The structure of the mid- and high-latitude ionosphere during the November 2004 storm event obtained from GPS observations

GPS data from the International GNSS Service (IGS) network were used to study the development of the severe geomagnetic storm of November 7–12, 2004, in the total electron content (TEC) on a global scale. The TEC maps were produced for analyzing the storm. For producing the maps over European and North American sectors, GPS measurements from more than 100 stations were used. The dense network of GPS stations provided TEC measurements with a high temporal and spatial resolution. To present the temporal and spatial variation of TEC during the storm, differential TEC maps relative to a quiet day (November 6, 2004) were created. The features of geomagnetic storm attributed to the complex development of ionospheric storm depend on latitude, longitude and local time. The positive, as well as negative effects were detected in TEC variations as a consequence of the evolution of the geomagnetic storm. The maximal effect was registered in the subauroral/auroral ionosphere during substorm activity in the evening and night period. The latitudinal profiles obtained from TEC maps for Europe gave rise to the storm-time dynamic of the ionospheric trough, which was detected on November 7 and 9 at latitudes below 50°N. In the report, features of the response of TEC to the storm for European and North American sectors are analyzed.     

2006年4月13～17日西太平洋地区电离层暴时特性研究

本文利用西太平洋地区的15个电离层台站的测高仪数据和国际GPS服务中心IGS 36个站提供的TEC数据,以及由美国喷气推进动力学实验室提供的Jason 1 TEC数据对2006年4月13～17日间一次由冕洞高速流所引发的磁暴所造成的电离层效应进行了分析.分析结果表明这次电离层暴呈现出显著的纬度效应,foF2和TEC等参量显示在磁暴主相期间对称分布的强正暴效应中心在磁纬±30°～±40°,且持续时间超过12 h.负暴效应被限制在中高纬地区,在磁暴进入恢复相时,开始向低纬渗透,且具有明显的地方时效应.TIMIED卫星测量的Σ［O/N2］显示磁暴发生后,暴时环流使得中低纬地区的Σ［O/N2］有大幅增加,而中高纬地区则显著下降.通过对hmF2的分析发现磁暴主相期间,有磁层电场向中低纬地区穿透,且持续时间较长为1～3 h.因此这次强正暴效应可能是由风场、电场和化学成分这三个因素的共同作用造成的.这次磁暴造成的电离层暴响应非常复杂,对造成各种正负暴的物理和化学机制还需要进一步的研究.     

Large-scale ionospheric gradients over Europe observed in October 2003

It is well known that ionospheric perturbations are characterised by strong horizontal gradients and rapid changes of the ionisation. Thus, space weather induced severe ionosphere perturbations can cause serious technological problems in Global Navigation Satellite Systems (GNSS) such as GPS. During the severe ionosphere storm period of 29–31 October 2003, reported were several significant malfunctions due to the adverse effects of the ionosphere perturbations such as interruption of the WAAS service and degradation of mid-latitudes GPS reference services. To properly warn service users of such effects, a quick evaluation of the current signal propagation conditions expressed in a suitable ionospheric perturbation index would be of great benefit. Preliminary results of a comparative study of ionospheric gradients including vertical sounding and Total Electron Content (TEC) data are presented. Strong enhancements of latitudinal gradients and temporal changes of the ionisation are observed over Europe during the 29–30 October storm period. The potential use of spatial gradients and rate of change of foF2 and TEC characterising the actual perturbation degree of the ionosphere is discussed. It has been found that perturbation induced spatial gradients of TEC and foF2 strongly enhance during the ionospheric storm on 29 October over the Central European region in particular in North–South direction exceeding the gradients in East–West direction by a factor of 2.     

Test of GPS for permanent ionospheric TEC monitoring at high latitudes

The Global Positioning System (GPS) observables are affected by the ionosphere. The dispersive nature of this effect and the use of two frequencies in the GPS observations make possible to measure the ionospheric total electron content (TEC) from dual frequency GPS data. In this work we test the concept of permanent monitoring of TEC using a network of GPS receivers at high latitudes. We have used GPS data from five permanent receivers in Scandinavia, from 1–30 January 1994, with geographic latitudes ranging from 57.4^°N to 78.9^°N. The results show the capability of the method to monitor the evolution of TEC as a function of time and geographical location. We have detected night-time enhancements almost every night for some of the stations, and we have also been able to produce maps of the instantaneous TEC as a function of both latitude and longitude around the GPS network. We also present some of the current limitations in the use of GPS for estimating TEC at high latitudes such as the difficulties in solving for cycle-slips, and the necessity of reliable values for the receiver and satellite differential instrumental biases.     

基于陆态网络GPS数据的电离层空间天气监测与研究

中国大陆构造环境监测网络(简称陆态网络)是以全球卫星导航定位系统(GNSS)为主,辅以多种空间观测技术,实时动态监测大陆构造环境变化,探求其对资源、环境和灾害的影响的地球科学综合观测网络.基于陆态网络约200个基准站的GPS观测数据,本文探讨了其在电离层空间天气监测与研究方面的应用.包括磁暴期间电离层暴扰动形态,大尺度电离层行进式扰动,太阳耀斑引起的电离层骚扰和低纬电离层不规则体结构等.研究结果表明:陆态网络布局合理,观测数据质量良好,完全可用于中国及周边地区电离层空间天气监测与研究,为进一步开展我国电离层空间天气预警和预报奠定了观测基础.     

TEC measurements and modelling over Southern Africa during magnetic storms; a comparative analysis

This paper presents the results from a study designed to investigate the ability of a newly developed neural network (NN) based model to follow total electron content (TEC) dynamics over the Southern African region. The investigation is carried out by comparing results from the NN model with actual TEC data derived from Global Positioning System (GPS) observations and TEC values predicted by the International Reference Ionosphere (IRI-2007) model during magnetic storm periods over Southern Africa. The magnetic storm conditions chosen for the study presented in this paper occurred during the periods 16–21 April 2002, 1–6 October 2002, and 28 October–01 November 2003. A total of six South African GPS stations were used for the validation of the two models during these periods. A statistical analysis of the comparison between the actual TEC behaviour and that predicted by the two models is shown. In addition, ionosonde measurements from the South African Louisvale (28.5°S, 21.2°E) station, located close to one of the validation GPS stations used, are also considered during the Halloween storm period of 28–31 October 2003. The generalisation of TEC behaviour by the NN model is demonstrated by producing predicted TEC maps during magnetic storm periods over South Africa. Presented results demonstrate the ability of NNs in predicting TEC variability over South Africa during magnetically disturbed conditions, and highlight areas for improvement.     

Automated daily process for global ionospheric total electron content maps and satellite ocean altimeter ionospheric calibration based on Global Positioning System data

The accuracy of single-frequency ocean altimeters benefits from calibration of the total electron content (TEC) of the ionosphere below the satellite. Data from a global network of Global Positioning System (GPS) receivers provides timely, continuous, and globally well-distributed measurements of ionospheric electron content. For several months we have been running a daily automatic Global Ionospheric Map process which inputs global GPS data and climatological ionosphere data into a Kalman filter, and produces global ionospheric TEC maps and ocean altimeter calibration data within 24 h of the end-of-day. Other groups have successfully applied this output to altimeter data from the GFO satellite and in orbit determination for the TOPEX/Poseidon satellite. Daily comparison of the global TEC maps with independent TEC data from the TOPEX altimeter is performed as a check on the calibration whenever the TOPEX data are available. Comparisons of the global TEC maps against TOPEX data will be discussed. Accuracy is best at mid-to-high absolute latitudes (∣latitude∣>30°) due to the better geographic distribution of GPS receivers and the relative simplicity of the ionosphere. Our highly data-driven technique is relatively less accurate at low latitudes and especially during ionospheric storm periods, due to the relative scarcity of GPS receivers and the structure and volatility of the ionosphere. However, it is still significantly more accurate than climatological models.     

Ionospheric disturbances in the east-Asian region during the geomagnetic period in November 2004

Results of the studies of ionospheric parameter variations during the intense geomagnetic storm on November 7–11, 2004, in the 20°–80° N, 60°–180° E sector are presented. The data of ionospheric stations and the results of total electron content (TEC) measurements at the network of the GPS ground-based receivers and of the GPS receiver onboard the CHAMP satellite were used. Periods of total absorption and blanketing sporadic E layers were observed at high latitudes, whereas durable negative disturbances typical of geomagnetic storms of high intensity were detected at midlatitudes. In the afternoon hours of local time on November 8, 2004, a large-scale ionospheric disturbance of a frontal type was detected on the basis of foF2 and TEC measurements. The disturbance propagated southwestward at a mean velocity of about 200 m/s. The comparison of the relative amplitude of this large-scale disturbance according to the total electron content (～70%) and foF2 (～80%) measurements made it possible to assume a large vertical scale of the disturbance.     

中国地区电离层TEC暴扰动研究

电离层总电子含量(TEC)是空间天气研究和监测预报的重要参量.本文引入了电离层TEC扰动指数DI, 对青岛等6个台站的DI数据进行分析,选取DI>0.35(DI≤-0.30)作为正(负)相电离层TEC扰动的强度标准,并以连续6 h及以上的DI满足该值来判定电离层TEC暴扰动事件.对电离层TEC暴扰动事件的统计分析表明,在地方时日落后至子夜前为发生高峰时段,正(负)相暴扰动事件平均持续时间约为10.9 h(10.5 h),正相暴发生率以冬季为多,夏季为少,而负相暴则以夏季略高.发现位于赤道异常驼峰区的广州站和位于高中纬度的海拉尔站比典型中纬地区的北京站电离层TEC暴扰动更易发生,且低纬地区以正相暴扰动为主.分析表明,约有70%的电离层TEC暴扰动伴随着有地磁扰动,但是电离层TEC暴扰动并不完全由地磁扰动所引起,强烈气象活动等局地环境因素也可能对电离层TEC暴扰动有着重要影响.     

Development of high latitude phase fluctuationsduring the January 10, April 10–11, and May 15, 1997magnetic storms

GPS satellite transmissions have been used to study the development of moderateionospheric phase irregularities. The use of the multi-station, multi-path observations of the GPSbeacons has allowed the study of the time development of irregularities as a function of latitudeand longitude of individual storms. The basic storms studied were those of January 10, April10–11, and May 15, 1997. The results from studying these storms showed the unique nature ofeach storm. For the three storms, data were available from four stations near 65° CorrectedGeomagnetic Latitude (CGL); the stations ranged from Fairbanks to Tromso. In addition, datafrom higher latitude stations are analysed. For the January storm, irregularity development startedat Fairbanks. Then as magnetic midnight approached longitudes to the west, the storm effectsreached the Tromso–Kiruna longitudes. For the April magnetic storm, at 65° CGL, irregularitydevelopment maximized at approximately the same UT at stations ranging in longitude fromFairbanks to Kiruna. For this storm, the development of irregularities was dominated by stormtime. The May storm irregularities were dominated by magnetic local time once the stormcommenced.With both total electron content and rate of change of total electron content (phasefluctuations) available, it was noted that over periods of minutes, clumps of irregularities wereaccompanied by increases in TEC. In addition total electron content increased over large areasduring maximum magnetic activity in the auroral oval. During the storms, ionograms showed thatthe altitude of maximum electron density fluctuated; at times the dominant maximum frequencywas noted in the E layer and at other times in the F layer. This fluctuation of electron density ineach layer during storms led to the conclusion that the turbulent activity within the auroral regiondominated the development of irregularities. The irregularities that are noted on trans-ionosphericpaths are therefore thought to be in both the E and the F layers with a combination of structuredhard and soft electron precipitation and coupling initiating the turbulent activity. The generalpositive correlation of one periods phase scintillation data with the Ultra Violet Imagerobservations as shown on POLAR indicates the importance of 100–200 km precipitation.However the very high occurrence of spread F at high latitudes as shown by both ground andsatellite ionosondes indicates the considerable contributions of F layer irregularities.     

Kalman filter-based algorithms for monitoring the ionosphere and plasmasphere with GPS in near-real time

Data collected from a GPS receiver located at low latitudes in the American sector are used to investigate the performance of the WinTEC algorithm [Anghel et al., 2008a, Kalman filter-based algorithm for near realtime monitoring of the ionosphere using dual frequency GPS data. GPS Solutions, accepted for publication; for different ionospheric modeling techniques: the single-shell linear, quadratic, and cubic approaches, and the multi-shell linear approach. Our results indicate that the quadratic and cubic approaches perform much better than the single-shell and multi-shell linear approaches in terms of post-fit residuals. The performance of the algorithm for the cubic approach is then further tested by comparing the vertical TEC predicted by WinTEC and USTEC [Spencer et al., 2004. Ionospheric data assimilation methods for geodetic applications. In: Proceedings of IEEE PLANS, Monterey, CA, 26–29 April, pp. 510–517] at five North American stations. In addition, since the GPS-derived total electron content (TEC) contains contributions from both ionospheric and plasmaspheric sections of the GPS ray paths, in an effort to improve the accuracy of the TEC retrievals, a new data assimilation module that uses background information from an empirical plasmaspheric model [Gallagher et al., 1988. An empirical model of the Earth's plasmasphere. Advances in Space Research 8, (8)15–(8)24] has been incorporated into the WinTEC algorithm. The new Kalman filter-based algorithm estimates both the ionospheric and plasmaspheric electron contents, the combined satellite and receiver biases, and the estimation error covariance matrix, in a single-site or network solution. To evaluate the effect of the plasmaspheric component on the estimated biases and total TEC and to assess the performance of the newly developed algorithm, we compare the WinTEC results, with and without the plasmaspheric term included, at three GPS receivers located at different latitudes in the American sector, during a solar minimum period characterized by quiet and moderate geomagnetic conditions. We also investigate the consistency of our plasmaspheric results by taking advantage of the specific donut-shaped geometry of the plasmasphere and applying the technique at 12 stations distributed roughly over four geomagnetic latitudes and three longitude sectors.     

Geomagnetic and Ionospheric Responses to the Interplanetary Shock Wave of March 17, 2015

The propagation of perturbation caused by the interplanetary shock wave of March 17, 2015 from the solar wind through the magnetosheath, magnetosphere, and ionosphere down to the Earth’s surface is analyzed. The onboard satellite measurements, global magnetometer network data, and records by the receivers of the global positioning system (GPS) providing the information about the total electron content (TEC) of the ionosphere are used for the analysis. By the example of this event, various aspects of the influence of the interplanetary shock wave on the near-Earth environment and ground-based engineering systems are considered. It is shown which effects of this influence are well described by the existing theoretical models and which ones need additional research. The formation of the fine structure of the magnetic impulse of the storm sudden commencement (SC)—the preliminary impulse (PI) and main impulse (MI)—is considered. The MI and compression of the magnetospheric magnetic field is observed by the GOES and RBSP satellites and on the geomagnetically conjugate stations; however, the PI was only noted on the Earth. The PI was detected in the afternoon sector practically simultaneously (within 1 min) with the shock wave impact on the magnetopause. The wave’s response to the SC includes the strongly decaying resonant oscillations of the magnetic shells and the magnetoacoustic cavity mode. This study supports the possibility of detecting the ionospheric response to the SC by the GPS method. The TEC response to the MI was detected in the auroral latitudes although not on every radio path. The TEC modulation can be associated with the precipitation of superthermal electrons into the lower ionosphere which is undetectable by riometers. The burst in the intensity of the geomagnetically induced currents caused by an interplanetary shock wave turns out to be higher than the currents during the storm’s commencement, although the SC’s amplitude is noticeably lower than the amplitude of the magnetic bay related to the substorm.     

Investigation of Ionospheric Response to Geomagnetic Storms over a Low Latitude Station,Ile-Ife,Nigeria

Due to several complexities associated with the equatorial ionosphere, and the significant role which the total electron content (TEC) variability plays in GPS signal transmission, there is the need to monitor irregularities in TEC during storm events. The GPS SCINDA receiver data at Ile-Ife, Nigeria, was analysed with a view to characterizing the ionospheric response to geomagnetic storms on 9 March and 1 October 2012. Presently, positive storm effects, peaks in TEC which were associated with prompt penetration of electric fields and changes in neutral gas composition were observed for the storms. The maximum percentage deviation in TEC of about 120 and 45% were observed for 9 March and 1 October 2012, respectively. An obvious negative percentage TEC deviation subsequent to sudden storm commencement (SSC) was observed and besides a geomagnetic storm does not necessarily suggest a high scintillation intensity (S₄) index. The present results show that magnetic storm events at low latitude regions may have an adverse effect on navigation and communication systems.     

中国电离层TEC现报系统

作为最重要的电离层参量之一,电离层电子浓度总含量(TEC)可以通过当前广泛使用的全球定位系统(GPS)的信标进行观测.我们在我国北起漠河、经北京和武汉、南到三亚四个观测站建立了GPS接收站,经单站数据处理后将原始的单站GPS TEC观测数据上载到北京数据处理中心;采用我们发展的经验基函数模式算法,用实测数据估算格点TEC并提供给用户,同时生成覆盖中国疆域的TEC地图并在因特网上实时发布.这一电离层TEC现报系统是我国首个类似的技术系统,在观测站布局和TEC地图算法上有所创新.该系统已用于实时监测我国电离层环境,并可为我国卫星定位导航和测控等技术系统的电波修正提供实测电离层数据.     

Relationships between GPS-signal propagation errors and EISCAT observations

When travelling through the ionosphere the signals of space-based radio navigation systems such as the Global Positioning System (GPS) are subject to modifications in amplitude, phase and polarization. In particular, phase changes due to refraction lead to propagation errors of up to 50 m for single-frequency GPS users. If both the LI and the L2 frequencies transmitted by the GPS satellites are measured, first-order range error contributions of the ionosphere can be determined and removed by difference methods. The ionospheric contribution is proportional to the total electron content (TEC) along the ray path between satellite and receiver. Using about ten European GPS receiving stations of the International GPS Service for Geodynamics (IGS), the TEC over Europe is estimated within the geographic ranges –20° 40°E and 32.5° ø 70°N in longitude and latitude, respectively. The derived TEC maps over Europe contribute to the study of horizontal coupling and transport processes during significant ionospheric events. Due to their comprehensive information about the high-latitude ionosphere, EISCAT observations may help to study the influence of ionospheric phenomena upon propagation errors in GPS navigation systems. Since there are still some accuracy limiting problems to be solved in TEC determination using GPS, data comparison of TEC with vertical electron density profiles derived from EISCAT observations is valuable to enhance the accuracy of propagation-error estimations. This is evident both for absolute TEC calibration as well as for the conversion of ray-path-related observations to vertical TEC. The combination of EISCAT data and GPS-derived TEC data enables a better understanding of large-scale ionospheric processes.     

2009年7月22日日全食引起的电离层扰动及其对定位的影响

2009年7月22日发生在亚太地区的日全食,从北半球中纬地区一直延伸到南半球中纬地区.这次日食期间发生的磁暴和日食时间同步,使得电离层变化较为复杂.为了分析日食期间电离层扰动及其对定位的影响,所采用的GPS数据来源于日全食带内的重庆CORS网(4个站)、武汉CORS网(8个站)数据、IGS站WUHN、SHAO的数据,以及日偏食区域内不同纬度处的若干IGS站.通过比较日食前后连续三天的各个地方TEC变化,以及利用高采样率的CORS网数据研究日食期间TEC的瞬时变化,根据位置和时间的不同,各地日食期间TEC下降约(1~4)TECU.但是,磁暴期间TEC的响应整体表现为正相暴,偏离值达50%以上,且和日食食甚后的TEC变化相重合.同时,求解了日食期间伪距单点定位的实时精度和CORS网内中短基线的实时精度,伪距单点定位的平面精度变化不显著,高程精度下降达数十米,日食初期CORS网中基线的平面精度仍在厘米级内,高程精度仍在分米级内,但是,日食后期发生的磁暴导致基线的平面精度下降到分米级,高程精度下降到米级.     

2004年11月强磁暴期间武汉电离层TEC的响应和振幅闪烁特征的GPS观测

本文利用设在武汉(11436°E,3053°N,磁纬194°)的GPS电离层TEC和电波闪烁监测仪的测量数据,分析了2004年11月强磁暴期间TEC的响应以及电波闪烁和TEC起伏的特征.结果表明,在这次强磁暴期间,武汉及其邻近地区电离层TEC的响应以正暴相为主,正暴相分别出现在两次主相期间,最大正偏离达到50 TECU.这次磁暴另一个重要影响是主相期间L波段振幅闪烁的活动性及其强度显著增强.S4指数最大接近10.伴随增强的闪烁活动,多次观测到深度耗尽的等离子体泡与TEC起伏,TEC变化率的标准差ROTI指数也显著增强.分析揭示, ROTI指数与S4指数呈正相关,相关系数达到097.线性回归计算得到,ROTI和S4的比率为964.     

1989年3月特强磁暴期间的电离层暴

用欧亚大陆地面电离层垂测站资料考察1989年3月12～16日磁暴期间的电离层暴形态及其发展变化. 特强磁暴引发的电离层暴是全球性的,但自磁层沉降的高能粒子对热层低部的加热程度及区域分布不同,因而各经度链区域内电离层暴的特征也有所差异. 本文研究表明,与理论推断对照,欧洲地区内F2层最大电子密度NmaxF2(或f0F2)并不出现正暴现象,而负暴自高纬向低纬的发展则与典型的热层环流结果相符. 此外,此磁暴过程期间在中低纬区存在明显的波动过程. 在亚洲高纬地区,磁暴初期13日有约10 h的正暴,而负暴过程则与欧洲地区类似,但不太清晰;且无波动现象. 磁暴期间,同一经度链的中低纬地区,夜间常发生多站同时的h′F突增. 本文再次证实这是一般磁暴期间常出现的普遍现象.     

欧洲扇区不同纬度电离层暴特征的统计分析

本文利用Madrigal数据库的TEC数据对2001—2010年间的156次单主相型磁暴事件,统计分析了欧洲扇区从赤道到极光带共5个纬度区域的电离层暴特征,结果表明:(1)电离层暴有明显的纬度分布特征,正负暴出现次数的比例随纬度的降低呈现明显的增加趋势,但夏季赤道地区趋势相反,正负暴比例比更高纬度的反而降低;(2)与主相相比,恢复相期间大部分纬度地区正暴数量减少,负暴数量增加,但赤道地区恢复相期间正暴数量反而增加;(3)中低纬地区电离层暴随磁暴MPO地方时分布特征明显,正暴所对应的MPO主要分布在白天,而MPO发生在夜间容易引起负暴;(4)电离层负暴主要发生在夜间,中、高纬地区负暴的开始时间存在‘时间禁区’,但不同纬度‘时间禁区’的地方时分布有一定差异,正暴分布则相对分散.     

Effects of the August 11, 1999 total solar eclipse as deduced from total electron content measurements at the GPS network

We present the results derived from measuring fundamental parameters of the ionospheric response to the August 11, 1999 total solar eclipse. Our study is based on using the data from about 100 GPS stations located in the neighborhood of the eclipse totality phase in Europe. The eclipse period was characterized by a low level of geomagnetic disturbance (D_st-variation from −10 to −20 nT), which alleviated significantly the problem of detecting the ionospheric response to the eclipse. Our analysis revealed a well-defined effect of a decrease (depression) of the total electron content (TEC) for all GPS stations. The delay between minimum TEC values with respect to the totality phase near the eclipse path increased gradually from 4 min in Greenwich longitude (10:40 UT, LT) to 8 min at the longitude 16° (12:09 LT). The depth and duration of the TEC depression were found to be 0.2–0.3 TECU and 60 min, respectively. The results obtained in this study are in good agreement with earlier measurements and theoretical estimates.