Influence of the ionosphere, modified by powerful oblique radiowaves, on HF radio wave propagation

Variations of HF probe radio wave parameters caused by the influence on the ionosphere of oblique powerful HF radiowaves are analysed. The analysis is made on the data obtained from the original experiments carried out on single-hop paths in the middle and subauroral latitudes. Powerful and probe waves with some difference in frequency were chosen near MUF and were transmitted in the same direction. The polar diagrams of both transmitting systems overlapped in both the horizontal and vertical planes. The results obtained indicate that the ionospheric plasma parameters can be varied by powerful oblique HF radiowaves under certain geophysical conditions.     

Alfven波在低纬电离层中的传播研究

Alfven波在低纬地区电离层的传播有其特殊性,一方面,低纬地区同样存在Alfven速度梯度的巨大变化,导致电离层Alfven谐振器(Ionospheric Alfven resonator, IAR)的形成;另一方面,由于在低纬地区磁倾角很小,所以剪切Alfven波在传播的过程中纬度方向跨度很大,不同纬度电离层参数将共同对其产生影响;并且,由于电离层水平分层,故磁力线与电离层不正交.本文选取双流体力学模型,在忽略场向电场的条件下,利用非正交坐标系,结合IRI07模型与MSISE00模型模拟低纬地区Alfven波的传播,得到其反射及耦合特性.结果表明,低纬地区同样存在电离层Alfven谐振现象,由耦合产生的压缩模有向磁赤道方向传播的趋势,夜间电离层状态相对于白天更适合IAR的形成,谐振频率沿磁力线L值增大单调递增.     

Excitation of ion-acoustic waves in the high-latitude ionosphere

The broadband electrostatic turbulence generally observed in the high-latitude ionosphere is a superposition of nonlocal waves of ion-acoustic and ion-cyclotron types. In the presence of a shear of ion parallel velocity, ion-acoustic modes can be induced by an instability emerging due to an inhomogeneous distribution of energy density. This paper is devoted to the studies of excitation of oblique ion-acoustic wave in background configurations with inhomogeneous profiles of both electric field and ion parallel velocity. A numerical algorithm has been developed, and instability was simulated at various parameters of background plasma. The general possibility of oblique ion-acoustic wave generation by a gradient of ion parallel velocity is shown. In this case, the wave spectrum is found to be broadband, which agrees with satellite observations.     

Specific propagation of radiowaves from the Intercosmos-19 satellite in the region of the nighttime equatorial anomaly crest

It has been indicated how a complex ionogram of topside sounding near the outer slope of the winter southern crest of the equatorial anomaly, where a large NmF2, gradient and a deep hmF2, minimum are observed, is formed. The model latitudinal cross-sectio n of the ionosphere, used to perform trajectory calculations, has been constructed based on the corrected Intercosmos-19 data. The ray trajectories have been modeled using the method of characteristics. It has been indicated that a complex Intercosmos-19 ionogram is formed by an oblique reflection from the equatorial anomaly crest slope (the main trace) and by a strongly oblique reflection from the crest bottom as a result of the wave capture by a large-scale inhomogeneity (the additional trace).     

Local adaptation of the IRI model by data of oblique incidence backscatter sounding

In view of the popularity of using empirical models in implementing SW radio communication at long distances and in problems of target detection, it became necessary to adapt these models to the real state of the ionosphere so that these models could be used in operational work. It is proposed to adapt the IRI model by optimizing the values of the global ionospheric index and the number of solar spots, i.e., the parameters used in the model when calculating the height distribution of electron concentration in the ionosphere, with the involvement of oblique incidence backscatter sounding data. The problem regarding the correctness of the adaptation problem was considered under some restrictions. An estimate of the adaptation error has been obtained.     

高频返回散射扫频电离图的反演

斜向返回探测可以对遥远地区的电离层进行连续监测,是探测电离层的主要手段之一,一般得到返回功率、群路径或时延与频率之间的关系,称为高频返回散射电离图.由于电离图包含了探测路径上电离层状态信息,可以通过对其反演获得电离层结构参数.本文提出了一种新的反演算法,使用模拟退火方法对返回散射扫频电离图前沿进行了反演,并用实际探测数...     

Variations in the horizontal correlation radius of the ionosphere during a magnetospheric substorm

A change in the correlation radius of the ionosphere during the magnetospheric substorm of February 14, 2011, which is considered to be 500 km at midlatitudes, has been estimated. The vertical sounding (VS) data from the St. Petersburg and Sodankyla (Finland) observatories, as well as the data of oblique incidence sounding (OIS) at the Sodankyla-St. Petersburg path with a length of 790 km, have been analyzed. A specific feature of the experiment consisted in that the signals of a VS transmitter from Sodankyla were synchronously received at the receiving point on the OIS path in St. Petersburg. The OIS path reflection point is located at a distance of ～400 km from the VS reflection point. Ionograms typical of the VS and OIS signal reflection points in the ionosphere, the distance between which was slightly smaller than the correlation radius of the ionosphere (500 km), and the data of the Sodankyla and St. Petersburg ionosondes have been compared. It has been indicated that a horizontal correlation radius of 400 km can only be considered acceptable during three disturbance phases: the initial phase before the reconfiguration of the ionosphere; the explosion phase (the disturbance maximum), when only the sporadic Es layer is the reflecting ionospheric layer; and the recovery phase, when a disturbance already ceases and the ionosphere returns to its initial undisturbed state. During other disturbance phases, the correlation radius (if it exists) is much smaller than 400 km.     

SCIPION, a new flexible ionospheric sounder in Senegal

SCIPION is a new state of the art digital sounder that has been developed by France Telecom-CNET for ionospheric monitoring and research. Extensive data processing using DSP technology has resulted in a low power, low cost and full featured system for both vertical and oblique soundings. A SCIPION system is in the process of being installed in Dakar, Senegal, to study HF propagation in the sub-equatorial ionosphere. However, preliminary results have still been obtained during experiments wit a prototype system. In this paper, the system is described and some illustrative examples of its capabilities are shown.     

Ionospheric effects of ground motion: The roles of magnetic field and nonlinearity

Transformation of infrasound to magnetic sound upon propagation from ground level up to the ionosphere is considered. It is shown that upon entering the ionospheric layers at altitudes of order 150–170 km, the wave dynamics changes sharply. Nonlinear effects, including shock formation, are also considered. The shocks are typically formed in a relatively narrow range of altitudes, or not formed at all. Generalization of the model to a case of oblique propagation is briefly considered, and the effects of atmospheric profile variation and of finite plasma conductivity are estimated. Along with providing qualitative insight, the model gives some realistic estimates for waves generated by earthquakes.     

Does the QBO and the Mt. Pinatubo Volcanic Eruption Affect the Gravity Wave Activity in the Lower Ionosphere ?

All existing data (6 years) on gravity wave activity, inferred from the nighttime A3 (oblique incidence on the ionosphere) radio wave absorption measurements in the lower ionosphere on 270 kHz at Prhonice in Central Europe, have been exploited to get information on the effects of QBO phases and the Mt. Pinatubo volcanic eruption on the gravity wave activity in the winter half of the year. There appears to be an enhancement of gravity wave activity in the two winters just after the strong volcanic eruption of Mt. Pinatubo. This enhancement is remarkable for long-period waves (T=2–3 hours). No clear effect of the phase of QBO on the level of gravity wave activity has been found; a possible effect of QBO on the correlations between gravity wave activities in individual period bands is indicated. The results are limited by a relatively short data series; however, no more data will he available.     

Diagnosing the effective parameters of the ionospheric fine structure from statistical characteristics of radio waves in the vicinity of a regular caustic

This paper is concerned with the oblique propagation of decametric radio waves in the ionosphere with random electron density irregularities. Effective parameters are introduced for calculating the influence of irregularities on the wave field structure. A technique is proposed for determining these parameters from measurements of statistical characteristics of the signal in the vicinity of a regular caustic. The technique uses asymptotic expressions obtained using the interference integral method and perturbation theory, as well as matching them to the numerical solution on the basis of the method of characteristics. A global semi-empirical model that is updated for current ionospheric conditions is used to specify the background medium. The proposed technique has been tested using data from a number of mid-latitude paths. Results obtained in this study testify that the technique deserves a practical implementation.     

基于混合遗传算法的斜测电离图参数反演

斜向探测是获取电离层状态信息的重要手段之一,对斜测电离图的反演可以得到电离层的相关结构参数.遗传算法是一种有效的并得到普遍应用的反演方法,该算法的求解不依赖于初值的选择,可以有效地减少反演问题解的非唯一性,但也存在“过早收敛”和局部搜索能力差等缺陷,从而导致反演精度下降,影响反演结果的可靠性.本文提出将基于模拟退火的混合遗传算法应用到斜测电离图的参数反演中,该算法不仅把握总体能力强,且具有较强的局部搜索能力,是遗传算法和模拟退火算法的优势互补.为了验证该算法反演结果的可靠性和稳定性,首先分别采用遗传算法、模拟退火算法和混合遗传算法对合成的电离图进行反演,反演参数包括临界频率,最大电子浓度和半厚度.通过对三种算法反演结果的对比,得出混合遗传算法的反演结果最接近真实值,需要的迭代次数也远远小于其他两种算法;通过改变种群大小和总迭代次数来判断参数值的改变对三种算法反演结果的影响,得出混合遗传算法有效地降低了参数的选取对反演结果的影响.然后用这三种反演算法对实测电离图进行反演,并将它们的反演结果与斜测链路中点的实际垂测数据进行比较,结果显示混合遗传算法84.62%的反演结果可以控制在误差范围之内,高于遗传算法（76.93%）和模拟退火算法（65.38%）.这些都表明了混合遗传算法的反演结果具有较强的可靠性,在反演的寻优能力和稳定性上要明显优于遗传算法和模拟退火算法,对实测电离层图的反演具有很强的借鉴意义和应用价值.     

利用射线追踪研究电离层扰动

基于返回散射探测的电离层扰动电离图,本文建立了一个新的对称的准余弦电离层扰动数学模型.基于这种模型,利用HF射线追踪技术合成了HF电离层返回散射电离图,并利用迭代的技术拟合了高频返回散射设备探测的电离层扰动电离图的Pmin-f曲线(Pmin为最小时延,f为工作频率),从而推断了沿探测路径电离层扰动区域的位置及大小,扰动的临界频率波动的幅度.最后基于这种电离层扰动模型,利用射线追踪技术描述了不同电离层扰动参数下的电波传播情况,研究了其天波传播的跳距、覆盖区域的大小及射线“俘获”等.     

The ionosphere as an Alfven resonator in the Pc1 micropulsation range

Summary A local planar approximation of a stratified, inhomogeneous, anisotropic and dissipative ionosphere is presented as an Alfven quarter-wave plate resonator in the Pc1 micropulsation range. The frequency-amplitude structure of the resonance response of an isotropic Alfven wave on the Earth's surface and at a given altitude in the ionosphere is studied in comparison to standing waves in vacuum above an ideal conductor for a particular model of the ionosphere. An asymmetry in the response was found at both boundary of the resonator, at the Earth's surface and at the given altitude z₀. The results are related to the vertical changes of frequency dispersion in the dissipative medium of the ionosphere and to the vertical profile of the inhomogeneities of the resonator being considered.     

Regional ionosphere modeling in support of IRI and wavelet using GPS observations

Dual-frequency global navigation satellite systems (GNSS) observations provide most of the input data for development of global ionosphere map (GIM) of vertical total electron content (VTEC). The international GNSS service (IGS) develops different ionosphere products. The IGS tracking network stations are not homogeneously distributed around the world. The large gaps of this network in Middle East, e.g., Iran plateau, reduce the accuracy of the IGS GIMs over this region. Empirical ionosphere models, such as international reference ionosphere (IRI), also provide coarse forecasts of the VTEC values. This paper presents a new regional VTEC model based on the IRI 2007 and global positioning system (GPS) observations from Iranian Permanent GPS Network. The model consists of a given reference part from IRI model and an unknown correction term. Compactly supported base functions are more appropriate than spherical harmonics in regional ionosphere modeling. Therefore, an unknown correction term was expanded in terms of B-spline functions. The obtained results are validated through comparison with the observed VTEC derived from GPS observations.     

Detection and analysis of ion-acoustic waves in the ionosphere

Summary Propagating acoustic-like disturbances generated by nuclear explosions have been observed to split in the lower ionosphere. The resulting two disturbances propagate vertically into the upper ionosphere at different speeds, the slower at ordinary sound speed in a neutral medium and the faster at almost twice the speed of sound.The faster disturbance travels at the speed of an ion-acoustic wave in the ionic fluid. Such identification is prohibited theoretically by the large damping, or coupling, of the ionic mode to the neutral particle medium through ion-neutral elastic collisions; however, if inelastic collisions are included in the theory, the principal exothermic charge-exchange and charge-transfer reactions in the ionosphere provide enough additional coherent momentum in the charged particles to offset the losses through elastic collisions. It is shown quantitatively that in some regions of the ionosphere ionacoustic wave propagation can occur almost losslessly.It is possible that under some conditions the ionosphere approaches an unstable chemical equilibrium that is relieved by the spontaneous generation of ion-acoustic wavelets. Various ionospheric observations are examined in which there is some evidence of the effects of ionospheric ionacoustic disturbances.     

Ionosphere as an Indicator of Processes in the Geospace,Troposphere, and Lithosphere

The possible causes of the strong ionospheric day-to-day variability under the influence of processes in the geospace, troposphere, and lithosphere are considered based on the data of the critical frequency of the F2 layer of the ionosphere at two observation stations. It is shown that even in the absence of powerful events, the ionosphere is influenced both “from above” and “from below”; in this case, the ionosphere can respond to an external action as an open nonlinear dissipative system.     

Propagation of HF radiowaves on high-latitude radio paths during the magnetically disturbed period of October 24–28, 2003

The behavior of the HF signal parameters during magnetic storms and substorms has bee experimentally studied simultaneously on the Kiruna-Kirkenes auroral path, Kiruna-Longyearbyen polar path, and Murmansk-St. Petersburg subauroral path. The first two paths are equipped with the instruments making it possible to measure the values of the signal-to-noise ratio, Doppler frequency shift, and elevation angle. The method of oblique sounding of the ionosphere (OSI) was used on the Murmansk-St. Petersburg path. Two substantial substorms, a moderate storm, and an intense storm occurred during the studied period. Some new regularities have been revealed. On the Kiruna-Kirkenes and Kiruna-Longyearbyen paths, the signalto-noise ratio increased (due to the transition from the F ₂ signal reflections to the E _s reflections), the elevation angle increased (due to an increase in the ionospheric F ₂ layer height and a decrease in the critical frequency), and the Doppler shift increased (due to the variations in ionization and the appearance of ionospheric irregularities during a substorm) when the signal was reflected from the F ₂ layer close to the moment of the substorm or storm beginning T ₀. It is possible to control the so-called “main effect” in the ionosphere on the Murmansk-St. Petersburg path.     

Model of magnetosphere-ionosphere interactions in the field of auroral electrojets

The magnetosphere and ionosphere are coupled into a power circuit by field-aligned currents. If there were only Hall current in the ionosphere, the problem of magnetosphere-ionosphere interaction would not have arisen. Field-aligned currents could be seen as emerging as a result of the break in the magnetospheric current across the tail, since the Hall current is divergence-free and does not perform any work. In fact, the current in the ionosphere is complex. It always has a Pedersen component, and the ionosphere is a real energy consumer. Together with energy, an extrinsic electrical current should flow into the ionosphere. The current coming from the generator in front of the bow shock is a part of the extrinsic current. The aim of this paper is to generalize the previously obtained partial solution to the problem of magnetosphere-ionosphere interactions in the region of auroral electrojets, also taking into account the generation of the extrinsic current in front of the bow shock.