共查询到19条相似文献，搜索用时 140 毫秒
1.
等离子体层已有数十年研究历史,但对其核心等离子体区域却一直没有一个相对准确的界限和模型定义.基于范阿伦辐射带卫星RBSP-A在2012年9月18日至2014年10月13日约两年的观测,我们统计研究了磁宁静期间核心等离子体层电子密度随磁地方时(MLT)及磁壳指数(L-value)的分布特征.发现了核心等离子体层电子密度在不同MLT条件下随L值的变化趋势几乎一致,但与以前的等离子体层经验模式计算的电子密度存在较大的偏差.在不同L值下电子密度随MLT的变化趋势也相差不大,而且随MLT存在明显的逐日和半日变化.最后我们获得了等离子体层电子密度随L值和MLT变化的经验公式.研究结果对空间等离子体层建模及研究具有重要的意义. 相似文献
2.
本文利用IMAGE卫星EUV相机观测的等离子体层图像,并采用最小L算法反演磁赤道面等离子体层顶位置.文中选取了2000-2002年间的3579幅等离子体层图像,并反演得到了时间间隔为1 h的等离子体层顶位置数据库,包含48899个等离子体层顶位置数据.利用该数据库统计研究了等离子体层顶位形随地磁活动的变化特性.统计发现等离子体层顶高度依赖地磁活动,与地磁指数Kp、Dst和AE均呈负相关,且等离子体层顶随地磁指数的变化趋势具有显著的MLT分布特性;亚暴活动对等离子体层顶演化的贡献在不同地磁活动期间有所不同,磁暴期间亚暴活动的贡献小,而地磁平静期亚暴的贡献大.本文研究工作为后续建立等离子体层顶模型和了解等离子体层顶的动态结构提供了重要研究基础. 相似文献
3.
本文介绍了采用一维遗传算法从地球等离子体层极紫外图像反演地球等离子体层He+密度的原理.首先采用通量管近似和磁偶极近似将三维问题转化为一维问题.通过引入权矩阵,将极紫外光强积分离散为求和函数,再采用一维实数编码遗传算法反演得到磁赤道面等离子体层He+密度,最后通过磁力线追迹得到三维密度分布.算法采用动态全球核心等离子体模式模拟的密度和光强分布作为初始输入参数,并通过遗传算法得到相应密度分布.反演结果表明,等离子体层密度相对误差在8%以内,光强相对误差趋于0,算法有效可行.本文研究为中国探月二期工程中月基极紫外图像反演奠定了基础. 相似文献
4.
基于范艾伦辐射带探测卫星的观测数据(2012年9月至2015年11月),收集了584个等离子体层顶密度波动事件,研究了这些事件分布随磁地方时、磁壳值以及地磁活动的变化关系,并使用快速傅里叶变换分析了全部事件平均功率谱.统计结果表明,等离子体层顶密度波动事件主要发生在磁地方时黄昏扇区,其分布与磁地方时和地磁活动具有明显的相关性.等离子体层顶密度波动在1～100mHz区间内具有接近-5/3的功率谱斜率,表明存在二维磁流体动力学湍流.本文统计结果将有助于进一步深入理解等离子体层顶密度波动在内磁层中能量传输的具体作用,并且将促进对等离子体层顶波动的激发、增强与传播过程的进一步研究. 相似文献
5.
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
6.
亚暴期间磁尾等离子体片离子注入内磁层能够激发电磁离子回旋(EMIC)波.对应于这种EMIC波,地面磁力仪可观测到周期逐渐减小的地磁脉动(IPDP).利用GOES卫星数据,地磁指数和加拿大CARISMA地磁台站的数据,我们研究了IPDP事件的产生与亚暴磁尾注入的关系.同时利用CARISMA地磁台链中的MCMU和MSTK两个台站,从2005年4月到2014年5月期间的观测数据,统计分析了亚暴期间的IPDP事件,研究了IPDP事件的出现率关于季节和磁地方时的分布特征.我们总共获得128个两个台站同时观测的IPDP事件.该类事件关于季节分布的发生率,冬季最小,为13.28%,春季最大,为32.81%,结果表明IPDP事件关于季节分布的发生率受到电离层电导率及亚暴发生率的影响.两个台站同时观测到的IPDP事件最大出现率出现在15—18 MLT(磁地方时),结果表明IPDP事件主要由亚暴期间产生的能量离子注入内磁层,西向漂移遇到等离子体层羽状结构(Plume)区的高密度等离子体所激发. 相似文献
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8.
本文用多步隐格式方法,求解包含电阻的磁流体力学方程组,对磁层亚暴扩展相作数值模拟.计算结果展现了亚暴扩展相期间磁尾变化的主要特征.它表明,球向和尾向等离子体流与准稳态重联有关.等离子体团的尾向喷发,致使中性线尾侧电流片内的密度降低,等离子体片变薄.中性线近地侧的等离子体团朝着地球运动,并合并于地球附近的重联区内. 相似文献
9.
利用2010~2011年的THEMIS卫星观测的卫星电位数据反演电子密度,并用来确定等离子层顶的位置,研究其与地磁指数的关系.利用观测数据得到了一个THEMIS卫星等离子体层顶位置数据库.利用该数据库建立了新的等离子体层顶位置的磁地方时经验模型,并比较了其与现有的四个等离子体层顶位置经验模型的优劣.发现新建立的等离子体层顶位置模型明显优于其余四个经验模型.在模型的三种输入参数中,Kp指数和Dst指数模型的预测效果相当,并明显优于AE指数的模型,这说明磁层的大尺度对流强度是影响等离子体层顶位置最主要的因素. 相似文献
10.
E层占优电离层(ELDI)是一种特殊的电离层垂直结构,表现出与偶发Es明显不同的时空分布和形态特征,但其形成机理尚不清楚.本文报道了发生在2001年7月15日的一次长持续时间(～2.3 h)的ELDI事件.地面雷达观测表明,该ELDI事件可以按照电子密度剖面不同的变化特征分为两个阶段.在第1个阶段里,E层密度大幅度增强而F层密度未有明显变化;在第2个阶段里,E层密度回落至正常水平而F层密度强烈耗空.卫星及其他地面设备的协同观测数据表明,高能离子沉降是ELDI第1阶段的主导形成机制,而强等离子体对流是第2阶段的主导机制. 相似文献
11.
Adela Anghel Charles Carrano Attila Komjathy Adina Astilean Tiberiu Letia 《Journal of Atmospheric and Solar》2009,71(1):158-174
Data collected from a GPS receiver located at low latitudes in the American sector are used to investigate the performance of the WinTEC algorithm [Anghel et al., 2008a, Kalman filter-based algorithm for near realtime monitoring of the ionosphere using dual frequency GPS data. GPS Solutions, accepted for publication; for different ionospheric modeling techniques: the single-shell linear, quadratic, and cubic approaches, and the multi-shell linear approach. Our results indicate that the quadratic and cubic approaches perform much better than the single-shell and multi-shell linear approaches in terms of post-fit residuals. The performance of the algorithm for the cubic approach is then further tested by comparing the vertical TEC predicted by WinTEC and USTEC [Spencer et al., 2004. Ionospheric data assimilation methods for geodetic applications. In: Proceedings of IEEE PLANS, Monterey, CA, 26–29 April, pp. 510–517] at five North American stations. In addition, since the GPS-derived total electron content (TEC) contains contributions from both ionospheric and plasmaspheric sections of the GPS ray paths, in an effort to improve the accuracy of the TEC retrievals, a new data assimilation module that uses background information from an empirical plasmaspheric model [Gallagher et al., 1988. An empirical model of the Earth's plasmasphere. Advances in Space Research 8, (8)15–(8)24] has been incorporated into the WinTEC algorithm. The new Kalman filter-based algorithm estimates both the ionospheric and plasmaspheric electron contents, the combined satellite and receiver biases, and the estimation error covariance matrix, in a single-site or network solution. To evaluate the effect of the plasmaspheric component on the estimated biases and total TEC and to assess the performance of the newly developed algorithm, we compare the WinTEC results, with and without the plasmaspheric term included, at three GPS receivers located at different latitudes in the American sector, during a solar minimum period characterized by quiet and moderate geomagnetic conditions. We also investigate the consistency of our plasmaspheric results by taking advantage of the specific donut-shaped geometry of the plasmasphere and applying the technique at 12 stations distributed roughly over four geomagnetic latitudes and three longitude sectors. 相似文献
12.
The effects of the dayside and dusk plumes of the plasmasphere during the ring current recovery phase on the disturbance level
of the ground geomagnetic field horizontal component have been considered. It has been indicated that the geomagnetic field
horizontal component changes specifically and synchronously in the region corresponding to the plasmaspheric dayside plume.
Outside the plume the time variations in the geomagnetic field horizontal component pronouncedly differs. A spectral analysis
of disturbances in the geomagnetic field horizontal components in the range of geomagnetic pulsations indicated that the intensity
in the range of Pc4 pulsations increases at magnetic stations located on field lines corresponding to the dayside and dusk
plumes of the plasmasphere. These pulsations detected in the dynamic spectrum of the geomagnetic field horizontal components
in the dayside plume region of the plasmasphere, probably reflect the resonance oscillations of magnetic field lines in the
region of field-aligned currents at comparatively low altitudes. We assume that this is caused by the instability of field-aligned
currents originating as a result of the interaction between the ring current energetic ions and electromagnetic waves in the
region with a relatively dense background plasma of the dayside plume. 相似文献
13.
M. I. Verigin G. A. Kotova V. V. Bezrukikh V. V. Bogdanov A. V. Kaisin 《Geomagnetism and Aeronomy》2011,51(1):39-48
Based on the thermal plasma measurements in the Earth’s inner plasmasphere on the INTER-BALL-2 and MAGION-5 satellites it
has been indicated that the plasmaspheric ion temperature as a rule decreases during the main phase of magnetic storms; in
this case the plasma density increases or remains at the level typical of undisturbed conditions. The physical mechanism by
which the ion drift during a magnetic storm results in a temperature decrease is described. It is shown that the third adiabatic
invariant also remains in processes with a characteristic time shorter than the period of charged particle drift around the
Earth for cold equatorial plasma. The constructed model of the drift shell displacement from the Earth caused by a decrease
in the magnetic field in the inner magnetosphere during the development of a magnetic storm satisfactorily describes the decrease
in the proton temperature near the equatorial plane. 相似文献
14.
美国利用IMAGE卫星的极紫外辐射（EUV）探测器对地球等离子体层进行了连续5年的遥感成像观测。由于IMAGE卫星数据是沿观测路径上的积分投影数据,并且存在地球“遮挡”、“阴影”、“数据缺失”等问题,无法直接利用传统的CT方法对等离子体层进行三维重建。本文利用地球磁场模型,基于地球等离子体层的物理性质,建立一个联系地球磁赤道面密度与投影数据的EUV成像模型,实现了从单个角度的EUV观测图像进行地球等离子层三维重构的方法。 相似文献
15.
I. A. Kerimov 《Izvestiya Physics of the Solid Earth》2009,45(5):444-460
The basic theoretical foundations of the spectral analysis of gravity and magnetic data based on the approximation approach have been considered and corresponding expressions implementing various statements of the F-approximation method have been derived [Strakhov and Kerimov, 1999; 2000; 2001]. The author considered the algorithms and computer implementation of the F-approximation of anomalous gravity and magnetic fields presented in the results of testing with the use of a number of model examples and data on the accuracy of the model field approximation earlier on in [Kerimov, 2003]. In this paper, I consider methodological features of constructing the F-approximation from the detailed gravity and magnetic surveys, anomalous gravity and magnetic fields reconstructed with the use of the F -approximation, and examples of the field transforms obtained with the use of this approach. 相似文献
16.
An attempt is made to confirm the generation mechanism of plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite in the equatorial region both at small and large wave normal angles by calculating their magnetic field intensities in terms of incoherent Cerenkov radiation mechanism and cyclotron resonance instability mechanism, using appropriate and suitable plasma parameters. The ELF intensities calculated by Cerenkov radiation mechanism, being 4 to 5 orders of magnitude lower than the observed intensities, rule out the possibility of their generation by this mechanism. On the other hand, the intensities calculated under electron cyclotron resonance instability mechanism are found to be large enough to account for both the observed intensity and propagation losses and hence to confirm that plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite both at small and large wave normal angles were originally generated in the equatorial region by this mechanism just near the inner edge of the plasmapause. The difference in the observed intensities of two types of the emissions has been attributed to the propagation effect rather than the generation efffect. 相似文献
17.
S. Ghoshal 《Pure and Applied Geophysics》1970,81(1):223-229
Summary
Stewartson [1]2) has considered the inviscid flow past a sphere in the presence of a uniform magnetic field andMurray andLudford [2] have investigated a similar problem in which the magnetic field originates from an axially symmetric dipole field situated at the centre of the sphere. In connection with the study of earth's magnetic field, the toroidal part of this field plays a dominant part. This gives rise to the importance of studying the effect of a toroidal magnetic field on flows past different bodies of revolution; specially past spheres and spheroids. In the present note inviscid flows past a sphere, and a spheroid, are considered, for the case of a toroidal magnetic field originating in the fluid. In the case of the sphere the field inside the sphere consists of an electric dipole directed along the axis of symmetry together with a uniform electric field which produces a uniform current along the axis. In the case of the spheroid, the field inside it is due to an electric dipole and quadrupole directed along the axis of symmetry, together with a uniform electric field which produces a uniform current along this axis. 相似文献
18.
《Journal of Atmospheric and Solar》2007,69(3):341-350
The Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) Mission extreme ultraviolet (EUV) imager observes He+ plasmaspheric ions throughout the inner magnetosphere. Limited by ionizing radiation and viewing close to the sun, images of the He+ distribution are available every 10 min for many hours as the spacecraft passes through apogee in its highly elliptical orbit. As a consistent constituent at about 15%, He+ is an excellent surrogate for monitoring all of the processes that control the dynamics of plasmaspheric plasma. In particular, the motion of He+ transverse to the ambient magnetic field is a direct indication of convective electric fields. The analysis of boundary motions has already achieved new insights into the electrodynamic coupling processes taking place between energetic magnetospheric plasmas and the ionosphere. Yet to be fulfilled, however, is the original promise that global EUV images of the plasmasphere might yield two-dimensional pictures of mesoscale to macroscale electric fields in the inner magnetosphere. This work details the technique and initial application of an IMAGE EUV analysis that appears capable of following thermal plasma motion on a global basis. 相似文献
19.
Nigel Weiss FRAS 《Astronomy& Geophysics》2001,42(3):3.10-3.17
Nigel Weiss recounts his Presidential Address 2001, given to the RAS A&G Ordinary Meeting on 9 February 2001.
Recent high-resolution observations, from the ground and from space, have revealed the fine structure of magnetic features at the surface of the Sun. At the same time, advances in computing power have at last made it possible to develop models of turbulent magnetoconvection that can be related to these observations. The key features of flux emergence and annihilation, as observed by the MDI experiment on SOHO, are reproduced in kinematic calculations, while three-dimensional numerical experiments reveal the dynamical processes that are involved. The pattern of convection depends on the strength of the magnetic field: as the mean field decreases, slender rising plumes give way to a regime where magnetic flux is separated from the motion and then to one where locally intense magnetic fields nestle between broad and vigorously convecting plumes. Moreover, turbulent convection is itself able to act as a small-scale dynamo, generating disordered fields near the solar surface. 相似文献
Recent high-resolution observations, from the ground and from space, have revealed the fine structure of magnetic features at the surface of the Sun. At the same time, advances in computing power have at last made it possible to develop models of turbulent magnetoconvection that can be related to these observations. The key features of flux emergence and annihilation, as observed by the MDI experiment on SOHO, are reproduced in kinematic calculations, while three-dimensional numerical experiments reveal the dynamical processes that are involved. The pattern of convection depends on the strength of the magnetic field: as the mean field decreases, slender rising plumes give way to a regime where magnetic flux is separated from the motion and then to one where locally intense magnetic fields nestle between broad and vigorously convecting plumes. Moreover, turbulent convection is itself able to act as a small-scale dynamo, generating disordered fields near the solar surface. 相似文献