共查询到18条相似文献，搜索用时 187 毫秒
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磁暴的发生与环电流的变化密切相关.除了对称环电流外，部分环电流在磁暴的发展过程中也起到了重要的作用，同时部分环电流通过场向电流与极区电离层中的电流形成回路.本文应用INTERMAGNET地磁台网北半球中低纬区域地磁台站数据，对不同强度4个磁暴事件主相和恢复相期间部分环电流和场向电流的磁地方时分布进行了分析和讨论.对于每一个磁暴事件，在低纬地区（地磁纬度约0°—40°N）选用地磁经度上大致均匀的8个台站，通过坐标转换计算平行于磁偶极轴的地磁场水平分量H来分析磁暴期间环电流所引起的磁场扰动；在低纬地区8个台站的基础上增加中纬地区（地磁纬度约40°N—60°N）地磁经度上大致均匀的6个台站，计算地磁坐标系下地磁场东西分量Y来分析磁暴期间场向电流在中低纬地区引起的磁场扰动.结果表明，磁暴主相期间的部分环电流主要作用于磁地方时昏侧和夜侧扇区，并且主相和恢复相期间部分环电流引起的磁场变化随着磁暴级别的增大而增大；磁暴主相期间向下的场向电流多出现在夜侧至晨侧扇区，向上的场向电流多出现在昏侧至午后扇区，且中纬地区向下和向上场向电流的展布范围明显大于低纬地区；恢复相期间弱、中磁暴事件的场向电流呈现与部分环电流相同的减弱趋势，而强、大磁暴事件在恢复相末期场向电流引起的磁场变化明显不同于恢复相的其他时刻，这可能与高纬较强的亚暴活动有关. 相似文献
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利用ISEE－1和ISEE-2飞船观测的磁场数据，分析了地球内磁层场向电流的统计特征，包括场向电流的空间（L值和地方时）分布；流进和流出电离层的场向电流随地方时的变化；场向电流发生率与地磁活动水平（以AL指数表征）、行星际磁场（IMF）Bz的关系，电流强度和密度随地磁活动水平的变化等．发现，场向电流大都发生在夜间，且集中在L为6-10区域内，场向电流发生率，强度和密度随地磁活动增强而增大，行星际磁场南向时的发生率远远高于北向时的发生率．这些结果表明，内磁层场向电流的产生是太阳风和磁层、电离层间电动耦合增加的结果． 相似文献
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确定亚暴期间高纬地区的三维电流体系是磁层和电离层物理的基本问题之一,本文简述了近年来发展的根据地面地磁活动的记录及演三维电流体系的两种较新的方法:KRM（Kamide-Richmond-Matsushita）方法和K（Kisabeth）方法.在KRM方法和许多其它类似的计算中,都假定磁力线是垂直于电离层沿地球径向的直线.本文介绍了一种递推方法,可计算场向电流沿弯曲的偶极子场线流动的情况。同时,还介绍了高纬三维电流体系对亚暴期间中低纬度地磁扰动的贡献。最后介绍了在计算电流体系时所需的电离层电导率模式。 相似文献
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极光电集流指数(AE)被广泛用来定量描述由电离层电流引起的极光带地磁活动.AE指数也是宏观描述亚暴事件强度和发展过程的一个主要指标,它的优点在于简单直观和快速.本文对1998年8月6日系列亚暴事件的极光活动、电流体系和AE指数的形态特征进行了分析.结果表明,伪亚暴期间虽然AE指数大于500 nT 且有快速增长和缓慢恢复的形态,但是极光没有明显的极向或者赤道向的扩展,极区电流体系主要呈现对流特征;伪亚暴和亚暴期间AE指数的形态变化没有本质区别,但电集流中心的位置有很大差异.我们进一步分析了台站分布对AE指数计算的影响,探讨了伪亚暴和亚暴期间磁场扰动最大值所处的磁地方时的差异. 相似文献
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本文利用Swarm卫星2015—2016年高精度的磁场矢量数据,将晨昏地方时扇区高纬场向电流(Field-Aligned Currents,FACs)事件按极性和电流密度分为四类,并首次比较研究了四类FACs事件的时空分布特征及其影响因素,研究发现:极性正常事件(晨侧靠极侧电流元向下流入电离层,靠赤道侧电流元向上流出电离层,昏侧电流极性相反,即传统意义上的R1和R2FACs)发生率约为70%,其中R1FACs强于R2事件的发生率为R1FACs弱于R2的3~5倍;极性异常事件(与传统的R1和R2FACs流向相反,两片电流元定义为R1*和R2*FACs)发生率约占30%,其中R1*R2*的1.5~2.5倍.进一步分析发现极性正常事件主要发生在南向IMF Bz期间,与重联电场相关性较好,净电流密度随着重联电场和电离层电导率的增加而增加.其中R1R2*事件通常发生在IMF By<0期间,昏侧事件主要发生在IMF By>0期间,而R1*相似文献
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本文综述了不同类型电离层场向电流(亦称为Birkeland电流)及其在地磁扰动(磁暴和亚暴)期间的时空分布特征.首先简述了场向电流近70年的研究历程,总结了各种与太阳风—行星际磁场(interplanetary magnetic field,IMF)、电离层电导率空间分布不均匀相关的1区和2区场向电流,北向、晨昏向IM... 相似文献
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用电离层风发电机理论,对不同的电导率模型分别计算了磁静日和磁扰日期间不同月相的理论L电流体系。磁静日的L电流主要分布在纬度0°-60°之间的白天一侧,与平均太阴月的L电流相比,白天一侧的电流强度增大了1.2-1.7倍,而夜间减小到十分之一。磁扰日的L电流体系在高纬度区形成特征的电流分布（Lp）。磁扰日期间,极光带电导率的增大不仅影响极光带和高纬度地区的电流分布,而且使中低纬度的L电流增强了20-30％,使赤道电急流增强约20％,并使中低纬电流涡的焦点向高纬移动了4°左右。 相似文献
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分析了北京地区1998年1月1日至3月26日和4月24日至6月13日共136天记录的Pi2脉动事件特性,并与同时期亚暴AE指数进行了对比.结果发现,在北京地区越靠近日侧,观测到的Pi2脉动事件越少,幅度也越小.并不是每次亚暴都能激发空腔振荡模,亚暴强度的增加也并不代表空腔振荡模产生概率的增加.随着亚暴AE指数的增大,Pi2脉动的平均幅度基本上也在增大.但也有例外,可能是由于北京观测地点距离亚暴电流楔位置较远造成的.北京地区的Pi2脉动可以发生于亚暴的整个过程中,从AE指数开始增长期间（亚暴增长相）,一直到亚暴AE指数恢复正常（亚暴膨胀相后期）.某些亚暴没有对应着Pi2脉动事件,其AE指数从小于200nT一直到800nT以上.从观测数据来看,北京地区虽然纬度分区在低纬区域,但其Pi2脉动的特性与中纬Pi2特性更为靠近.所以不宜用北京地区Pi2来预报亚暴,以避免误报和漏报. 相似文献
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本文就地球电离层对行星际激波的动力学响应进行三维全球数值模拟研究．背景行星际磁场为螺旋场，南北分量为零；初始电离层由Ⅰ区场向电流和相应的晨昏电场所主导；行星际激波沿日地连线方向撞击地球．模拟结果表明，在激波的作用下，电离层Ⅰ区电流系统向子夜方向运动，在向阳侧相继出现与原Ⅰ区电流反向的异常场向电流对和同向的新生Ⅰ区电流对．该异常场向电流对在极盖区形成瞬间昏晨电场，尾随原Ⅰ区电流向夜侧方向漂移直至湮没．与此同时，新生的Ⅰ区电流不断增强并向夜侧和赤道方向延伸，最终取代原Ⅰ区电流，相应极盖区又恢复到原来的晨昏电场状态．这一响应过程和行星际激波强度有关：激波强度越强，新生的Ⅰ区场向电流也越强，它向赤道方向延伸的距离也越大，能到达的纬度也越低．上述结果在趋势上与观测到的输运对流涡旋和亚极光块的运动特征一致． 相似文献
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本文统计分析了2001—2005年的39次大磁暴事件(Dst-100nT)期间TIEGCM模式和CHAMP卫星大气密度数据.研究结果表明,模式结果与实测数据具有较好的一致性,但仍存在一定的偏差.大气密度及增量与SYM-H指数相关性较好,并且随纬度、光照条件和地磁活动水平变化.模式低估了磁暴期间大气密度的增幅,特别是在地磁活动水平较强时模式与实测的偏差较大.模式的偏差在高纬地区高于低纬地区,日侧高于夜侧.Dst指数越低,偏差越大,而当Dst指数低于-150nT以后,绝对偏差和相对偏差变化不明显. 相似文献
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利用法国DEMETER卫星观测的电场数据,研究了中国及邻区(0°—60°N,60°E—140°E),频段为10kHz—3MHz,时间段为2008年1月1日—2008年9月12日期间的平均功率谱密度特征.文中选择了Kp指数的日平均值小于或等于4的数据,获得LF频段(10—20kHz)和MF频段(20kHz—3MHz)以16天为周期的昼侧和夜侧的平均功率谱密度空间分布图,得到了以下初步结果.LF频段:①昼侧,不同频率的谱在对应时段上形态相似度不高,主要呈现纬度分带特征.夜侧,不同频率的谱在对应时段上形态相似度较高,主要差异在于谱的幅度,同一频率不同时段的谱分带特征不明显;②昼侧谱的幅度值跨度要比夜侧的小很多,前者一般为1—1.5个数量级,而后者一般在2个以上,甚至达到4个数量级;③在汶川地震前后,平均功率谱密度在成都—兰州一线存在明显的变化.MF频段:①昼侧,不同频率对应时段的谱形态没有明显的相似性,同一频率不同时段的谱形态可能具有较好、弱或不具有相似性,具有明显、弱或不具纬度分带特征.夜侧,某些频段对应时段的谱形态具有明显的相似性,同一频率不同时段或者分时期的不同时段的谱形态具有较好的相似性,不具有明显的纬度分带特征,具有弱分区或者弱经度分带特征;②昼侧和夜侧的谱幅度变化都不大,基本都在0.5个数量级之内;③在汶川地震前后没有发现明显的平均功率谱密度变化. 相似文献
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This review is devoted to auroral fading before beginning of the substorm active phase. This initial stage of the active phase called breakup is accompanied by a sharp brightening of auroras and their rush toward the pole. Auroral fading before breakup was first detected in discrete auroras in the nightside sector and consisted in that a short-term decrease in brightness of an arc moving toward the equator below the level observed during the preliminary phase was observed during the substorm preliminary phase 2–3 min before breakup. During fading, the velocity of equatorward motion of auroral arcs decreased up to their complete stoppage. Auroral fading in the noon sector was registered simultaneously with fading on the Earth’s nightside before the beginning of the active phase. Short-term background fading was also observed both equatorward and poleward of an arc on the nightside. It was subsequently indicated that similar fading is observed in various geophysical phenomena. It was detected that a radar aurora signal fades before breakup, if auroral substorm is observed in a radar pattern and substorm source is located under good aspect conditions. Riometer absorption decreases simultaneously with auroral fading. Geomagnetic pulsations decay on dayside and nightside immediately before breakup. Such a multiform manifestation of fading in various geophysical phenomena indicates that fading is related to some global processes proceeding in the magnetosphere when energy accumulation in this region comes to the end before its explosive release into the polar ionosphere. 相似文献
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《Journal of Atmospheric and Solar》2007,69(6):649-660
Recent observations from the CHAMP satellite indicate that neutral density enhancements are common in the northern dayside cusp. The neutral density in this region can be nearly a factor of 2 larger than in adjacent regions of the thermosphere on the poleward and equatorward sides of the cusp. The presence of density enhancements implies that the neutral atmosphere is being heated in the cusp region causing upwelling. A high-resolution model of the global thermosphere is used to study the thermospheric response to heating in the northern dayside cusp. It is found that heating in the cusp results in the creation of a neutral fountain. Specifically, upward drift of the thermosphere within the cusp region is followed at higher altitudes by poleward and equatorward movement out of the cusp region and the gradual subsidence of the neutral gas. Density enhancements of the magnitude observed by the CHAMP satellite occur in the model results for sufficiently strong heating in the cusp. Neutral temperature enhancements also occur and are strongest near the poleward and equatorward boundaries of the cusp region. 相似文献
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Recently it has been shown that isotropic precipitation of energetic protons on the nightside is caused by a non-adiabatic effect, namely pitch-angle scattering of protons in curved magnetic field lines of the tail current sheet. Here we address the origin of isotropic proton precipitation on the dayside. Computations of proton scattering regions in the magnetopheric models T87, T89 and T95 reveal two regions which contribute to the isotropic precipitation. The first is the region of weak magnetic field in the outer cusp which provides the 1–2° wide isotropic precipitation on closed field lines in a 2–3 hour wide MLT sector centered on noon. A second zone is formed by the scattering on the closed field lines which cross the nightside equatorial region near the magnetopause which provides isotropic precipitation starting 1.5–2 h MLT from noon and which joins smoothly the precipitation coming from the tail current sheet. We also analyzed the isotropic proton precipitation using observations of NOAA low altitude polar spacecraft. We find that isotropic precipitation of >30 to > 80 keV protons continues around noon forming the continuous oval-shaped region of isotropic precipitation. Part of this region lies on open field lines in the region of cusp-like or mantle precipitation, its equatorward part is observed on closed field lines. Near noon it extends 1–2° below the sharp boundary of solar electron fluxes (proxy of the open/closed field line boundary) and equatorward of the cusp-like auroral precipitation. The observed energy dispersion of its equatorward boundary (isotropic boundary) agrees with model predictions of expected particle scattering in the regions of weak and highly curved magnetic field. We also found some disagreement with model computations. We did not observe the predicted split of the isotropic precipitation region into separate nightside and dayside isotropic zones. Also, the oval-like shape of the isotropic boundary has a symmetry line in 10–12 MLT sector, which with increasing activity rotates toward dawn while the latitude of isotropic boundary is decreasing. Our conclusion is that for both dayside and nightside the isotropic boundary location is basically controlled by the magnetospheric magnetic field, and therefore the isotropic boundaries can be used as a tool to probe the magnetospheric configuration in different external conditions and at different activity levels. 相似文献
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Mishin V. M. Saifudinova T. I. Karavaev Yu. A. Kurikalova M. A. Bazarzhapov A. D. 《Geomagnetism and Aeronomy》2009,49(7):975-982
The regular appearance of the chain of oppositely directed field-aligned current (FAC) pairs near the noon-midnight meridian
during three considered substorms has been described. The FAC pairs (FACs flowing into the ionosphere in the morning and flowing
out of this region in the evening and vice versa) are observed in each of three Iijima and Potemra zones. The FAC direction
in the fixed LT sector periodically varies along the chain. The scenario, according to which each FAC pair (seven pairs) is
identified with a hump or trough of one of the waves propagating from the Earth and toward the Earth in different magnetospheric
domains, has been described. The estimated wave velocities differ from ∼100 to >1000 km/s depending on the propagation region
but everywhere agree with the corresponding velocities of magnetosound waves (MSWs). The hypothesis is proposed, according
to which these MSWs are excited by plasma ejection during current disruption and reconnection near the dayside magnetopause
and in the near/middle regions of the nightside tail. 相似文献
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A. G. Yahnin T. A. Yahnina N. V. Semenova T. A. Popova A. G. Demekhov 《Geomagnetism and Aeronomy》2018,58(5):577-585
Different types of proton auroras observed by the IMAGE satellite equatorward of the proton aurora oval are briefly reviewed. These auroras are caused by the precipitation of energetic protons from the Earth’s magnetosphere during the development of the ion-cyclotron instability. In addition to the previously considered types of proton auroras (spots, evening arcs, and dayside flashes), a new type is described: longlasting proton auroras on the dayside. The scheme of interrelation between different proton auroras equatorward of the oval with the distribution of cold plasmaspheric plasma is given. 相似文献
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利用2005年1月至2010年11月DEMETER卫星记录的NWC发射站的VLF电场功率谱数据,采用指数拟合的方法,分析了VLF电磁波在卫星高度激发的电场空间分布和衰减特征.研究结果表明:(1)VLF电场在发射站上空及其磁共轭区有着很强的对应关系,存在南、北2个强电场中心涡;(2)相对于发射站的位置,VLF电场中心点具有经度和纬度偏移,日侧地磁经度偏移均值大于夜侧,而地磁纬度偏移均值则小于夜侧;(3)日侧VLF电场强度呈现出周期性的年变化;(4)在VLF电场中心10°范围内,电场强度随距离快速衰减,衰减常数b在长达6年的时间内保持稳定.在以上研究结果基础上初步构建的卫星高度人工源电磁波空间分布特征,将为研究地表-电离层电磁波传播机理提供基础技术支撑. 相似文献