【作者】 徐彤；

【导师】 吴振森； 吴健；

【作者基本信息】 西安电子科技大学 ， 无线电物理， 2009， 博士

【摘要】 电离层模型研究对短波通讯电路设计及探究电离层物理过程有着重要意义。论文建立了中低纬电离层经验模型和中纬电离层物理模型,并利用电离层物理模型进行电离层暴时变化数值模拟及地震电离层异常扰动分析。论文在分析电离层主要控制因素及电离层结构变化的基础上,获得的主要成果如下:第一、太阳和地磁指数周期特征EMD分析及长期预测研究。利用经验模态分解方法(EMD)对太阳黑子数R和地磁活动指数(Ap、aa和Dst)进行周期性分解,分析了不同时间尺度分量的物理形成机理及太阳黑子数与地磁指数11年周期分量之间的关系。在此基础上,利用自回归方法(AR)进行太阳黑子数R和地磁指数Ap长期预测研究,获得提前一个太阳周11年的R和Ap的预测值。第二、电离层foF2月中值太阳循环变化及单站模型。利用遍及我国中低纬地区的9个电离层观测站1977-1997年约20年的foF2月中值数据,考虑太阳活动和地磁活动对电离层foF2月中值的非线性影响,建立了单站foF2月中值经验模型,对模型误差进行了详细分析,并将其与国际参考电离层IRI2001进行了比较,精度有显著提高。第三、强地磁扰动条件下foF2与月中值偏差模型及暴时短期预报。利用时间累积地磁指数ap(τ),建立了强地磁扰动条件下电离层foF2与月中值偏差经验模型。由于地磁指数与电离层暴时变化相关性不高,使得该经验模型精度较低。作者借鉴气象预报中常用的Kalman滤波方法对模型的系数进行实时修正,提高预报精度,并对长春站1986-1995年近一个太阳周foF2数据进行提前一小时预报试验。该预报方法与包含暴时修正模型STORM的国际参考电离层IRI2001进行了比较,展示了Kalman滤波方法实时修正模型系数的能力和良好的应用前景。第四、建立了中纬电离层物理模型并进行暴时电离层数值模拟。模型比较周密地考虑了中纬度地区电离层的主要动力学过程和光化学过程,通过求解离子的连续性方程和动量方程,给出了O+、O2+、NO+、N2+、N+、He+六种离子和电子密度剖面。对宁静背景电离层条件下北京站进行了数值模拟。利用该模型模拟了磁暴期间热层大气温度、成分和中性风扰动对电离层电子密度剖面结构,特别是对峰值密度和高度变化的影响。第五、地震电离层异常扰动研究。简要地介绍了地震电离层异常扰动时空分布特点,并利用重庆、昆明、兰州和拉萨站foF2数据,对512汶川地震前电离层扰动进行了分析。利用已建立的电离层物理模型,借助电场异常假说对地震前电离层电子密度午后异常变化进行了数值模拟,并进行了详细的讨论。更多还原

【Abstract】 The investigation on ionospheric model is of great significance for design of communication ciruit and understanding of ionospheric mechanisms. The aim of this dissertation is to establish empirical and physical models to describe the variation of mid-latitude ionosphere, as well as low-latitudes with empirical models. Based on the physical model, the storm-time variation is simulated and pre-earthquake anomalous variation is investigated preliminarily. As basis, a brief review is given on mainly sources affecting on ionosphere and corresponding variation of ionosphere, firstly. The main topics and results are as follows:First, extracting of periodic components and long-term prediction of the indices of solar activity and geomagnetic activity are investigated by use of EMD (empirical mode decomposition) and AR (auto-regressive model). With EMD method, sunspot number R and geomagnetic indices, i.e. Ap, aa and Dst, are decomposed and physical mechanisms of their periodic components are discussed. Furthermore, EMD and AR are applied to the long-term prediction of sunspot number and the lead time reaches up to 11 years, which gives a possibility to realize the long-term prediction of ionosphere with ionospheric models.Second, hourly values of the critical frequency of the ionospheric F region, foF2, observed at the nine ionosonde stations in China about two solar cycles have been used to investigate the dependence of the monthly median foF2 on solar activity and geomagnetic activity, and to construct single-station model (SSM) using Fourier expansion. The results of the present analysis show that there is a significant nonlinear relationship between monthly median foF2 and sunspot number R especially at daytime in each month and nighttime in summer and the nonlinear relationship are more evident as the latitude decreases. Furthermore, introducing geomagnetic index Ap further improves the description of variation of monthly median foF2, and the standard deviations decrease also dependently on time and month. Based on the nonlinear relationships, we develop a new SSM for the each station and the SSMs are compared with IRI, which show a much better agreement with observation.Third, with the time weighted accumulation index ap(τ), an empirical storm-time model of the relative deviation of foF2 from its monthly median is established. Because of low correlation between variation of foF2 and geomagnetic indices, the model has low accuracy. The method used widely in weather, hydrography, et al., Kalman filter, is used to update the coefficients of the empirical model and expected to make better improvement. The proposed method is tested by the data of hourly values from 1986 to 1995 over Changchun station. Simultaneously the method is compared with IRI2001 including the STORM model for several disturbed events, which shows this method has a powerful ability of updating the model coefficients and prospect of application.Fourth, one-dimensional time-dependent theoretical ionospheric model for mid-latitude is established with which variation of storm-time ionosphere are discussed. Thoroughly taking the mainly kinetic and photochemical process into account, the model can give six ionic species, O+, O2+, NO+, N2+, N+, He+ and electron through solution of continuity and momentum equations. The foF2 over Beijing station is simulated in undisturbed condition. Moreover, the variation of ionospheric density profile during geomagnetic storms, considering the disturbances of the thermospheric temperature, composition and neutral wind are discussed in detail.Fifth, ionospheric anomalous disturbances of earthquakes are investigated. The characteristics of ionospheric perturbations on temporal and spatial distribution are represented briefly. Then the hourly ionospheric data foF2 are analyzed before Wenchuan great earthquake over four ionospheric observatories Kunming, Chongqing, Lhasa and Lanzhou. The possible mechanisms that could be responsible for the observed pre-earthquake ionospheric anomalies are discussed with the physical model of mid-latitude ionosphere and the hypothesis of abnormal vertical atmospheric electric fields.更多还原