小波分解与Prophet框架融合的电离层VTEC预报模型

在全球导航卫星系统(global navigation satellite system,GNSS)的应用中,电离层垂直总电子含量(vertical total electron content,VTEC)是直接决定电离层延迟误差的重要参数.为提高其短期预报精度,在综合考虑地磁扰动影响的基础上,提出了小波分解与Prop...     

A simulation study of ionization depletion in the auroral ionosphericF-region caused by strong convection electric field

THe effects of strong convection electric field on the electron density in the auroral ionosphericF-region have been simulated numerically by means of a physical model. It is found that an enhancement of electric field directed west-northward in post-noon or west-southward in pre-noon results in an ionization depletion with its maximum at altitudes 40–50 km higher than that of theF ₂ peak. When the enhanced electric field lasts for 45 min and has a maximum about 32 mV/m, the resulted ionization depletions reach their maximum at the time just ∼10 min behind the time when the convection electric field and ion temperature enhancements reach their maximum. This is consistent well with EISCAT observations. The magnitudes of the percentage ionization depletions and their recovery time are dependent not only on the intensity of the electric field, but also on the diurnal variation phase of the background electron density. Foundation item: Supported by the National Natural Science Foundation of China (49674241, 40074039) and the Research Fund for the Doctoral Program of Higher Education in China Biography: Cai Hong-tao (1976-), male, Ph. D. candidate, research direction: polar ionospheric modeling.     

短波信道相干带宽的计算

介绍了一种双层平谷电离层电子密度模式。从该电子密度模式和电离层波传播特性出发确定多径分量,计算短波信道相干带宽。计算并分析了不同工作频率以及不同通信距离下的相干带宽。与采用单层电子密度的模型相比,由于双层平谷模型可以更准确地分析由电离层反射的多径分量以及它们的路径损耗,因此其计算的相干带宽比单层模型更接近实际测量值。     

EISCAT observations of main ionization troughs in the high-latitude ionosphere

F-region electron density depletions associated with main ionization troughs in the high-latitude ionosphere are studied using EISCAT CP3 data of meridian scanning experiments. The troughs in our observations are found to appear mainly in dusk sector, extending from late afternoon to pre-midnight, with higher occurrence rate during equinox and winter. Simultaneous ion drift velocity inF-region shows that the main trough minimum is mostly located at the equator ward edge of the plasma convection flow, rather than in the region where the largest ion flow are observed. Foundation item: Supported by the National Natural Science Foundation of China (49674241) and the Research Fund for the Doctoral Program of Higher Education Biography: LIU Peng (1978-), male, Master candidate. Research direction: studying high-latitude ionosphere using EISCAT radar.     

基于频域GPS信标提取电离层闪烁信息的方法

GPS(global positioning system)信标提取电离层闪烁信息的传统方法十分依赖于GPS硬件接收机对电离层闪烁信号的连续捕获和准确跟踪,而电离层闪烁发生特别是强闪烁情况下信号往往很弱,极易发生接收机的信号失锁,导致闪烁信息丢失的现象.针对这一问题,以构建软件GPS接收机为基本前提,提出一种基于快速傅里叶变换的频域处理方法用于计算电离层幅度闪烁指数.模拟计算结果表明:新方法计算得到的闪烁指数避免了系统误差,具有较高的精度.     

Ionospheric structure in the region of East-Asian equatorial anomaly reconstructed by tomography

A chain of low latitudinal ionospheric tomography along 120°E meridian has been operating since 1993. This chain is composed of six stations from Shanghai to Manila receiving signals from the transit NNSS satellites. In this paper several reconstruction examples are presented, which give the 2-D imaging of electron density distribution obtained from the observed TEC data by means of computerized tomography technique. In reconstruction process a multi-station method was used to determine the unknown phase offset. To overcome the limitation of incomplete projection data, a technique of backprojection in combination with a normalized ionospheric model was introduced to obtain the initial guess of electron density distribution. The results demonstrate that ionospheric tomographic technology is very useful and effective to investigate the equatorial and low-latitudinal ionospheric structures and dynamics. Supported by the National Natural Science Foundation, of China & the Science Fourdation of State Education Committee of China Xu Jisheng: born in Nov. 1946, Professor     

星星间无线电掩星探测火星电离层的仿真

用于探测火星电离层的星星间无线电掩星技术较以前的星地间探测技术相比,有可接收高信噪比的信号、掩星发生次数多且覆盖范围大和反演精度高等优点,首先介绍了两颗卫星的运行轨道以及在一定时间内两星间所有掩星事件的仿真结果,论述了利用无线电掩星数据进行火星电离层反演的理论、模型及相应的计算流程,并结合火星电子密度模型模拟的原始载波相位数据,反演计算了电离层电子密度剖面.反演结果和模型值符合很好,从而表明了该方法的优越性和可行性.     

Nonlinear dispersive scale Alfvén waves inmagnetosphere-ionosphere coupling: Physical processes and simulation results

Dispersive Alfvén waves(DAWs)have been demonstrated to play a significant role in auroral generation of the magnetosphereionosphere coupling system.Starting from a two fluid reduced MHD model,we summarize the frequency,temporal and spatial characteristics of magnetospheric DAWs.Then,the nonlinear kinetic and inertial scale Alfveén waves are studied,and we review some theoretical aspects and simulation results of dispersive Alfve′n waves in Earth’s magnetosphere.It is shown that dispersive standing Alfve′n waves can generate the field-aligned currents which transport energy into the auroral ionosphere,where it is dissipated by Joule heating and energy lost due to electron precipitation.The Joule dissipation can heat the ionospheric electron and produce changes in the ionospheric Pedersen conductivity.As a feedback,the conducting ionosphere can also strongly affect the magnetospheric currents. The ponderomotive force can cause the plasma to move along the field line,and generate ionospheric density cavity.The nonlinear structuring can lead to a dispersive scale to accelerate auroral particle,and the Alfvn waves can be trapped within the density cavity. Finally,we show the nonlinear decay of dispersive Alfvén waves related to two anti-propagating electron fluxes observed in the auroral zone.     

短波单站定位中电离层的模型选择与修正

短波单站定位实现了仅用一个测向站就能确定短波发射台的方向及位置,在短波单站定位中,影响单站定位精度的主要因素来源于电离层模型及电离层参数是否与实际情况相符.作者介绍了短波单站定位机理和两种实用的电离层模型,并对基于这两种电离层模型的射线反跟踪算法进行了分析比较.为了进一步提高单站定位精度,还提出了利用已知台修正电离层模型,并设计实现了该模型.     

Performance analysis of a 3D ionosphere tomographic model

A 3D high precision ionospheric model is developed based on tomography technique. This tomographic model employs GPS data observed by an operational network of dual-frequency GPS receivers. The methodology of developing a 3D ionospheric tomography model is briefly summarized. However emphasis is put on the analysis and evaluation of the accuracy variation of 3D ionosphere modeling with respect to the change of GPS data cutoff angle.Three typical cutoff angle values (15°, 20° and 25°) are tested. For each testing cutoff angle, the performances of the3D ionospheric model constructed using tomography technique are assessed by calibrating the model predicted ionospheric TEC with the GPS measured TEC and by employing the model predicted TEC to a practical GPS positioning application single point positioning (SPP).Test results indicate the 3D model predicted VTEC has about 0.4 TECU improvement in accuracy when cutoff angle rises from 15° to 20°. However, no apparent improvement is found from 20° to 25°. The model's improvement is also validated by the better SPP accuracy of 3D model than its counterpart-dual frequency model in the 20° and 25° cases.