非球对称电离层掩星数据反演

电离层掩星数据的传统反演方法是电离层球对称假设下的Abel变换反演方法,但是实际的电离层电子密度分布不是球对称的,电离层的非球对称分布给电离层电子密度反演带来误差.发展了一种新的非球对称电离层掩星反演方法,利用国际参考电离层模型提供的三维电离层电子密度分布先验信息来修正掩星总电子含量 ,再通过球对称假设下的Abel变换反演出电离层电子密度.利用新方法反演了星座气象、电离层和气候观察系统掩星实测数据,并将得到的反演结果与电离层探测器资料进行了比较.结果表明,新方法能够较好地反演出电离层电子密度. 关键词： 电离层掩星 电子密度 国际参考电离层模型     

用于火星电离层探测的星-星无线电掩星技术

火星和地球类似,周围束缚了不同密度的电离层.利用无线电掩星技术可以对火星电离层进行观测.星-地无线电掩星在探测精度和探测区域方面都受到一定的限制.中俄联合火星探测计划将于2011年10月一箭双星发射俄罗斯的Phobos-Grunt探测器和中国的萤火1号火星探测器.该计划将开展国际上首次火星电离层的星-星无线电掩星观测试验,重点是对星-地无线电掩星无法观测的正午和子夜区域的火星电离层进行探测.星-星无线电掩星观测试验采用双频工作模式,接收机灵敏度为-145dBm,相位测量精度优于5%周.在地面对接收机进行了动态模拟测试,测试得到的相位数据能很好地反演出火星电离层电子密度廓线.     

基于改进的单差法计算GPS掩星附加相位

从GPS掩星探测数据中反演的参数可同化入数值天气预报模式. 附加相位的计算精度受参考链电离层噪音及L2噪音影响, 在L2信号加密情况下噪音影响更为显著.为提高附加相位处理精度, 减少一般单差法(single difference, SD)从参考链传入掩星链的噪音,本文采用改进的单差法 (updated single difference, USD)计算大气附加相位.参考链数据采用组合频率LC观测数据, 并以一定时间窗口(2 s)做平滑处理,逐项考虑天线相位中心改正、 相对论效应改正等因素的影响.利用COSMIC掩星观测数据对上述方法进行了验证. 上升及下降典型掩星事件分析表明:USD计算的附加相位与 COSMIC官方发布的附加相位有很好的一致性;计算了全球分布的440次掩星事件附加相位, 结果表明USD法可明显改进附加相位平均偏差与标准差的分布, 证明了我们算法的可靠性. USD法可应用于风云三号气象卫星掩星仪器半无码跟踪L2得到的数据处理中.     

无线电掩星滑动频谱方法和后传播方法的分析比较

本文详细介绍了滑动频谱方法,并通过模拟仿真和实测资料处理与后传播方法进行比较. 通过对模拟仿真信号反演发现:后传播方法和滑动频谱方法均能削弱大气多路径的影响,后传播方法在一定程度上优于滑动频谱方法;在模拟信号的相位中加入高斯噪声对后传播方法影响不大,但对滑动频谱方法影响较大,尤其在边界层以下. 分别用后传播方法和滑动频谱方法对2007年第71天至73天共约4500个COSMIC掩星数据进行处理. 将折射率反演结果与ECMWF分析场资料进行统计比较,结果显示:滑动频谱方法反演的掩星廓线深度大于后传播方法;后 关键词： GPS/LEO掩星 多相位屏模型 后传播方法 滑动频谱方法     

不同释放高度的化学物质的电离层扰动特性

在电离层释放H₂O, CO₂, H₂和SF₆等中性气体能导致释放区域电子损耗, 形成明显的人工电离层洞, 是电离层人工变态的重要而有效的手段之一. 本文在改进电离层化学物质释放三维动力学模型的基础上, 对不同释放量级的H₂O 和SF₆在不同释放高度下产生的电离层洞形态结构及其时空演化规律进行了系统对比研究, 探讨了释放高度对化学物质释放电离层扰动效果、电离层洞形态及其动力学特性等的影响, 并对其成因进行了分析. 关键词： 化学物质释放 电离层扰动 人工电离层洞 三维动力学模型     

应用一维变分法反演GPS掩星大气温湿廓线

GPS掩星观测的折射率是大气温度、湿度状态的函数, 应用一维变分方法 (1DVAR) 可以从折射率资料中同时反演出大气温、湿度廓线, 利用COSMIC 2011年中国区域掩星观测数据对这一方法进行了测试, 背景场采用ECMWF大气廓线, 反演结果与相匹配的探空观测有较好一致性. 重点研究了一维变分反演方法中非理想气体效应 (non-ideal effect) 对温度、湿度反演误差的影响, 不同月份的比较结果表明, 非理想气体效应对掩星反演大气廓线是一种系统性影响, 考虑这一效应可对温度反演改进0.1 K的偏差 (bias), 对比湿可改进约0.5%偏差. 掩星资料作为数值天气预报资料同化中少数无需偏差改正的卫星遥感资料, 非理想气体效应改正是无疑是非常重要的, 此外, 考虑这一效应对掩星资料的气候应用也有重要价值. 关键词： 一维变分 掩星 非理想气体效应     

GPS/LEO掩星正则变换反演方法

利用无线电全息方法, 如正则变换方法或全谱反演方法, 可以有效地解决大气多路径条件下GPS掩星信号的反演问题. 本文采用正则变换方法反演掩星资料, 模拟仿真反演结果显示正则变换方法可以准确地反演包含大气多路径效应的信号. 在模拟信号的相位中加入不同程度的高斯相位噪声后, 正则变换方法的反演结果会受到不同程度的影响. 用正则变换方法对2007年第71天至73天共约4500个COSMIC数据进行处理. 将其折射率反演结果和atmPrf资料 (利用全谱反演方法计算得到) 一起, 与对应的ECMWF 分析场资料进行统计比较, 结果表明: 在5 km以下, 正则变换方法计算的折射率的相对误差的平均值普遍大于atmPrf资料. 其原因可能为: 正则变换方法将信号从LEO轨迹后传播至辅助屏, 造成孔径缩小, 精度下降. 同时也讨论了信号截断对低对流层中反演精度和掩星个数的影响. 关键词： 无线电掩星 大气多路径 多相位屏技术 正则变换方法     

利用FY-3(D)卫星电离层光度计数据反演电离层O/N2

磁暴等空间天气事件会引起热层中性成分O和N₂浓度的显著变化,故常将氧原子和氮分子的柱密度之比O/N₂作为电离层热层受扰动的标志。研究表明,O和N₂柱密度之比O/N₂与远紫外气辉OⅠ 135.6 nm和N₂ Lyman-Birge-Hopfield(LBH)的柱辐射强度之比135.6/LBH具有很好的相关性,因此远紫外光学遥感探测对于监测磁暴等空间天气事件显得尤为重要。自20世纪70年代以来,国外就开展了远紫外气辉电离层探测的研究工作,并相继发射了多颗相关卫星,尤其是美国、日本以及瑞典等国家。而我国在轨运行的星载光学遥感探测仪器中,只有一些工作在微波波段、可见光波段的载荷,还没有在远紫外波段工作的遥感探测仪器,直到2017年11月风云三号D气象卫星的成功发射,卫星上搭载的电离层光度计是我国首台星载远紫外气辉遥感探测载荷,它为我们提供了一系列具有自主知识产权的远紫外探测数据,为开展电离层O/N₂特性的研究奠定了基础。首先阐述了利用柱辐射强度之比135.6/LBH来反演热层中性成分柱密度之比O/N₂的理论依据。其次,基于MSISE-00大气模型,利用AURIC来仿真计算135.6/LBH与O/N₂之间的比例系数,然后利用电离层光度计实时观测的远紫外气辉数据来反演电离层O/N₂,进一步验证磁暴期间电离层中性成分受扰动的情况。在数据处理过程中,采用了切比雪夫滤波器滤波方式针对数据中的带外杂散光进行了处理,进一步抑制了杂散光信号对远紫外光谱信号的影响。最后,将电离层光度计O/N₂的反演结果与国外光学遥感载荷全球紫外成像仪GUVI（Global Ultraviolet Imager）的结果进行对比,结果显示二者对磁暴的响应一致,O/N₂的产品误差RMS约为0.319 6,文中对造成两者差异的可能原因做出了初步分析,为后续工作的开展奠定了基础。此次研究,首次利用我国自主研发的远紫外气辉遥感探测载荷进行数据反演和分析,这对我国电离层远紫外遥感探测技术的发展具有重要意义。     

Ni75Cr25-xAlx合金中L12相和D022相形核孕育期的微观相场模拟

基于微观相场动力学模型,运用原子图像、平均长程序参数和平均成分偏离序参数,研究了Al浓度对Ni₇₅Cr_25-xAl_x合金中L1₂相和D0₂₂相形核孕育期的影响以及孕育期与沉淀相析出顺序之间的关系.结果表明,L1₂相和D0₂₂相的形核孕育期不仅与Al浓度有关,而且与两相析出的先后顺序密切相关.当Al浓度小于7.5%时,先析出相为D0₂₂相,随着Al浓度的增大,D0₂₂相形核孕育期延长,后析出的L1₂相的形核孕育期也延长,L1₂相的原子簇?聚?速度加快;当Al浓度大于7.5%时,先析出相为L1₂相,随着Al浓度的增大,L1₂相的形核孕育期缩短,后析出的D0₂₂相形核孕育期也缩短.当Al浓度为7.5%时,L1₂相和D0₂₂相几乎同时析出,两者的孕育期没有明显的差别. 关键词： 形核孕育期 序参数 沉淀 微观相场模拟     

几种典型化学物质的电离层释放效应研究

建立了一个包括中性释放气体扩散、离子化学反应及等离子体扩散等过程的化学物质电离层释放三维动力学模型,基于该模型构建了化学物质释放数值模拟软件平台,对H₂O,CO₂,H₂和SF₆等几种典型化学物质的电离层释放进行了数值模拟,给出了这些物质在电离层释放后产生的扰动特性和释放区域主要粒子的时空变化规律. 关键词： 典型化学物质释放 三维动力学模型 电离层扰动效应     

Modeling of variations of the peak F2 layer electron density and total electron content during the recovery period after the magnetic storm of April 15–20, 2002

The results of numerical modeling by using the global upper atmosphere model of the Earth (UAM) for reproducing the peak F2 layer electron density (N _m F2) and total electron content (TEC) during recovery period after the magnetic storm of the April 15–20, 2002 are discussed. According to the simulations, the time it takes to reach a stationary regime of N _m F2 and TEC diurnal variations is 24 hours, much shorter then the plasmasphere refilling time. The results are compared with the predictions of the IRI-2007 empirical model and GPS data on the TEC and found in good quantitative agreement for the latitudinal variations of N _m F2 and TEC for daytime conditions in the southern hemisphere. The worst agreement occurs in the region of the main ionospheric trough.     

Improvements of The L3 TEC Track Resolution at Vertex

Two methods are used to improve the L3 TEC resolution at track vertex.First,refit the lepton tracks by constrained curvature from high precision measurements on electron energy and muon momenta. Second, correct the average value of track offsets in each half sector of TEC.Combined methods improve the lepton track resolution at vertex from 137μm to 60μm.     

Modeling of total electron content disturbances caused by electric currents between the Earth and the ionosphere

The results of simulation of ionospheric total electron content (TEC) caused by the electric field induced by an electric current between the Earth and the ionosphere are reported. The calculations are performed using a model of the upper atmosphere of the Earth (UAM). The equation for the electric potential in the UAM is solved by specifying vertical electric currents in a limited area of the lower boundary of the ionosphere, presumably over the epicenter of a forthcoming earthquake. The dependence of the intensity of TEC disturbances on the electric current direction, latitudinal location of the sources, and their configurations is examined. The most intense TEC disturbance are predicted when the sources are located within 30°–45° geomagnetic latitude. Simulating the concurrent action of vertical currents and compensating “return” currents uniformly distributed around the globe outside the region of “direct” currents showed no significant changes in the TEC disturbances compared with the situation where merely “direct” currents are considered. The role of the vertical and horizontal components of the electromagnetic drift of ionospheric plasma in the variations of the electron density in different areas relative to the electric current source is discussed.     

Determining the intensity of solar flare ionizing radiation from data of the GPS/GLONASS navigation systems

The possibility of solar flare detection using data derived from the GPS/GLONASS navigation systems is demonstrated. Sudden increase of the total electron content (TEC) in the ionosphere is investigated on the basis of GPS data. The dependence of the TEC variations on solar ultraviolet and X-ray ionizing fluxes is analyzed. A technique of using the TEC variation rate to determine the effective intensity of solar ionizing radiation during a strong flare is proposed.     

Nighttime enhancements in TEC near the crest of northern equatorial ionization anomaly during low solar activity period

Enhancement in nighttime total electron content (TEC) near the crest of equatorial ionization anomaly at Bhopal (Geog. 23.2°N, 77.4°E, and MLAT 14.2°N) has been studied for the solar minimum period March 2005- November 2006. TEC data recorded by GPS Ionospheric Scintillation and TEC Monitor (GISTM) GSV4004A receiver is used for the study and results are presented in the paper. More than 10% increase in TEC with respect to background content is considered for analysis. Out of total 138 enhancements, 65 observed during pre midnight hours and 73 during post midnight hours. It is observed that nighttime enhancement in TEC at Bhopal occurs in all seasons; it is more frequent during summer, less during equinox and least during winter months. The enhancement in nighttime TEC can be observed both in geomagnetic disturbed time and in quiet time. We found that mean peak amplitude for pre-midnight TEC enhancement are more in equinox and less in winter, while in post-midnight TEC enhancement it is highest in summer and less in winter. Post-midnight enhancements have smaller peak amplitude as compared to pre-midnight. Also the most probable values for pre- and post-midnights are 4.4 TECU and 2.17 TECU respectively. The percentage occurrence of nighttime TEC enhancement does not show any dependence on solar activity whereas the peak amplitude depends on solar activity. The percentage occurrence of nighttime TEC enhancement decreases as the magnetic activity increases whereas there is no such dependency found with peak amplitude. It is also observed that majority of nighttime TEC enhancements are occurred without scintillation. The localised nighttime TEC enhancements near the crest of equatorial ionization anomaly region have been observed most of the nights during the period of study.     

Earthquakes and global electrical circuit

Based on recent experimental and theoretical model results, the role of earthquakes and processes of their preparation as electricity sources in the global electric circuit (GEC) is discussed. In addition to the traditional elements of the GEC, such as thunderstorm currents, ionosphere currents, fair weather currents, and telluric currents, hypothetical seismogenic currents flowing between the faults and the ionosphere are considered. The ionization sources for these currents are presumably the radiation of radioactive gases and the ionization by the electric field of so-called “positive holes” created by the compression of tectonic plates, whereas transportation of electric charges between the Earth and the ionosphere occurs under the action of electric fields and turbulent diffusion (for heavy charged species). Seismogenic currents deliver electric charges into the ionosphere, which give rise to electric fields in it and in the magnetically conjugated region. The drift of magnetized plasma in the ionosphere F2-region and plasmasphere plasma under the action of these fields causes disturbances in the electron density and total electron content (TEC) of the ionosphere, which are observed by GPS satellites before strong earthquakes. The typical features of these disturbances (magnitudes, dimensions, stability, nighttime predominance of the relative TEC disturbances, geomagnetic conjugacy) are well reproduced in theoretical model calculations based on the solution of the equation for the electric ionosphere potential with specified seismogenic electric current at the lower boundary of the ionosphere if this current is strong enough (comparable with thunderstorm currents). The feasibility of such seismogenic currents is discussed. It is argued that the TEC disturbances observed before strong earthquakes cannot be explained by neutral atmosphere disturbances. These TEC disturbances can be treated as ionospheric earthquake precursors created by seismogenic GEC disturbances.     

Wave ionosphere perturbations with small periods under magnetic storm conditions

The characteristics of total electron content (TEC) variations obtained using the data of middle-latitude stations for receiving GPS satellite signals were studied. An analysis showed that perturbations of diurnal TEC variations during a geomagnetic storm were determined by strengthening of harmonics with periods of 4–5 and 6–8 h. Perturbations in diurnal TEC variations were retained for several days after a geomagnetic storm. An analysis of the frequency and amplitude characteristics of perturbed variations showed that differences between variations at different latitudes could be explained by the propagation of Poincaré planetary waves in an atmospheric wave channel. The atmospheric channel was formed because of increased heating of pole regions during geomagnetic storms. A comparative analysis of observations made at different stations was used to estimate the width of the atmospheric channel and Poincaré wave frequencies and wave vector components.     

New reconstruction and forecasting algorithm for TEC data

To reconstruct the missing data of the total electron content(TEC) observations, a new method is proposed, which is based on the empirical orthogonal functions(EOF) decomposition and the value of eigenvalue itself. It is a self-adaptive EOF decomposition without any prior information needed, and the error of reconstructed data can be estimated. The interval quartering algorithm and cross-validation algorithm are used to compute the optimal number of EOFs for reconstruction.The interval quartering algorithm can reduce the computation time. The application of the data interpolating empirical orthogonal functions(DINEOF) method to the real data have demonstrated that the method can reconstruct the TEC map with high accuracy, which can be employed on the real-time system in the future work.     

Application of the models of the middle and upper atmosphere to simulation of total electron content perturbations caused by the 2009 stratospheric warming

Sudden stratospheric warming (SSW) is a unique atmospheric phenomenon, which consists in a rapid rise of temperature at altitudes of ~30–40 km in high latitudes of the winter, typically, northern hemisphere. Modeling SSW effects in the mesosphere, thermosphere, and ionosphere is a challenging problem, because it must be done on a global scale, with consideration of numerous physical and chemical processes. This paper reports the results of calculations of the characteristics of total electron content (TEC) perturbations for the conditions of the SSW event in January 2009. The calculations are performed using the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) supplemented by the lower boundary conditions in the form of space–time distributions of the basic parameters of the mesosphere at an altitude of 80 km, as calculated by the SOCOL, KASIMA, and TIME GCM models. The simulation results show that, for some versions, the spatial distribution of total electron content disturbances ΔTEC shows a qualitative agreement with experimental data; however, the values of ΔTEC in all variants of calculations proved to be an order of magnitude lower than the measured.