电离层扰动的GPS探测

提出了一种利用短基线GPS接收阵探测研究电离层扰动的实验新技术,在此基础上发展了一种消除观测点运动速度的影响,从探测结果中确定扰动传播参量的数据分析算法．实验结果表明,短基线GPS接收阵用于探测研究TID一类电离层扰动时,精度高,可靠性好,并能有效地探测大范围电离层扰动的传播特性．     

1984年4月份兰州地区电离层行波扰动的观测结果及初析

１９８４年４月份兰州地区电离层行波扰动的观测结果及初析张秀菊（中国电波传播研究所,新乡,４５３００３）关键词高频返回探测,多普勒频率,电离层行波扰动１９８４年４月我们利用高频返回探测系统在新乡一西北（反射点在兰州地区）电路上多次测到电离Ｆ层的行波扰动...     

台风激发的声重力波的可探测性研究

通过对北京大学高频多普勒台站(39.4°N,116.2°E)多年的观测资料及相关台风资料的统计分析,着重研究了高频多普勒探测手段对由台风引起的扰动电离层响应的可探测性问题.通过对台风登陆前后的高频多普勒观测记录的细致分析及与宁静条件下记录的对比研究,表明高频多普勒观测手段可以很好地探测由台风激发的声重力波,尤其是对台风登陆前后所激发的扰动具有较高的可探测性.在所分析的24次台风事件中有明显扰动记录的高达22次(22/24).结合观测事实与Huang等的统计结果(2/12)进行了比较,并进行了可能的原因分析.通过数值模拟的方法对观测到的主要扰动的非线性传播过程进行了模拟再现,结果基本上与观测结果及线性传播理论一致.确认了一般情况下高可探测性这一事实,但同时也表明可探测性和台风激发源与探测位置及中尺度TIDs在电离层中的传播模式有密切关系.      

电离层中小尺度扰动的多频多普勒快速探测与分析

电离层反射回波的高频多普勒频移测量是研究电离层扰动的重要方法之一.利用基于单频信号相位变化率测量的实时探测方法,获取连续高精度多频多普勒频高图,以实现中小尺度电离层扰动的快速探测研究.该方法被应用于敏捷式高性能电离层无线电多频探测系统样机平台.经验证在该平台上获取的多普勒频移分辨率可达0.039Hz,频高图探测周期最短小于1min.基于这种快速探测方法和平台在武汉观测站进行了较长时间的观测和数据采集,获得高精度多普勒频移并反演出电子浓度等值面法向运动速度,得到电离层反射寻常波的多普勒频高图和垂直扰动速度等信息,进而推演出电离层扰动随时间和空间的实时变化特征.对这些时域信号进行频谱分析,初步结果显示这些扰动主要是由极区活动激发的中国中部地区冬季出现率较高的中尺度TID.此外,对三种常用的电离层扰动反演分析方法进行了对比研究,结果显示电离层扰动的变化趋势基本一致,说明观测数据和研究方法可靠稳定,为多频多点电离层扰动的传播特性观测研究提供了基础.      

高精度多普勒频高图的获取和分析

电离层高频反射回波的多普勒频移是研究电离层扰动的一个重要参数。在数字测高仪探测中，高分辩率的多普勒频移一般在漂移测量中获得，但这种测量方式探测的频点少，不能获得扰动的高度剖面；而在频高图模式下，虽然工作的频点多，能够获得电子浓度的高度剖面的信息，但探测的多普勒频移的分辩率低，无法用来精确检测电离层扰动。实际的电离层高频回波一般为窄带信号，由此本文中提出了一种新的分析方法，利用DGS-256数字测高仪频高图模式下记录的16个多普勒通道的数据，通过反傅里叶变换还原成时域信号，采用最小二乘法估计相邻时间点的相位差，获得高精度多普勒频高图。作为实例，利用该方法分析武汉电离层观象台数字测高仪观测站的观测数据，得到了多频点的多普勒频移曲线。结果表明：在DGS-256数字测高仪频高图模式下能够得到高精度多普勒频高图，这在电离层扰动探测和研究中很在意义。     

电离层H2O释放扰动效应的数值模拟研究

为充分研究化学物质在电离层释放的扰动效应和后期发展效果,基于化学物质在电离层的扩散模型、化学反应和电离层扩展F的控制模型,通过电离层H₂O的释放,研究电子e,H₂O,O+和H₂O+共4种粒子的分布状态,分析点源、多源和线源释放对电离层的扰动效果,比较不同高度、不同量和不同时间释放的影响结果,模拟夜间释放后期所激发的扩展F发展差异.结果表明,H₂O在电离层释放后,能有效耗散背景电子形成空洞,O+和H₂O+数密度呈椭圆形分布;点源、多源和运动目标线源等不同释放方式对电离层的扰动效果不同,证实了人工影响一定形态和区域电离层的可能性;H₂O释放扰动幅度,低层大于高层,白天强于夜晚,释放量越多扰动越突出;夜间化学释放能激发扩展F,并且释放量越多,激发效果越好.      

电离层多普勒接收机的设计与实验

利用软件无线电技术设计了一种电离层多普勒接收机. 该接收机采用DSP, FPGA等数字芯片与PXI总线进行架构, 使用GPS作为接收机的时间和频率同 步模块, 能够灵活设置系统参数. 实验接收来自中国蒲城陕西天文台的高 频时间信号, 实时获取由于电离层扰动所产生的多普勒频率偏移信息. 使用通过MATLAB语言实现的信号处理软件平台, 对接收到的高频信号进行处理. 观测结果表明, 接收机能够分析电离层回波信号的多普勒频移随时间的变化, 是获取不同空间尺度电离层扰动信息的一种有效手段.      

中纬地区日间类扩展F不规则结构的观测研究

基于高频多普勒观测,研究中纬地区日间类扩展F现象及其与其他电离层扰动现象的关联.结果表明:日间类扩展F具有出现时间覆盖面广、持续时间长、与其他电离层扰动相互伴随等特征;形态特征表现为回波弥散（与夜间扩展F相似）,弥散回波的频移多倾向于正向偏移,有时与行进电离层扰动（TIDs）相互伴随.日间类扩展F现象虽然是偶发事件,且发生率极低,但其出现时间及区域的广泛性充分体现了该现象对空间天气及空间环境的影响具有不可忽视的重要性.      

敏捷数字电离层测高仪系统研制及初步观测

在小型天线和低发射功率条件下，保证电离层测高仪观测数据质量和提高观测速度一直是电离层垂测的技术难点.针对这一问题，基于新近发展的高速数字芯片和射频器件，采用窄带跟踪滤波、脉冲压缩、编码复用和天线均衡匹配等技术，设计和研制一种敏捷数字电离层测高仪.该系统采用数米高的小型收发天线和便携式主机系统，配置任意频率扫描方式频高图、高分辨率多普勒频高图和斜向探测等多种工作模式，具有可流动观测布站、系统参数灵活捷变及适合快速电离层扰动探测等能力.敏捷数字电离层测高仪为组网观测获得大范围电离层时空变化和电离层快速扰动及传播提供了一种有效的探测手段.      

基于IGS电离层TEC格网的扰动特征统计分析

电离层总电子含量（TEC）是研究空间天气特性的重要参量,通过分析电离层TEC,可以了解空间环境的变化特征.利用IGS提供的1999—2016年全球电离层TEC格网数据,按照地磁纬度将全球划分为高、中、中低、低磁纬四个区域,计算不同区域的电离层扰动;利用大量统计数据选取电离层扰动事件的判定阈值,分析电离层扰动与太阳活动、时空之间的关系;计算电离层扰动指数与地磁活动之间的相关系数.结果显示:电离层扰动与太阳活动变化具有较强的正相关特性.在太阳活动低年,电离层扰动事件发生的概率约为1.79%,在太阳活动高年发生扰动的概率约为10.18%.在空间分布上,无论是太阳活动高年还是低年,高磁纬地区发生扰动事件的概率均大于其他磁纬出现扰动事件的概率.计算得到的中磁纬和中低磁纬地区电离层扰动指数与全球地磁指数Ap的相关系数分别为0.57和0.56,说明电离层扰动指数与Ap具有较好的相关关系;高磁纬电离层扰动指数与Ap的相关系数为0.44;低磁纬扰动指数与Ap的相关系数为0.39.以上结果表明,不同区域电离层扰动与全球地磁指数Ap的相关性不同,测定区域地磁指数可能会提高与电离层扰动的相关性.      

我国中低纬地区上空低电离层中的行星波

本文通过5年的电离层吸收观测资料与平流层增温事件对比及吸收资料的谱分析,得出以下几点初步结论:1)极区平流层增温事件的影响可能通过子午环流和行星波传播,经过5—9天后到达中低纬地区,从而引起那里的电离层吸收变化;2)冬季行星波沿子午方向的平均速度大约在10m/s到15m/s之间变化;3)全年均有周期为32天、18天、10天、8天和2天的行星波出现,它对大气湍流系数有明显影响。计算得出行星波扰动引起中层的NO浓度偏离未扰值可高达40%。      

内重力波传播的3维传输函数模式研究

在考虑背景风场及大气耗散的条件下,建立了3维内重力波传输函数数值模式.分析了300 km高度3维传输函数在频率波数域的特性,并以近地面单位脉冲点源为激发源,得到了内重力波在3维空间中的时空分布.讨论了不同时空尺度地面方波源激发的内重力波在电离层高度的能量分布特征.结果表明,(1)对内重力波而言,背景大气相当于一个带通滤波器,只有波动周期和波长分别在15～30 min和200～400 km之间的重力波扰动最容易上传到300km高度;(2)在背景风场的作用下水平面上以同心圆扩散的波阵面以及垂直方向上成漏斗状的波阵面发生了变形,并且逆风方向比顺风方向更有利于声重力波由对流层向电离层高度传播;(3)300km高度对时间尺度和空间尺度分别在20～30 min和150～250 km之间的地面方波源响应的总能量最强.      

Use of global ionospheric maps for HF Doppler measurements interpretation

The HF Doppler technique, a method of measurement of Doppler frequency shift of ionospheric signal, is one of the well-known and widely used techniques of ionosphere research. It allows investigation of various disturbances in the ionosphere. There are different sources of disturbances in the ionosphere such as geomagnetic storms, solar flashes, meteorological effects and atmospheric waves. The HF Doppler technique allows us to find out the influence of earthquakes, explosions and other processes on the ionosphere, which occurs near the Earth. HF Doppler technique has high sensitivity to small frequency variations and high time resolution but interpretation of results is difficult. In this paper, we attempt to use GPS data for Doppler measurements interpretation. Modeling of Doppler frequency shift variations with use of TEC allows separation of ionosphere disturbances of medium scale.     

DEMETER卫星记录到的电离层加热现象

在法国DEMETER卫星运行期间, 地基电离层加热装置SURA和HAARP开展了一系列加热试验, 记录到各类电离层异常信息, 发现电离层加热过程中卫星观测的电离层扰动信号包括HF发射泵波及边带泵波、VLF人工源增强及频谱拓展、ULF/ELF/VLF调制波、ELF电磁扰动、ULF谐振波、等离子体特征参量扰动及高能粒子沉降等. 由于传播及耦合机制的差异, 发射泵波可以穿透电离层直达卫星高度, 其观测概率最高达到68%以上, 其他扰动受发射调制模式及当地电磁环境等影响,观测概率相对较低, 均在40%左右, 有些甚至是某次试验中出现的个别事例. 结合中国地震电磁监测试验卫星飞行轨道设计及载荷配置等,对未来开展加热试验进行了分析论证, 并参考DEMETER卫星试验结果给出了一些建议.      

Global characteristics of ionospheric electric fields and disturbances during the first hours of magnetic storms

The ionospheric plasma density can be significantly disturbed during magnetic storms. In the conventional scenario of ionospheric storms, the negative storm phases with plasma density decreases are caused by neutral composition changes, and the positive storm phases with plasma density increases are often related to atmospheric gravity waves. However, recent studies show that the global redistribution of the ionospheric plasma is dominated primarily by electric fields during the first hours of magnetic storms. In this paper, we present the measurements of ionospheric disturbances by the DMSP satellites and GPS network during the magnetic storm on 6 April 2000. The DMSP measurements include the F region ion velocity and density at the altitude of ∼840 km, and the GPS receiver network provides total electron content (TEC) measurements. The storm-time ionospheric disturbances show the following characteristics. The plasma density is deeply depleted in a latitudinal range of ∼20° over the equatorial region in the evening sector, and the depletions represent plasma bubbles. The ionospheric plasma density at middle latitudes (20°–40° magnetic latitudes) is significantly increased. The dayside TEC is increased simultaneously over a large latitudinal range. An enhanced TEC band forms in the afternoon sector, goes through the cusp region, and enters the polar cap. All the observed ionospheric disturbances occur within 1–5 h from the storm sudden commencement. The observations suggest that penetration electric fields play a major role in the rapid generation of equatorial plasma bubbles and the simultaneous increases of the dayside TEC within the first 2 h during the storm main phase. The ionospheric disturbances at later times may be caused by the combination of penetration electric fields and neutral wind dynamo process.     

Thermospheric F-region travelling disturbances detected at low latitude by an OI 630 nm digital imager system

Gravity wave effects in the nocturnal thermospheric F-region domain are seldom detected in the intertropical region by optical (airglow) techniques, especially during geomagnetically quiet times, in part because the low inclination of the magnetic field, as opposed to the case of the mid-latitude region, does not favor significant vertical excursions of ionospheric plasma in response to meridional winds. Such difficulty in detecting gravity wave signatures in the F-region by means of optical techniques tends to increase in the absence of geomagnetic storms because of the lack of strong forcing mechanisms necessary to generate high intensity gravity waves. The purpose of this work is to show that during the quiet day of 9 August 1999, the Terminator may have been a source region of wave-like disturbances in the nocturnal F-region at the low-latitude station Cachoeira Paulista (22°41'S; 45°00W, dip 30°). A digital all-sky OI 630nm imager system located at that station has shown propagating wave-like spatial structures in the airglow intensity near the Terminator. This observation supports a previous study on the evidence of the presence of gravity waves during the post-sunset period at the same location by means of a scanning photometer system (1997, Sobral, J. Atmos. Terr. Phys. 59, 1611–1623). The absence of range-type spread-F as monitored by a local digisonde and the absence of radio wave scintillation as monitored by a local GPS receiver, excludes the hypothesis that the wave-like airglow structures are associated with the occurrence of the ionospheric plasma bubbles. Downwards motion of the iso-density real height contours at 22.0 ms⁻¹ and 33.1 ms⁻¹ are observed. The wave detection by the imager system is reported and discussed here.     

中低纬电离层对行星际磁场南向翻转的响应

利用卫星和地面台站的历史数据, 研究了中低纬电离层f0F2 对强行星际磁场南向翻转的响应. 结果表明, 行星际磁场南向翻转能引起电离层扰动式响应, 响应特性与纬度、季节和翻转时刻的地方时有关. 在中纬, 发生在夏分季和夜间的翻转能造成较强的电离层负响应, 其幅度随纬度的降低而变弱, 在恢复过程中存在不规则振荡; 在低纬, 南向翻转引起的电离层响应在夏分季较强, 在冬季则较弱, 且易被淹没在电离层自身的扰动中. 分析指出电离层最大负响应与翻转后南向磁场极大值之间有着较好的线性关系.      

Sources and losses of ring current ions: An update

The cleft ion fountain has been identified as a prodigious source of upflowing suprathermal ionospheric plasma. Modeling efforts have traced the path of these ions from the polar ionosphere along trajectories where the ions are energized to keV energies and deposited in the near earth plasma sheet. Mass and energy dispersion of these ions accounts in a natural way for the observed variation in heavy ion content of the plasma sheet. Observations of ion composition in the plasma sheet by the AMPTE and ISEE spacecraft establish that ionospheric ions dominate in the near earth plasma sheet but solar wind ions become significant tailward. The heavy ion content of the plasma sheet increases with both solar cycle and magnetic activity. Direct injection of ionospheric ions into the ring current has been observed in the outer plasmasphere. Several mechanisms for the direct injection of ions from the plasmasphere and ionosphere into the ring current have appeared. Estimation of ionospheric source strengths and residence times have led to an estimate of the magnetospheric densities that would result solely from an ionospheric outflow populating the magnetosphere. Estimated densities were quite reasonable even without inclusion of a solar wind source of ions. Ring current ions decay primarily via charge exchange with the hydrogen geocorona, however, the roles of pitch angle diffusion and Coulomb collisions in this decay process are being clarified.

Modeling and observations of ENA by the 1SEE1 spacecraft has led to a re-affirmation of the dominant role of charge exchange in ring current decay. Ion cyclotron waves contribute to ring current decay in the dusk bulge region. The role of low frequency. (< 1 Hz) ion cyclotron waves in the plasmasphere is still unclear. Other wave modes may be responsible for the pitch angle diffusion and subsequent loss of ring current ions. Coulomb collisional energy losses from ring current O⁺ to thermal electrons are sufficient to power SAR arcs and represent an energy sink for ring current O⁺ within the plasmasphere. Coulomb collisions may be important for decay of low energy (< 10 KeV) ring current ions in the plasmasphere.     

A Review on the Ionospheric Research:Chinese Works During 2006—2008

This paper reviews various progresses on the ionospheric studies by the scientists in China during the last two years.The main contents concern the 4 aspects of the ionospheric re-search:(1) ionospheric weather and coupling with magnetosphere(polar and auroral ionosphere,ionospheric response to substorms,ionospheric storms);(2) mid-and low-latitude ionospheric clima-tology(ionospheric properties,yearly variations and solar activity dependence,long term variation);(3) ionospheric coupling with neutral atmosphere(gravity waves,tides,planetary waves,background upper atmosphere,and ionospheric response);and(4) ionospheric diagnostics(observation,modeling,and prediction).