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.     

国际参考电离层模型输出参数峰值高度性能

电离层峰值高度H_mF₂是描述电离层形态的重要参数之一,国际参考电离层模型IRI-2016中融入了大量电离层测高仪和无线电掩星探测数据,用以提升H_mF₂的预测精度.本文利用太阳活动低年（2007—2010年）气象、电离层和气候卫星联合观测系统COSMIC探测数据描述全球范围内COSMIC H_mF₂的三维形态变化,对比分析了IRI-2016与IRI-2012模型的预测结果,同时分析了IRI-2016模型输出H_mF₂的性能.结果表明,IRI模型在中高纬度地区的输出结果高于COSMIC反演结果,而赤道及低纬地区则大都偏低.与IRI-2012模型相比,IRI-2016模型的输出结果在夜间至凌晨时段呈现较为明显的纬向梯度变化且大部分区域输出值偏高,但在白天时段赤道附近区域的输出值大都偏低.上述结果为电离层IRI模型的完善提供了一定参考.      

基于IRI-2012模型广州地区f_0F_2实测与预测的对比分析

利用广州台站(23.2°N,113.3°E)的实测数据和IRI-2012模型提供的预测数据,对比分析了2013年广州地区f_0F2的变化特征.结果表明,IRI-2012模型能够较好预测该地区f_0F_2的变化趋势,并且CCIR参数得到的预测值比URSI参数更接近实测值;预测值与实测值存在系统偏差,在11:00 LT-06:00 LT时段,观测值均比预测值大,其他时段则相反.在日落后至午夜前时段,预测值与实测值有较大差距.绝对偏差的极值点通常出现在20:00 LT左右,最大超过4 MHz.相对偏差变化比较明显的时段是午夜后至凌晨;在02:00 LT或04:00 LT及06:00 LT附近,可能会出现双误差峰值点,最大超过0.4;但在σ变化很大的20:00 LT附近,相对偏差却变化不大.夜间增强现象会使得偏差增大,导致预测值不能很好反映实测f_0F2的变化.     

基于神经网络的磁平静期赤道电集流预测

利用BP神经网络技术分别对2008年后磁平静期印度扇区、秘鲁扇区以及CHAMP卫星的赤道电集流(EEJ)变化进行预测,其中神经网络训练数据为对应的2000-2007年磁平静期EEJ观测数据,输入参量为天数、地方时、太阳天顶角、太阳活动指数(F10.7)、太阴时以及卫星地理经度,输出参量为EEJ.对EEJ预测结果进行了统...     

夏季强对流活动对东亚低纬电离层不规则体影响的事件分析

利用海南台站和东南亚地区的多种地基和天基观测手段,对2014年7月28日夜间观测到的东亚低纬F区不规则体事件的时空变化及其物理过程进行分析。结果表明,海南台站观测到了罕见的长时间持续的F区电离层不规则体,不同手段观测到的电离层不规则体存在明显的形态差异。不同台站观测到的电离层不规则体活动存在明显的差异。海南台站经度区南北异常峰附近的TEC起伏活动在日落后至午夜附近明显增强,在午夜后明显减弱。C/NOFS卫星轨迹午夜后逐渐接近于磁赤道,且处于较低高度上,几乎总会观测到弱等离子体扰动/泡的发生,与该区域地基观测的弱电离层不规则体活动存在明显的联系。SWARM卫星在黎明海南台站附近经度区仍观测到较强的赤道异常双峰结构,且西侧异常峰区附近仍存在明显的等离子体密度耗空/泡结构。海南台站西侧磁赤道区附近（中南半岛）强对流活动（MCC）激发的重力波种子扰动对东亚低纬区等离子体泡及准周期结构的产生发挥了重要作用。      

赤道地区和中纬度地区扩展F的特点和比较

通过数值模拟研究了赤道地区和中纬度地区扩展F的触发机制间的联系,发现相同的触发机制在不同纬度的条件下所演化出的结构形态不相同,因此观测上会有所不同;研究了西向电场在赤道地区的作用,发现在适合的电离层参数组合下会产生观测到的电离层F区顶部扰动出现率高于底部扰动出现率的状况;在数值模拟的基础上提出了一个中纬度地区电波散射的模型,用以解释观测到的中纬度地区电波散射的出现率高于线性理论预期的现象.      

论赤道扩展F的密度不规则体(Ⅰ)

本文从等离子体二流体方程组出发,导出适于描述晚间赤道F层现象的DFA模型。证明该模型存在大量偶极涡解。它们可望用于解释赤道扩展F过渡区和中小尺度两区域内存在的大量密度不规则体事实。      

电离层N_mF_2的准27天变化

利用1969-1980年期间东亚和澳大利亚扇区不同地磁纬度11个台站的电离层垂直探测数据,采用带通滤波的方法,分析了白天NmF2的准27天变化特征及其与太阳活动指数F10.7的相关关系.结果表明,在大多数年里,太阳活动指数F10.7和NmF2的短周期(2～70天)频谱中,27天周期附近都出现明显的极大值;在27天波段,F10.7和NmF2的标准偏差有逐年变化特征,F10.7的平均标准偏差为10.9%,NmF2 的标准偏差随地磁纬度变化,赤道地区最小,纬度越高标准偏差越大,11个站的平均标准偏差为8.2%;在27天波段,NmF2与F10.7存在显著的相关,在0.05的显著水平下,显著相关的概率在90%以上;NmF2相对于F10.7的准27天变化平均滞后2天左右;从总体上看,太阳EUV辐射的准27天变化是造成NmF2准27天变化的主要原因.     

赤道地区热层纬向风反转时间和风速的经度分布差异

使用CHAMP卫星观测资料和TIEGCM模拟数据,研究了太阳活动低年春秋分季节赤道地区热层纬向风的反转时间和风速在经度分布上的差异,重点分析了离子拖曳力在不同地磁场构型下对纬向风速地理经度分布的影响.研究发现,纬向风一般在清晨时段由东向转为西向,下午时段由西向转为东向,但反转时间存在明显的经度差异,最大经度差异可达1....     

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.     

A comparative study of decision tree,random forest,and convolutional neural network for spread-F identification

Ionospheric spread-F (SF) is a commonly observed phenomenon of electron density perturbation in the F-layer. The ionospheric irregularities structure has an adverse effect on the propagation of electromagnetic waves in the ionosphere. The automatic identification of ionospheric spread-F and statistical study of the formation of spread-F are of great significance to the study of the physical mechanism of ionospheric inhomogeneity and for prediction of ionospheric irregularities. In this paper, we describe and implement three automatic identification methods of spread-F based on machine learning: decision tree, random forest, and convolutional neural network (CNN). The performance of these automatic identification methods was verified using a large set of test data. Results show that the accuracy of all three methods on identifying ionograms with spread-F exceeded 90%. After comparing the results of the three methods, we found that the decision tree method was the simplest and with the structure easiest to be understood, and it required the shortest interpretation time. In terms of the identification results, the random forest method provided better results than the decision tree method, and the CNN method was the best at accurately identifying ionograms with spread-F.     

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.     

中纬地区日间类扩展F不规则结构的观测研究

基于高频多普勒观测,研究中纬地区日间类扩展F现象及其与其他电离层扰动现象的关联.结果表明:日间类扩展F具有出现时间覆盖面广、持续时间长、与其他电离层扰动相互伴随等特征;形态特征表现为回波弥散（与夜间扩展F相似）,弥散回波的频移多倾向于正向偏移,有时与行进电离层扰动（TIDs）相互伴随.日间类扩展F现象虽然是偶发事件,且发生率极低,但其出现时间及区域的广泛性充分体现了该现象对空间天气及空间环境的影响具有不可忽视的重要性.      

A comparative study of ionospheric spread-F and scintillation at low- and mid-latitudes in China during the 24th solar cycle

The spread-F echo of ionograms and scintillation of satellite signal propagation along the Earth-space path are two typical phenomena induced by ionospheric irregularities. In this study, we obtained spread-F data from HF (high frequency) digital ionosonde and scintillation index (S4) data from L-band and UHF receivers at low- and mid-latitudes in China during the 24th solar cycle. These four sites were located at Haikou (HK) (20°N, 110.34°E), Kunming (KM) (25.64°N, 103.72°E), Qingdao (QD) (36.24°N, 120.42°E), and Manzhouli (MZL) (49.56°N, 117.52°E). We used these data to investigate spread-F and scintillation occurrence percentages and variations with local time, season, latitude and solar activity. A comparative study of spread-F and scintillation occurrence rates has been made. The main conclusions are as follows: (a) FSF occurred mostly during post-midnight, while RSF and scintillation appeared mainly during pre-midnight at HK and KM; (b) FSF occurrence rates were larger at QD and MZL than expected; (c) the FSF occurrence percentages were anti-correlated with solar activity at HK and KM; meanwhile RSF and scintillation occurrence rates increased with the increase of solar activity at this two sites; (d) the highest FSF occurrence rates mostly appeared during the summer months, while RSF and scintillation occurred mostly in the equinoctial months at HK and KM; (e) the scintillation occurrence was usually associated with the appearance of RSF, probably due to a different physical mechanism comparing with FSF. Some of these results verified the conclusions of previous papers, whereas some show slight difference. These results are important in understanding ionospheric irregularities variations characteristic at low- and mid-latitudes in China.     

Statistical characteristics of locally generated ESF during equinoctial months over Sanya

Understanding the local generation rate of equatorial spread-F (ESF) is important for forecasting ionospheric scintillation. Using the GPS ionospheric scintillation/TEC and VHF radar data during March-April and September-October from 2010 to 2014, the occurrence of ionospheric scintillation, TEC fast fluctuation, and backscatter plume were studied. Through analyzing the simultaneous occurrence of ionospheric scintillation, TEC fast fluctuation and backscatter plume, the local generation rate of ESF over Sanya was investigated. The results show that the monthly generation rate varies between 0% and 68%. A significant equinoctial asymmetry of local generation rate of ESF can be found in 2010, 2013 and 2014. The local generation rate of ESF increases from 2010 to 2014 during March-April, while it does not have similar trend during September-October. The plasma vertical drift influenced by solar activity has a significant impact on the monthly generation rate. The equinoctial asymmetry of plasma vertical drift may contribute a lot to the equinoctial asymmetry of the generation rate of ESF.     

Predicting the probability of occurrence of spread-F over Brazil using neural networks

The probability of occurrence of spread-F can be modeled and predicted using neural networks (NNs). This paper presents a feasibility study into the development of a NN based model for the prediction of the probability of occurrence of spread-F over selected equatorial stations within the Brazilian sector. The input space included the day number (seasonal variation), hour (diurnal variation), sunspot number (measure of the solar activity), magnetic index (measure of the magnetic activity) and magnetic position. Twelve years of spread-F data from Brazil (covering the period 1978–1989) measured at the equatorial site Fortaleza (3.9°S, 38.45°W) and low latitude site Cachoeira Paulista (22.6°S, 45.0°W) are used in the development of an input space and NN architecture for the model. Spread-F data that is believed to be related to plasma bubble developments (range spread-F) was used in the development of the model. The model results show the probability of spread-F occurrence as a function of local time, season and latitude. Results from the Brazilian Sector NN (BSNN) based model are presented in this paper, as well as a comparative analysis with a Brazilian model developed for the same purpose.     

Role of neutral winds in generating irregularities in equatorial F-region

Electron density and neutral wind velocity measurements were carried out by rocketborne probes from rocket ranges in India. The experiments were carried out at the time of the onset of spread-F at sunset hours. The results show that a neutral wind velocity in north-south direction greater than 100 m/sec is required to trigger spread-F. It is suggested that spread-F is generated by the interaction of neutral gas with ionospheric plasma.     

A method for automatic detection of equatorial spread-F in ionograms

A method is presented for automatic detection of spread-F. The method is based on an image recognition technique and is applied to ionograms recorded at the ionospheric station of Tucumán (26.9°S, 294.6°E). The performance achieved is statistically evaluated and demonstrated with significant examples. The proposed method improves Autoscala's ability to reject ionograms with insufficient information, including those featuring Spread-F. Automatic identification of cases of spread-F is of additional interest in Space Weather applications, when it helps detect degraded radio propagation conditions.The present data analysis is a retrospective study but forms the basis for real-time application as an extension of Autoscala’s capabilities.     

海口站与Huancayo站扩展F的差异

本文统计分析了我国海口站太阳黑子高年和低年的扩展F的资料,得出了该站扩展F的出现率随地方时、季节和太阳活动周期的某些变化规律并与Huancayo站扩展F的资料进行了比较,指出了两站扩展F的差异。      

Occurrence of Ionospheric irregularities over Brazil and Africa during the 2019 Antarctic minor sudden stratospheric warming

The influence of sudden stratospheric warming (SSW) on the ionosphere and ionospheric irregularities has been studied extensively over the years. However, majority of these investigations have been conducted using warming events originating from the northern hemisphere. Only a few studies have been done on ionospheric variations due to the Antarctic SSW events and to the best of our knowledge, there have not been any studies on southern hemisphere SSW and the occurrence of ionospheric irregularities. In this study, the occurrence of ionospheric irregularities during the 2019 minor Southern hemisphere (SH)/Antarctic SSW is investigated. The event occurs in a relatively calm solar and geomagnetic activity period which makes it possible to identify the effects of SSW on the occurrence of irregularities. Three ionosondes located in different latitudinal regions in Brazil as well as a network of ground-based GPS receiver stations located in both Brazil and Africa were used for this undertaking. Complimentary data from the same ionosonde stations using the same months from 2017 and 2018 were also used. On average more Spread-F was observed in 2019 than in 2017 or 2018 at all stations. ROT observations showed more occurrence in the Brazil sectors followed by West Africa and thenEast Africa. It was observed that the occurrence frequency decreased between 8% and 46 % from the pre-SSW phase to ascending/peak phases and from 2018 to 2019 for the peak phase.