新乡上空Es层不均匀体的闪烁特性

本文介绍新乡1989和1990年夏季ES层不均匀体引起的ETS-II卫星136MHz信号幅度闪烁的观测结果。揭示了闪烁出现与f₀E_s的关系、闪烁强度和持续时间的概率分布、准周期性闪烁特点以及闪烁谱特征。导出了ES层不均匀体的尺度和漂移速度等物理特性。      

磁赤道异常区电离层F区不均匀体发展过程中的闪烁谱研究

本文对我国磁赤道异常区海口站的夜间电离层不均匀体引起的闪烁进行了谱分析，并进行了理论模拟。大部分闪烁出现在午夜前后且持续时间较长。分析结果发现：这种持续时间较长的闪烁的末期和初期的闪烁谱结构有显著差异，末期闪烁谱高频段较初期要明显陆峭，即谱指数显著增大。由此推测出不均匀体发展末期费涅耳尺度以下的不均匀体首先衰减消失，这与国外某些轨道卫星就地测量结果大致相符。同时还从闪烁谱推测出不均匀体发展末期的漂     

宇宙噪声的电离层闪烁

本文给出了薄相屏近似条件下的电离层闪烁Fourier功率谱和Bessel功率谱与电离层不均匀结构电子密度涨落空间谱之间的关系。对窄波瓣天线Riometer获得的宇宙噪声资料进行了分析,结果表明:宇宙噪声资料包含着电离层不均匀结构的信息。Riometer观测结果也可用于电离层闪烁问题的研究。     

赤道电离层F区底部准正弦型不均匀体引起闪烁的数值模拟

本文采用多重相屏模型, 考虑不均匀体特征尺度随高度的变化, 模拟了赤道电离层F区底部准正弦型(BSS)不均匀体引起的闪烁。模拟计算结果表明:BSS不均匀体的特征尺度随高度变化可以导致闪烁谱和不均匀体谱之间谱指数的显著差异。      

基于GPS的广州地区电离层闪烁谱分析

利用广州站GPS电离层闪烁监测仪2014和2015年的观测数据,从150例典型闪烁事件中提取出4820例闪烁谱和闪烁谱指数,分析发现广州地区闪烁对应单幂律谱和双幂律谱两大典型闪烁谱.这些闪烁谱可以细分为5类,初步分析了这5类闪烁谱的特征和产生原因.通过统计分析发现,谱指数分布在0.63~9.57,平均谱指数为3.86,78.5%以上的谱指数分布在0~6,83.4%中弱闪烁强度的谱指数值分布在0~7,89.27%的强闪烁强度的谱指数分布在5~10,谱指数随闪烁强度的增强有上升趋势.      

海口站电离层闪烁强度功率谱分析与建模应用

基于中国海口站(20.00°N, 110.33°E)获取的2013全年UHF 频段电离层闪烁信号强度数据, 利用Welch算法, 分析给出了四类典型电离层闪 烁强度功率谱. 利用功率谱时序图分析方法, 发现电离层不均匀体存在东西向水 平周期性变化结构. 提取全年功率谱指数p, 通过统计分析发现谱指数p存在规律变化, 据此建立一个谱指数经验模型, 该谱指数模型已用于中国低纬 区域电离层闪烁发生预报概率模型(CMSOP), 进而对海口站UHF频段电离层闪烁发生 概率观测数据和预报结果进行了对比分析.      

基于GPS信号的电离层S4指数计算方法研究

电波穿越电离层时,由于受到电离层不均匀结构的影响,电波的幅度、相位、时延等有时会发生快速抖动,这就是所谓的电磁波电离层闪烁现象.电离层闪烁会影响卫星通信系统的质量和导航系统的精度.本文分析了GPS信号研究电离层闪烁的基本原理,讨论了电离层闪烁监测中S4指数的计算方法及其修正方法.通过数据模拟,评估了原始S4指数计算方法及其修正方法的性能特点.针对原始S4指数计算方法及修正方法的不足,提出了一种新的修正方法,并采用实测GPS数据对上述方法进行了检验.结果表明,上述方法是有效的和可靠的.      

高频电波在背景备向异性和不均匀的随机起伏电离层中的传播

运用波动理论,讨论背景为各向异性、不均匀的随机起伏电离层中高频电波的传播和散射问题,给出了电离层不均匀体散射引起的反射回波波场的起伏,并在垂测条件下计算了接收波场的相位与振幅起伏的谱分布。      

宇宙噪声的电离层闪烁与电离层不规则结构的结构参数

利用宇宙噪声是均匀的。各向同性的背景电磁辐射的假设,对电子密度涨落空间分布波数谱为负幂律函数的电离层不规则结构,用射线光学方法导出了闪烁功率谱的表示式。与射电星和轨道人造卫星信标的电离层闪烁相比,减少了因相对运动弓队的变量。用数值计算方法研究了电离层不规则结构的结构参量L_y、l_y、p、η对功率谱的影响。与实测资料比较,发现电离层吸收事件期间且Riometer记录的闪烁资料中,60%以上相应的不规则结构有L_y>103,η>η₀(0.2<η₀<0.5).      

电离层闪烁对导航接收机性能的影响

为定量分析电离层闪烁对接收机环路的影响,利用信号在电离层闪烁影响下的等效传输信道模型,通过数值仿真对比分析了电离层闪烁对接收信号幅度、载波相位、码相位、载噪比和I/Q支路跟踪值的性能影响。结果表明：电离层闪烁会使接收载噪比出现深度的快速衰落,严重时会出现高达5dB的突降,从而显著地影响用户的定位性能;在相同的电离层闪烁强度下,较小的环路带宽会发生较弱的载波相位周跳。     

Characterization of ionospheric amplitude scintillations using wavelet entropy detrended GNSS data

The extensive monitoring networks of Global Navigation Satellite System (GNSS) ionospheric scintillation have been established to continuously log observation data. Further, the amplitude scintillation index and the phase scintillation index, which are derived from scintillation observations, are anticipated to accommodate the accuracy requirement of both the user level and the monitoring station level. However, raw scintillation observations essentially measure superposed waveform impairments of GNSS signals propagating through ionosphere and troposphere. It implies that fluctuations of raw scintillation observations are caused by multiple factors from the entire radio propagation environment. Hence, it is crucial to characterize ionospheric scintillations from GNSS observation data. And the characterization is implemented through extracting fluctuations of raw observations merely induced by ionospheric scintillations. Designed to address this problem by means of Fourier filtering detrending, the present work investigates the influence of varying detrending cutoff frequencies on wavelet statistical energy and wavelet entropy distributions of scintillation data. It consequently derives criteria on the optimum detrending cutoff frequency for three types of raw amplitude scintillation data, which are classified by their wavelet energy distributions. Results of the present work verify that detrending with specific optimum cutoff frequencies rather than the fixed and universally applicable one renders the validity and credibility of characterizing ionospheric scintillations as the part of GNSS observation fluctuations purely induced by ionosphere electron density irregularities whose scale sizes are comparable with or smaller than the Fresnel scale.     

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.     

同步卫星讯号的闪烁研究

本文研究了我国中纬台站西安观测到的日本同步卫星ETS-2 136 MHz讯号的幅度和相位闪烁特性。发现幅度谱和相位谱的高频特性可用弱闪烁理论来解释。在低频端,幅度谱和相位谱经过一个平坦的频域后开始下降,这与弱闪烁理论矛盾。文本将解释这些矛盾。似乎此处的结论更为合理些。      

Radio-scintillation observations of interplanetary disturbances

Recent developments in the studies of interplanetary disturbances by scintillation (IPS) techniques are briefly reviewed. The turbulent post-shock region of an interplanetary disturbance produces transient enhancements in the scintillation level and the flow speed in many cases. An empirical method to determine three-dimensional angular distribution of propagation speed of the disturbance on the basis of IPS measurements of post-shock flow speeds is applied to 17 events which took place in 1978–1981. Among them, four representative examples including two events which were associated with disappearing solar filaments are described in detail. Several disturbances had oblate configurations; the latitudinal extent is smaller than the longitudinal extent. On an average, the angular distribution of propagation speed at 1 AU heliocentric distance is quasi-isotropic over a longitudinal range of 100° centered at the normal of relevant solar phenomenon. The net excess mass and energy in an interplanetary disturbance associated with a disappearing solar filament can be comparable to those of an interplanetary disturbance associated with a large solar flare.     

重力波波包在时变背景场中传播的数值研究

采用二阶算子分裂格式对高斯型重力波波包在时变背景温场和时变背景风场中的非线性传播过程分别进行了数值模拟和分析.研究表明,时变背景场对波包空间结构演变影响不明显,各物理量的偏振关系与线性理论偏振关系较一致;在时变背景温场中传播,水平群速度和垂直群速度的变化趋势与线性理论结果相反,波频率的变化也与线性理论色散方程计算结果有一定的差别,这表明了线性重力波理论的局限性;在时变背景风场中传播,波频率的变化比时变背景温场中更显著.传播路径与在稳恒背景场中比较,更接近线性理论计算出的路径.      

Simulation and analysis of chemical release in the ionosphere

Ionospheric inhomogeneous plasma produced by single point chemical release has simple space-time structure, and cannot impact radio wave frequencies higher than Very High Frequency (VHF) band. In order to produce more complicated ionospheric plasma perturbation structure and trigger instabilities phenomena, multiple-point chemical release scheme is presented in this paper. The effects of chemical release on low latitude ionospheric plasma are estimated by linear instability growth rate theory that high growth rate represents high irregularities, ionospheric scintillation occurrence probability and high scintillation intension in scintillation duration. The amplitude scintillations and the phase scintillations of 150?MHz, 400?MHz, and 1000?MHz are calculated based on the theory of multiple phase screen (MPS), when they propagate through the disturbed area.     

Study of CME transit speeds for the event of 07-NOV-2004

Several methods for CME speed estimation are discussed. These include velocity derivation based on the frequency drifts observed in metric and decametric radio wave data using a range of coronal density models. Coronagraph height–time plots allow measurement of plane-of-sky and expansion speeds. These in turn can enable propagation speeds to be derived from a range of empirical relations. Simple geometric e.g., cone, models can provide propagation velocity estimates for suitable halo or partial halo events. Interplanetary scintillation observations allow speed estimates at large distances from the Sun detecting in particular the deceleration of the faster CMEs. Related interplanetary shocks and the arrival times and speeds of the associated magnetic clouds at Earth can also be considered. We discuss the application of some of these methods to the transit to Earth of a complex CME that originated earlier than 16:54 U.T. on 07-NOV-2004. The difficulties in making velocity estimates from radio observations, particularly under disturbed coronal conditions, are highlighted.     

电离层不规则结构对GPS性能的影响

电离层不规则结构的存在可引起无线电信号的幅度和相位发生随机起伏, 这 种电离层闪烁现象会影响全球定位系统(Global Positioning System, GPS)的 性能, 降低定位精度, 严重时导致信号失锁. 电离层不规则结构对GPS性能的 影响涉及电离层物理、接收机设计和表征卫星几何分布的精度衰减因子(Dilution of Positioning, DOP)等多方面因素. 本文通过对表征电离层不规则结构参数 的分析, 根据GPS接收机跟踪环路和闪烁信号模型, 综合研究了电离层闪烁对 GPS接收机载波跟踪环和码跟踪环跟踪误差的影响; 结合实际观测, 评述 了电离层不规则结构对单频和双频GPS接收机定位性能的影响, 在此基础上 提出了有待深入研究的问题及具体建议.      

Quantitative analyses of complexity and nonlinear trend of radio refractivity gradient in the troposphere

In this paper, the complexity and nonlinear trends of Radio Refractivity Gradient (RRG) in the troposphere over selected locations in Nigeria are analyzed and discussed extensively. The RRG is an important parameter in estimating path clearance and propagation effects such as ducting, surface reflection and multi-path on terrestrial line of-sights links. Also, radio wave signal propagating in the troposphere is affected by unpredictability of a weather condition which includes the variations of meteorological parameters such as temperature, pressure and relative humidity. The complex state of the atmosphere, which is the medium for the transmission of radio signals tend to have very strong influence such as scintillation and ducting on the quality of the radio signal, amplitude and phase. Variations in the meteorological parameters also induce variations in the refractive index of the atmosphere which in-turn results in the effect known as radio refractivity. For effective prediction and modeling of radio signal propagation, one should be able to characterize the nature and predictability of the computed RRG information. Chaotic Quantifiers (CQ) such as Phase Plot Reconstruction (PPR), Average Mutual Information (AMI), False Nearest Neighbor (FNN), Recurrence Plot (RP) and Recurrence Quantification Analyses (RQA) are used to assess the RRG. The information reveal, however, is based on the prediction techniques, design and frequency planning of microwave networks which may be useful for optimum performances during atmospheric turbulence.     

磁暴对赤道地区L波段电离层闪烁的影响研究

利用赤道地区Vamimo站闪烁数据, 选取两次典型大磁暴时段重点分析, 对比磁暴发生前、发生时以及发生后连续几天电离层幅度闪烁强度和发生率的变化, 引入瑞利elax-elax泰勒不稳定性(Rayleigh-Taylor, R-T不稳定性)线性增长率γ₀, 对磁暴影响闪烁的机制进行初步探讨. 结果表明, 磁暴可能触发闪烁发生, 也可能抑制闪烁发生, 这既与观测季节有关, 也与磁暴不同发展阶段的地方时有关. 触发发生于闪烁少发季节磁暴主相所在的午夜至黎明时段, 可能是磁层穿透电离层的东向电场所致; 抑制发生于闪烁多发季节磁暴恢复相所在的午夜前时段, 可能是西向电场作用的结果. 磁暴发生时的电场变化可能是抑制或触发闪烁的主导因素, 但仍需进一步分析研究.