A three-dimensional model of ionospheric F-region

The three-dimensional stationary in solar-terrestrial system numerical model of the global ionosphere at F-region altitudes is developed. The input parameters are: the structural parameters of empirical thermospheric models (temperature, composition), electric fields, solar UV-radiation spectrum, corpuscular flows at high latitudes. The model includes the calculations of thermospheric circulation, electron density, electron and ion temperatures. The model reproduces the main morphological peculiarities of the distribution of thermospheric circulation and ionospheric plasma parameters. A comparison analysis of the results of the model calculation corresponding to different thermospheric models (DTM, MSIS, Jacchia-77, MSIS-83) is carried out. It is shown, that thermospheric circulation systems are the effective indicator of faithfulness of thermospheric models.     

三维模式约束的电离层掩星反演方法

目前电离层掩星数据反演是基于电离层电子密度分布局部球对称近似的Abel反演方法,实际电离层的非球对称性会给电子密度反演结果带来误差.本文研究利用三维电离层模式来提供电子密度水平变化的先验信息约束电离层掩星反演的方法,即三维模式约束法;并将该方法应用于模拟掩星观测数据和实测掩星数据的反演.模拟观测数据的反演结果表明,与Abel反演方法相比,三维模式约束法能够减小反演误差.采用IRI2001模式作为约束,对COSMIC电离层掩星实测数据反演,将反演结果与全球的垂测仪数据进行比较,结果表明,三维模式约束法和Abel反演方法都能很好地反演电离层掩星.     

A neural network-based ionospheric model for the auroral zone

A new empirical model for the lower ionosphere in the auroral zone, called IMAZ, has been developed, tested and refined for use in the International Reference Ionosphere (IRI) global model. Available ionospheric data have been used to train neural networks (NNs) to predict the high latitude electron density profile. Data from the European Incoherent Scatter Radar (EISCAT), based near Tromsø, Norway (69.58°N, 19.23°E), combined with rocket-borne measurements (from 61° to 69° geomagnetic latitude) make up the database of reliable D- and E-region data.NNs were trained with different combinations of the following input parameters: day number, time of day, total absorption, local magnetic K index, planetary Ap index, 10.7 cm solar radio flux, solar zenith angle and pressure surface. The output that the NNs were trained to predict was the electron density for a given set of input parameters. The criteria for determining the optimum NN are (a) the root mean square (RMS) error between the measured and predicted output values, and (b) the ability to reproduce the absorption they are meant to represent. An optimum input space was determined and then adapted to suit the requirements of the IRI community. In addition, the true quiet electron densities were simulated and added to the database, thus allowing the final model to be valid for riometer absorptions down to 0 dB.This paper discusses the development of a NN-based model for the high-latitude, lower ionosphere, and presents results from the version developed specifically for the IRI user community.     

一个中纬电离层E层理论模式

本文建立了一个中纬电离层E层理论模式. 该模式从NO+,O２＋,O+和N２＋这四种主要离子的连续性方程出发,通过数值模拟得到中纬电离层E层电子和各种离子密度随时间和高度的变化情况. 计算结果能较好地反映出E层电子密度峰值（NmE）或E层临界频率（foE）的日变化、季节变化以及随太阳活动的变化趋势. 将模式的计算结果与武汉地区测高仪的观测数据进行比较,结果证明模式能够较为客观地反映中纬电离层E层的实际形态. 针对以往电离层E层理论模式存在的主要问题,本文还进一步讨论了几种重要因素,包括二次离化源,λ<150?谱段的辐射通量,吸收截面以及NO分布对于模式计算结果的影响.     

基于SAMI2模式的电离层加热模拟

通过在SAMI2模式的电子能量方程中添加人工加热项,数值模拟了在加热条件下磁场线上电子温度与电子密度的扰动情况,并对比了不同加热条件下的扰动效应.结果表明,入射到电离层中的大功率无线电波与等离子体相互作用,能够有效造成整条磁场线上电子温度的升高而产生电子温度扰动,尤其是加热点处,温度可增加3倍多;由于电子温度升高,压力平衡受到破坏,引发等离子体扩散进而导致电子密度扰动;电子密度扰动使得垂直于磁场线的电子密度梯度发生变化,这有可能形成电离层管（Ionosphere duct）;电子温度和电子密度的扰动幅度随着加热时间的推移而减小,即扰动逐渐趋于稳定.电子温度与密度的扰动与加热率存在一种非线性关系.     

Calibration of a numerical ionospheric model with EISCAT observations

A set of EISCAT UHF and VHP observations is used for calibrating a coupled fluid-kinetic model of the ionosphere. The data gathered in the period 1200–2400 UT on 24 March 1995 had various intervals of interest for such a calibration. The magnetospheric activity was very low during the afternoon, allowing for a proper examination of a case of quiet ionospheric conditions. The radars entered the auroral oval just after 1900 UT: a series of dynamic events probably associated with rapidly moving auroral arcs was observed until after 2200 UT. No attempts were made to model the dynamical behaviour during the 1900–2200 UT period. In contrast, the period 2200–2400 UT was characterised by quite steady precipitation: this latter period was then chosen for calibrating the model during precipitation events. The adjustment of the model on the four primary parameters observed by the radars (namely the electron concentration and temperature and the ion temperature and velocity) needed external inputs (solar fluxes and magnetic activity index) and the adjustments of a neutral atmospheric model in order to reach a good agreement. It is shown that for the quiet ionosphere, only slight adjustments of the neutral atmosphere models are needed. In contrast, adjusting the observations during the precipitation event requires strong departures from the model, both for the atomic oxygen and hydrogen. However, it is argued that this could well be the result of inadequately representing the vibrational states of N₂ during precipitation events, and that these factors have to be considered only as ad hoc corrections.     

An upgrade of the solar-wind-driven empirical model for the middle latitude ionospheric storm-time response

Based on recent advances in ionospheric storm dynamics that correlate the ionospheric storm effects with space weather parameters such as the magnitude of the interplanetary magnetic field (IMF), its rate of change and the IMF's orientation in the north–south direction and on the availability of these parameters in real time by NASA ACE spacecraft from the vantage L1 point, an empirical storm-time ionospheric model for the middle latitude ionosphere, namely STIM, was recently envisaged. STIM is significantly upgraded and validated here. The model introduces a correction factor to the quiet daily ionospheric variation to anticipate storm conditions. It is triggered by an alert signal for upcoming ionospheric disturbances obtained from the analysis of the IMF measurements provided by ACE spacecraft. In its final version, STIM method includes quantitative criteria for the online analysis of the ACE's observations. The determination of the ionospheric storm onset and the empirical formulation of the ionospheric storm-time response, both in terms of the local time and the latitude of the observation point are also specified here. STIM's forecasts are provided from 13 to 45 h ahead for any middle latitude ionospheric location. Validation tests carried out for 27 storm-time intervals and for four European locations show that the model captures successfully the onset and the recovery of the ionospheric disturbance and follows sufficiently the disturbance pattern, providing also significant improvement over climatology during storm days. STIM was also compared with two well-known prediction models, the IRI2001 and the GCAM, and the findings demonstrate improved performance in favour of STIM, in both quantitative and qualitative aspect. In general, the results presented here support the efficiency of the proposed methodology in providing reliable ionospheric forecasts at middle latitudes several hours in advance. The operational implementation of STIM can support ionospheric forecasting space weather services and is based on the availability of real-time IMF observations from the vantage L1 point.     

基于深度学习的SuperDARN雷达极区电离层对流电势模型构建及预测

电离层等离子体对流是表征电离层电动力学的重要现象,对空间天气有着重要的指示作用.SuperDARN雷达网是研究中高纬电离层对流的重要手段,也是获得对流电势数据的重要来源.本文基于SuperDARN雷达12月份的对流电势数据,采用BP模型、FC-LSTM模型以及ED-ConvLSTM时空序列模型构建了高纬电离层等离子体对流电势30min预测模型,然后采用独立的数据集,基于预测值与实测值的结构相似度（SSIM）、均方根误差（RMSE）以及线性相关系数（LC）三个统计指标对模型的性能进行了评估,同时分析对比了三种模型预测的越极盖电势（CPCP）和越极盖电场（CPEF）与实测值的统计分布情况.结果表明,BP模型和FC-LSTM模型由于没有充分挖掘到空间上的信息,因此整体误差较大,前者SSIM、LC以及RMSE分别为0.80、0.89、4.38 kV,后者为0.76、0.86、4.96 kV,而ED-ConvLSTM模型则分别为0.83、0.91、3.96 kV,因其能充分捕捉到空间上的信息,三个指标明显优于前两种模型,同时在CPCP分布和CPEF分布的相似度上,ED-ConvLSTM模型性能也表现得最好.本文结果证明了时空序列模型ED-ConvLSTM在对流电势预测上的有效性.

     

Parameters of the medium-scale traveling ionospheric disturbances model deduced from measurements

Using three radio techniques for determining the spatial and terminal distribution of the electron concentration in the ionospheric F region, a number of parameters of medium-scale travelling ionospheric disturbances (the effective thickness of the atmospheric waveguide and height of its axis, spatial and time periods, propagation speeds, and maximum amplitudes of the disturbances) are determined.     

单层模型对GNSS海啸电离层扰动探测的影响分析

本文全面分析了电离层单层模型高度以及投影函数对GNSS海啸电离层扰动探测的影响.利用GNSS计算的电离层扰动绝对空间分布位置随单层高度变化而变化,但对同颗卫星而言,其相对空间分布位置随单层高度变化较小.采用投影函数将倾斜方向的电离层扰动转化到垂直方向上,可以消除海啸传播方向垂直平面外的不一致性;由于电离层扰动存在水平梯度,不能消除海啸传播方向垂直平面上的不一致性.为了减弱单层模型参数对GNSS海啸电离层扰动探测的影响,在数据处理时,除了选择最大电子密度高度作为单层模型高度,还应当对每颗卫星单独进行分析.

     

Optimum design of single-frequency dynamic dampers

The problem of damping the vibration amplitude of machines and structures has considerable practical importance. This paper discusses the design of optimum vibration absorbers for linear damped systems operating at a certain excitation frequency. The problem is first formulated as a mathematical programming scheme. The systematic design discussed in this paper has significant advantages for those vibratory systems run primarily at a specific frequency.     

A numerical study of ionospheric profiles for mid-latitudes

This paper presents a numerical model and results for the mid-latitude ionospheric profile below the peak of the F₂-layer. The basis of the model is the solving of equations for four ionic species O⁺, NO⁺, O⁺₂ and N⁺₂, as well as the meta-stable O⁺(²D) and O⁺(²P). Diffusion and wind-induced drifts and 21 photo-chemical reactions are also taken into account. Neutral atmospheric density and temperature are derived from the MSIS86 model and solar extreme ultraviolate irradiance from the EUV91 model. In an effort to obtain a more realistic ionospheric profile, the key point at foF₂ and hmF₂ is fitted from the simulation to observations. The model also utilizes the vertical drifts derived from ionosonde data with the help of the Servo model. It is shown that the ionospheric height of peak can be reproduced more accurately under the derived vertical drifts from the Servo theory than with the HWM90 model. Results from the simulation are given for Wuchang (30.5°N, 114.4°E) and Wakkanai (45.6°N, 141.7°E), showing the profile changes with season and solar activity, and the E-F valley structure (the depth and the width). This simulation also reveals the importance of meta-stable ions and dynamical transport processes on the formation of the F₁-ledge and F₁-F₂ valley.     

综合半参数核估计和自回归补偿的全球电离层总电子含量预报模型

针对电离层半参数球谐函数模型中窗宽参数选择引起的估计偏差,本文在传统的电离层球谐函数模型中引入半参数核估计和自回归(Autoregressive model,AR)模型,分别用于分离球谐函数模型的系统误差和窗宽参数引起的估计偏差,提出一种全球电离层总电子含量(Total Electron Content,TEC)组合预...     

GPS-based ionospheric corrections for single frequency radar altimetry

The global ionospheric total electron content maps (GIMs) provide integrated electron densities between the ground and the GPS satellite altitude (20,200 km). Satellite altimeter ionospheric delay corrections require integrated electron densities between the ground and altimeter satellite altitude. In the case of the Geosat Follow-On (GFO) spacecraft, flying at 800 km, we estimated that using GIM TEC data alone, up to a 2 cm path delay can be introduced into the GFO measurements for high solar activity period by not taking into account the electron content above this altitude. Furthermore, the GIMs can have errors of 20–30 TECU in low latitudes for high solar activity in areas where there is little GPS data (such as over the oceans). In this paper, we describe the results of ingesting GIM TEC data into the International Reference Ionosphere model (IRI-95) to mitigate these two effects.     

Modeling of vertical sounding ionograms for nonmonotonous ionospheric layers

The problem of radiosignal reflection from a plane layered isotropic ionosphere has been considered. The vertical sounding ionograms for ionospheric layers with a complicated structure have been modeled. It has been demonstrated that the structure of reflected signals depends on the degree of ionospheric irregularities. Diffuse reflection of radiosignals, caused by the vertical irregularity of the ionosphere, has been detected.     

震前电离层TEC异常探测新方法

本文提出一种利用时间序列法(ARIMA模型)进行震前电离层异常探测的新方法.首先,对比分析了该方法与传统探测方法(四分位距法、滑动时窗法)预测TEC背景值的精度.结果表明,时间序列法预测背景值的精度要明显高于传统方法,且预报背景值的平均偏差要比传统方法小2倍左右,说明传统探测方法预测的背景值具有较大系统偏差.为更准确地探测震前电离层扰动,除了得到准确的参考背景值,还需得到更加合理的探测限值,由此本文提出一种更为合理的限差确定策略.最后,以2012年1月10日苏门答腊岛7.2级地震为例,利用该方法分析了其震前电离层的异常扰动情况,并验证了该方法的有效性,实验结果表明:在震前第13天、第8~9天、第1~2天和地震当天电离层均会发生较为明显的异常.而且,其正异常(观测值高于正常值)一般发生在震中以北,距发震时间相对较远;负异常(观测值低于正常值)则在震中各方向均会出现,且距发震时间较近.同时,通过对异常结果分时段统计,发现在发震时刻前,距发震时刻越近的时段发生异常的频率越高,此规律将会对未来更为准确的预报发震时段提供重要参考.