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1.
极盖等离子体云块是极区电离层常见特征之一,其形成演化过程是当前重要研究课题.光电离高密度等离子体在对流输送作用下从日侧穿过极隙,通过极盖到达夜侧,已成为共识.日侧磁场重联作用下的极区对流输运过程,在舌状等离子体结构（TOI）"断裂"形成极盖等离子体云块中发挥重要作用.利用极区全域GPS/TEC观测数据,结合SuperDARN雷达实测的对流速度,对等离子体云块形成过程进行案例研究,重点分析两种TOI断裂形成等离子体云块的发生机制.研究结果显示,等离子体对流输运过程在TOI断裂形成等离子体云块过程中发挥关键性作用,对流形态或局部对流速度矢量急剧变化都可能导致TOI结构不稳定,使TOI结构断裂形成等离子体云块. 相似文献
2.
极盖区等离子体云块是一种经常出现在极区电离层F层的高密度块状结构,其电子密度一般是背景电子密度的两倍及以上,水平尺度约为100～1 000 km.极盖区等离子体云块的产生及演化过程可以示踪磁层-电离层/热层耦合过程中的能量及动量传输过程.同时,这种电子密度不均匀体（尤其是其边沿区域）对跨极盖区的无线电波传播具有很强的干扰,经常影响无线电通讯导航定位等应用.因而,极盖区等离子体云块研究不仅是空间物理领域的热点问题,而且也是空间天气监测及准确预报等应用的重要基础.本文简述了近十年来极盖区等离子体云块的研究进展,主要内容包括：概括了极盖区等离子体云块几种可能的形成机制;提出了极盖区冷/热等离子体云块的分类研究;统计了极盖区等离子体云块的时空分布特征及其对外部条件的依赖性;追踪了极盖区等离子体云块的完整演化过程;最后,讨论了极盖区等离子体云块引起的离子上行现象及电离层闪烁效应. 相似文献
3.
在极区电离层模式中,考虑了软电子沉降引起的电离,并对差分方法的应用提出了改进意见.模拟了不同特征的沉降电子对极区电离层的影响,发现平均能量低的电子束能够形成明显的电离层F层,平均能量较高的电子束能使得最大电离的高度下移,形成明显的E层,甚至其电子浓度高于F层.将电子沉降的卫星测量结果作为电离层模型的输入,所得F层临频与观测结果符合较好.通过分析中山站电离层统计结果,综合电子沉降在极隙区的分布特征和上述模拟结果,认为中山站磁中午现象主要由电子沉降所致. 相似文献
4.
综合分析EISCAT雷达与卫星当地测量数据,并利用磁层磁场模式对磁力线进行追踪,研究了发生在极光椭圆朝极盖边界附近电离层中,一例反常的背离太阳流动的强等离子体对流事件,及相关的太阳风-磁层-电离层耦合过程.结果表明,磁暴期间IMFBz指向南时观测到这一反常高速对流,及其相应的等离子体性态特征,很可能是向阳侧磁层顶磁重联过程在电离层中的印记. 相似文献
5.
F-lacuna是高纬极区电离层测高仪频高图上经常出现的一种F层回波描迹部分或全部消失的现象,直接影响电离层参数的标定,其表征的电离层物理过程尚未定论.利用南极中山站测高仪频高图数据,本文统计分析了Flacuna在不同太阳风速度水平下的发生频率,主要对2012年2月15日一次F2-lacuna观测实例的粒子沉降及电离层特性进行了分析.观测特征表明,F2-lacuna发生期间,电离层电子总含量TEC明显减小,昭和站SuperDARN高频雷达观测到的中山站上空电离层Bragg后向散射增强,但对应来自磁层的电子和离子沉降并不明显.这可能是由磁层亚暴引起的极区电离层电流体系扰动,触发电离层F-B不稳定性,产生沿场向排列的小尺度不规则体,其热效应导致F2层密度减小,F2-lacuna出现. 相似文献
6.
用三维可压缩MHD数值模拟研究了在磁场重联过程中电子压力梯度项的效应研究结果发现在较高等离子体β,较小离子惯性尺度条件下,广义欧姆定理中压力梯度项在重联过程的作用不可忽略.在磁重联过程中,压力梯度项虽然没有明显改变磁场拓扑结构和重联速度,但它使电子和离子速度明显增大.由于在离子惯性尺度下,离子和电子运动解耦,电子是电流的主要载流子,所以场向电流也增大,并导致核心磁场明显增大.考虑到场向电流是磁层电离层耦合的一个重要因素,所以电子压力梯度项的引入加强了行星际磁场南向期间磁层电离层的耦合.电子压力梯度项还在重联区激发了波动,该波动可向重联区外传播. 相似文献
7.
利用极区电离层自洽模型,考虑沉降电子引起的电离,计算了极区电离层的高度积分电导率和F层电子浓度,模拟了不同能谱分布的沉降电子对极区电离层的影响.研究发现不同能谱分布沉降电子对电离层电导率的影响不大,在能通量一定的情况下,平均能量是影响电导率大小的决定因素.而能谱对F层电子密度影响较大,随着平均能量的增加,能谱对电子浓度的影响越显著.在平均能量大于1 keV（甚至更低）时,修正的麦克斯韦分布谱能明显地增强F层电子浓度. 相似文献
8.
地球等离子体层作为内磁层的重要组成部分,在空间天气过程的发生和发展过程中都起着非常重要的作用.地球等离子体层是由上行电离层粒子被地球磁力线捕获而形成的圆环状冷的等离子体区域.等离子体层的外边界称为等离子体层顶,在该区域的等离子体层密度在0.5个地球半径内下降了1～2个数量级.地球等离子体层结构的动态变化特征是空间环境扰动状态的指示器,其结构形态和动力学过程受地磁场和电场控制,而地磁场短期变化源于太阳活动引起的日地扰动.地磁暴期间等离子体层的大规模结构演化影响等离子体层中波的产生和传播,从而影响波-粒子相互作用,导致内磁层中电子和离子的空间分布发生变化,进而影响其它磁层和电离层过程.对地球等离子体层进行进一步研究,对揭示太阳风-磁层-电离层耦合过程中的质量输运和能量转移、空间天气预报等方面都具有重要的意义.本文对等离子体层和地磁活动的关系、等离子体层中的波、顶部电离层及等离子体层电子含量的变化规律和等离子体层模型等方面的研究进展进行了介绍.最后,我们还对等离子体层研究方面一些亟待解决的问题进行了展望. 相似文献
9.
联合利用EISCAT和E-Svalbard非相干散射雷达数据,研究l997年5月强磁暴期间向阳侧极盖与极光椭圆区电离层F区负暴.发现在磁暴主相和恢复相初期,极光椭圆和极盖区电离层都在大约l90km高度出现类似F1的峰,F2主峰完全消失,F区电子密度大幅度下降.但离子温度的变化在两个区域很不相同,在极光椭圆区大幅度升高,而在极盖区没有显著变化,反映出引起F区负暴的主要机制在两个区域不尽相同.强对流电场引起大气焦耳加热与离子增温而使O+离子消失的化学反应速率增大所导致的电离损失,对极光椭圆区负暴起主要作用;而输运过程,特别是持续长达数小时的沿场上行离子流,对极盖区负暴起重要作用.磁暴主相期间,当EISCAT雷达位于等离子体对流涡旋转换区下方时,在无焦耳加热与离子摩擦增温的情况下,观测到由顶部电离层O+离子沿场高速外流引起的F区电子密度耗空. 相似文献
10.
磁场重联与等离子体波动之间存在显著的联系.其中准静态波动、激波和动力学阿尔芬波的本征模是磁重联结构的重要组成部分.而其它的高频波动,不仅能吸收粒子的自由能,还可以导致粒子的加热和反常电阻的产生.这些多尺度的波动过程揭示了磁重联中能量转换的多尺度性质.本文探讨了地球磁层磁重联过程中的各种等离子体波动,涵盖了动力学阿尔芬波、低混杂波、哨声波、静电孤波、离子声波以及电子尺度的高频静电波,并分析了它们在磁重联中的特性和作用.近期的研究成果表明,动力学阿尔芬波（kinetic Alfven wave, KAW）能够描述磁重联区域的微观结构,其中包括霍尔磁场、霍尔电场、平行电场、霍尔电流以及场向电流.在这一过程中,霍尔电场作用于离子,有助于提高重联速率.低混杂波主要在电流片的密度梯度较大处被激发,并对电子进行平行加热.而哨声波是由朗道共振和回旋共振机制驱动的.据当前研究所示,低混杂波和哨声波对于重联过程中的反常电阻效应的影响是次要的.静电孤波多在磁重联分界线区域出现,其对等离子体的加热效应仍需进一步研究.与此同时,关于高频静电波（例如高混杂波和电子伯恩斯坦波）的研究重点在于磁重联的扩散区,这些波被... 相似文献
11.
Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm 总被引：2，自引：0，他引：2
The high-latitude ionospheric response to a major magnetic storm on May 15, 1997 is studied and different responses in the polar cap and the auroral oval are highlighted. Depletion of the F2 region electron density occurred in both the polar cap and the auroral zone, but due to different physical processes. The increased recombination rate of O+ ions caused by a strong electric field played a crucial role in the auroral zone. The transport effect, however, especially the strong upward ion flow was also of great importance in the dayside polar cap. During the main phase and the beginning of the recovery phase soft particle precipitation in the polar cap showed a clear relation to the dynamic pressure of the solar wind, with a maximum cross-correlation coefficient of 0.63 at a time lag of 5 min. 相似文献
12.
The work describes experimental observations of enhancements in the electron density of the ionospheric F-region created by cusp/cleft particle precipitation at the dayside entry to the polar-cap convection flow. Measurements by meridian scanning photometer and all-sky camera of optical red-line emissions from aurora are used to identify latitudinally narrow bands of soft-particle precipitation responsible for structured enhancements in electron density determined from images obtained by radio tomography. Two examples are discussed in which the electron density features with size scales and magnitudes commensurate with those of patches are shown to be formed by precipitation at the entry region to the anti-sunward flow. In one case the spectrum of the incoming particles results in ionisation being created, for the most part below 250 km, so that the patch will persist only for minutes after convecting away from the auroral source region. However in a second example, at a time when the plasma density of the solar wind was particularly high, a substantial part of the particle-induced enhancement formed above 250 km. It is suggested that, with the reduced recombination loss in the upper F-region, this structure will retain form as a patch during passage in the anti-sunward flow across the polar cap. 相似文献
13.
Sharp changes of the solar wind parameters determining the dynamic pressure jump lead to strong magnetosphere-ionosphere disturbances. Here the effect on the Earth’s ionospheric high latitudes of the solar wind dynamic pressure pulse caused only by the increase of the interplanetary plasma density under southward constant IMF is considered. We investigate reaction of the cross-polar cap potential on the increase of AL index and/or jump of the solar wind density. It is found that for the case of 10 January 1997 the main contribution to the polar cap potential drop increase gave the growth of AL index relative to the input of the solar wind density jump. We also study the influence of the solar wind density increase on the crosspolar cap potential for the quiet magnetospheric conditions. It occurred that the polar cap potential difference decreases with the great increase of the interplanetary plasma density. For the disturbed magnetosphere the main role in the polar cap potential drop increase plays increase of AL. Thus, we found the change of the cross-polar cap potential due to the AL index variations and/or the solar wind density drop even in a case when the interplanetary electric field is constant. 相似文献
14.
《Journal of Atmospheric and Solar》2007,69(15):1884-1892
Plasma patches are regions of enhanced ionization that are created in the dayside cusp or equatorward of the cusp in the sunlit hemisphere during northward interplanetary magnetic field. After formation, and a change to a southward interplanetary magnetic field, they drift across the polar cap with the prevailing convection speed. As a plasma patch propagates, charge exchange reactions occur, which lead to the production of both ion and neutral particles throughout the patch. In the region directly above the patch, an upward jet of H+ and O+ forms. This ion jet, in turn, acts to produce an upward flux of neutral H and O stream particles because of charge exchange reactions between the ion jet and the background neutral atmosphere. A three-dimensional, time-dependent model of the ion and neutral polar winds was used in order to study the evolution of the neutral stream particles that are produced in a ‘representative’ propagating plasma patch, with the anticipation that the neutral stream particles produced by the ion jet would display a distinct signature. However, the outflow of neutral H atoms above a patch is only slightly visible in the simulation due to a continuous outflow flux of H (∼109 cm−2 s−1) across the entire polar cap. On the other hand, the upward flux of neutral O from the patch is more dependent on both the state of the ionosphere and the amount of heating, with increased upward fluxes over areas where the heating is high. Typically, the upward neutral O streams are predominantly located in the pre-midnight auroral oval. 相似文献
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16.
Central polar cap convection changes associated with southward turnings of the Interplanetary Magnetic Field (IMF) are studied using a chain of Canadian Advanced Digital Ionosondes (CADI) in the northern polar cap. A study of 32 short duration (1 h) southward IMF transition events found a three stage response: (1) initial response to a southward transition is near simultaneous for the entire polar cap; (2) the peak of the convection speed (attributed to the maximum merging electric field) propagates poleward from the ionospheric footprint of the merging region; and (3) if the change in IMF is rapid enough, then a step in convection appears to start at the cusp and then propagates antisunward over the polar cap with the velocity of the maximum convection. On the nightside, a substorm onset is observed at about the time when the step increase in convection (associated with the rapid transition of IMF) arrives at the polar cap boundary. 相似文献
17.
《Journal of Atmospheric and Solar》1999,61(1-2):127-139
This topical review provides an overview of the progress achieved under Project 3.1, entitled Global Aspects of Plasma Structures (GAPS) during the lifetime of the Solar Terrestrial Energy Program (STEP) from 1990–97. The mandate of the GAPS project covered middle and high latitude plasma structuring. However, given the requirement of limited length for this overview, only high latitude studies will be covered because of the particularly collaborative nature of the effort, made possible by an international program such as STEP. High latitude plasma structuring studies have progressed from joint experimental campaigns involving many locations and diagnostic techniques, and several focused international workshops that united experimenters and modelers. They have provided the groundwork for studying the macroscale (hundreds of km) and mesoscale (km and smaller) plasma structures at high latitudes under two distinct configurations of the interplanetary magnetic field (IMF).When the IMF is directed southward, we observe macroscale, enhanced density structures known as patches. We have documented much on their origin, modification by the electric field structure in the cusp, airglow signatures in the polar cap, interaction with the neutral medium, mesoscale structuring causing scintillations, convection through the polar cap, and eventual exit into the auroral oval. This has led to several modeling efforts, demonstrating patch formation via temporal changes in the large-scale flow configuration in the cusp. Additionally, we have successfully linked the climatology of the macroscale structure model to the mesoscale structure in the polar regions, an advance that may lead to truly predictive irregularity models for forecasting effects on communication and navigation systems during the upcoming solar maximum.For northward IMF conditions, we have advanced our ability to simulate Sun-aligned arcs using a magnetosphere–ionosphere (M–I) coupled model, driven by realistic magnitudes of electric fields, conductivities and currents. The simulation has been enabled by utilizing an extensive ground-based optical database supported by satellite measurements of their morphological characteristics, including their dawn-dusk motion, dependence on IMF By, and propensity for multiple structuring. We soon expect significant advances resulting from several newly established powerful instruments in the northern and southern polar regions. 相似文献
18.
The magnetosphere–ionosphere–thermosphere system at high latitudes is strongly coupled via electric fields, particle precipitation, plasma and neutral outflows, and field-aligned currents. Although the climatology of the coupled system is fairly well established, our understanding of the variability of the disturbed state (weather) is rudimentary. This variability is associated with magnetic storms and substorms, nonlinear processes that operate over a range of spatial scales, time delays, and feedback mechanisms between the different domains. The variability and resultant structure of the ionosphere can appear in the form of propagating plasma patches and polar wind jets, pulsing ion and neutral polar winds, auroral and boundary blobs, and ionization channels associated with polar cap arcs, discrete auroral arcs, and storm-enhanced densities (SEDs). The variability and structure of the thermosphere can appear in the form of propagating atmospheric holes, neutral gas fountains, neutral density patches, and transient neutral jets. In addition, during periods of enhanced plasma convection, the neutral winds can become supersonic in relatively narrow regions of the polar cap. The spatial structure in the ionosphere–thermosphere system not only affects the local environment, but the cumulative effect of multiple structures may affect the global circulation and energy balance. A focused topical review of recent results in our modeling the variability and structure of the high-latitude ionosphere–thermosphere system is presented. This review was given at the Greenland Space Science Symposium (May 2007). 相似文献