太阳活动低年广州地区地磁扰动与电离层闪烁的统计特征分析

基于肇庆地磁台的地磁监测数据和广州气象卫星地面站建立的华南地区GPS电离层闪烁监测网的监测数据, 统计分析了2008年7月至2010年7月太阳活动低年期间广州地区地磁扰动与电离层闪烁的关系. 用肇庆台地磁水平分量H的变化量换算出肇庆地磁指数K, 以此来代表广州地区地磁扰动情况.分析结果表明, 磁暴/强地磁扰动对广州地区电离层闪烁的发生总体表现为抑制作用, 电离层闪烁主要发生在低K值期间, 而在K ≥ 4时电离层闪烁的发生呈下降趋势. 电离层闪烁发生率随季节和地磁活动的变化规律表现在, 春季的弱闪烁发生率、夜间中等以上闪烁发生率和夏季中等以上闪烁的发生率明显与地磁活动指数K相关, 即随$K$指数的增大而减小; 在秋季和冬季闪烁发生率与K指数变化无明显关系. 同时还综合分析了地磁与太阳活动的变化对电离层活动的影响, 广州地区闪烁主要发生在太阳活动较低的磁静日期间.      

Effects observed in the ionospheric F-region in the South American sector during the intense geomagnetic storm of 14 December 2006

This investigation presents observations related to the generation of equatorial ionospheric irregularities (also known as equatorial spread F (ESF)) including ionospheric plasma bubbles and dynamic behavior of the ionospheric F-region in the South American sector during an intense geomagnetic storm in December 2006 (a period of low solar activity). In this work, ionospheric sounding observations and GPS data obtained between 13 and 16 December 2006 at several stations in the South American sector are presented. On the geomagnetically disturbed night of 14 and 15 December, ionospheric plasma bubbles were observed after an unusual uplifting of the F-region during pre-reversal enhancement (PRE) period. The unusual uplifting of the F-region during PRE was possibly associated with prompt penetration of electric field of magnetospheric origin. During the geomagnetic disturbance night of 14 and 15 December, strong oscillations due to the propagation of traveling ionospheric disturbances (TIDs) by the Joule heating in the auroral region were observed in the F-region at São José dos Campos (SJC, 23.2°S, 45.9°W; dip latitude 17.6°S), Brazil, and Port Stanley (PST, 51.6°S, 57.9°W; geom. latitude 41.6°S). The VTEC-GPS observations presented on the night of 14 and 15 December 2006 show both positive and negative storm phases in the South American sector, possibly due to changes in the large-scale wind circulation and changes in the O/N₂ ratio in the southern hemisphere, respectively.     

Ionospheric correction using GPS Klobuchar coefficients with an empirical night-time delay model

We proposed an ionospheric correction approach called NKlob to mitigate the ionospheric delay errors. NKlob is a modification of the original GPS Ionospheric Correction Algorithm (ICA), which uses an empirical night-time model depending on the time, geomagnetic location and periodicities of the ionospheric behavior to replace the night-time constant delay in GPS ICA. Performance of NKlob was evaluated by the independent total electron contents (TECs) derived from Global Ionospheric Maps (GIMs) of the International GNSS Services (IGS) and Jason-2 altimetry satellite during 2013–2017. Compared to GIM TECs, NKlob corrects 51.5% of the ionospheric delay errors, which outperforms GPS ICA by 6.3%. Compared to Jason-2 TECs, NKlob mitigates the ionospheric errors by 58.1%, which is approximately 3.7% better than that of GPS ICA. NKlob shows significant improvement in low-latitude and equatorial regions with respect to GPS ICA, meanwhile exhibiting comparable performance at middle and high latitudes. Since NKlob only requires slight technical changes at the processing level of GPS receivers, we suppose that it can be easily implemented for better ionospheric delay corrections of real-time GPS single-frequency applications.     

2008—2009年电离层对重现型地磁活动的响应

利用2008—2009年的GPS TEC数据,分析了电离层对冕洞引起的重现型地磁活动的响应. 结果表明,在太阳活动低年,电离层TEC表现出与地磁 ap指数（采用全球3h等效幅度指数ap来表征）和太阳风速度相似的9天和13.5天短周期变化,表明TEC的这种短周期特性主要与重现型地磁活动相关. 地磁纬度和地方时分析表明,夜间高纬地区正负相扰动明显,中低纬地区则以正相扰动为主,较大的TEC变幅主要发生在南北半球高纬地区,夜间南半球高纬地区TEC变化相对ap指数变化有相位延迟. 白天中低纬地区正负相扰动明显,TEC短周期变化与ap指数变化相位基本一致. 2008年TEC的9天和13.5天周期变化幅度大于2009年.      

Variation of ionospheric total electron content in Indian low latitude region of the equatorial anomaly during May 2007–April 2008

The ionospheric total electron content (TEC), derived by analyzing dual frequency signals from the Global Positioning System (GPS) recorded near the Indian equatorial anomaly region, Varanasi (geomagnetic latitude 14°, 55′N, geomagnetic longitude 154°E) is studied. Specifically, we studied monthly, seasonal and annual variations as well as solar and geomagnetic effects on the equatorial ionospheric anomaly (EIA) during the solar minimum period from May 2007 to April 2008. It is found that the daily maximum TEC near equatorial anomaly crest yield their maximum values during the equinox months and their minimum values during the summer. Using monthly averaged peak magnitude of TEC, a clear semiannual variation is seen with two maxima occurring in both spring and autumn. Statistical studies indicate that the variation of EIA crest in TEC is poorly correlated with Dst-index (r = −0.03) but correlated well with Kp-index (r = 0.82). The EIA crest in TEC is found to be more developed around 12:30 LT.     

磁暴期间电离层扰动的GPS台网观测分析

给出了一种利用GPS台网观测获取TEC快速变化的计算方法，并将该方法用于东亚一澳大利亚扇区的GPS台网观测数据，分析了2000年7月14—18H大磁暴期间的电离层响应，揭示出电离层暴期间赤道异常峰的压缩和移动等特性．计算结果表明，在站点分布不均匀、原始观测数据不足且随时间跳变等多种不利因素的影响下，这种新的算法仍能保持很好的计算稳定性，并能快速地提取给定时空范围内的三维TEC短时变化的特征，适用于研究电离层暴等情况下引起的TEC扰动．     

第24太阳活动周中国地区电离层闪烁统计特性研究

利用第24太阳活动周中国多个地区GNSS电离层闪烁监测站数据,统计分析中国中低纬地区电离层闪烁特性.结果显示:电离层闪烁主要发生在春秋分及夜间20:00—02:00LT时段;在28°N以南地区,纬度越低电离层闪烁强度和发生概率越高;电离层闪烁发生概率与太阳活动呈正相关,太阳活动上升年电离层闪烁发生概率高于下降年;不同强度地磁活动条件下,电离层闪烁均可能发生,且与地磁活动强度整体呈负相关.通过研究电离层闪烁统计特性,可以为电离层闪烁机理的深入研究、预报及工程应用提供参考.      

2004年11月一次磁暴期间全球电离层TEC扰动分析

利用全球分布的GPS原始观测数据提取的电离层总电子含量(TEC)分析了2004年11月6日至12日期间全球电离层暴的形态特点与发展过程.结果表明,11月8日磁暴主相期间电离层暴以大范围的强烈正暴为主,在11月10日的恢复相,Dst又一次降到最低值前后期间,电离层再次受到很强的扰动,大范围的正暴和负暴交替出现.这次磁暴期间夏季半球的负暴更加强烈,反映出负暴偏向于在夏季半球发生的季节变化特点.另外,磁暴期间,夜晚TEC值普遍比磁暴前的平静期要低,具体是什么机制导致还需要进一步收集数据和分析.      

一种电离层场向不规则体各向异性散射模型

电离层场向不规则体散射具有很强的方向性, 利用电离层场向不规则体散 射进行VHF频段超视距通信时, 需要准确可靠地确定其散射分布特性及路径损 耗等参数. 基于电离层不规则体场向散射的特点, 以地球地磁场为坐标系统, 提出了一种电离层场向不规则体各向异性散射模型, 该模型能够计算前向和后 向散射链路的路径损耗分布、时延展宽和相干带宽等参数, 同时运用该模型对 雷达横向截面的计算结果与已有文献的数据结果进行对比, 证明了该模型的准确性. 该模型能够计算电离层场向不规则体VHF频段的散射分布及路径损耗等参数, 为VHF散射通信链路的设计、布站提供依据和技术指导.      

Spread-F occurrence during geomagnetic storms near the southern crest of the EIA in Argentina

This work presents, for the first time, the analysis of the occurrence of ionospheric irregularities during geomagnetic storms at Tucumán, Argentina, a low latitude station in the Southern American longitudinal sector (26.9°S, 294.6°E; magnetic latitude 15.5°S) near the southern crest of the equatorial ionization anomaly (EIA). Three geomagnetic storms occurred on May 27, 2017 (a month of low occurrence rates of spread-F), October 12, 2016 (a month of transition from low to high occurrence rates of spread-F) and November 7, 2017 (a month of high occurrence rates of spread-F) are analyzed using Global Positioning System (GPS) receivers and ionosondes. The rate of change of total electron content (TEC) Index (ROTI), GPS Ionospheric L-band scintillation, the virtual height of the F-layer bottom side (h'F) and the critical frequency of the F2 layer (foF2) are considered. Furthermore, each ionogram is manually examined for the presence of spread-F signatures.The results show that, for the three events studied, geomagnetic activity creates favorable conditions for the initiation of ionospheric irregularities, manifested by ionogram spread-F and TEC fluctuation. Post-midnight irregularities may have occurred due to the presence of eastward disturbance dynamo electric fields (DDEF). For the May storm, an eastward over-shielding prompt penetration electric field, (PPEF) is also acting. A possibility is that the PPEF is added to the DDEF and produces the uplifting of the F region that helps trigger the irregularities. Finally, during October and November, strong GPS L band scintillation is observed associated with strong range spread-F (SSF), that is, irregularities extending from the bottom-side to the topside of the F region.     

Response of the ionospheric F-region in the Brazilian sector during the super geomagnetic storm in April 2000 observed by GPS

The response of the ionospheric F-region in the equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 06–07 April 2000 has been studied in the present investigation. The geomagnetic storm reached a minimum D_st of −288 nT at 0100 UT on 07 April. In this paper, we present vertical total electron content (VTEC) and phase fluctuations (in TECU/min) from GPS observations obtained at Imperatriz (5.5°S, 47.5°W; IMPZ), Brasília (15.9°S, 47.9°W; BRAZ), Presidente Prudente (22.12°S, 51.4°W; UEPP), and Porto Alegre (30.1°S, 51.1°W; POAL) during the period 05–08 April. Also, several GPS-based TEC maps are presented from the global GPS network, showing widespread and drastic TEC changes during the different phases of the geomagnetic storm. In addition, ion density measurements on-board the satellite Defense Meteorological Satellite Program (DMSP) F15 orbiting at an altitude of 840 km and the first Republic of China satellite (ROCSAT-1) orbiting at an altitude of 600 km are presented. The observations indicate that one of the orbits of the DMSP satellite is fairly close to the 4 GPS stations and both the DMSP F15 ion-density plots and the phase fluctuations from GPS observations show no ionospheric irregularities in the Brazilian sector before 2358 UT on the night of 06–07 April 2000. During the fast decrease of D_st on 06 April, there is a prompt penetration of electric field of magnetospheric origin resulting in decrease of VTEC at IMPZ, an equatorial station and large increase in VTEC at POAL, a low latitude station. This resulted in strong phase fluctuations on the night of 06–07 April, up to POAL. During the daytime on 07 April during the recovery phase, the VTEC observations show positive ionospheric storm at all the GPS stations, from IMPZ to POAL, and the effect increasing from IMPZ to POAL. This is possibly linked to the equatorward directed meridional wind. During the daytime on 08 April (the recovery phase continues), the VTEC observations show very small negative ionospheric storm at IMPZ but the positive ionospheric storm effect is observed from BRAZ to POAL possibly linked to enhancement of the equatorial ionospheric anomaly.     

基于IGS电离层TEC格网的扰动特征统计分析

电离层总电子含量（TEC）是研究空间天气特性的重要参量,通过分析电离层TEC,可以了解空间环境的变化特征.利用IGS提供的1999—2016年全球电离层TEC格网数据,按照地磁纬度将全球划分为高、中、中低、低磁纬四个区域,计算不同区域的电离层扰动;利用大量统计数据选取电离层扰动事件的判定阈值,分析电离层扰动与太阳活动、时空之间的关系;计算电离层扰动指数与地磁活动之间的相关系数.结果显示:电离层扰动与太阳活动变化具有较强的正相关特性.在太阳活动低年,电离层扰动事件发生的概率约为1.79%,在太阳活动高年发生扰动的概率约为10.18%.在空间分布上,无论是太阳活动高年还是低年,高磁纬地区发生扰动事件的概率均大于其他磁纬出现扰动事件的概率.计算得到的中磁纬和中低磁纬地区电离层扰动指数与全球地磁指数Ap的相关系数分别为0.57和0.56,说明电离层扰动指数与Ap具有较好的相关关系;高磁纬电离层扰动指数与Ap的相关系数为0.44;低磁纬扰动指数与Ap的相关系数为0.39.以上结果表明,不同区域电离层扰动与全球地磁指数Ap的相关性不同,测定区域地磁指数可能会提高与电离层扰动的相关性.      

First evidence of anisotropy of GPS phase slips caused by the mid-latitude field-aligned ionospheric irregularities

The mid-latitude field-aligned irregularity (FAI) along the magnetic field line is a common phenomenon in the ionosphere. However, few data reveal the field-aligned ionospheric irregularities. They are insufficient to identify FAIs effects so far, particularly effect on global positioning system (GPS) signals. In this paper, the mid-latitude FAIs by line-of-sight angular scanning relative to the local magnetic field vector are investigated using the denser GPS network observations in Japan. It has been the first found that total GPS L2 phase slips over Japan, during the recovery phase of the 12 Feb 2000 geomagnetic storm were caused by GPS signal scattering on FAIs both for the lines-of-sight aligned to the magnetic field line (the field of aligned scattering, FALS) and across the magnetic field line (the field of across scattering, FACS). The FALS results are also in a good agreement with the data of the magnetic field orientation control of GPS occultation observations of equatorial scintillation during thorough low earth orbit (LEO) satellites measurements, e.g. Challenging Minisatellite Payload (CHAMP) and Satellite de Aplicaciones Cientificas-C (SAC-C). The role of large-angle scattering almost along the normal to the magnetic field line in GPS scintillation is determined by attenuation of the irregularity anisotropy factor as compared with the other factors.     

The impact of large solar events on the total electron content of the ionosphere at mid latitudes

Ionospheric disturbances associated with solar activity may occur via two basic mechanisms. The first is related to the direct impact on the ionosphere of EUV photons from a flare, and the second by prompt electric field penetration into the magnetosphere during geomagnetic storms. In this paper we examine the possibility that these two mechanisms may have an impact at mid latitudes by calculating the total electron content (TEC) from GPS stations in Mexico during several large X-ray flares. We have found that indeed large, complex flares, which are well located, may affect the mid latitude ionosphere. In fact, in the solar events of July 14, 2000 and April 2001 storms, ionospheric disturbances were observed to increase up to 138 and 150 TECu, respectively, due to the influence of EUV photons. Also, during the solar events of July 2000, April 2001, Halloween 2003, January 2005 and December 2006, there are large ionospheric disturbances (up to 393 TECu in the Halloween Storms), due to prompt penetration electric field, associated with CME producing geomagnetic storm.     

Traveling ionospheric disturbances observed at South African midlatitudes during the 29–31 October 2003 geomagnetically disturbed period

This paper presents traveling ionospheric disturbances (TIDs) observations from GPS measurements over the South African region during the geomagnetically disturbed period of 29–31 October 2003. Two receiver arrays, which were along two distinct longitudinal sectors of about 18°-20° and 27°-28° were used in order to investigate the amplitude, periods and virtual propagation characteristics of the storm induced ionospheric disturbances. The study revealed a large sudden TEC increase on 28 October 2003, the day before the first of the two major storms studied here, that was recorded simultaneously by all the receivers used. This pre-storm enhancement was linked to an X-class solar flare, auroral/magnetospheric activities and vertical plasma drift, based on the behaviour of the geomagnetic storm and auroral indices as well as strong equatorial electrojet. Diurnal trends of the TEC and foF2 measurements revealed that the geomagnetic storm caused a negative ionospheric storm; these parameters were depleted between 29 and 31 October 2003. Large scale traveling ionospheric disturbances were observed on the days of the geomagnetic storms (29 and 31 October 2003), using line-of-sight vertical TEC (vTEC) measurements from individual satellites. Amplitude and dominant periods of these structures varied between 0.08–2.16 TECU, and 1.07–2.13 h respectively. The wave structures were observed to propagate towards the equator with velocities between 587.04 and 1635.09 m/s.     

Study of mid-latitude ionospheric convection during quiet and disturbed periods using the SuperDARN Hokkaido radar

Westward ionospheric convective flows around midnight are frequently observed at mid-latitudes. They can be generated by so-called disturbance dynamo mechanisms working mainly in the mid-latitudes. To understand the influence of disturbance dynamo effects in the mid-latitudes, we studied the latitudinal distribution of westward flows in association with several kinds of geomagnetic disturbances using the SuperDARN Hokkaido radar. This radar creates high temporal resolution (1 s to 2 min), two-dimensional observations measuring the line-of-sight velocities of ionospheric plasma irregularities, which can be regarded as line-of-sight velocities of ionospheric convection in the mid-latitude region from 40° to 50°. This region could not be monitored using preexisting SuperDARN radars. In this study, we used ionospheric echo data obtained by the SuperDARN Hokkaido radar over 5 years (December 2006 to November 2011). We identified westward flows around midnight at about 40° to 55° geomagnetic latitude. Additionally, the data showed that the westward flow around midnight intensified under high geomagnetic activity (high Kp). This suggests that the disturbance dynamo could affect the mid-latitude ionospheric convection. We performed Superposed Epoch Analysis (SEA) to study the influences from the geomagnetic disturbances on mid-latitude ionospheric convection. We found no obvious influence during major storms (minimum Dst below −60 nT). SEA was also used to study the temporal and latitudinal dependence on the influences from substorms. From analysis of 36 events of AL-defined substorms, we saw that the influence of substorms lasted from 5 to 20 h after the onset between 44° and 53° geomagnetic latitude. The westward flow at mid-latitude grew to a maximum at 12 h after the geomagnetic substorm onset. This is consistent with the results of past numerical simulation studies of the disturbance dynamo effects.     

Trans-ionospheric GPS signal delay gradients observed over mid-latitude Europe during the geomagnetic storms of October–November 2003

Ionospheric disturbances are known to have adverse effects on the satellite-based communication and navigation. One particular type of ionospheric effects, observed during major geomagnetic storms and threatening the integrity performance of both ground-based and space-based GNSS augmentation systems, is the sharp increase/decrease in the ionospheric delay that propagates in horizontal direction, thus called for convenience ‘moving ionospheric wall’. This paper presents preliminary results from researching such anomalous ionospheric delay gradients at European middle latitudes during the storm events of 29 October 2003 and 20 November 2003. For the purpose, 30-s GPS data from the Belgian permanent network was used for calculating and analysing the slant ionospheric delay and total electron content values. It has been found that, during these two particular storm events, substantial gradients did occur in Europe although they were not so pronounced as in the American sector.     

An investigation of ionospheric disturbances over South Africa during the magnetic storm on 15 May 2005

The effects of the 15 May 2005 severe geomagnetic storm on the South African ionosphere are studied using ground-based and satellite observations. Ionospheric disturbances have less frequently been investigated over mid-latitude regions. Recently, a number of studies investigated their evolution and generation over these regions. This paper reports on the first investigation of travelling ionospheric disturbances (TIDs) over mid-latitude South Africa. Using global positioning system (GPS)-derived total electron content (TEC) variations from the South African network of dual frequency GPS receivers, we were able to examine the effects of the disturbance on the TEC. During this storm, two TEC enhancements were observed at low- and mid-latitudes: the first enhancement was observed between 30–45°S geomagnetic latitudes associated with equatorward neutral winds and the passage of a TID, while the second TEC enhancement is associated with a second TID. In addition, the F-region critical frequency (foF2) values observed at two ionosonde stations show response features that differ from those of the TEC during the disturbance period. The dissimilarity between the TEC and the foF2 suggests that two competing drivers may have existed, i.e., the westward electric field and equatorward neutral wind effects.     

Total electron content of the ionosphere at two stations in East Africa during the 24–25 October 2011 geomagnetic storm

The equatorial ionosphere has been known to become highly disturbed and thus rendering space-based navigation unreliable during space weather events, such as geomagnetic storms. Modern navigation systems, such as the Global Positioning System (GPS) use radio-wave signals that reflect from or propagate through the ionosphere as a means of determining range or distance. Such systems are vulnerable to effects caused by geomagnetic storms, and their performance can be severely degraded. This paper analyses total electron content (TEC) and the corresponding GPS scintillations using two GPS SCINDA receivers located at Makerere University, Uganda (Lat: 0.3^o N; Lon: 32.5^o E) and at the University of Nairobi, Kenya (Lat: 1.3^o S; Lon: 36.8^o E), both in East Africa. The analysis shows that the scintillations actually correspond to plasma bubbles. The occurrence of plasma bubbles at one station was correlated with those at the other station by using observations from the same satellite. It was noted that some bubbles develop at one station and presumably “die off” before reaching the other station. The paper also discusses the effects of the geomagnetic storm of the 24–25 October 2011 on the ionospheric TEC at the two East African stations. Reductions in the diurnal TEC at the two stations during the period of the storm were observed and the TEC depletions observed during that period showed much deeper depletions than on the non-storm days. The effects during the storm have been attributed to the uplift of the ionospheric plasma, which was then transported away from this region by diffusion along magnetic field lines.     

利用人工神经网络提前1h预报电离层TEC

提出了一种利用人工神经网络提前1h预报电离层TEC的简便方法. 考虑到实际工程应用要求, 没有使用其他空间天气参数, 而是选择电离层TEC观测数据本身作为输入参数. 输入参数为当前时刻TEC、一阶差分、相对差分和时间, 输出参数为预报时刻TEC. 利用文中介绍的GPS/TEC处理方法解算厦门站2004年电离层TEC观测数据, 对预报方法进行评估, 全年平均相对误差为9.3744%, 预报结果与观测值相关性达到了0.96678. 结果表明, 利用人工神经网络方法提前1h预报电离层TEC有很好的应用前景.