Dynamical Climatology of the Upper Mesosphere, Lower Thermosphere and Ionosphere     

E. S. Kazimirovsky  V. D. Kokourov  G. V. Vergasova 《Surveys in Geophysics》2006,27(2):211-255

The main features of upper atmosphere dynamics as an important part of upper atmosphere climatology are presented. The dynamics of the mesosphere and lower thermosphere (MLT) are of special interest. The results are based on the long series of investigations in East Siberia and data from a world-wide network of observatories. We present the regional climatic norms for the prevailing wind and semi-diurnal tide and the main features of the quasi-periodic structure of the wind field. The non-zonality of MLT dynamics is demonstrated as well as regional differences in the response of the wind field to stratospheric disturbances, solar activity variations and geomagnetic storms.  相似文献   

电离层对台风响应的全过程的特例研究   总被引：8，自引：0，他引：8       下载免费PDF全文

肖赛冠  郝永强  张东和  肖佐 《地球物理学报》2006,49(3):623-628

作为特例研究，本文对1988年和1990年两次强台风影响期间的电离层多普勒记录及相应的台风资料进行了细致的相关分析，目的是利用多普勒记录的连续性优点来了解电离层对登陆（或近海）强台风通过声重波响应的演化全过程.分析表明，在这两次台风影响期间，电离层形态中除有明显的波状扰动（中尺度声重波）出现外，还有一些值得注意的新现象：波动的时间演化表现出明显的幅度逐渐增加以及频率由高频向低频转变，在振幅很大的情况下日落后同时出现扩展F（Spread F）现象，显示了声重波在激发电离层不规则结构方面的种子作用.这一演化过程与电离层中TIDs的线性传播理论一致，文中开展了对这一现象的非线性数值模拟，模拟结果基本上也与上述观测现象相吻合.  相似文献   

空间电磁环境研究在军事上的应用   总被引：1，自引：8，他引：1       下载免费PDF全文

徐文耀  国连杰 《地球物理学进展》2007,22(2):335-344

由磁层、电离层和高层大气组成的近地空间系统是现代战争和未来战争活动的主要空间领域，地磁场和地球电磁环境与军事通信、遥感侦察、导航定位以及高空核打击等军事行动有着密切的关系.本文根据已经公开发表于学术刊物的材料，对比分析高空核爆炸产生的人工辐射带和天然辐射带的主要特点以及灾害性空间天气事件（如亚暴和磁暴）对空间飞行器的损害，简要介绍电离层骚扰和不均匀性对通信的影响，探讨地磁场在导航定位中的可能应用.  相似文献   

Proton transport model in the ionosphere. 2. Influence of magnetic mirroring and collisions on the angular redistribution in a proton beam     

M. Galand  J. Lilensten  W. Kofman  D. Lummerzheim 《Annales Geophysicae》1998,16(10):1308-1321

We investigate the influence of magnetic mirroring and elastic and inelastic scattering on the angular redistribution in a proton/hydrogen beam by using a transport code in comparison with observations. H-emission Doppler profiles viewed in the magnetic zenith exhibit a red-shifted component which is indicative of upward fluxes. In order to determine the origin of this red shift, we evaluate the influence of two angular redistribution sources which are included in our proton/hydrogen transport model. Even though it generates an upward flux, the redistribution due to magnetic mirroring effect is not sufficient to explain the red shift. On the other hand, the collisional angular scattering induces a much more significant red shift in the lower atmosphere. The red shift due to collisions is produced by < 1 -keV protons and is so small as to require an instrumental bandwidth <0.2nm. This explains the absence of measured upward proton/hydrogen fluxes in the Proton I rocket data because no useable data concerning protons < 1 keV are available. At the same time, our model agrees with measured ground-based H-emission Doppler profiles and suggests that previously reported red shift observations were due mostly to instrumental bandwidth broadening of the profile. Our results suggest that Doppler profile measurements with higher spectral resolution may enable us to quantify better the angular scattering in proton aurora.  相似文献   

A study of transient variations in the Earth’s electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)     

J. Vassal  M. Menvielle  Y. Cohen  M. Dukhan  V. Doumouya  K. Boka  O. Fambitakoye 《Annales Geophysicae》1998,16(6):677-697

In the framework of the French-Ivorian participation to the IEEY, a network of 10 electromagnetic stations were installed at African longitudes. The aim of this experiment was twofold: firstly, to study the magnetic signature of the equatorial electrojet on the one hand, and secondly, to characterize the induced electric field variations on the other hand. The first results of the magnetic field investigations were presented by Doumouya and coworkers. Those of the electric field experiment will be discussed in this study. The electromagnetic experiment will be described. The analysis of the electromagnetic transient variations was conducted in accordance with the classical distinction between quiet and disturbed magnetic situations. A morphological analysis of the recordings is given, taking into consideration successively quiet and disturbed magnetic situations, with the results interpreted in terms of the characterization of external and internal sources. Particular attention was paid to the effects of the source characteristics on the induced field of internal origin, and to the bias they may consequently cause to the results of electromagnetic probing of the Earth; the source effect in electromagnetic induction studies. During quiet magnetic situations, our results demonstrated the existence of two different sources. One of these, the S_R^E source, was responsible for most of the magnetic diurnal variation and corresponded to the well-known magnetic signature of the equatorial electrojet. The other source (the S_R*^E source) was responsible for most of the electric diurnal variation, and was also likely to be an ionospheric source. Electric and magnetic diurnal variations are therefore related to different ionospheric sources, and interpreting the electric diurnal variation as induced by the magnetic field diurnal variation is not relevant. Furthermore, the magnetotelluric probing of the upper mantle at dip equator latitudes with the electromagnetic diurnal variation is consequently impossible to perform. In the case of irregular variations, the source effect related to the equatorial electrojet is also discussed. A Gaussian model of equatorial electrojet was considered, and apparent resistivities were computed for two models of stratified Earth corresponding to the average resistive structure of the two tectonic provinces crossed by the profile: a sedimentary basin and a cratonic shield. The apparent resistivity curves were found to depend significantly on both the model used and the distance to the center of the electrojet. These numerical results confirm the existence of a daytime source effect related to the equatorial electrojet. Furthermore, we show that the results account for the observed differences between daytime and night-time apparent resistivity curves. In particular, it was shown that electromagnetic probing of the Earth using the classical Cagniard-Tikhonov magnetotelluric method is impossible with daytime recordings made at dip latitude stations.  相似文献   

The spatial structure of the dayside ionospheric trough     

S. E. Pryse  L. Kersley  M. J. Williams  I. K. Walker 《Annales Geophysicae》1998,16(10):1169-1179

Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.  相似文献   

Geophysical phenomena during an ionospheric modification experiment at Tromsø, Norway     

N. F. Blagoveshchenskaya  V. A. Kornienko  A. V. Petlenko  A. Brekke  M. T. Rietveld 《Annales Geophysicae》1998,16(10):1212-1225

We present an analysis of phenomena observed by HF distance-diagnostic tools located in St. Petersburg combined with multi-instrument observation at Tromsø in the HF modified ionosphere during a magnetospheric substorm. The observed phenomena that occurred during the Tromsø heating experiment in the nightside auroral E_s region of the ionosphere depend on the phase of substorm. The heating excited small-scale field-aligned irregularities in the E region responsible for field-aligned scattering of diagnostic HF waves. The equipment used in the experiment was sensitive to electron density irregularities with wavelengths 12–15 m across the geomagnetic field lines. Analysis of the Doppler measurement data shows the appearance of quasiperiodic variations with a Doppler frequency shift, f_d and periods about 100–120 s during the heating cycle coinciding in time with the first substorm activation and initiation of the upward field-aligned currents. A relationship between wave variations in f_d and magnetic pulsations in the Y-component of the geomagnetic field at Tromsø was detected. The analysis of the magnetic field variations from the IMAGE magnetometer stations shows that ULF waves occurred, not only at Tromsø, but in the adjacent area bounded by geographical latitudes from 70.5° to 68° and longitudes from 16° to 27°. It is suggested that the ULF observed can result from superposition of the natural and heater-induced ULF waves. During the substorm expansion a strong stimulated electromagnetic emission (SEE) at the third harmonic of the downshifted maximum frequency was found. It is believed that SEE is accompanied by excitation of the VLF waves penetrating into magneto-sphere and stimulating the precipitation of the energetic electrons (10–40 keV) of about 1-min duration. This is due to a cyclotron resonant interaction of natural precipitating electrons (1–10 keV) with heater-induced whistler waves in the magnetosphere. It is reasonable to suppose that a new substorm activation, exactly above Tromsø, was closely connected with the heater-induced precipitation of energetic electrons.  相似文献   

CUTLASS Finland radar observations of the ionospheric signatures of flux transfer events and the resulting plasma flows   总被引：1，自引：0，他引：1  

G. Provan  T. K. Yeoman  S. E. Milan 《Annales Geophysicae》1998,16(11):1411-1422

The CUTLASS Finland radar has been run in a two-beam special scan mode, which offered excellent temporal and spatial information on the flows in the high-latitude ionosphere. A detailed study of one day of this data revealed a convection reversal boundary (CRB) in the CUTLASS field of view (f.o.v) on the dayside, the direction of plasma flow either side of the boundary being typical of a dawn-cell convection pattern. Poleward of the CRB a number of pulsed transients are observed, seemingly moving away from the radar. These transients are identified here as the ionospheric signature of flux transfer events (FTEs). Equatorward of the CRB continuous backscatter was observed, believed to be due to the return flow on closed field lines. The two-beam scan offered a new and innovative opportunity to determine the size and velocity of the ionospheric signatures associated with flux transfer events and the related plasma flow pattern. The transient signature was found to have an azimuthal extent of 1900 ± 900 km and an poleward extent of 250 km. The motion of the transient features was in a predominantly westward azimuthal direction, at a velocity of 7.5 ± 3 km.  相似文献   

GAIM电离层同化方法进展   总被引：2，自引：0，他引：2  

黄珹  郭鹏  洪振杰  严豪健  胡小工  丁金才  张训械 《天文学进展》2007,25(3):236-248

电离层是复杂的空间层结,其变化受太阳活动强度、地球磁场等因素影响。随着空间技术发展的需求,电离层天气变化成为目前空间天气预报最重要的内容之一。最近10年,人们利用卫星在电离层观测方面取得了重大进展,尤其引人注意的是:无线电掩星观测技术正走向应用的新阶段,加上已经建立的全球大量的地基GPS观测网,它们不仅为电离层动力学模式研究提供了丰富的电离层资料,而且为电离层预报提供了很好基础。因此,电离层天气预报成为当前重要的、前瞻性的研究方向,电离层资料同化是电离层预报最重要的研究内容之一。该文系统介绍这方面国际动态,重点是美国的USC/JPL和犹他州大学开展全球电离层同化模型研究、全球电离层同化研究的进展,以及在电离层天气预报中应用的初步成果。  相似文献   

一种新的北斗Klobuchar模型及其精度分析     

徐李冰  蔡成林  陈光喜  李春华 《大地测量与地球动力学》2015,35(5):788-792

针对传统Klobuchar模型电离层延迟修正精度不高的问题,提出一种新的Klobuchar模型,以提高北斗导航系统的精度。利用欧洲定轨中心CODE的全球格网数据作为参考,使用松弛搜索法分别对覆盖中国区域的格网点和9个测站的观测数据进行算例分析。比较两种方法得出,新模型的修正精度相对于广播模型有大幅提高;新模型预报7d内的电离层时延值修正效果也比广播模型有明显改善;格网点上的平均修正精度从67.89%提高到78.44%,观测数据的平均修正精度从69.81%提升至82.34%。  相似文献