【作者】 左平兵；

【导师】 魏奉思； 冯学尚；

【作者基本信息】 中国科学院研究生院（空间科学与应用研究中心） ， 空间物理， 2008， 博士

【摘要】 本文对太阳风中的慢激波观测、磁云边界层的磁层响应以及磁云边界层中朗缪尔波活动现象三个方面作了初步观测研究,主要研究结果如下:1.历史上太阳风中慢激波的观测非常少,利用WIND飞船的高分辨率磁场和粒子观测数据,我们严格证认了一例典型的慢激波事件,该慢激波正好位于某磁云边界层的前边界.该事件也是文献上首次和磁云相关的慢激波事件的报道.在证认慢激波事件过程中,我们提出一种新的基于Rankine–Hugoniot解的激波法向自洽确定方法.基于此方法确定激波法向,并且与其它方法如磁场共面法、最小方差法作比较,我们发现此方法确定的激波法向更准确.随后我们又证认了一例罕见的双间断事件,该双间断事件也位于某磁云边界层的前边界.通过WIND飞船和Geotail飞船在磁层外的联合观测发现该双间断是不稳定的,这与前人报道的双间断事件不同.2.综合考察了磁云边界层穿越磁层时磁层各区域的响应.首先我们统计分析了WIND飞船1995–2006年探测的35例磁云前边界层和磁层亚暴的相关性问题,发现“SF”型边界层与亚暴有很好的相关性,是触发亚暴的重要行星际源.边界层触发亚暴的必要条件是紧邻鞘区有持续南向磁场.随后我们全面分析了WIND飞船2004年11月9日探测的磁云边界层引起的磁层活动.该磁云边界层本身持续较强南向磁场驱动了一个强磁暴.相对于紧邻鞘区和磁云本体,磁云边界层是一个动压增强区.此边界层把磁层压缩至一个很小区域,甚至地球同步轨道向阳侧的多颗卫星穿越磁层顶,以致很长时间内直接暴露在太阳风中,构成极端空间天气条件.磁云边界层内部磁场等离子体结构触发了一个典型亚暴.另外,磁云边界层前边界是一个快速强动压脉冲结构,此动压脉冲结构会引起磁层电场、磁场、电流、电流层对流以及高能粒子全面的响应.对我们分析的35例磁云前边界层,57%的前边界为快速强动压脉冲增强结构,这些响应是边界层前边界压缩磁层引起磁层扰动的共性.最后根据Shue(1998)磁层顶模型,我们计算了磁云边界层穿越磁层时对磁层的普遍压缩作用.磁云边界层强动压区会使磁层顶被压缩至非常靠近地球的位置.而在我们考察的34个边界层事件(35个样本里面其中一个缺少等离子体观测数据)中,有21个事件(62%)对应的由于磁层顶的被压缩使日下点位置距地心的最小距离r0min≤8.0 RE.另外结合GOES卫星的观测和Shue(1998)模型,发现有8个事件(占总样本的24%)对应的向阳面磁层顶被压缩至地球同步轨道以内,可能导致灾害性空间天气事件的发生,所以须引起足够的重视.磁云边界层相对于鞘区和磁云本体,对磁层的压缩能力更强.3.对磁云边界层内朗缪尔波动作了初步分析,发现两类磁云边界层内特有的朗缪尔波活动现象:一类是相对于邻近鞘区和磁云本体,整个边界层内朗缪尔波活动增强;另一类是短时间的朗缪尔波爆发现象,同时伴随着宽频带的离子声波活动.随后我们考察了其中一例朗缪尔波爆发的事件对应的高分辨率电子分布函数数据,发现速度约为7×103 km/s的高能电子束流形成尾峰分布不稳定性导致了朗缪尔波的爆发.更多还原

【Abstract】 In this dissertation, observational study on the magnetic cloud boundarylayers (MCBLs) and the related micro-scale structures are made with emphasis onthe slow shock identification, the global magnetospheric responses to the passagesof MCBLs as well as the plasma waves within MCBLs.The observations of the slow shocks associated with the interplanetary coro-nal mass ejections near 1 AU have seldom been reported in the past severaldecades. Here we report the identification of an interplanetary slow shock ob-served by WIND on September 18, 1997. This slow shock is found to be just thefront boundary of a MCBL. A novel self-consistent method based on the entireRankine-Hugoniot relations is introduced to determine the shock normal. It isfound that the observations of the jump conditions across the shock are in goodagreement with the Rankine-Hugoniot solutions. In addition, the typical interiormagnetic structure inside the shock layer is also analyzed using the 3s time res-olution magnetic field data since the time for the spacecraft traversing the shocklayer is much longer (about 17 s). As a potential explanation to the formationof this kind of slow shock associated with magnetic clouds, this slow shock couldbe a signature of reconnection that probably occurs inside the magnetic cloudboundary layer.A double discontinuity is a rarely observed compound structure composedof a slow shock layer and an adjoining rotational discontinuity layer in the down-stream region. Also we report the observations of a double discontinuity detectedby WIND on May 15, 1997. This double discontinuity is found to be the frontboundary of a magnetic cloud boundary layer. We strictly identify the shocklayer and the rotational discontinuity layer by using the high resolution plasmaand magnetic field data from WIND. The observed jump conditions of the up-stream and downstream region of the slow shock layer are in good agreementwith the Rankine-Hugoniot relations. The magnetic cloud boundary layer ob-served by WIND was also detected by Geotail 48 min later when the spacecraft was located outside the bow shock of the magnetosphere. Whereas, Geotail ob-servations showed that its front boundary was no longer a double discontinuityand the rotational discontinuity layer disappeared. It indicated that this doublediscontinuity was unstable when propagating from WIND to Geotail.The MCBL is a disturbance structure that is located between the magneticcloud and the ambient solar wind. We statistically analyze the characteristicsof the magnetic field Bz component (in GSM) inside MCBLs as well as therelationship between MCBLs and the magnetospheric substorms based on 35typical MCBLs observed by WIND in 1995?2006. It is found that the magneticfield Bz components are more turbulent inside the MCBLs than those insidethe adjacent sheath regions and the magnetic clouds. The substorm onsets areidentified by the auroral breakups that are the most reliable substorm indicatorsby using the Polar UVI image data. The UVI data are available only for 17MCBLs. The statistical analysis indicated that 9 of the 17 events triggered thesubstorms when MCBLs crossed the magnetosphere, and that the southwardfield in the adjacent sheath region is a necessary condition for these triggeringevents. In addition, the“SF”type MCBLs, which are named by their featuresof the Bz components inside MCBLs and adjacent sheath regions, can easilytrigger the substorms during their passage through the magnetosphere.“SF”type MCBLs have the characteristics that there are sustaining strong southwardmagnetic fields persisting for at least 30 minutes in the adjacent sheath regionsand the polarity of the Bz component inside the MCBLs changes for at least onetime. 7 out of 8 such type MCBL events triggered the substorm expansion phase,which suggests that the“SF”type MCBLs are another important interplanetarydisturbance source of substorms.The global magnetospheric responses to the passage of one MCBL observedby WIND on November 9 2004 are intensively investigated. An intense geo-magnetic storm main phase is driven by the sustaining strong southward mag-netic field within MCBL. A typical magnetospheric substorm is also triggeredby southward turning after strong southward magnetic field lasting for about30 min. Compared with magnetic cloud body and adjacent sheath region, theMCBL is the enhanced dynamic pressure region which compresses the magneto- sphere into the geosynchronous orbit so that many spacecraft are directly exposedin energetic particles in the solar wind. Furthermore, the front boundary of thismagnetic cloud boundary layer is a rapid dynamic pressure pulse structure whichcan cause global responses of the magnetic field, current, energetic particles inthe magnetosphere and the plasma convection in ionosphere. Most front bound-aries of MCBLs (57%) are rapid strong dynamic pressure pulse structures. Thisexample shows the common characteristics of the magnetospheric responses tosuch dynamic pressure pulse structures. In terms of shue (1998) magnetopausemodel and GOES spacecraft observations, we found MCBLs can intensively com-press the magnetosphere due to the strong dynamic pressure. 8 MCBLs out of 35discussed events even compress the magnetopause into the geosynchronous orbitwhich potentially catastrophic in the point of view of space weather.Two particular types of Langmuir wave activities are found within MCBLs:Langmuir waves enhancement in entire region of MCBLs compared with theadjacent magnetic cloud body and sheath region for majority MCBLs and therapid Langmuir waves burst phenomena associated with broad-band ion-acousticwave activities for a few MCBLs. The analysis by using high resolution electrondistribution data indicates that the bump-on-tail instability resulting from theenergetic electron beam with beam velocity Vb～7×103 km/s is responsible forthe rapid Langmuir waves burst.更多还原