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1.
亚暴期间极光电集流带的变化   总被引:3,自引:1,他引:2       下载免费PDF全文
极光活动加剧和极光电集流增强是磁层-电离层能量耦合的两种重要表现形式,它们同为磁层带电粒子向电离层沉降的结果,但是变化规律却非常不同.本文用地基磁场资料,反演极区等效电流体系,研究地磁平静期和扰动期极光电集流带的运动特点.研究表明,Harang间断把极光电集流带分为两段:下午—黄昏段的东向电集流带较弱,而晨侧和子夜—凌晨段的西向电集流带较强.在亚暴膨胀相,随着AE指数增大,整个极光卵向赤道扩展,而极光电集流带却表现出分段差异的特点:下午—黄昏东向电集流带向低纬移动,晨侧西向电集流带也向赤道移动,而子夜—凌晨西向电集流带则向极移动.电动力学分析表明,在不同地方时段,控制电流的主要因素不同,因而,电流及其磁扰有不同的特点:下午—黄昏东向电集流和晨侧西向电集流组成了DP2电流体系,主要受控于磁层对流电场,反映了“驱动过程”的行为;而子夜—凌晨西向电集流是DP1电流体系的基本部分,主要受控于电导率,反映了“卸载过程”的特点.  相似文献   

2.
磁层亚暴的发生与近磁尾(约6~8 RE)电流片中断和中磁尾(约20~30 RE)磁场重联密切相关,而极光的极向扩展、电流片中断和磁尾重联的时序过程对于认识亚暴的触发机制至关重要. 本文利用位于中磁尾的CLUSTER卫星,同步轨道附近LANL-01、LANL-97卫星,近磁尾POLAR和 极区IMAGE卫星的观测,分析了单个亚暴事例.结果表明,在此事件中,中磁尾磁场重联起始比近尾电流片中断早3 min发生,电流片中断发生4 min后,IMAGE卫星观测到极光增亮,同时AE指数突然增大,亚暴膨胀相起始. 观测结果与亚暴中性线模型较为吻合.  相似文献   

3.
极区地磁亚暴等效电流体系的本征模分析   总被引:1,自引:1,他引:0  
亚暴是空间天气预报非常关注的磁层事件一般来说, 每一次亚暴事件都包含“直接驱动过程”和“卸载过程”两物理机制的贡献, 它们分别对应磁层大尺度对流过程和亚暴电流楔形成过程为了定量地分离这两种过程所对应的电流体系, 本文使用自然正交分量法对每一时刻的极区电流体系进行本征模分析, 试图得到两种过程所对应的特征电流图案及其随时间的变化分析结果表明, 第一本征模的电流图案呈双涡结构, 对应于“直接驱动过程”, 第二本征模的电流图案反映了极光带西向电集流的基本特征, 对应于“卸载过程”前者无论在平静期间, 还是亚暴期间始终存在, 其强度从亚暴增长相开始增加, 膨胀相期间快速增长, 恢复相期间逐渐减小; 后者在平静期间几乎为零, 亚暴增长相期间变化不大, 直到膨胀相开始才迅速增长, 恢复相期间逐渐减小根据上述分解, 可以对目前普遍用来描述亚暴强度的AE指数进行修正, 得到分别反映对流过程和电流楔形成过程的相应指数  相似文献   

4.
场向电流在不同的等离子体区之间传递能量、动量和质量,是磁层与电离层之间的关键耦合过程.本文利用CHAMP卫星高精度的空间磁场测量数据,研究亚暴期间极区电离层场向电流的统计学分布特征.研究表明场向电流的大小与所在位置呈现明显的日夜和晨昏不对称性,具体为:(1)场向电流的大小与亚暴极光电急流指数(AL)密切相连,AL愈大,电流愈强,亚暴期间电流强度相对平静期来说可增加约5倍,昏侧和夜侧电流强度与AL指数的相关性较好,晨侧和白天侧两者相关性较差;(2)电流的峰值密度所在位置与AL指数的相关性不高,昏侧电流所处纬度低于晨侧,而夜晚电流所处纬度低于白天侧.  相似文献   

5.
准确界定亚暴起始时刻是理解亚暴相关问题的关键.已有研究主要集中在两方面:一是从极光图像中人工挑选亚暴事件进行案例分析或统计分析来研究亚暴发生机制及亚暴期间的地磁环境;二是基于一些空间物理参数,如AE指数、SME(SuperMAG electrojet)指数、Pi2、正弯扰等,采用人眼判断或是模式识别的方法从中找出亚暴起始时刻.本文尝试采用模式识别的方法从紫外极光图像中自动地检测出亚暴膨胀期起始时刻.首先,将紫外极光图像通过网格化处理转换到磁地方时-地磁纬度(MLT-MLAT)直角坐标下,然后通过模糊c均值聚类方法提取亮斑,再考察亮斑强度是否增强、面积是否极向膨胀来判断是不是亚暴事件.本文方法在1996年12月-1997年2月这三个月的Polar卫星紫外极光图像上进行了实验验证.我们将检测到的亚暴起始时刻与Liou(J. Geophys. Res., 2010, 115: A12219)的人工标记进行了对比,并详细分析了与标记不一致的多检和漏检事件.本文提出的自动检测方法可以快速地从海量紫外极光图像中完成亚暴事件的初步筛选,方便研究人员进一步深入研究极光亚暴.  相似文献   

6.
极光电激流是极区电流系的重要组成部分.本文利用CHAMP卫星10年的高精度标量磁场数据研究了极光电激流的地方时和季节变化特征,并对卫星与地面台站观测到的极光电激流进行了对比分析.结果表明,日侧极光电激流主要受太阳辐射的影响,而夜侧极光电激流主要受亚暴的影响.极光电激流具有明显的年、半年变化特征.夏季东向电激流和日侧西向电激流强于冬季,而夜间西向电激流冬季强于夏季.东向电激流和日侧的西向电激流在两至点增强,夜侧的西向电激流则在两分点增强.西向电激流与AL、SML指数有较好的相关性,东向电激流与SMU指数有较好的相关性,而与AU指数有一定差异,这与地磁台站的有效探测范围有关.  相似文献   

7.
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   

8.
利用南极中山站极光全天空摄相、地磁、地磁脉动数据和Wind卫星的行星际磁场IMF观测数据,分析了7个亚暴期间高纬黄昏-子夜扇区极光弧的短暂增亮现象.极光弧特征是,短暂增亮随后很快衰减,历时10-20min,基本沿着日-地方向,有明显黄昏方向运动.这些事件大都发生在IMFBz南转之后,亚暴增长相或膨胀相期间,极光浪涌到达之前10-73min消失.相应的IMFBx>0,IMFBy<0.这种极光弧和亚暴极光不同,它们与地磁活动及Pi2脉动不相关.这7个极光弧的形态和IMF特征表明,极光弧的增亮很可能由尾瓣重联产生,很快衰减归因于IMFBz南向条件,而黄昏方向运动受IMFBy控制.  相似文献   

9.
通过对北极斯瓦尔巴特( Svalbard )岛Longyearbyen台站的 极光扫描光度计和地磁 观测数据在地磁亚暴膨胀相期间的对比分析,发现扫描光度计记录中的极光边缘的快速极向 运动和地磁数据x分量的陡峭负弯之间有着良好的对应关系,地磁数据可用来研究两极 高纬 地区极光亚暴的地磁共轭特征. 对南极中山站、挪威Troms Svalbard台链和东格陵兰岛 地 区共15个地磁台站在7个典型极光亚暴事件中的地磁数据进行对比分析后发现, 中山站的地 磁共轭点位置存在明显的漂移特征,漂移的范围在斯瓦尔巴特岛与东格陵兰岛之间,纬度值 与CGM模型值近似.  相似文献   

10.
极区电离层电流与极光电集流指数关系的定量分析   总被引:2,自引:0,他引:2  
极区电离层电流体系主要是由场向电流产生的. 在平静状态下, 极区电流由一对晨昏电流涡组成, 而当亚暴发生时, 强度为几百万安培的西向电集流造成极区地磁场的剧烈扰动. 极光电集流的强度通常用极光电集流指数AL, AU, AEAO来描述. 本文用国际磁层研究计划(IMS)执行期间, 由北半球71个高纬地磁台的资料所得到的极区电流函数, 定量分析极区电流特征与极光电集流指数的关系. 研究结果表明, AL, AU指数与AE指数有很好的线性关系, 所以可以用AE(乘以适当比例因子)近似代替ALAU, AE指数可以近似表征极区总电流以及晨昏电流涡强度, 定量分析表明, AE指数的1 nT对应极区总电流1000 A. AE指数与最大西向电流密度有很好的正比关系, AE指数的1 nT对应地磁子夜最大西向电流密度1 A/km. 在夜间扇区的不同地方时, 电流密度随纬度变化的趋势大体相似, 最大西向电流密度一般位于地磁子夜附近和地磁纬度65°~70°处, 而东向电流密度在80°附近达到极大值. 分析还表明, 就5 min平均值而言, AE指数的饱和值约为700 nT, AL的饱和值约为−500 nT. 所以, 在研究磁层-电离层过程时, 使用饱和值以上的极光电集流指数需十分谨慎.  相似文献   

11.
研究了Polar卫星的极区电离层X射线成像仪(PIXIE)得到的极光X射线成像强度AI(Auroral Intensity)与磁层亚暴指数的相关关系.本文发现,在所选取的1997年至2001年的部分数据中,从完整的X射线图像得到的极光X射线总强度和AE指数有很好的线性相关关系,在全部83组数据中有566%的数据的线性相关系数都在060以上(相关系数最大为097).所以本文认为极光X射线总强度可以作为新的磁层亚暴卫星实时监测指数.  相似文献   

12.
On 17 March 1991, five clear substorm onsets/intensifications took place within a three hour interval. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were available, in addition to data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation. This interval of substorm activity has been interpreted as being in support of a near-Earth current disruption model of substorm onset. In the present study the ionospheric convection response, observed some four hours to the west in MLT by the Halley HF radar in Antarctica, is related to the growth, expansion and recovery phases of two of the substorm onsets/expansions observed in the Northern Hemisphere. Bursts of ionospheric flow and motion of the convection reversal boundary (CRB) are observed at Halley in response to the substorm activity and changes in the IMF. The delay between the substorm expansion phase onset and the response in the CRB location is dependent on the local time separation from, and latitude of, the initial substorm onset region. These results are interpreted in terms of a synthesis of the very near-Earth current disruption model and the near-Earth neutral line model of substorm onset.  相似文献   

13.
A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at \sim0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (\sim0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is “pinched off”, and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked “viscous-like” momentum transfer across the magnetopause.  相似文献   

14.
On August 21st 1998, a sharp southward turning of the IMF, following on from a 20 h period of northward directed magnetic field, resulted in an isolated substorm over northern Scandinavia and Svalbard. A combination of high time resolution and large spatial scale measurements from an array of coherent scatter and incoherent scatter ionospheric radars, ground magnetometers and the Polar UVI imager has allowed the electrodynamics of the impulsive substorm electrojet region during its first few minutes of evolution at the expansion phase onset to be studied in great detail. At the expansion phase onset the substorm onset region is characterised by a strong enhancement of the electron temperature and UV aurora. This poleward expanding auroral structure moves initially at 0.9 km s-1 poleward, finally reaching a latitude of 72.5°. The optical signature expands rapidly westwards at ~6 km s-1, whilst the eastward edge also expands eastward at ~0.6 km s-1. Typical flows of 600 m s-1 and conductances of 2 S were measured before the auroral activation, which rapidly changed to ~100 m s-1 and 10–20 S respectively at activation. The initial flow response to the substorm expansion phase onset is a flow suppression, observed up to some 300 km poleward of the initial region of auroral luminosity, imposed over a time scale of less than 10 s. The high conductivity region of the electrojet acts as an obstacle to the flow, resulting in a region of low-electric field, but also low conductivity poleward of the high-conductivity region. Rapid flows are observed at the edge of the high-conductivity region, and subsequently the high flow region develops, flowing around the expanding auroral feature in a direction determined by the flow pattern prevailing before the substorm intensification. The enhanced electron temperatures associated with the substorm-disturbed region extended some 2° further poleward than the UV auroral signature associated with it.  相似文献   

15.
16.
Enhancements in the auroral electrojets associated with magnetospheric substorms result from those in either the electric field or the ionospheric conductivities, or both. Their relative importance varies significantly, even during a single substorm, depending on the location as well as on the substorm phases. It is predicted that different parts of the electrojets tend to respond in different ways to substorm activity. The unprecedented, unique opportunity for CLUSTER spacecraft observations of electric/magnetic fields and precipitating particles, combined with radar measurements of ionospheric quantities and with ground magnetometers, will provide us with crucial information regarding the physical nature of the separation between the “electric field-dominant” and “conductivity-dominant” auroral electrojets. This study also discusses the implications of these two auroral-electrojet components in terms of solar wind-magnetosphere-ionosphere interactions.  相似文献   

17.
We have used the global numerical model of the coupled ionosphere-thermosphere-protonosphere system to simulate the electric-field, ion- and electron-temperature and -concentration variations observed by EISCAT during the substorm event of 25 March 1987. In our previous studies we adopted the model input data for field-aligned currents and precipitating electron fluxes to obtain an agreement between observed and modelled ionospheric variations. Now, we have calculated the field-aligned currents needful to simulate the substrom variations of the electric field and other parameters observed by EISCAT. The calculations of the field-aligned currents have been performed by means of numerical integration of the time-dependent continuity equation for the cold mag-netospheric electrons. This equation was added to the system of the modelling equations including the equation for the electric-field potential to be solved jointly. In this case the inputs of the model are the spatial and time variations of the electric-field potential at the polar-cap boundaries and those of the cold magnetospheric electron concentration which have been adopted to obtain the agreement between the observed and modelled ionospheric variations for the substorm event of 25 March 1987. By this means it has been found that during the active phase of the substorm the current wedge is formed. It is connected with the region of the decreased cold magnetospheric electron content travelling westwards with a velocity of about 1 km s–1 at ionospheric levels.  相似文献   

18.
南极中山站电离层的极区特征   总被引:8,自引:1,他引:8       下载免费PDF全文
本文利用1996年的电离层数字测高仪DPS-4所测的f0F2、f0E以及美国NOAA和DMSP卫星观测估算的半球功率指数和午夜极光区赤道侧边界纬度等资料,考察中山站电离层的极区特征。结果表明,在太阳和地磁宁静环境下,冬季极夜磁正午中山站处于极隙区中心时,电离层内的电离密度达全天的最大值;上、下午各有数小时间隔位极光带内时,高能粒子的电离作用也很重要;夜间进入极差区后,电子密度则很低。夏季极昼时,太阳EUV辐射的电离效应使电离层电离密度比冬季值大许多,而且,日变化的最大值时间也提前了1~2h,强磁扰时,极隙区和极光带均向低纬侧移动;中山站上空的电子密度会大幅度下降。在中等扰动环境下情况要加复杂:磁正午前后极隙区内软粒子沉降的电离强度有所减小,而上、下午极光区的高能粒子电离则有较大增加。  相似文献   

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