【作者】 张清和；

【导师】 黄际英； 刘瑞源；

【作者基本信息】 西安电子科技大学 ， 无线电物理， 2008， 博士

【摘要】 日侧磁层顶边界层是太阳风-磁层耦合和相互作用的重要区域。太阳风可以通过日侧磁层顶向地球磁层输运或转换质量、动量和能量,而磁重联则是这一输运或转换过程中最为重要的物理过程之一。本文基于我国南极中山站和北极黄河站白天处在极隙区并形成地磁共轭的优越地理条件,联合Cluster卫星簇和我国双星(TC-1、TC-2)及超级双极光雷达网(SuperDARN)和欧洲非相干散射雷达(EISCAT)的协同观测,对于行星际磁场(IMF)南向和北向两种情况选取了五个典型的日侧磁层顶磁重联事件并加以详细分析,试图揭示日侧磁重联产生的通量传输事件(FTEs)和高纬尾瓣重联的演化特征和物理特性。在南向行星际磁场(IMF BZ<0)条件下,本文详细分析了2004年4月1日11:48-13:00 UT期间、2004年2月11日09:00-12:00 UT期间和2004年3月13日12:00-12:40 UT期间Cluster/TC-1卫星穿越磁层顶前后的磁通门磁力计(FGM)和电子/电流试验仪(PEACE)及EISCAT和SuperDARN雷达的同时观测资料。采用最小变化量分析法(MVA)将磁场数据投影到局地磁层顶法线坐标系(LMN)并结合卫星PEACE记录的电子能谱数据发现在卫星穿越磁层顶前后观测到了一系列日侧磁层顶低磁纬重联产生的FTEs,这些FTEs具有准周期性。采用最小方向微分法(Minimum Directional Derivative (or Difference),简称MDD)和时空微分法(Spatio-temporal Difference,简称STD)对这些FTEs的维数、运动速度和尺度大小进行详细分析发现这些FTEs通常是径向尺度约为0.60-1.05 RE的准二维结构,具有尾向和昏向(或晨向)运动速度,与Cooling模型预测的通量管运动方向基本一致。通量管内电流密度较大,可达10-7A/m2。详细分析发现2004年2月11日事件中可能存在一对FTEs产生于同一条重联X-线(与北半球极隙区相连的FTEs被Cluster卫星观测到,而与南半球极隙区相连的FTEs被TC-1卫星观测到)。采用Cooling模型对这一对FTEs进行预测并与Cluster卫星观测的FTEs的运动速度进行比较,推算出TC-1卫星观测到的FTEs的运动速度和尺度,从而得出随着FTEs的尾向运动,其速度和尺度均有所增加。这些FTEs的运动与CUTLASS(或Stokkseyri)SuperDARN雷达观测的“极向运动雷达极光”结构(PMRAFs)(或“脉冲式电离层流”(PIFs))有着很好的对应关系,也与EISCAT Svalbard雷达观测的极向对流和软电子沉降特征有一定的对应关系。同时,这些FTEs的运动方向及Cooling模型预测的通量管运动方向与SuperDARN雷达共轭观测的南北极极区电离层对流增强方向基本一致,该对流增强的持续时间大约为4-8分钟,进而推出自磁重联发生到FTEs融入极盖区开放磁力线中的演化时间大约为4-8分钟;然而,这些FTEs在南极和北极极区电离层的响应时间(对流增强的开始时间)是不同的,进而推测出产生这些FTEs的重联点位于日下点以南(或以北)的日侧磁层顶区域。在北向行星际磁场条件(IMF BZ>0)下,本文还详细分析了2004年3月26日09:00-10:00 UT期间和2005年1月11日09:00-14:00 UT期间Cluster/TC-1卫星穿越磁层顶前后的磁通门磁力计(FGM)和电子/电流试验仪(PEACE)及地面CUTLASS SuperDARN雷达和我国北极黄河站全天空极光的同时观测资料,并考察了相应时刻低轨卫星DMSP_F13观测的粒子沉降和等离子体对流数据。分析被投影到局地磁层顶法线坐标系(LMN)的磁场数据和卫星PEACE记录的电子能谱数据发现在北向行星际条件下卫星观测到了一些典型的磁重联特征,该特征伴随有明显的粒子加速和等离子体混合特征。这些磁重联可能是高纬尾瓣重联。地面CUTLASS SuperDARN雷达观测到了“赤向运动雷达极光结构”和向阳对流的增强,该对流增强的持续时间大约为8分钟,说明这些高纬尾瓣重联的演化时间大约为8分钟。我国北极黄河站全天空极光观测显示了北极极区电离层对磁层顶磁重联有很好的响应,并且发现极光增亮的区域与行星际磁场(IMF)时钟角有很强的依赖关系。DMSP_F13卫星观测的电离层相应区域软电子沉降和离子色散特征进一步证实了尾瓣重联的发生,该卫星观测的等离子体对流方向和Cluster卫星观测的高纬重联产生的FTEs的运动方向及我国北极黄河站观测的该区域的极光运动趋势基本一致。日侧磁层顶磁重联过程及其动力学效应十分复杂,本文仅分析和研究了五个典型的事件。尽管本文揭示了一些新的结构和现象,并对FTEs的演化过程形成了一些新的认识,但对磁层顶磁重联的整体形态、磁重联的三维几何结构、磁层顶磁重联对极区电离层的影响等问题尚待进一步深入研究。更多还原

【Abstract】 The dayside magnetopause boundary layer is the key region for the solar wind-magnetosphere coupling and interaction. Solar wind plasma can easily cross this region to transfer mass, momentum and energy into the magnetosphere. One of the most important ways of these transferring processes is the magnetic reconnection. Based on the good geographic locations of magnetic conjugate between Chinese Zhongshan Station in Antarctic and Yellow River Station in Arctic, this thesis coordinated Cluster/Double Star (TC-1 and TC-2), Super Dual Auroral Radar Network (SuperDARN) and EISCAT radar observations for five selected cases of the magnetic reconnections on the dayside magnetopause during southward or northward interplanetary magnetic field (IMF). The five cases were analyzed in some detail for trying to reveal the evolutions and physical characteristic of the flux transfer events (FTEs) originated by the magnetic reconnections on the dayside magnetopause.Under southward IMF (BZ<0) condition, this thesis analyzed the observations of the flux gate magnetometer (FGM) and PEACE instruments onboard the Cluster/TC-1 Spacecraft, and the EISCAT and SuperDARN radars between 11:48 and 13:00 UT on 1 April 2004, 09:00 and 12:00 UT on 11 February 2004, and 12:00 and 12:40 UT on 13 March 2004. The magnetic field data are expressed in local boundary normal coordinates (LMN), which have been found by performing minimum variance analysis (MVA) on the local magnetopause crossing of Cluster 3 and TC-1. Combining with the electron spectrograms data from the PEACE instrument onboard Cluster/TC-1, it is shown that a series of FTEs, which originated from the low-latitude magnetic reconnections on the dayside magnetopause, was observed before and after the magnetopause crossing of Cluster/TC-1. These FTEs appeared quasi-periodically.We applied the four-spacecraft techniques of“Minimum Directional Derivative (or Difference)”(MDD) and“Spatio-temporal Difference”(STD) to calculate the dimension, motion and scale of these FTEs. With a quasi-2-D structure and a scale of 0.60~1.05RE with the current density reaching as high as about 10-7A/m2, the inferred northwardly reconnected flux tubes for these FTEs are shown to move northward, duskward (or downward) and tailward, which consistent with the expected motion of the reconnected magnetic flux tubes by running the Cooling model. It is found that there was one pair of FTEs which might be originated from the same reconnection X-line (the FTE connected to the northern cusp was observed by Cluster, and the one connected to the southern cusp was observed by TC-1) for the case of 11 February 2004. Using the Cooling model to predict the motions of the above pair of FTEs and comparing the expected motion with the motion observed by Cluster, this thesis inferred the motion of FTE measured by TC-1, and found that the speed and scale of the FTEs were increasing with its tailward motion.The motions of these FTEs are good corresponding with the“poleward-moving radar auroral forms”(PMRAFs) (or“pulsed ionospheric flows”(PIFs)) observed by CUTLASS (or Stokkseyri) SuperDARN radar, and also corresponding with the bursts of poleward flow and low-energy electron precipitation recorded by the EISCAT radars. Furthermore, the motion direction of the FTEs observed by Cluster/TC-1 and the expected flux tubes predicted by Cooling model are temporally correlated with clear velocity enhancements in the ionospheric convections conjugate measured by SuperDARN radar in both hemispheres. The duration of these velocity enhancements imply that the evolution time of the FTEs is about 4-8 minutes from its origin on magnetopause to its addition into the polar cap. However, the ionospheric response time was different in each hemisphere. This suggests the reconnection site is located southward (or northward) of the subsolar region.Under northward IMF (BZ>0) condition, this thesis also analyzed the simultaneous observations of the FGM and PEACE instruments onboard the Cluster Spacecraft, the CUTLASS SuperDARN radar and the all sky imager at Chinese Yellow River Station in Ny-?lesund, Arctic during 09:00-10:00 UT on 26 March 2004 and 09:00-14:00 UT on 11 January 2005. Combining the magnetic field data expressed in LMN coordinates with the electron spectrograms data from the PEACE instrument onboard Cluster 1, it is shown that a series of high-latitude lobe reconnection signatures were observed, with clear accelerating and mixing of magnetosheath and magnetospheric plasma populations. These magnetic reconnection signatures might be originated by the high-latitude/lobe reconnection on the dayside magnetopause. A series of“equator-ward moving radar auroral forms”(EMRAFs) and enhanced sunward flows were observated by CUTLASS SuperDARN radar. The durations of the flow enhancements is about 8 minutes, suggested that the evolution time of the magnetic lobe reconnections is about 8 minutes from its origin on magnetopause to its addition into the polar cap. The optical aurora measurements showed that the observational ionospheric region was good response to the magnetopause reconnections. The regions of the aurora brightening were much dependent on the IMF clock angle. The low-altitude particle precipitation, observed by the Defense Meteorological Satellite Program (DMSP) F13, are presented to show the intense magnetosheath-like electron precipitation and a stepped ion dispersion signature, which are the good response to the pulse magnetopause reconnections (FTEs) and the boundary structure crossing. The plasma flow measurements by F13 were consistent with the motion of the FTE (originated by lobe reconnection) observed by Cluster and the trending of the aurora motions in the corresponding regions of the observation from the all sky imager at Chinese Yellow River Station.The magnetic reconnections on the dayside magnetopause and their dynamic effect are quite complicated. This thesis only detailedly analyzed and studied five typical cases. Although this thesis revealed some new structures and phenomena, and formed some new understanding, the global configurations of the magnetic reconnections on the dayside magnetopause, the 3-D geometry structure of magnetic reconnections, and the ionosperic response to the dayside magnetic reconnection in polar region still remain to be further analyzed and studied.更多还原