共查询到17条相似文献，搜索用时 125 毫秒
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2001年3月2日11:00 至11:15 UT 期间,Cluster Ⅱ在南半球极尖区晨侧附近磁鞘内探测到3个通量传输事件（简称FTEs）. 本文利用Cluster Ⅱ星簇4颗卫星观测到的磁场和等离子体资料研究了这些通量传输事件的磁场形态和粒子特征. 并利用它们探测到的空间磁场梯度资料由安培定律直接求出星簇所在区域的电流分布. 结果指出：（1）BY占优势的行星际磁场结构在磁层顶的重联可以在极尖区附近发生;（2）FTEs通量管形成初期内外总压差和磁箍缩应力不一定平衡,达到平衡有一发展过程;（3）FTEs通量管截面在L M平面内的线度约为1.89RE;（4）FTEs通量管中等离子体主要沿轴向场方向流动,整个通量管以慢于背景等离子体的速度沿磁层顶向南向尾运动;（5）FTEs通量管中不仅有轴向电流,也存在环向电流. 轴向电流基本沿轴向磁场方向流动. 轴向和环向电流在管内均呈体分布,因而轴向电流产生的环向磁场接近管心时不断减小到零,而环向电流生成的轴向场则不断增大到极值;（6）在通量管的磁鞘部分观测到磁层能量粒子流量的增强,这表明通量管通过磁层顶将磁鞘和磁层内部连通起来了. 相似文献
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2004-03-18 23:10～23:50 UT期间,“双星（Double Star）”探测一号卫星（TC 1）在向阳面磁层顶高纬晨侧由内向外穿越磁层顶,其时TC_1的GSM坐标为 (75RE, -55RE, -54RE), RE为地球半径.穿越过程中TC_1观测到了8个通量管和1个磁通量传输事件（FTEs）.在此期间Cluster星簇位于向阳面太阳风内,其GSM坐标为(180RE, -31RE, -62RE),其4颗卫星监测到行星际磁场（IMF）的BZ分量持续南向,BＹ有较大的负值.本文的研究表明：TC_1观测到的前7个通量管具有准周期重现性,周期大约是1～4 min,明显小于以前所观测到的FTEs的平均周期(8～11 min);所有的通量管都具有较强的核心场.本文分别使用最小方差分析法（MVA）和Grad_Shafranov反演方法（GSR）对通量管的轴向进行了分析和对比,发现所有的通量管主轴基本沿晨昏向,结果显示GSR方法在轴向分析上比MVA优越.本文使用GSR方法对通量管的磁场结构进行了分析,恢复出了通量管的磁场在卫星穿越面的结构图;此外,本文还对这次多重通量管事件进行了deHoffmann Teller(HT)分析,结果表明,所有通量管大致朝南极方向运动,均来源于向日面低纬区域.这说明它们可能起源于向日面低纬区,由该区的磁场分量重联产生. 相似文献
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本文分析了2001年2月和3月期间Cluster Ⅱ穿越磁层顶前后的观测资料,检测到13个通量传输事件（FTEs）.用多颗卫星磁场测量资料的最小方差分析（MVAB）方法确定FTE的管轴方向（其中6个方向较可靠）.FTE管轴方向的分布和低纬处不同,在磁顶法线坐标系LMN中对M轴有较大偏离,比较靠近L轴.deHoffmann Teller(HT)分析指出,13个FTEs都存在一个很好的HT参考系,表明它们以一个准稳的MHD结构运动.对垂直于管轴方向的运动分析表明FTEs并不一定和背景等离子体一起对流,它们可快于或慢于背景流,但FTEs的运动和背景流基本沿相同方向,其间可有一不大的夹角.在HT坐标系中,10个FTEs的等离子体速度接近零, 其他3个FTEs的等离子体速度约为局地Alfven波速的14%,都不符合Walen关系.其中北半球事件的Walen曲线为正斜率,南半球事件为负斜率,这说明等离子体沿磁力线（北半球顺着磁场,南半球逆着磁场）流向磁层. 相似文献
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利用星簇Cluster的三颗卫星(C1, C3和C4)在2001年和2002年的数据,研究磁尾爆发性整体流（BBF, Bursty Bulk Flow）事件及其与亚暴的关系. 三颗卫星可以同时观测到同一次BBF事件, 有时只有一颗或两颗观测到BBF,其原因有:（1）等离子体整体流的速度峰值满足BBF选取原则中的峰值要求, 但卫星的运行轨道不满足;（2）卫星处于所要求的区域内,等离子体整体流的速度峰值不满足;（3）中性片的复杂结构及其运动使得选取条件不能同时满足;（4）BBF空间分布高度局域化. 统计研究结果表明：单颗卫星观测存在局限性, C1、C3和C4卫星独立观测到BBF的持续总时间分别占它们联合观测到的5507%、7748%和5552%; 大部分亚暴爆发期间都能观测到BBF, 甚至在一次亚暴爆发期间观测到多次BBF; 少数亚暴爆发期间没有观测到BBF. 相似文献
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黄宗英 濮祖荫 肖池阶 宗秋刚 傅绥燕 谢伦 史全岐 曹晋滨 刘振兴 沈超 史建魁 路立 王迺权 陈涛 T Fritz K-H Glassmeier P Daly H Rème 《地球物理学报》2004,47(2):181-189
2001年1月26日11:10～11:40UT, ClusterⅡ卫星簇位于午后高纬磁鞘边界层和磁鞘区,此 时行星际磁场Bz为南向. 本文对在此期间观测到的多次磁通量管事件作了详细的研究 ,获得一系列的新发现：（1）高纬磁鞘边界层磁通量管的出现具有准周期性,周期约为78s ,比目前已知的磁层顶向阳面FTE的平均周期（8～11min）小得多. （2）这些通量管都具有 强的核心磁场;其主轴多数在磁场最小变化方向,少数在中间变化方向,有些无法用PAA判 定其方向（需要用电流管PAA确定）,这与卫星穿越通量管的相对路径有关. （3）每个事件 都存在很好的HT参考系,在HT参考系中这些通量管是准定常态结构;所有通量管都沿磁层顶 表面运动,速度方向大体相同,都来自晨侧下方. 通量管的径向尺度为1～2RE, 与通 常的FTE通量管相当. （4）起源于磁层的强能离子大体上沿着管轴方向由磁层向磁鞘运动; 起源于太阳风的热等离子体沿管轴向磁层传输. 通量管为太阳风等离子体向磁层输运和磁层 粒子向行星际空间逃逸提供了通道. （5）每个通量管事件都伴随有晨昏电场的反转,该电 场为对流电场. 相似文献
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2001年8月19日2011～2030UT，AE指数相对较小(40～130 nT)，Cluster 卫星穿越磁尾电流片.利用Cluster 观测资料分析，发现宁静期间有双峰电流片存在，这期间没有明显的高速流，没有明显的电流片振荡. 同时，进一步分析双峰电流片中的离子特性发现:质子数密度Np在中性线（<Bx> = 0）附近相对较大，呈非对称性分布；质子温度分布比较均匀；在中性线两侧，质子y方向上的流速Vy方向相反. 最后讨论LHDI（低混杂漂移不稳定性）的非线性演化可能是形成宁静期间双峰电流片的主要机制. 这些对进一步完善电流片形成机制可能有很重要的意义. 相似文献
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2007年3月3日位于磁层昏侧THEMIS的5颗卫星、同步轨道晨侧和午前的GOES 3颗卫星和地面地磁台站同时观测到了持续近4 h的Pc5 ULF波.我们用交叉小波相关分析计算脉动的传播速度,用MVA分析求解脉动的传播方向,然后结合两者的计算结果获得了Pc5相速度矢量信息.THEMIS卫星观测到Pc5具有压缩特性,且向阳传播,速度约在6~20 km/s左右,相比于磁层中阿尔芬速度(1000 km/s)较低.这些Pc5 ULF波动可能产生于磁尾或磁层内部不稳定性.GOES 3颗卫星观测到不同情况的Pc5 ULF波,极向模占主要成分,且具有波包结构,具有阿尔芬驻波特性,可能产生于K-H(Kelvin-Helmholtz)不稳定性.地面台站观测到ULF波扰动幅度随纬度升高而增强,Pc5脉动在地理纬度60°附近达到最大值, Dumont durville台站观测到的脉动与THEMIS观测到波形有很好的相似性. 相似文献
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本文利用星簇CLUSTER的三颗卫星数据分析了磁宁静期磁尾爆发性整体流（BBFs, Bursty Bulk Flows）的时间尺度, 并与单个卫星的结果做了比较. 事例研究表明, 利用三颗卫星观测数据判断的BBFs的时间尺度比单个卫星的大一倍左右. 对于三颗卫星观测到的同一个BBFs, BBFs在晨昏方向上的摆动决定了CLUSTER的三个卫星观测到BBFs的先后次序. 三颗卫星的观测也显示了BBFs的高度局域化特征. 磁宁静期磁尾BBFs寿命的增大, 使得BBFs携带的质量和能量的地向输运增加. 这种地向输运增加的结果是: 磁尾储存的能量得到较为平稳的释放, 改变了亚暴起始产生的时间, 为解决磁层压力平衡矛盾（PBI, Pressure Balance Inconsistency）问题提供了新的思路. 相似文献
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A statistical survey of dayside pulsed ionospheric flows as seen by the CUTLASS Finland HF radar 总被引：1，自引：0，他引：1
Nearly two years of 2-min resolution data and 7- to 21-s resolution data from the CUTLASS Finland HF radar have undergone Fourier analysis in order to study statistically the occurrence rates and repetition frequencies of pulsed ionospheric flows in the noon-sector high-latitude ionosphere. Pulsed ionospheric flow bursts are believed to be the ionospheric footprint of newly reconnected geomagnetic field lines, which occur during episodes of magnetic flux transfer to the terrestrial magnetosphere - flux transfer events or FTEs. The distribution of pulsed ionospheric flows were found to be well grouped in the radar field of view, and to be in the vicinity of the radar signature of the cusp footprint. Two thirds of the pulsed ionospheric flow intervals included in the statistical study occurred when the interplanetary magnetic field had a southward component, supporting the hypothesis that pulsed ionospheric flows are a reconnection-related phenomenon. The occurrence rate of the pulsed ionospheric flow fluctuation period was independent of the radar scan mode. The statistical results obtained from the radar data are compared to occurrence rates and repetition frequencies of FTEs derived from spacecraft data near the magnetopause reconnection region, and to ground-based optical measurements of poleward moving auroral forms. The distributions obtained by the various instruments in different regions of the magnetosphere were remarkably similar. The radar, therefore, appears to give an unbiased sample of magnetopause activity in its routine observations of the cusp footprint. 相似文献
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Line-of-sight Doppler velocities from the SuperDARN CUTLASS HF radar pair have been combined to produce the first two-dimensional vector measurements of the convection pattern throughout the ionospheric footprint of a flux transfer event (a pulsed ionospheric flow, or PIF). Very stable and moderate interplanetary magnetic field conditions, along with a preceding prolonged period of northward interplanetary magnetic field, allow a detailed study of the spatial and the temporal evolution of the ionospheric response to magnetic reconnection. The flux tube footprint is tracked for half an hour across six hours of local time in the auroral zone, from magnetic local noon to dusk. The motion of the footprint of the newly reconnected flux tube is compared with the ionospheric convection velocity. Two primary intervals in the PIFs evolution have been determined. For the first half of its lifetime in the radar field of view the phase speed of the PIF is highly variable and the mean speed is nearly twice the ionospheric convection speed. For the final half of its lifetime the phase velocity becomes much less variable and slows down to the ionospheric convection velocity. The evolution of the flux tube in the magnetosphere has been studied using magnetic field, magnetopause and magnetosheath models. The data are consistent with an interval of azimuthally propagating magnetopause reconnection, in a manner consonant with a peeling of magnetic flux from the magnetopause, followed by an interval of anti-sunward convection of reconnected flux tubes. 相似文献
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A flux transfer event observed at the magnetopause by the Equator-S spacecraft and in the ionosphere by the CUTLASS HF radar 总被引：2，自引：0，他引：2
D. A. Neudegg T. K. Yeoman S. W. H. Cowley G. Provan G. Haerendel W. Baumjohann U. Auster K.-H. Fornacon E. Georgescu C. J. Owen 《Annales Geophysicae》1999,17(6):707-711
Observations of a flux transfer event (FTE) have been made simultaneously by the Equator-S spacecraft near the dayside magnetopause whilst corresponding transient plasma flows were seen in the near-conjugate polar ionosphere by the CUTLASS Finland HF radar. Prior to the occurrence of the FTE, the magnetometer on the WIND spacecraft ≈226 RE upstream of the Earth in the solar wind detected a southward turning of the interplanetary magnetic field (IMF) which is estimated to have reached the subsolar magnetopause ≈77 min later. Shortly afterwards the Equator-S magnetometer observed a typical bipolar FTE signature in the magnetic field component normal to the magnetopause, just inside the magnetosphere. Almost simultaneously the CUTLASS Finland radar observed a strong transient flow in the F region plasma between 78° and 83° magnetic latitude, near the ionospheric region predicted to map along geomagnetic field lines to the spacecraft. The flow signature (and the data set as a whole) is found to be fully consistent with the view that the FTE was formed by a burst of magnetopause reconnection. 相似文献
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M. Uspensky P. Eglitis H. Opgenoorth G. Starkov T. Pulkkinen R. Pellinen 《Annales Geophysicae》2001,18(12):1560-1575
Observations and modelling are presented which illustrate the ability of the Finland CUTLASS HF radar to monitor the afternoon-evening equatorward auroral boundary during weak geomagnetic activity. The subsequent substorm growth phase development was also observed in the late evening sector as a natural continuation of the preceding auroral oval dynamics. Over an 8 h period the CUTLASS Finland radar observed a narrow (in range) and persistent region of auroral F- and (later) E-layer echoes which gradually moved equatorward, consistent with the auroral oval diurnal rotation. This echo region corresponds to the subvisual equatorward edge of the diffuse luminosity belt (SEEL) and the ionospheric footprint of the inner boundary of the electron plasma sheet. The capability of the Finland CUTLASS radar to monitor the E-layer SEEL-echoes is a consequence of the nearly zero E-layer rectilinear aspect angles in a region 5/10° poleward of the radar site. The F-layer echoes are probably the boundary blob echoes. The UHF EISCAT radar was in operation and observed a similar subvisual auroral arc and an F-layer electron density enhancement when it appeared in its antenna beam. 相似文献
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Statistical observations of the MLT, latitude and size of pulsed ionospheric flows with the CUTLASS Finland radar 总被引：1，自引：0，他引：1
A study has been performed on the occurrence of pulsed ionospheric flows as detected by the CUTLASS Finland HF radar. These flows have been suggested as being created at the ionospheric footprint of newly-reconnected field lines, during episodes of magnetic flux transfer into the terrestrial magnetosphere (flux transfer events or FTEs). Two years of both high-time resolution and normal scan data from the CUTLASS Finland radar have been analysed in order to perform a statistical study of the extent and location of the pulsed ionospheric flows. We note a great similarity between the statistical pattern of the coherent radar observations of pulsed ionospheric flows and the traditional low-altitude satellite identification of the particle signature associated with the cusp/cleft region. However, the coherent scatter radar observations suggest that the merging gap is far wider than that proposed by the Newell and Meng model. The new model for cusp low-altitude particle signatures, proposed by Lockwood and Onsager and Lockwood provides a unified framework to explain the dayside precipitation regimes observed both by the low-altitude satellites and by coherent scatter radar detection. 相似文献
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M. Lockwood I. W. McCrea S. E. Milan J. Moen J. C. Cerisier A. Thorolfsson 《Annales Geophysicae》2000,18(9):1027-1042
We report high-resolution observations of the southward-IMF cusp/cleft ionosphere made on December 16th 1998 by the EISCAT (European incoherent scatter) Svalbard radar (ESR), and compare them with observations of dayside auroral luminosity, as seen at a wavelength of 630 nm by a meridian scanning photometer at Ny Ålesund, and of plasma flows, as seen by the CUTLASS (co-operative UK twin location auroral sounding system) Finland HF radar. The optical data reveal a series of poleward-moving transient red-line (630 nm) enhancements, events that have been associated with bursts in the rate of magnetopause reconnection generating new open flux. The combined observations at this time have strong similarities to predictions of the effects of soft electron precipitation modulated by pulsed reconnection, as made by Davis and Lockwood (1996); however, the effects of rapid zonal flow in the ionosphere, caused by the magnetic curvature force on the newly opened field lines, are found to be a significant additional factor. In particular, it is shown how enhanced plasma loss rates induced by the rapid convection can explain two outstanding anomalies of the 630 nm transients, namely how minima in luminosity form between the poleward-moving events and how events can re-brighten as they move poleward. The observations show how cusp/cleft aurora and transient poleward-moving auroral forms appear in the ESR data and the conditions which cause enhanced 630 nm emission in the transients: they are an important first step in enabling the ESR to identify these features away from the winter solstice when supporting auroral observations are not available. 相似文献
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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
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