利用IGS-TEC数据分析中国华南地区电离层赤道异常北驼峰的变化特征

利用2010年11月至2011年10月IGS提供的全球电子浓度总含量(TEC)数据, 分析太阳活动上升期华南地区(经度110°E, 纬度5°—35°N) 上空电离层赤道异常(EIA)北驼峰的变化特征. 结果显示, 电离层赤道异常北驼峰区TEC峰值I具有明显的季节和半年变化特征; 北驼峰峰值出现的时间T和纬度L的日变化有一个相对较大的变化区间, 其季节和半年变化特征并不明显; 太阳活动对北驼峰变化影响比较明显, 而地磁活动对北驼峰变化影响不明显.      

电离层赤道异常峰区的微分多普勒跟踪

本文介绍在武汉(30.5°N,114.4°E)地区利用微分多普勒方法对电离层赤道异常峰进行跟踪的结果.由观测资料的分析表明,东经115°线附近,电离层赤道异常峰区在我国长沙(28.1°N,113.0°E)以南和广州(23.2°N,113.3°E)以北地段,其北‘驼峰’顶位于衡阳(26.8°N,112.5°E)至英德(24.2°N,113.5°E)一带上空.对异常峰活动特征的研究也获得了一些有益结果.     

利用聚类算法区分小尺度电离层行扰事件与赤道等离子体泡事件

利用Swarm卫星2015年1月1日至2019年12月31日的50Hz高频磁场数据,根据阈值判断垂直于主磁场方向的扰动,对磁纬45°N-45°S之间的小尺度电离层行扰事件进行探测.为避免混淆而产生的干扰,可以根据阈值判断平行于主磁场方向是否发生扰动,从而排除典型的赤道等离子体泡事件.但对于较弱的赤道等离子体泡事件,扰动阈值判断无效.为避免弱赤道等离子体泡事件的污染,根据小尺度电离层行扰事件和赤道等离子体泡事件在不同参数空间中的密度分布差异,利用基于密度的聚类算法将赤道等离子体泡事件进一步甄别提取.结果表明,聚类算法能够有效地将赤道等离子体泡事件从小尺度电离层行扰事件中甄选出来,并使小尺度电离层行扰事件聚类与赤道等离子体泡事件聚类形成清晰的边界.由聚类算法导出的弱赤道等离子体泡事件主要分布在磁纬15°N-15°S,地理经度20°-60°W,月份10至3月之间,并且在20:00MLT-24:00MLT存在高发生率,同时依赖于太阳活动,这也验证了前人的相关研究结果.      

用高分辨率地磁资料考察磁层耦合的特征

用取自１００°Ｅ和３００°Ｅ的两条地磁经度链附近１１个台站的１ｍｉｎ均值地磁资料,分析了１９９４年１１月２６日磁暴期间的磁扰特征,由Ｈ和Ｚ分量变得知,一区和二区场向电流的变化发展是磁层－电离层电动耦合中的重要过程,它们对于极光区和中纬区电离层的作用效果有很大差异。     

广州地区上空电离层F_2层异常

广州电离层观测站位于磁赤道附近(地磁经纬度:183.0°E,11.5°N).根据对18个站电离层资料的分析,广州站位于f_0F_2极大值双驼峰现象北侧的位置;在太阳活动高年期间,f_0F_2极大值在夜间仍然保持存在;另外,电离层骚扰发生的次数多于国内各电离层观测站发生的次数.这些特性都是F_2层赤道异常现象.     

F2层对地磁扰动的响应

利用37个电离层垂直探测站1974-1986年的数据,采用f0F2与地磁ap指数相关分析的方法,首次得到一个太阳活动周期各年东亚-澳大利亚扇区,欧洲-非洲扇区和美洲-东太平洋扇区F2层对地磁扰动响应随地磁纬度的分布.结果指出,地磁高纬和中纬地区为负响应,低纬和赤道地区为正响应,大约在±30°附近换向.最大正响应在磁赤道附近,最大负响应在地磁纬度±50°附近,最大负响应的幅度大于最大正响应的幅度.存在明显的经度差别和南北半球不对称性.     

地磁暴期间中国中低纬电离层的CIT研究

利用电离层层析成像技术(Computerized Ionospheric Tomography, CIT)处理115°E子午圈附近6个台站的GPS观测数据, 分析了2004年11月地磁暴期间中国中低纬电离层的响应情况. 结果表明, 电离层呈正相扰动, 且不同高度上的响应不同, 800 km以下电子密度有不同程度的增加, 且在峰值高度附近增幅最大, 800 km以上地磁暴的影响并不显著; 伴随地磁能量的注入, 赤道异常峰极向扩展; 随磁扰强度的降低, 电子密度也逐渐恢复至平静水平. 这些结果与以往的理论和观测结果一致, 初步估计扰动是由热层暴环流引起的, 并受到赤道异常峰移动的影响.      

一次中等磁暴期间全球电离层TEC及ROTI指数变化分析

地磁暴发生时,电离层会有偏离平均水平的强烈扰动.基于全球电离层TEC及其时间变化率ROTI(Rate of TEC Index)数据,对2014年8月一次中等强度磁暴期间的全球电离层影响进行了分析,探讨了磁暴所引发电离层暴的可能机制.研究发现,本次磁暴伴随有明显的电离层暴效应.磁暴期间:南半球电离层以正相暴为主,北半球电离层暴则整体表现为短暂正相暴后长时间强的负相暴;电离层在北半球的下降比南半球强,并且这种下降持续了约一周时间;低纬区域电离层变化幅度明显小于中纬区域,高纬区域则主要表现为负暴效应;赤道北驼峰出现了明显的南移现象,直至磁赤道两侧双驼峰结构消失.对磁暴期间三个不同扇区的电离层ROTI变化的分析表明:欧洲-非洲扇区磁暴前有电离层闪烁发生,磁暴发生后消失,而东亚-澳大利亚及美洲扇区则无此现象出现.研究结果表明,此次磁暴期间的电离层变化存在明显的时间和空间差异.     

一次中等磁暴期间全球电离层TEC及ROTI指数变化分析

地磁暴发生时,电离层会有偏离平均水平的强烈扰动.基于全球电离层TEC及其时间变化率ROTI(Rate of TEC Index)数据,对2014年8月一次中等强度磁暴期间的全球电离层影响进行了分析,探讨了磁暴所引发电离层暴的可能机制.研究发现,本次磁暴伴随有明显的电离层暴效应.磁暴期间:南半球电离层以正相暴为主,北半球电离层暴则整体表现为短暂正相暴后长时间强的负相暴;电离层在北半球的下降比南半球强,并且这种下降持续了约一周时间;低纬区域电离层变化幅度明显小于中纬区域,高纬区域则主要表现为负暴效应;赤道北驼峰出现了明显的南移现象,直至磁赤道两侧双驼峰结构消失.对磁暴期间三个不同扇区的电离层ROTI变化的分析表明:欧洲-非洲扇区磁暴前有电离层闪烁发生,磁暴发生后消失,而东亚-澳大利亚及美洲扇区则无此现象出现.研究结果表明,此次磁暴期间的电离层变化存在明显的时间和空间差异.     

低纬(海南)电离层等离子体漂移对地磁活动的响应

利用2003-2016年期间子午工程海南站（19.5°N,109.1°E）数字测高仪观测到的电离层等离子体漂移数据,分析了高低两种太阳活动条件下纬向和垂直向漂移对近磁静、中等磁扰和强磁扰三种地磁活动水平的响应特性.结果表明:日间纬向漂移各季节均以西向为主,随地磁活动无明显变化,白天日出附近和夜间漂移在各季节均以东向为主,随地磁活动增强而减弱,减弱程度在分季最大,在夏季最小;日间垂直漂移在零值附近变化,且不受地磁活动和季节影响,日落附近漂移仅在分季受到地磁活动的抑制,午夜前垂直漂移在分季受到抑制,在冬季因强磁扰而反向,夏季无明显规律,子夜至日出后垂直漂移在各季节随地磁活动增强而减小.与赤道区Jicamarca相比,两地漂移对地磁活动的响应相近,但在幅度和相位上存在差异,这可能是两地区的地理位置、背景电场和风场结构等不同造成的.      

赤道异常峰区电离层的某些特点

由于赤道异常北峰覆盖我国整个南部地带,因此对峰区电离层特征的研究就成为掌握中国电离层特点的关键之一。本文试图对以下六个问题作些介绍和评述:1.逐日起伏和子夜前极大;2.峰位置的移动;3.赤道异常的经度效应;4.不均匀结构引起的强闪烁和快速法拉第衰落;5.顶部电离层的离化突起和中性赤道异常;6.粒子沉降的双峰分布.      

TEC计算方法探讨和赤道异常北驼峰时空特征测量初析

本文探讨了应用最小曲率原理由单站微分多普勒频移数据计算TEC时所遇到的问题和解决办法。处理了用MX1502大地定位接收机于1989年8月和9月先后在陕西临潼和北京观测的NNSS卫星多普勒频移数据,得到了TEC时空分布曲线。分析这些曲线,得到了TEC赤道异常北驼峰时空特征在太阳活动高年(尤其是8月中旬太阳特大质子事件中)的某些结果。     

赤道异常的行星波周期振荡的统计特征与逐年变化及其QBO调制

利用赤道异常峰区台站(Okinawa)观测的, f₀F₂资料(1977—1990), 分析计算了赤道电离层行星波周期振荡(2日、3—4日、5—7日及10—16日)的特征及其变化规律, 发现其在一年四季都有出现, 但相对强度在冬、夏季较大, 且冬季更强;其振荡周期也随季节有所变化, 以2日波而言, 夏季更接近于2日, 而冬季则多在2日多至2日半区间振荡;更长周期的波的所谓夏季峰值的出现, 还有向夏初和夏末过渡的趋势。并发现振荡与太阳活动性呈负相关, 即低年的相对幅度要强于高年, 并且周期越长负相关越显著;同时显示出振荡的出现率及频率变化受到QBO的调制, QBO东风相期间比西风相更易于出现长周期振荡。这些结果说明赤道电离层明显受到中低层大气动力学变化的向上耦合的影响。      

Solar cycle effect on temporal and spatial variation of topside ion density measured by SROSS C2 and ROCSAT 1 over the Indian longitude sector

We investigated the diurnal, seasonal and latitudinal variations of ion density Ni over the Indian low and equatorial topside ionosphere within 17.5°S to 17.5°N magnetic latitudes by combining the data from SROSS C2 and ROCSAT 1 for the 9 year period from 1995 to 2003 during solar cycle 23. The diurnal maximum density is found in the local noon or in the afternoon hours and the minimum occurs in the pre sunrise hours. The density is higher during the equinoxes as compared to that in the June and December solstice. The local time spread of the daytime maximum ion density increases with increase in solar activity. A north south asymmetry with higher ion density over northern hemisphere in the June solstice and over southern hemisphere in December solstice has been observed in moderate and high solar activity years. The crest to crest distance increases with increase in solar flux. Ion density bears a nonlinear relationship with F_10.7 cm solar flux and EUV flux in general. The density increases linearly with solar flux up to ∼150 sfu (1 sfu = 10⁻²²Wm⁻²Hz⁻¹) and EUV flux up to ∼50 units (10⁹ photons cm⁻² s⁻¹). But beyond this the density saturates. Inverse saturation and linear relationship have been observed in some season or latitude also. Inter-comparison of the three solar activity indices F_10.7 cm flux, EUV flux and F_10.7P (= (F_10.7 + F_10.7A)/2, where F_10.7A is the 81 day running average value of F_10.7) shows that the ion density correlates better with F_10.7P and F_10.7 cm fluxes. The annual average daytime total ion density from 1995 to 2003 follows a hysteresis loop as the solar cycle reverses. The ion density at 500 km over the Indian longitude sector as obtained by the international reference ionosphere is in general lower than the measured densities during moderate and high solar activity years. In low solar activity years the model densities are equal or higher than measured densities. The IRI EIA peaks are symmetric (±10°) in equinox while densities are higher at 10°N in June solstice and at 10°S in the December solstice. The model density follows F_10.7 linearly up to about F_10.7 > ∼150 sfu and then saturates.     

Some ionospheric storm effects at equatorial and low latitudes

In this paper, the response of the equatorial and low latitude ionosphere to three intense geomagnetic storms occurred in 2002 and 2003 is reported. For that, critical frequency of F2-layer foF2 and the peak height hmF2 hmF2 for the stations Jicamarca (11.9°S), Ascension Is (7.92°S) and Tucuman (26.9°S) are used. The results show a “smoothing” of the Equatorial Anomaly structure during the development of the storms. Noticeable features are the increases in foF2 before the storm sudden commencement (SC) at equatorial latitudes and the southern crest of the Equatorial Anomaly. In some cases nearly simultaneous increases in foF2 are observed in response to the storm, which are attributed to the prompt electric field. Also, positive effects observed at equatorial and low latitudes during the development of the storm seem to be caused by the disturbance dynamo electric field due to the storm-time circulation. Increases in foF2 above the equator and simultaneous decreases in foF2 at the south crest near to the end of a long-duration main phase are attributed to equatorward-directed meridional winds. Decreases in foF2 observed during the recovery phase of storms are believed to be caused by composition changes. The results indicate that the prompt penetration electric field on the EA is important but their effect is of short lived. More significant ionospheric effects are the produced by the disturbance dynamo electric field. The role of storm-time winds is important because they modify the “fountain effect” and transport the composition changes toward low latitudes.     

Role of Equatorial Anomaly in Earthquake time precursive features: A few strong events over West Pacific zone

The earthquake (EQ) time coupling processes between equator-low-mid latitude ionosphere are complex due to inherent dynamical status of each latitudinal zone and qualified geomagnetic roles working in the system. In an attempt to identify such process, the paper presents temporal and latitudinal variations of ionization density (foF₂) covering 45°N to 35°S, during a number of earthquake events (M?>?5.5). The approaches adopted for extraction of features by the earthquake induced preparatory processes are discussed in the paper through identification of parameters like the ‘EQ time modification in density gradient’ defined by δ?=?(foF_{2 max}???foF_{2 min})∕τ_mm, where τ_mm – time span (in days) between EQ modified density maximum and minimum, and the Earthquake time Equatorial Anomaly, i.e. EEA, one of the most significant phenomenon which develops even during night time irrespective of epicenter position. Based on the observations, the paper presents the seismic time coupling dynamics through anomaly like manifestations between equator, low and mid latitude ionosphere bringing in the global Total Electron Content (TEC) features as supporting indices.     

Comparison of GPS TEC variations with IRI-2007 TEC prediction at equatorial latitudes during a low solar activity (2009–2011) phase over the Kenyan region

This work presents an analysis of the Total Electron Content (TEC) derived from the International GNSS Service (IGS) receivers at Malindi (mal2: 2.9^oS, 40.1^oE, dip −26.813^o), Kasarani (rcmn: 36.89^oE, 1.2^oS, dip −23.970^o), Eldoret (moiu: 35.3^oE, 0.3^oN, dip −21.037^o) and GPS-SCINDA (36.8^oE, 1.3^oS, dip −24.117^o) receiver located in Nairobi for the period 2009–2011. The diurnal, monthly and seasonal variations of the GPS derived TEC (GPS-TEC) and effects of space weather on TEC are compared with TEC from the 2007 International Reference Ionosphere model (IRI-TEC) using the NeQuick option for the topside electron density. The diurnal peaks in GPS-TEC is maximum during equinoctial months (March, April, October) and in December and minimum in June solstice months (May, June, July). The variability in GPS-TEC is minimal in all seasons between 0:00 and 04:00 UT and maximum near noon between 10:00 and 14:00 UT. Significant variability in TEC at post sunset hours after 16:00 UT (19:00 LT) has been noted in all the seasons except in June solstice. The TEC variability of the post sunset hours is associated with the occurrence of the ionization anomaly crest which enhances nighttime TEC over this region. A comparison between the GPS-TEC and IRI-TEC indicates that both the model and observation depicts a similar trend in the monthly and seasonal variations. However seasonal averages show that IRI-TEC values are higher than the GPS-TEC. The IRI-TEC also depicts a double peak in diurnal values unlike the GPS-TEC. This overestimation which is primarily during daytime hours could be due to the model overestimation of the equatorial anomaly effect on levels of ionospheric ionization over the low latitude regions. The IRI-TEC also does not show any response to geomagnetic activity, despite the STORM option being selected in the model; the IRI model generally remains smooth and underestimates TEC during a storm. The GPS-TEC variability indicated by standard deviation seasonal averages has been presented as a basis for extending the IRI-model to accommodate TEC-variability.     

Temporal and spatial variation of equatorial ionization anomaly by using multistation ionosonde data for the 19th solar cycle over the Indian region

The paper deals with the study of temporal and spatial variation of equatorial ionization anomaly (EIA) phenomenon along with its dependence on solar activity and season during the 19th solar cycle by using seven Indian ionosonde stations. Present study is an attempt to carry out the comprehensive study of EIA by using the limited number of ground based instruments. This has been achieved by performing the Gaussian fitting over the latitudinal distribution of F2-region critical frequency (foF2) data. Results reveal that the phenomenon of EIA has a strong dependence on solar activity and seasons. The EIA crest exhibits the feature of latitudinal shifting and expansion with increasing solar activity. It is found out that the effect of solar cycle and seasons on EIA is local time dependent. The observations were also compared with the IRI-2001 model predictions and results reveal that the model values are in general agreement with the observed values with some discrepancies, particularly during the high solar activity period and morning sector. The results have been discussed in the light of relative contribution from transequatorial interhemispheric neutral wind and strength of equatorial fountain process during different local time, season and solar activity levels. Furthermore, an attempt is made to parameterize the location and foF2 of the EIA crest by using the regression analysis. These results can be used to predict the latitudinal position and foF2 of the EIA crest for any given 12-month running average sunspot number (R12).     

Variation of ionospheric total electron content in Taiwan region of the equatorial anomaly from 1994 to 2003

The ionospheric total electron content (TEC) in the northern hemispheric equatorial ionospheric anomaly (EIA) region is studied by analyzing dual-frequency signals of the Global Position System (GPS) acquired from a chain of nine observational sites clustered around Taiwan (21.9–26.2°N, 118.4–112.6°E). In this study, we present results from a statistical study of seasonal and geomagnetic effects on the EIA during solar cycle 23: 1994–2003. It is found that TEC at equatorial anomaly crests yield their maximum values during the vernal and autumnal months and their minimum values during the summer (except 1998). Using monthly averaged I_c (magnitude of TEC at the northern anomaly crest), semi-annual variations is seen clearly with two maxima occurring in both spring and autumn. In addition, I_c is found to be greater in winter than in summer. Statistically monthly values of I_c were poorly correlated with the monthly Dst index (r = −0.22) but were well correlated with the solar emission F_10.7 index (r = 0.87) for the entire database for the period during 1994–2003. In contrast, monthly values of I_c were correlated better with Dst (r ? 0.72) than with F_10.7 (r ? 0.56) in every year during the low solar activity period (1994–1997). It suggests that the effect of solar activity on I_c is a longer term (years), whereas the effect of geomagnetic activity on I_c is a shorter term (months).