共查询到20条相似文献，搜索用时 31 毫秒
1.
A. V. Medvedev K. G. Ratovsky M. V. Tolstikov D. S. Kushnarev 《Geomagnetism and Aeronomy》2009,49(6):775-785
The method for studying the spatial-temporal structure and propagation characteristics of traveling ionospheric disturbances,
using the spectral and cross-correlation analysis of electron density disturbances at different altitudes, obtained with the
incoherent scatter radar and vertical sounding ionosonde, is considered. Different algorithms for detecting traveling ionospheric
disturbances and calculating the total vector of the disturbance propagation velocity are presented. The results of the method
application have been considered in detail, using September 11, 2005, as an example. 相似文献
2.
E. D. Tereshchenko M. O. Kozlova O. V. Evstafiev B. Z. Khudukon T. Nygrén M. Rietveld A. Brekke 《Annales Geophysicae》2000,18(9):1197-1209
Results on heating the ionospheric F region above Tromsø, Norway are presented. The ionosphere was monitored by satellite tomography and amplitude scintillation methods as well as the EISCAT incoherent scatter radar. No effect of heating was observed in the daytime. In the evening and in the pre-midnight sector, noticeable tilts of the F region were observed during heating periods. The tilts overlapped the heating cone, where the electron density decreased and irregularities exceeding 10 km in size appeared. Between the heating periods the F layer was restored to its horizontal shape. The anisotropic parameters of small-scale irregularities with scale lengths of hundreds of metres were also determined. It was found that the perpendicular anisotropy points in the direction of F region plasma flow. In some cases the results can be explained by assuming that the small-scale irregularities were generated within the heating cone and drifted out of the heating region where they were subsequently observed. 相似文献
3.
本文基于IRI模型、地面数字测高仪和GNSS TEC数据,提出了一种利用经验正交函数(Empirical Orthogonal Function,简称EOF)估算顶部电离层电子密度剖面的方法,并将其应用于美国Millstone Hill测高仪和GNSS数据以估算顶部电离层电子密度剖面.通过将估算的临界频率、峰值高度、400km以上电子密度分别与测高仪实测临界频率、测高仪实测峰值高度以及非相干散射雷达实测400km以上电子密度作对比以对方法的有效性进行验证.统计结果显示估算临界频率、峰值高度与测高仪实测数据基本一致,400km以上估算电子密度相较于非相干散射雷达实测的绝对误差平均值仅是测高仪推算400km以上电子密度绝对误差平均值的一半左右.所以本文提出的方法可以更加精确地估算顶部电离层电子密度. 相似文献
4.
A series of experiments on modification of the ionosphere by a powerful ground HF transmitter was performed using the EISCAT
heating facility in order to generate artificial magnetic pulsations in the frequency range 0.1–3 Hz. In several cases, the
ionospheric electric field and the electron density vertical profile were measured with the EISCAT incoherent scatter radar.
The measurement of the background values of the ionospheric parameters made it possible to verify the numerical model for
generating artificial emissions. The calculated amplitudes of magnetic pulsations correspond to the values measured on the
Earth’s surface. However, the model cannot explain the sporadic nature of artificial signals, which indicates that this model
is incomplete. Disturbances of the neutral particle density in the upper atmosphere are one of the possible causes explaining
a difference between the calculations and the experimental values. The numerical simulation indicated that the amplitude variations
caused by such disturbances can be 20%. For artificial emissions whose intensity is comparable with the intensity of artificial
noise, variations in the neutral components can result in the disappearance of an artificial signal on the spectrogram. 相似文献
5.
The inversion of incoherent scatter spectra with a non-Maxwellian electron distribution 总被引：1，自引：0，他引：1
Bin Xu Zhange Wang Kun Xue Jian Wu Zhensen Wu Jun Wu Yubo Yan 《Journal of Atmospheric and Solar》2010,72(5-6):492-497
With the action of powerful, high-frequency (HF) radio waves, the ionosphere plasma will depart from the equilibrium state and the non-Maxwellian distribution function can be produced. An artificial field-aligned irregularities (AFAI) model is introduced to describe the distortion from the normal shape, and the measured data are analyzed with this model during ionosphere heating at a 186-km height on August 15th, 2006. The electron temperature and density deduced from the AFAI model are compared with the results obtained from a standard procedure. The inversion of the electron temperature is evidently affected, and the overestimation is up to 22.9%. Owing to the introduction of the AFAI model, the new irregularities’ parameters can be obtained, which implies that incoherent scatter radar is feasible as a ground-based instrument to diagnose information on irregularities. 相似文献
6.
The results of studying the ionospheric response to solar flares, obtained from the data of the GPS signal observations and incoherent scatter radars and as a result of the model calculations, are presented. It is shown that, according to the GPS data, a flare can cause a decrease in the electron content at altitudes of the topside ionosphere (h > 300 km). Similar effects of formation of a negative disturbance in the ionospheric F region were also observed during the solar flares of May 21 and 23, 1967, with the Arecibo incoherent scatter radar. The mechanism by which negative disturbances appear in the topside ionosphere during solar flares has been studied in this work based on the theoretical model of the ionosphere-plasmasphere coupling. It has been indicated that the formation of the electron density negative disturbance in the topside ionosphere is caused by an intense removal of O+ ions into the overlying plasmasphere under the action of an abrupt increase in the ion production rate and thermal expansion of the ionospheric plasma. 相似文献
7.
First EISCAT measurement of electron-gas temperature in the artificially heated D-region ionosphere 总被引：4，自引：0，他引：4
The ionospheric electron gas can be heated artificially by a powerful radio wave. According to our modeling, the maximum effect of this heating occurs in the D-region where the electron temperature can increase by a factor of ten. Ionospheric plasma parameters such as Ne,Te and Ti are measured by EISCAT incoherent scatter radar on a routine basis. However, in the D-region the incoherent scatter echo is very weak because of the low electron density. Moreover, the incoherent scatter spectrum from the D-region is of Lorentzian shape which gives less information than the spectrum from the E- and F-regions. These make EISCAT measurements in the D-region difficult. A combined EISCAT VHF-radar and heating experiment was carried out in November 1998 with the aim to measure the electron temperature increase due to heating. In the experiment the heater was switched on/off at 5 minute intervals and the integration time of the radar was chosen synchronously with the heating cycle. A systematic difference in the measured autocorrelation functions was found between heated and unheated periods. 相似文献
8.
C. N. Mitchell I. K. Walker S. E. Pryse I. Kersley I. W. McCrea T. B. Jones 《Annales Geophysicae》1998,16(11):1519-1522
Experimental results are presented from ionospheric tomography, the EISCAT Svalbard radar and the CUTLASS HF radar. Tomographic measurements on 10 October 1996, showing a narrow, field-aligned enhancement in electron density in the post-noon sector of the dayside auroral zone, are related to a temporal increase in the plasma concentration observed by the incoherent scatter radar in the region where the HF radar indicated a low velocity sunwards convection. The results demonstrate the complementary nature of these three instruments for polar-cap ionospheric studies. 相似文献
9.
Large-scale disturbances in the ionospheric plasma, caused by the spacecraft launches from the Baikonur site, have been analyzed based on the incoherent scatter radar measurements. The altitude-time dependences of the main plasma parameters (electron density and electron and ion temperatures at altitudes of ～100–600 km) have been analyzed. It has been indicated that spacecraft launches and flights are accompanied by the generation of wave-like disturbances in all considered parameters. It has been obtained that the relative amplitudes of these wave-like disturbances were usually 0.03–0.10, and the variation period was 20–60 min. The variations were shifted in phase relative to each other. The propagation velocities of wave-like disturbances were ～0.5–0.6 and 1.5–2 km/s. The up-to-date methods of spectral analysis, including the wavelet analysis, were used to estimate the parameters of the wave-like disturbances. 相似文献
10.
Observations of traveling ionospheric disturbances (TIDs) associated with atmospheric gravity waves (AGWs) generated by the moving solar terminator have been made with the Millstone Hill incoherent scatter radar. Three experiments near 1995 fall equinox measured the AGW/TID velocity and direction of motion. Spectral and cross-correlation analysis of the ionospheric density observations indicates that ST-generated AGWs/TIDs were observed during each experiment, with the more-pronounced effect occurring at sunrise. The strongest oscillations in the ionospheric parameters have periods of 1.5 to 2 hours. The group and phase velocities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the group velocity of 300–400 m s–1 that corresponds to the ST speed at ionospheric heights. The high horizontal group velocity seems to contradict the accepted theory of AGW/TID propagation and indicates a need for additional investigation. 相似文献
11.
Results of studying the ionospheric response to solar flares, obtained based on the incoherent scatter radar observations
of the GPS signals and as a result of the model simulations, are presented. The method, based on the effect of partial “shadowing”
of the atmosphere by the globe, has been used to analyze the GPS data. This method made it possible to estimate the value
of a change in the electron content in the upper ionosphere during the solar flare of July 14, 2000. It has been shown that
a flare can cause a decrease in the electron content at heights of the upper ionosphere (h > 300 km) according to the GPS data. Similar effects in the formation of a negative disturbance in the ionospheric F region
were also observed during the solar flares of May 21 and 23, 1967, at the Arecibo incoherent scatter radar. The mechanism
by which negative disturbances are formed in the upper ionosphere during solar flares has been studied based on the theoretical
model of the ionosphere-plasmasphere coupling. It has been shown that an intense ejection of O+ ions into the above located plasmasphere under the action of a sharp increase in the ion production rate and the thermal
expansion of the ionospheric plasma cause the formation of a negative disturbance in the electron concentration in the upper
ionosphere. 相似文献
12.
F. R. E. Forme 《Annales Geophysicae》1999,17(9):1172-1181
We present a model that describes the decay of beam generated Langmuir waves into ion-acoustic waves in the topside ionosphere. This calculation is done within the frame of the weak turbulence approximation. We study the spectral signature of such a process as seen by a VHF incoherent scatter radar. An incoherent scatter (IS) spectrum is characterized by two maxima at kradar and −kradar, the right and left ion lines respectively. It is shown that, for reasonable beam parameters, the parametric decay of beam-generated Langmuir waves can enhance either the right, the left or both ion lines simultaneously. The shape of the spectrum can change drastically on time scale of about 0.1 to 1 s. The role of the beam parameter as well as the ionospheric parameters is also investigated. For a given beam number density, the beam energy or the background density are important to trigger either the left or the right ion line. A large energy spread of the beam or low electron collision frequencies can explain the simultaneous observations of the left and the right ion line. The importance of the electron collision frequency can explain the altitude distribution of the coherent echoes observed by incoherent scatter radars. 相似文献
13.
本文利用经验正交函数（Empirical Orthogonal Function,简称EOF）方法分析了Millstone Hill非相干散射雷达（Incoherent Scatter Radar,简称ISR）近三个太阳黑子周期（1976年2月～2006年4月）的实测电离层160～700 km的电子浓度剖面资料,并分别用Chapman-α函数拟合了平均电子浓度剖面和带有均值的前三阶EOF级数．结果表明：电子浓度剖面的EOF级数的第一阶项主要控制F2层峰值浓度NmF2,第二阶项同时控制F2层的峰高hmF2和等效标高Hm,第三阶项主要控制等效标高Hm．进一步分析了对应的EOF系数的周日变化、季节变化和太阳活动周期变化,这些变化反映了NmF2,hmF2,Hm的气候学变化规律,例如电离层的冬季异常、半年异常等．EOF方法在级数展开方面收敛速度快,很少数低阶项即能反映电子浓度剖面的主要变化,因此可用于提取出电子浓度剖面的主要分布特征及其周日变化与气候学变化特性,并可用于进一步构建相应的经验模式． 相似文献
14.
We propose a mechanism to explain suggested links between seismic activity and ionospheric changes detected overhead. Specifically, we explain changes in the natural extremely low-frequency (ELF) radio noise recently observed in the topside ionosphere aboard the DEMETER satellite at night, before major earthquakes. Our mechanism utilises increased electrical conductivity of surface layer air before a major earthquake, which reduces the surface-ionosphere electrical resistance. This increases the vertical fair weather current, and (to maintain continuity of electron flow) lowers the ionosphere. Magnitudes of crucial parameters are estimated and found to be consistent with observations. Natural variability in ionospheric and atmospheric electrical properties is evaluated, and may be overcome using a hybrid detection approach. Suggested experiments to investigate the mechanism involve measuring the cut-off frequency of ELF “tweeks”, the amplitude and phase of very low frequency radio waves in the Earth–ionosphere waveguide, or medium frequency radar, incoherent scatter or rocket studies of the lower ionospheric electron density. 相似文献
15.
Parameters of field-aligned currents reconstructed by ground-based measurements of magnetic field in the Scandinavian countries (IMAGE) and ionospheric conductivity for specific events of the 6 and 8 December 2004 are represented here. Ionospheric conductivity was calculated from precipitating electron flux measured at DMSP-13 satellite and electron density EISCAT incoherent scattering radar direct measurements. There is a high correlation between field-aligned currents, calculated from DMSP-13 satellite data and field-aligned currents calculated from radar measurements for the December 6, 2004 in the presence of developed ionospheric current system. The comparison of field-aligned currents, reconstructed by the proposed method, with the currents calculated by the variation of magnetic field on the DMSP satellites, confirms correctness of the offered algorithm. 相似文献
16.
A comparison of veloCity measurements from the CUTLASS Finland radar and the EISCAT UHF system 总被引：2，自引：0，他引：2
The CUTLASS Finland radar, which comprises an integral part of the SuperDARN system of HF coherent radars, provides near continuous observations of high-latitude plasma irregularities within a field-of-view which extends over some four million square kilometres. Within the Finland radar field-of-view lie both the EISCAT mainland and EISCAT Svalbard incoherent scatter radar facilities. Since the CUTLASS Finland radar commenced operation, in February 1995, the mainland EISCAT UHF radar has been run in common programme 1 and 2 modes for a total duration exceeding 1000 h. Simultaneous and spatially coincident returns from these two radars over this period provide the basis for a comparison of irregularity drift veloCity and F-region ion veloCity. Initial comparison is limited to velocities from four intervals of simultaneous radar returns; intervals are selected such that they exhibit a variety of veloCity signatures including that characteristic of the convection reversal and a rapidly fluctuating veloCity feature. Subsequent comparison is on a statistical basis. The velocities measured by the two systems demonstrate reasonable correspondence over the veloCity regime encountered during the simultaneous occurrence of coherent and incoherent scatter; differences between the EISCAT UHF measurements of F-region ion drift and the irregularity drift velocities from the Finland radar are explained in terms of a number of contributing factors including contamination of the latter by E-region echoes, a factor which is investigated further, and the potentially deleterious effect of discrepant volume and time sampling intervals. 相似文献
17.
G. L. Gdalevich V. D. Ozerov N. Bankov S. Chapkanov L. Todorieva 《Geomagnetism and Aeronomy》2006,46(4):485-491
The satellite low-latitude and midlatitude measurements of the disturbed postsunset plasma density and electron temperature at altitudes of ～900 km have been compared with the data of incoherent scattering and high-altitude rocket launching at the corresponding local time. It has been found that plasma density disturbances are independently caused by the turbulent interaction between atmospheric masses of gas and plasma ascending from heated and not yet cooled ionospheric regions and cooling masses descending from protonospheric altitudes. Plasma regions with an energetically nonequilibrium vertical density distribution of the mixture of heavy ion impurity (O+) and major light ions (H+) can simultaneously appear, as a result of which the gradient-drift impurity instability is generated. If this instability is sufficiently developed, there appears an anomalous ion drift with the formation of real plasma regions of decreased density. All these phenomena generate different irregularities in a wide range of scales: from several tens or hundreds of meters to several hundreds of kilometers. 相似文献
18.
E. D. Tereshchenko B. Z. Khudukon M. O. Kozlova O. V. Evstafiev T. Nygrén M. T. Rietveld A. Brekke 《Annales Geophysicae》2000,18(8):918-926
Results are shown from an experimental campaign where satellite scintillation was observed at three sites at high latitudes and, simultaneously, the F region plasma flow was measured by the nearby EISCAT incoherent scatter radar. The anisotropy parameters of field-aligned irregularities are determined from amplitude scintillation using a method based on the variance of the relative logarithmic amplitude. The orientation of the anisotropy in a plane perpendicular to the geomagnetic field is compared with the direction of F region plasma flow. The results indicate that in most cases a good agreement between the two directions is obtained. 相似文献
19.
T. D. Borisova N. F. Blagoveshchenskaya I. M. Ivanova M. T. Rietveld 《Geomagnetism and Aeronomy》2013,53(1):32-42
The interaction between the Earth’s ionosphere and magnetosphere in a situation when artificial disturbances are generated in the F region of the auroral ionosphere with the EISCAT/Heating facility is studied. An experiment was performed in the daytime when the facility effective radiated power changed in a stepwise manner. Wavelike disturbances with periods of (130–140) s corresponding to Pc4 pulsations were simultaneously registered by the method of bi-static backscatter and with ground magnetometers. The variations in the Doppler frequency shift were correlated with the changes in the facility power. Incoherent scatter radar measurements at a frequency of 930 MHz (Tromsö) and numerical calculations were used in an analysis. It has been indicated that the ionospheric drift of small-scale artificial ionospheric irregularities was modulated by magnetospheric Alfvén waves. The possible effect of powerful HF radioemission on the Alfvén wave amplitude owing to the modification of the magnetospheric resonator ionospheric edge reflectivity and the generation of an outgoing Alfvén wave above the region where the ionospheric conductivity is locally intensified has been considered. 相似文献
20.
J. Watermann O. de la Beaujardière D. Lummerzheim J. Woch P. T. Newell T. A. Potemra F. J. Rich M. Shapshak 《Annales Geophysicae》1994,12(12):1144-1157
Coincident multi-instrument magnetospheric and ionospheric observations have made it possible to determine the position of the ionospheric footprint of the magnetospheric cusp and to monitor its evolution over time. The data used include charged particle and magnetic field measurements from the Earth-orbiting Viking and DMSP-F7 satellites, electric field measurements from Viking, interplanetary magnetic field and plasma data from IMP-8, and Sondrestrom incoherent scatter radar observations of the ionospheric plasma density, temperature, and convection. Viking detected cusp precipitation poleward of 75.5○ invariant latitude. The ionospheric response to the observed electron precipitation was simulated using an auroral model. It predicts enhanced plasma density and elevated electron temperature in the upper E- and F-regions. Sondrestrom radar observations are in agreement with the predictions. The radar detected a cusp signature on each of five consecutive antenna elevation scans covering 1.2 h local time. The cusp appeared to be about 2○ invariant latitude wide, and its ionospheric footprint shifted equatorward by nearly 2○ during this time, possibly influenced by an overall decrease in the IMF Bz component. The radar plasma drift data and the Viking magnetic and electric field data suggest that the cusp was associated with a continuous, rather than a patchy, merging between the IMF and the geomagnetic field. 相似文献