Results of Russian experiments dealing with the impact of powerful HF radiowaves on the high-latitude ionosphere using the EISCAT facilities

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.     

Determining the ionospheric irregularity velocity vector based on doppler measurements in the artificially modified <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript> region of the polar ionosphere

The method for estimating the behavior of the ionospheric irregularity motion vector in the artificially disturbed HF ionospheric region has been proposed, and this behavior has been analyzed based on the simultaneous Doppler observations performed on several paths using the method of bi-static backscatter of diagnostic HF signals by small-scale artificial ionospheric irregularities. The Doppler measurements were performed during the modification of the auroral ionosphere by powerful HF radiowaves emitted by the EISCAT heating facility (Tromsø, Norway). It has been obtained that the dynamics of the ionospheric irregularity directions in the F region, calculated based on the Doppler measurements of the total vector of the ionospheric irregularity velocity above the Tromsø EISCAT radar at a frequency of 931 MHz, is in satisfactory agreement with such calculations performed using the three-position method.     

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.     

Response of mesospheric ozone to the heating of the lower ionosphere by high-power HF radio emission

We detected a decrease in the intensity of microwave radiation at the atmospheric ozone line at a frequency of 110836.04 MHz during ionospheric modification by high-power HF radiowaves radiated by the Sura Ionospheric Heating Facility. The obtained experimental data allowed us to hypothesize that this effect was caused by the fact that mesospheric ozone was affected by internal gravity waves generated in the E region of the ionosphere during its high-power HF radiowave heating.     

Atmospheric parameters measured using artificial periodic irregularities with different spatial scales

The parameters of the neutral atmosphere have been studied using artificial periodic irregularities of the ionospheric plasma. A few measurement cycles were carried out in 2006–2007 using the new method, in particular: irregularities were created by powerful radiowaves at two separated frequencies. The possibilities of the method have been demonstrated. Based on the relaxation times of artificial periodic irregularities measured at two frequencies, the N(z) electron density profiles in the 95–115 km height interval have been determined and have been used to estimate the parameters of the neutral atmosphere. The results of determining the temperature and density of the neutral atmosphere are presented and compared with the data obtained earlier.     

Doppler selection of HF radiosignals on long paths

The long-term registration of the Doppler spectra of HF radiosignals has been performed on the Moscow-Akademik Vernadsky Ukrainian Antarctic station path. It has been revealed that the spectra are split when the solar terminator crosses direct and return radio lines. The spectral and energy characteristics of direct and return signals have been calculated within the scope of the asymptotic theory of long-range propagation of decametric radiowaves.     

Peculiarities of artificial ionospheric radiation under the action of high-power HF radiowaves, emitted by the SPEAR facility, on the sporadic E layer of the polar ionosphere

The results of the experimental studies of the ionospheric effects originating under the action of high-power HF radiowaves, emitted by the SPEAR heating facility into the sporadic E _s layer of the polar ionosphere, are presented. The experiment was performed on March 2, 2007, simultaneously at two spaced points: Barentsburg (Spitsbergen, a distance of about 40 km from the SPEAR facility) and Gor’kovskaya observatory near St. Petersburg, located at a distance of about 2000 km from SPEAR. The distributions of the heating signal intensity in the 100 kHz frequency band were measured in Barentsburg. Bistatic backscatter of diagnostic HF signals by small-scale artificial ionospheric irregularities was observed at Gor’kovskaya observatory. Based on an analysis of the experimental data obtained in Barentsburg, it has been found out that a broadband noise-like component originated and additional maximums appeared in the heating signal spectrum. The broadband emission intensity was a factor of 1.5–3 as high as the noise level. The additional maximums were formed in the regions of the positive and negative frequency shift relative to the heating signal frequency and were observed when the heating frequency was lower than the critical frequency of the E _s layer; e.g., a high-power HF radiowave reflected from E _s . The expression for determining the frequency shift of the additional maximum in the heating signal spectrum at altitudes of the ionospheric E region, taking into account the ion-electron collision frequency, has been obtained. The heating signal spectrum registration was compared with the observations of small-scale artificial ionospheric irregularities and the trajectory modeling of signals scattered by the considered irregularities. The observation results have been analyzed and interpreted taking into account the magnetic and ionospheric data characterizing the background geophysical conditions.     

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.     

Model prediction of the most effective frequency for the large-scale modification of the midlatitude ionospheric <Emphasis Type="Italic">F</Emphasis><Subscript>2</Subscript> layer by powerful HF radiowaves

The response of the midlatitude F ₂ layer to the effect of powerful HF radiowaves is studied using the numerical model of the ionosphere. The large-scale modification of the F ₂ layer over the Sura heating facility near Nizhni Novgorod is considered for autumnal conditions. The calculations are performed for various cases when the heating wave has different frequencies under the daytime and nighttime conditions. The calculation results show that large-scale changes in the electron temperature and density in the F ₂ layer caused by the artificial heating should substantially depend on the heating radiowave frequency. It is found that there should exist such, most effective, heating wave frequency at which a decrease in the electron density at the F ₂ layer maximum height over the heating facility should be maximal.     

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...     

Temporal behaviour of artificial small-scale ionospheric irregularities: Review of experimental results

Features of artificial small-scale ionospheric irregularities (ASI) induced at F-region heights by powerful HF waves are discussed. The investigations presented here were performed during the past two decades at the Zimenki and Sura heating facilities, located at middle latitudes near Nizhniy Novgorod, Russia, as well as at the Gissar facility located at a lower latitude near Dushanbe, Tadzhikistan. The measurements were made by a variety of diagnostic methods employing artificial field-aligned scattering of HF and VHF radio waves, sounding of the disturbed region by means of low-power probing waves and testing of the artificial turbulence by means of stimulated electromagnetic emission (SEE). The dependence of ASI on such parameters as transverse scale length of the artificial irregularities, their location in the disturbed region, the power of the heating wave, the duration of HF radiation, geophysical conditions, aftereffects of the preceding modification, and the schedule of heater operation is considered for both the development stage after pump turn-on and the decay stage after pump turn-off. The temporal evolution of ASI spectral characteristics during the heater period is discussed. An empirical model for the ASI, based on the data available, was elaborated and verified by computer simulation of SEE generation.     

Modelling of the lower ionosphere

The model of calculations of electron density profiles in D-region is suggested. The model includes four positive ions, four negative ions and electrons. The effective rate coefficients were received from detailed models of ionization-recombination cycle. The calculations, which were made, and the comparisons with experimental data (Ne-profiles and their variations, absorption of radiowaves) have showed, that in general the model described the basic features of D-region parameters.     

Controlled injection of high-power radio pulses into the ionosphere-magnetosphere system and appearance of microsubstorms on October 2, 2007

Insignificant geomagnetic disturbances, which originated during the experimental injection of high-power radio pulses into the magnetosphere-ionosphere system with the help of an HF transmitter of the Sura heating facility, are considered. The experiment was performed at 1840–1900 UT on October 2, 2007 (～2100 MLT) at geomagnetic latitudes close to the zone of generation of the current wedge westward branch, responsible for geomagnetic substorms. The series of two magnetic microsubstorms, with a sudden initial pulse and an insignificant delay relative to the facility switching, was observed at 1840–2000 UT. A disturbance was registered at many stations in the Northern Hemisphere as a global event. The equivalent ionospheric current system of an initial pulse was similar to such a system of the westward auroral surge and had an intensity maximum at Karpogory magnetic observatory, which is the closest station to the Sura facility. Under the conditions of a quiet solar wind and low planetary geomagnetic activity, the AE auroral index correlated with the interplanetary medium parameters (the correlation coefficient reached 0.65) at 1710–2000 UT. It has been confirmed that an initial geomagnetic pulse is generated as a result of radiowave injection. The arguments for and against the generation of microsubstorms due to stimulated precipitation of magnetospheric electrons, as well as the assumption that the geoeffective impact of the interplanetary medium is intensified during the injection of high-power radiowaves near the zone where the westward branch of the current wedge of magnetospheric substorms is generated, are considered.     

利用高频返回散射技术探测远地核爆炸电离层效应

本文叙述利用高频返回散射技术探测我国1976年的一次低空大当量核爆炸电离层效应的结果。返回散射探测设备设于离爆炸点2205km的新乡。本文得到了核爆炸产生的附加电离区和电离层扰动的参数。这些结果与爆炸区附近其他手段观测的结果相符。     

The inversion of incoherent scatter spectra with a non-Maxwellian electron distribution

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.     

On the structural parameters of macroinhomogeneities of the ionosphere based on data of radio sounding from altitudes below the F2 layer maximum

The series of ionograms of the satellite radio sounding from altitudes below the ionospheric maximum, which were called a delayed lower track, is considered. The method for analyzing ionograms in such a series has been described. The appearance of the delayed lower track on ionograms is explained by the presence of a large ionospheric inhomogeneity which turns radiowaves of many frequencies toward a satellite. It has been assumed that the series of ionograms diagnoses the same inhomogeneity, the structural parameters of which can be determined. The electron density profiles in individual vertical sections of inhomogeneity and the inhomogeneity plasma frequency gradient have been presented, and an attempt to construct the spatial model of inhomogeneity has been made.     

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.     

Prediction of the maximum observed frequency of the ionospheric HF radio channel using the method of artificial neural networks

The algorithm for predicting one of the main parameters of the ionospheric HF radio channel—maximum observed frequency (MOF)—for the interval 0.5–3 h has been synthesized based on the technology of artificial neural networks (ANNs). The data of oblique-incidence LFM sounding obtained on the Inskip (England)-Rostov-on-Don path have been used for this purpose. The studies have been performed under different geophysical conditions. The relation of MOF to the variations in the key parameters of the solar wind and IMF, responsible for the succession of development of magnetospheric-ionospheric disturbances leading to a change in the HF radiocommunication conditions, has been established. The time scales of the ionospheric response have been determined. The practical value of the performed work consists in that the obtained results are used to increase the reliability of ionospheric HF radiocommunication.     

Spatial structure of auroral day-time ionospheric electron density irregularities generated by a powerful HF-wave

We describe an experiment in satellite radio-wave probing of the ionosphere, modified by powerful waves from the HF heating facility at Tromsø (Norway) in May 1995. Amplitude scintillations and variations of the phase of VHF signals from Russian navigational satellites passing over the heated region were observed. We show that both large-scale electron density irregularities (several tens of kilometers in size) and small-scale ones (from hundreds of meters to kilometers) can be generated by the HF radiation. Maximum effects caused by small-scale irregularities detected in the satellite signals are observed in the directions sector approximately parallel to the geomagnetic field lines although large-scale structures can be detected within a much larger area. The properties of small-scale irregularities (electron density fluctuations) are investigated by applying a statistical analysis and by studying experimental and model mean values of the logarithm of the relative amplitude of the signal. The results indicate that satellite radio probing can be a supporting diagnostic technique for ionospheric heating and add valuable information to studies of effects produced by HF modification.