工调制数值模拟   总被引：6，自引：3，他引：3       下载免费PDF全文
利用高频泵波能对低电离层进行有效的人工扰动.采用ELF/VLF调幅高频电波对电离层进行加热,电子温度会随着调制频率振荡,并引起电导率周期性变化,从而使加热区内电离层电流周期性变化,形成等效的ELF/VLF电离层虚拟天线,辐射调制频率范围内的无线电波.早期的电离层人工调制研究主要集中在高纬和极区,本文讨论低纬地区电离层人工调制的可能性.本文的理论研究和数值模拟结果表明,低纬地区低电离层电导率在周期性加热的条件下能有效地被调制,使加热区域形成ELF/VLF波的电流辐射源,并分析了不同加热参数和入射条件对调制效果的影响.  相似文献   

16.
The possibility of determining the field of critical frequencies of the ionospheric F2 layer (foF2) using the maps of the total electron content, constructed based on the registration of signals from satellite radio navigation system of the GPS and GLONASS types, is considered. The calculation of foF2 is based on the SPIM (Standard Plasmasphere-Ionosphere Model) model specifying the ionospheric index of solar activity, which is determined at grid points of the map of the total electron content. The proposed method has been verified using the data of the hourly maps of the total electron content in the North American region during September 1–7, 2005. The variations in the critical frequencies for Boulder and Dyess sites, selected from the reconstructed foF2 maps, were compared with the data of the vertical sounding. The average error is ～10% during the entire period of measurements. The conclusion has been drawn that the proposed method can be used as an ionospheric support of HF radiocommunication in the cases when errors of tenths of MHz in foF2 values are permissible.  相似文献   

17.
基于低电离层加热理论和甚低频电波在地-电离层波导中传播理论,建立低电离层扰动对甚低频电波传播影响的分析模型,并利用实验数据验证了该模型的正确性.据此模型,研究了加热功率、加热波极化以及背景参数所导致的低电离层扰动对不同频率甚低频电波传播的影响.结果表明,低电离层扰动越强,则通过该区域内甚低频波幅度和相位的相对变化越强,通过研究地-电离层波导甚低频信号通过人工扰动区域后幅度和相位的变化,可望用于诊断人工电离层扰动强度.  相似文献   

18.
银河宇宙线是电离层D层的重要电离源之一,它的急剧变化会使D层电子密度发生改变,从而影响VLF波的夜间传播。本文根据在西安接收英国GBR台的VLF波（16kc/s）的相位变化,讨论了在有宇宙线暴（Forbush下降）和强磁暴时,中纬D层电子浓度的变化和相应的VLF波的相位漂移;并根据VLF的相位变化,估计了相应的宇宙线强度变化。由于D层中的宇宙线强度变化通常难于观测,通过VLF波的相位漂移来估计它,这是很有意义的。所以,VLF波的传播效应可能成为间接探测宇宙线强度变化的有用工具。  相似文献   

19.
Time variations in the amplitude and phase of signals of the Russian telecommunication station (the frequency is 25 kHz) on the Arkhangelsk—Kharkov path with a length of about 1600 km on the day of the August 1, 2008 solar eclipse (SE) and on the adjacent days are analyzed. Two types of effects are detected. An increase of the signal amplitude by approximately 32% in comparison with the background days and the 2.1 μs time shift of the signal during 2—2.5 h is referred to the first type. Changes in the spectral composition of the quasiperiodic disturbances in the ionosphere presented the second type of the effects. For spectral analysis of the quasiperiodic variations in the amplitude and phase of the radio signal, the window Fourier transform, adaptive Fourier transform, and wavelet transformation were applied simultaneously. In the period of SE and after it, oscillations with periods of 10—15 min (according to the amplitude data) and also about 10 and 18 min (according to the phase data) were intensified. Based on radio signal characteristics, the parameters of ionospheric disturbances are estimated.  相似文献   

20.
The height-latitude distributions of the electron density in the European Arctic sector of the subauroral and high-latitude ionosphere have been reconstructed based on the data of satellite radio tomography. The reconstructions have been compared with the results of the numerical modeling obtained using the UAM global numerical model and the IRI-2001 empirical ionospheric model. The goal of the paper was to find the degree of adequacy of these models to the observational data during geomagnetic disturbances. The UAM theoretical model adequately reproduces the dynamics of the main ionospheric trough, in particular, the position of its equatorward wall, and to a certain degree better describes the behavior of the high-latitude ion-osphere than the IRI empirical model. The discrepancies are observed in the regions of increased electron density poleward of the trough. To eliminate such disagreements, it was proposed to correct the model input distributions of precipitating high-energy electron fluxes with an energy of about 0.5 keV; i.e., the inverse problem of determining these distributions has been solved for extremely strong geomagnetic disturbances.  相似文献   

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