Determining parameters of large-scale traveling ionospheric disturbances of auroral origin using GPS-arrays

The intention in this paper is to investigate the form and dynamics of large-scale traveling ionospheric disturbances (LS TIDs) of auroral origin. We have devised a technique for determining LS TID parameters using GPS-arrays whose elements can be selected from a large set of GPS stations forming part of the International GPS Service network. The method was used to determine LS TID parameters during a strong magnetic storm of September 25, 1998. The North-American sector where many GPS stations are available, and also the time interval 00:00–06:00 UT characterized by a maximum value of the derivative Dst were used in the analysis. The study revealed that this period of time was concurrent with the formation of the main ionospheric trough with a conspicuous southward wall in the range of geographic latitudes 50–60° and the front width of no less than 7500 km. The auroral disturbance-induced large-scale solitary wave with a duration of about 1 h and the front width of at least 3700 km propagated in the equatorward direction to a distance of no less than 2000–3000 km with the mean velocity of about 300 m/s. The wave front behaved as if it ‘curled’ to the west in longitude where the local time was around afternoon. Going toward the local nighttime, the propagation direction progressively approximated an equatorward direction.     

On ionospheric disturbances in relation to geomagnetic disturbances

Summary Disturbances in the critical frequency of theF2-region of the ionosphere at Watheroo on international magnetically disturbed days are analyzed together with simultaneous geomagnetic data at the same station. The results show that the daily average disturbanceDm (foF2) becomes negative or positive according as the maximum of the disturbance daily variationSD (foF2) takes place in night time or in daytime respectively. This fact may show that bothDm (foF2) andSD (foF2) are due to the condition that the daytime increase in the daily variation of theF2-region is reduced or enhanced owing to vertical drift of the ionosphere caused by electric currents responsible for geomagneticSD.     

利用全球电离层地图分析芦山地震电离层异常变化

近年来,作者们经过长期的分析研究后发现,采用迭代法分析电离层数据时获取的电离层TEC异常与中强地震发生具有较好的空间对应关系,并根据总结的异常特征在地震中长期监测预报方面取得了一定的进展。本文在迭代法分析预报确定异常区域的基础上,采用滑动四分位法对预测区域发生的中强地震前后短时间序列内的电离层TEC数据进行分析,剔除干扰因素后找到较为明显的电离层TEC变化异常。综合利用两种分析方法判断中强地震前后电离层TEC异常,从而为地震前兆研究提供一个新的思路。     

地震期间电离层扰动现象研究

介绍了大量的关于地震电离层扰动现象研究的最新进展,研究表明地震发生前的几天或者几个小时电离层扰动被观测到,电离层前兆是确实存在.但要将震前的电离层扰动作为地震短临预报的工具,还有许多值得我们去深入研究和解决的问题.应用空间技术开展大区域范围内电离层参数的实时观测,如用地震电磁卫星、GPS台网、并和地面电离层垂测仪观测相结合,建立“电离层地震前兆监测系统”,无疑会加速这项研究的进程.     

Height profiles of the amplitudes of large-scale traveling ionospheric disturbances

Nighttime height profiles of the amplitudes of large-scale traveling ionospheric disturbances (LSTIDs) obtained from the data of vertical sounding in Almaty (76°55′ E, 43°15′ N) for the period 2000–2007 are analyzed. The height profiles are plotted using the time variations in electron density N _h (t) at a series of heights for the F region in the ionosphere with a height step of 10 km. In total, observations were conducted during 1166 nights, among which 581 nights are characterized by wave activity. Nights with the maximum amplitude of variations in N _h (t) exceeding 25% are selected for analysis. The total number of such nights is 63; LSTIDs have been recorded in both magnetically quiet and active periods. The regressive ratios between the height of the F-region maximum and the height that corresponds to the maximum absolute amplitude of a wave, as well as between the values of the maximum amplitude at a height profile and the value of the amplitude of variations in N _m F(t) at the layer maximum, are obtained.     

An experimental study of wave packets in travelling ionospheric disturbances

The complex demodulation method was employed to analyse observations of TIDs carried out by means of multifrequency HF Doppler sounding at vertical incidence over Almaty (76°55′E, 43°15′N). Two types of behaviour of the amplitude and phase in the band-pass filtered Doppler shift oscillations were revealed. These were packet-like wave structures and quasi-stochastic TIDs. A study of the phase behaviour inside wave packets showed that most of them had a quasi-monochromatic structure, some of them had oscillations with a period which increased with time, and none had oscillations with a period which decreased with time. Phase jumps between nearby packets were explained as a result of interference between two adjacent packets having similar oscillation periods. A method of calculating the correlation coefficient for the wave packets propagating on a background of quasi-stochastic TIDs was developed. This showed that wave packets (having periods between 7 and 50 min) travelled in the vertical plane practically without any loss of coherence, while quasi-stochastic TIDs had a short coherence length; the velocity of the quasi-stochastic TIDs was noticeably larger than that of the wave packets.     

On ionospheric disturbances caused by the solar activity of November 1960

Summary On November 1960 a special solar activity occured, producing characteristic disturbances in the ionosphere. Athens center followed this activity by vertical sounding and by Riometer recordings. They are evidences for proton events producing deep absorption in the ionosphere and aurora extending till 38° latitude. Some observations concerning July 1961 solar activity are reported. World wide decrease of the maximum electron density reported during the November period was observed also in Athens. Ionospheric disturbances following vertical sounding observations are of «negative» type.     

Thermospheric wind oscillations during the propagation of large-scale traveling ionospheric disturbances

The parameters of meridional thermospheric wind oscillations during the propagation of largescale traveling ionospheric disturbances, obtained based on the nighttime observations in the ionospheric F region performed at the Institute of the Ionosphere (Almaty, 76°55′ E, 43°15′ N) in 2000–2007 using a digital ionosonde, have been analyzed. The processing of ionospheric sounding data made it possible to obtain electron density time variations N(t) at fixed altitudes and variations in the altitudes of the F region maximum (h _m F) and bottom (h _bot F). During the indicated period, 1166 observation sessions were performed, and 581 sessions were characterized by wave activity. Sessions with a relative amplitude of N(t) variations larger than 25% were selected for analysis. The total number of such sessions was 63. The expression for calculating the meridional wind oscillation amplitudes was obtained based on the measured amplitudes of h _bot F oscillations. It was indicated that increased amplitudes of thermospheric wind oscillations are obtained when this expression for h _m F is used. The diffusion term, which causes increased h _m F oscillation amplitudes as compared to the h _bot F oscillation amplitudes, was estimated using the regression expression.     

On the production of traveling ionospheric disturbances by atmospheric gravity waves

This paper deals with how atmospheric gravity waves produce the traveling ionospheric disturbances (TIDs) that are observed by ionosondes. It is shown that, rather than directly producing variations of ionospheric height, a likely mechanism involves changes in ionization density by gradients in the horizontal atmospheric gravity wave air motion. These density changes can be observed as variations of the height of an ionospheric isodensity surface (the usual way of measuring TIDs). This mechanism involving enhancement/depletion of ionospheric density requires quite moderate atmospheric gravity wave air motion speeds, and works well at almost all latitudes.     

Parameters of the medium-scale traveling ionospheric disturbances model deduced from measurements

Using three radio techniques for determining the spatial and terminal distribution of the electron concentration in the ionospheric F region, a number of parameters of medium-scale travelling ionospheric disturbances (the effective thickness of the atmospheric waveguide and height of its axis, spatial and time periods, propagation speeds, and maximum amplitudes of the disturbances) are determined.     

Relationships between magnetospheric and ionospheric disturbances in the auroral and subauroral zones

A joint analysis of variations in the ionospheric parameters at three vertical-incidence stations (Heiss Island, Dixon Island, and Sodankyla) and the solar wind plasma characteristics (i.e., the PC magnetic index characterizing the IMF geoeffective part) indicated that the PC index can be used as a predictor in order to diagnose the electron density level in the polar ionosphere. An increase in the PC level corresponds to positive and negative gradients in variations in the F region??s critical frequencies. As PC becomes larger than 1.5, the electron density increases at night in winter and, on the contrary, decreases during the day in summer and during daylight hours in winter. A delay in the ionospheric F region??s response to PC variations depends on the station latitude: this delay is no more than 1 and 2 h at the Heiss Island and Dixon Island stations and can be more than 6 h in summer and 0?C1 h in winter at Sodankyla. An increase in the PC amplitude as a rule corresponds to an anomalous increase in foEs relative to the median values at these stations with a delay of 1 h.     

On some characteristics of ionospheric disturbances at Genova,Italy

Summary Ionospheric disturbances recorded at Genova are studied in relation to the corresponding geomagnetic disturbances. Storm time and disturbance daily variation are derived, as well as some characteristic features of ionospheric perturbations. Generally these perturbations are dealyed with respect to the corresponding geomagnetic disturbances: the mean time-lag referred to the whole day is of the order of 1h30m, but if thessc occurs in the morning or near noon the mean time-lag is nearly of 4h.The main results of this paper have been presented at the Symposium on Ionospheric Soundings in the IGY-IGC, held in Nice, France, on 11–16 December 1961 (and organized by the CIG-Committee of the URSI).     

Studying large-scale traveling ionospheric disturbances according to the data of oblique-incidence sounding

The morphological features of wave-like ionospheric disturbances with periods of 1–2 h and the spatial extent exceeding 1000 km are studied. Oblique-incidence sounding data of the ionosphere, obtained in eastern Siberia during several continuous monthly experiments on three radio paths from 2006 to 2010, have been used. Large-scale traveling ionospheric disturbances generated during magnetic storms and large-scale wave-like ionospheric disturbances registered during geomagnetically quiet periods are considered. Small-scale ionospheric structures were also observed against a background of large-scale traveling iono-spheric disturbances considered in this study.     

基于GNSS数据的朝鲜核爆电离层效应观测研究

本文分析了电离层对2009年、2013年和2016年朝鲜核试验中地下核爆(Underground Nuclear Explosion,UNE)的响应.利用南北半球IGS站的GNSS-TEC观测数据,发现了在3次核试验期间的磁共轭电离层扰动现象.观测结果表明,3次UNE所产生的电离层扰动分别以228m·s^-1、173m·s^-1和147m·s^-1的速度从核试验爆心地区径向传播.本文研究提出,UNE所产生的电离层TEC扰动是岩石圈-大气层-电离层耦合(Lithosphere-Atmosphere-Ionosphere Coupling,LAIC)电场渗透到电离层高度引发电动力学过程的结果.此外,LAIC电场可以沿磁力线映射到共轭半球,从而在共轭地区造成电离层TEC扰动.因此,在核试验地区附近以及其对应的磁共轭地区,UNE所产生的LAIC电场在电离层TEC扰动的形成中起着关键性的作用.     

Sudden ionospheric disturbances and flare activity in the course of the solar cycle no 20

a¶rt;a ma nu an u u (SID) u nu n a (a n¶rt; au) mu 1965–1975 . u u SID na¶rt;am nau, mum u nm R.     

Features of statistical distributions of large-scale traveling ionospheric disturbances over Almaty

The seasonal dependence of the probability of large-scale traveling ionospheric disturbances is analyzed based on nighttime ionospheric parameters measured over Almaty during 2000–2007, as well as the dependence of annual average probabilities of their occurrence on the sunspot cycle. The behavior of these probabilities is compared with magnetic activity.     

Parameters of traveling ionospheric disturbances estimated from satellite beacon observations in low-earth orbit

Based on beacon sounding the ionosphere using coherent signals of low-orbiting navigation satellites, the following parameters of medium-scale traveling ionospheric disturbances have been determined: the effective thickness of the atmospheric waveguide and the altitude of its longitudinal axis, the horizontal spatial period, the velocity, the maximum amplitudes of disturbances, and the inclination of the disturbance phase front. It has been found that the horizontal spatial period of studied disturbances increases with increasing distance to an initiating impact location and its delay. In this case the minimum value of the horizontal spatial period always exceeds ∼150 km, and the disturbance amplitude increases with increasing horizontal period and distance from the initiating disturbance location and with decreasing altitude of the main ionization maximum. All disturbance parameters are independent of the initiating impact nature. It has been found that disturbances with relative amplitudes of 0.1–0.7 are often observed. Disturbances that are registered more often travel southward, and their absolute velocities are 7–60 m/s.     

Geomagnetic signatures of sudden ionospheric disturbances during extreme solar radiation events

We performed a comparative study of geomagnetic variations, which are associated with sudden ionospheric disturbances (SIDs) caused by great X-class solar flares on July 14, 2000 (Bastille flare) and on October 28, 2003 (Halloween flare). Intense fluxes of solar X-rays and EUV radiation as well as solar energetic particles (SEP) were considered as sources of abundant ionization of the ionosphere and upper atmosphere. Flare-initiated SIDs are revealed as transient geomagnetic variations, which are generated by enhanced electric currents flowing mainly in the bottom-side ionosphere. Those so-called solar flare effects (SFEs) were studied by using of geomagnetic data from INTERMAGNET worldwide network of ground-based magnetometers. In subsolar region the SFE is mainly controlled by the flare X-rays and/or EUV radiation. We found that in the Halloween flare the contribution of X-rays was comparable with the EUV, but in the Bastille flare the EUV flux was dominant. The ionization at high latitudes is generated by the SEP, which energy flux is comparable and even exceeds the solar electromagnetic radiation in that region. It was shown that in the Halloween event the pattern of SFE is formed by a two-vortex current system, which is similar to the quiet day Sq current system. However, during the Bastille flare, the pattern of induced currents is quite different: the northern vortex shifts westward and southern vortex shifts eastward such that the electroject is substantially tilted relative to the geomagnetic equator. From numerical estimations we found that at middle latitudes the SEP-initiated geomagnetic effect becomes comparable with the effects of solar electromagnetic radiation. It was also shown that the SEP contribute to the SFE in the nightside hemisphere. The revealed features of the SEP impact to the ionosphere were found in a good agreement with the theory of energetic particle penetration to the bottom-side magnetosphere.     

Solar terminator and auroral sources for traveling ionospheric disturbances in the midlatitude F region

The occurrence of Traveling Ionospheric Disturbances (TIDs) at a midlatitude location (London, Canada, 43°N, 81°W) has been examined using data recorded by standard 5 min ionograms during the year 2000. It is found that the dominant source of TIDs during daytime appears to be the sunrise terminator but during nighttime the sunset terminator and magnetic disturbances both contribute to the TIDs. The daytime TIDs show a weak semiannual variation with maxima in solstices. The nighttime TIDs show insignificant annual variation.