电导率分布、对流电场转向区与场向电流形态(模式分析)

本文利用一些简单模式讨论对流转向区形态、电离层电导率的分布变化对场向电流形态的影响。结果表明,一区场向电流是最基本的,与对流转向区直接相联。二区场向电流的产生不仅与对流电场的屏蔽相联,也与电导率变化有关。电导率的变化还可产生一区电流高纬侧的零区电流和二区电流低纬侧的反向电流。此外,剪切转向区和旋转转向区所对应的场向电流分布也有所不同。本文结果有助于理解观测的场向电流之复杂形态,也可以解释同样的行星际磁场状况下,场向电流的不同变化。      

极光西向涌浪的二维模式(线性部分)

极光西向涌浪(WTS)被定义为磁层亚暴开始的重要标志, 它是伴随带电粒子沉降过程在极光带电离层出现的特定的极光运动形态.本文给出了极光西向涌浪的二维动力学模式, 亚暴开始, 伴随粒子沉降在电离层产生离子密度梯度(电导率梯度), 在背景电场中激发出低频漂移波, 它的传播给出极光西向涌浪运动的主要特性.      

量子阱激光器的Pspice电路温度模型

在考虑量子阱激光器的温度特性基础上,对激光器的速率方程进行了适用性修正,增加了与温度相关的势垒区的辐射复合电流I_br、非辐射复合电流I_bnr和有源区的非辐射复合电流I_wnr、俄歇复合电流Ia等项,并根据修正后的速率方程得出了量子阱激光器的大信号等效 Pspice电路温度模型和直流稳态工作时的等效Pspice电路温度模型,然后采用GaAS/AlGaAS 量子阱激光器,根据量子阱激光器直流稳态工作时的等效Pspice电路温度模型对量子阱激光器的输出光功率、驱动电流和结点温度之间特性进行了模拟,得出它们之间的关系曲线.     

On the effect of near-equatorial thunderstorms on the global distribution of ionospheric potential

We develop our earlier attempts to perform an indirect quantitative examination of the hypothesis that electric currents flowing up from thunderstorms to the ionosphere (also known as Wilson currents) charge the ionosphere to a large positive potential with respect to the Earth. First, we take the electrostatic potential arising from the interaction of the solar wind with the Earth’s magnetosphere derived from an experimental data-based model of the high-latitude field-aligned currents. We then obtain the global distribution of ionospheric potential, utilizing a thin shell model, based on integration along field lines of the current continuity equation with a realistic model of ionospheric conductivity. Next, we include additional upward currents to simulate the effect of the three main thunderstorm regions over equatorial Asia/Oceania, Africa and the Americas. We compare the local time variation of the eastward electric field in the ionosphere produced by these three equatorial sources separately, and seek to understand the substantial differences between them. Finally, we examine the variation with local time of the eastward electric field in the ionosphere at low latitudes.     

化学物质释放人工改变电离层

考虑中性气体在电离层高度的扩散过程和相应的电离层离子化学过程，研究了利用主动化学物质释放来改变电离层的方法，理论计算了H2O和SF6两种气体释放后电离层随时间的响应过程，结果表明，在电离层高度上气体的扩散过程非常迅速，电离层F区的电子密度有很大程度的减少，而扩散慢且化学反应快的气体对电离层的影响更大，就更加有利于电离层洞的形成。     

利用TIE-GCM模式计算电离层电流及夜间电离层磁场

电离层电流产生的磁场是地磁场卫星测绘时需要剔除的干扰源.利用电离层热层模式TIE-GCM计算电离层中的中性风、重力驱动和压强梯度等形成的电离层电流的全球分布,分析电流在特定位置产生的磁场及磁场三分量随纬度的变化规律.结果表明,E层尤其是磁赤道和极区的电流密度较大,可达103nA·m-2量级,F层电流密度量级约为10nA·m-2.在磁静日（Kp≤ 1）夜间22:00LT-04:00LT,电离层电流在中低纬度（南北纬50°之间）产生的磁场量级为几个nT,且磁场的南北向分量和径向分量基本大于东西向分量.通过与CHAMP卫星磁测数据分析比较,发现TIE-GCM模式计算电离层干扰磁场在中低纬度可以取得较好的结果,但在高纬度地区的效果不理想,还需进一步改进模式以提高计算精度.      

Statistical average estimates of high latitude field-aligned currents from the STARE and SABRE coherent VHF radar systems

Two bistatic VHF radar systems, STARE and SABRE, have been employed to estimate ionospheric electric fields in the geomagnetic latitude range 61.1 – 69.3° (geographic latitude range 63.8 – 72.6°) over northern Scandinavia. 173 days of good backscatter from all four radars have been analysed during the period 1982 to 1986, from which the average ionospheric divergence electric field versus latitude and time is calculated. The average magnetic field-aligned currents are computed using an AE-dependent empirical model of the ionospheric conductance. Statistical Birkeland current estimates are presented for high and low values of the Kp and AE indices as well as positive and negative orientations of the IMF B_z component. The results compare very favourably to other ground-based and satellite measurements.     

Response of the ionosphere to super geomagnetic storms: Observations and modeling

The relative importance of the main drivers of positive ionospheric storms at low-mid latitudes is studied using observations and modeling for the first time. In response to a rare super double geomagnetic storm during 07–11 November 2004, the low-mid latitude (17°–48°N geomag. lat.) ionosphere produced positive ionospheric storms in peak electron density (NmF2) in Japan longitudes (≈125°–145°E) on the day of main phase (MP1) onset (06:30 LT) and negative ionospheric storms in American longitudes (≈65°–120°W) on the following day of MP1 onset (13:00–16:00 LT). The relative effects of the main drivers of the positive ionospheric storms (penetrating daytime eastward electric field, and direct and indirect effects of equatorward neutral wind) are studied using the Sheffield University Plasmasphere Ionosphere Model (SUPIM). The model results show that the penetrating daytime (morning–noon) eastward electric field shifts the equatorial ionisation anomaly crests in NmF2 and TEC (total electron content) to higher than normal latitudes and reduces their values at latitudes at and within the anomaly crests while the direct effects of the equatorward wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) combined with daytime production of ionisation increase NmF2 and TEC at latitudes poleward of the equatorial region; the later effects can be major causes of positive ionospheric storms at mid latitudes. The downwelling (indirect) effect of the wind increases NmF2 and TEC at low latitudes while its upwelling (indirect) effect reduces NmF2 and TEC at mid latitudes. The net effect of all main drivers is positive ionospheric storms at low-mid latitudes in Japan longitude, which qualitatively agrees with the observations.     

Controlling factors of Region 2 field-aligned current and its relationship to the ring current: Model results

One essential component of magnetosphere and ionosphere coupling is the closure of the ring current through Region 2 field-aligned current (FAC). Using the Comprehensive Ring Current Model (CRCM), which includes magnetosphere and ionosphere coupling by solving the kinetic equation of ring current particles and the closure of the electric currents between the two regions, we have investigated the effects of high latitude potential, ionospheric conductivity, plasma sheet density and different magnetic field models on the development of Region 2 field-aligned currents, and the relationship between R2 FACs and the ring current. It is shown that an increase in high latitude potential, ionospheric conductivity or plasma sheet density generally results in an increase in Region 2 FACs’ intensity, but R2 FACs display different local time and latitudinal distributions for changes in each parameter due to the different mechanisms involved. Our simulation results show that the magnetic field configuration of the inner magnetosphere is also an important factor in the development of Region 2 field-aligned current. More numerical experiments and observational results are needed in further our understanding of the complex relationship of the two current systems.     

电离层水平电场与风场的耦合模拟研究

设计了一个将电离层水平电场与风场耦合的模拟方案,研究了电流函数和风场在耦合前后的变化与差异. 研究发现,水平电场与风场相互反馈后,风场的变化比电流函数小. 经向风在白天有较明显的差异,夜晚的差异比白天小,主要出现在中高纬地区,并随高度的增加而增大,300km左右达到最大值,其后几乎保持不变. 纬向风有与经向风相似的变化,但纬向风耦合前后的差异比经向风小. 电流函数在耦合后有较大改变,两个涡旋强度都有较强增加,并且北半球的增强大于南半球,而夜晚差异较小. 结果表明,在研究的高度范围内,风场对电场的控制作用大于电场对风场的影响.      

非径向地磁力线对计算电离层电场及三维电流系的部分影响

本文对Kamide等人的由地面磁变化计算电离层电场、电流及场向电流的方法做了改进。给出了计入非径向地磁力线对电离层电导率影响下的电位φ的二阶偏微分方程。通过实例计算考查了由地面磁资料计算电离层电场、电流及场向电流中地磁力线非径向性的部分效应。结果表明,即使在高纬极光区,这部分效应也是重要的、不能忽视的;此外,计入这一效应使得计算量明显减少。      

Klobuchar电离层模型误差分析及预测

电离层延迟误差是全球导航卫星系统（global navigation satellite system，GNSS）中的重要误差源之一。目前在电离层延迟改正模型中，应用最广泛的是Klobuchar参数模型，但是该模型的改正率仅能达到60%左右，无法满足日益增长的精度需求。将国际GNSS监测评估系统（international GNSS monitoring & assessment system，iGMAS）发布的高精度电离层格网数据作为对照，对Klobuchar电离层模型误差进行计算和分析，结果发现在中纬度区域误差存在明显的周期性特征。为进一步提高Klobuchar电离层模型在中纬度区域的改正精度，建立了基于粒子群优化反向传播（back propagation，BP）神经网络的Klobuchar电离层误差预测模型,并以2019年10月的采样数据为例进行误差预测。结果表明，用该模型对中纬度区域电离层延迟提供误差补偿，可将精度提高到90%左右。     

A numerical study of noontime bite-outs in F2-region electron density

Noontime bite-outs in ionospheric F₂-region electron density in the geomagnetic equatorial, low, and middle latitudes have been reproduced in this study using the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). The different driving mechanisms of F₂-region noontime bite-outs at different latitudes were further verified by modeling simulation. In the geomagnetic equator, the upward ExB plasma drifts are the main process to produce the noontime bite-outs in ionospheric electron density. In the geomagnetic low latitudes, both the electrical fields and poleward meridional winds play a crucial role in forming the noontime bite-outs. In contrast to the case at the geomagnetic equator, a weaker fountain effect might be an favorable condition for the noontime bite-outs to occur at low latitudes. For geomagnetic middle latitudes, an upward plasma flux and poleward meridional winds are the dominated drivers in producing the noontime bite-outs. Modeling results show that a large upward plasma flux and poleward meridional winds make the noontime bite-outs to occur and observable over middle latitudes.     

电离层Es对HF和VHF传播信号的影响

Es层是存在于电离层中的电子密度非常高的偶发E层（Sporadic E）,其电子密度可达常规E层的100倍.电离层Es能够反射原本穿透F层的VHF低频段（30~150MHz）无线电波,而且对HF高频段（10~30MHz）无线电波传播具有显著影响.运用垂测和斜测观测数据,研究HF频段Es层电波传播特征,得到了不同类型及不同高度Es层的衰减系数.根据f₀E_s的日变化规律,可得HF频段衰减系数的日变化规律,进而分析并得到Es层对短波传播的影响.不存在电离层Es时,通常无法通过电离层实现VHF超远距离通信.为了对VHF链路通过电离层Es的传播衰减进行定量分析,根据EBU多条链路的观测结果,拟合并建立了电离层Es衰减模型.将该模型、ITU模型和观测数据进行对比,发现本文建立的模型准确度更高.利用建立的模型,对电离层Es不同临频f₀E_s条件下接收信号场强和电压随传播距离的变化进行了计算,结果可为VHF链路设计及建立提供参考.      

Disturbances in the ionospheric F-region peak heights in the American longitudinal sector during geomagnetic storms of September 2005

In this paper, we use the modified GSM TIP model to explore how the thermosphere–ionosphere system in the American longitudinal sector responded to the series of geomagnetic storms on September 9–14, 2005. Comparison of modeling results with experimental data at Millstone Hill, USA (42.6°N, 71.5°W), Ramey, Puerto Rico (18.3°N, 66.8°W) and Jicamarca, Peru (11.9°S, 76.9°W) has shown a good agreement of ionospheric disturbances in the F-region maximum height. We examine in detail the formation mechanisms of these disturbances at different latitudes and describe some of the important physical processes affecting the behavior of the F-region. In addition, we consider the propagation of thermospheric wind surge and the formation of additional layers in the low-latitude ionosphere during geomagnetic storms.     

The generator system of field-aligned currents during the April 06, 2000, superstorm

Using ground-based magnetometer data of the April 6–7, 2000, superstorm, we obtained maps of ionospheric and field-aligned currents (FACs). Based on these, we deduced the electrical circuit of the disturbed magnetosphere/ionosphere and a conceptual model of its magnetospheric generators, which supply both hemispheres. This model implies that the generator system creates primarily the Region-1 FACs of Iijima and Potemra at both hemispheres, while the Region-2 and Region-0 FACs form by spreading of the Region-1 currents through the ionosphere. This conclusion is supported by observations.     

GNSS电离层模型改正精度评估与分析

电离层时延误差是导航定位信号在空间传播路径上的主要误差源之一,因此全面了解GNSS电离层模型的改正精度具有一定现实意义.根据GPS,BDS和Galileo系统所采用的电离层修正模型,利用2014年电离层校正参数,以高精度全球电离层图为基准,评估分析了三大系统电离层时延的改正精度.结果表明:目前GNSS使用的几种电离层修正模型的改正率在65~75%左右;Galileo系统使用的第二版NeQuick模型与第一版NeQuick模型相比在修正精度上并无显著提高;GPS使用的Klobuchar 8参数模型在北半球25°-45°N的中纬度地区精度很高,但是在全球其他区域精度较低,分布性较差,而NeQuick模型全球改正率分布则较为平均且平滑.      

The importance of conductivity gradients in ground-based field-aligned current studies

Magnetosphere-ionosphere coupling is achieved primarily through magnetic field-aligned currents. Such currents are difficult to measure directly and are usually inferred from satellite magnetometer recordings or from ground-based measurements of the divergence of ionospheric electric fields. The latter technique requires a knowledge of the ionospheric conductance distribution. Although it is possible to obtain the ionospheric electric field distribution over large spatial areas with good temporal resolution from coherent backscatter radars, these instruments cannot measure conductivity. Since the equation for computing field-aligned currents explicitly requires the gradient in conductance to be known, the use of statistically averaged models is excluded for case studies. If a dense enough array of magnetometers is available, these data may be used in combination with radar data to produce a measured conductance distribution within the overlapping fields of view. This has been done for data obtained in northern Scandinavia. Comparing field-aligned currents, computed with and without knowing the ionospheric conductance distribution, shows that gradients in conductance can not be ignored, even for quiet geomagnetic conditions.     

The ionosphere,radio navigation,and global navigation satellite systems

This article is a review of Global Navigation Satellite Systems (GNSS) for space scientists who are interested in how GNSS signals and observables can be used to understand ionospheric dynamics and, conversely, how ionospheric dynamics affect the operational capabilities of GNSS receivers. The most common form of GNSS is the Global Positioning System (GPS); we will first review its operating principles and then present a discussion of errors, of which ionospheric propagation is the most significant. Methods and systems for mitigating errors will be introduced, along with a discussion of modernization plans for GPS and for entirely new systems such as Galileo. In the second half of this article the effects of the ionosphere on GPS signals will be examined in more detail, particularly ionospheric propagation, leading to a discussion of the relation of TEC to ranging errors. Next, the subject of scintillations will also be introduced and connected to the presence and scale sizes of irregularities. Scintillations will be examined as spatial and temporal structures. The method of measuring scintillation pattern drift and ionospheric velocity will be discussed. We conclude by examining ionospheric effects on GPS at midlatitudes.     

Auroral signatures of transient processes in the outer magnetosphere

We present an analysis of sporadic and recurrent injections of magnetospheric ions in the midnight auroral oval during substorms and of the associated ionospheric ion outflows. The source of plasma sheet precipitating ions is determined using a simple method, based on the measured relation between the ion inverse velocity and time (l = v × t). This method is applied here to two typical passes of the Interball-Auroral (IA) satellite at distances of 3 R_E above the auroral regions. Substorm related ion injections are shown to be mainly due to time of flight effects. In contrast with particle trajectory computations (Sauvaud et al., 1999), the inverse velocity method does not require magnetic and electric field models and can thus be used systematically for the detection of time of flight dispersed ion structures (TDIS). This allowed us to build a large database of TDIS events and to perform a statistical analysis of their spatial distribution. For the cases presented here the source region of the injected ions is found at radial distances from 18 to 30 R_E near the equatorial magnetosphere. At Interball altitudes ( 3 R_E), ion injections detected at the poleward boundary of the nighside auroral oval are associated with shear Alfvén waves superimposed over large-scale quasi-static current structures. We show that the most poleward TDIS are collocated with a large outflow of ionospheric H⁺ and O⁺ displaying pitch-angle distributions peaked in the pitch-angle range 90°–120°. These ions are thus accelerated perpendicularly to the magnetic field not only in the main auroral acceleration region but also up to at least 3 R_E. The expanding auroral bulge thus constitutes a significant source of H⁺ and O⁺ ions for the mid-tail magnetosphere.