Simulation of the SMILE Soft X-ray Imager response to a southward interplanetary magnetic field turning

The Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)Soft X-ray Imager(SXI)will shine a spotlight on magnetopause dynamics during magnetic reconnection.We simulate an event with a southward interplanetary magnetic field turning and produce SXI count maps with a 5-minute integration time.By making assumptions about the magnetopause shape,we find the magnetopause standoff distance from the count maps and compare it with the one obtained directly from the magnetohydrodynamic(MHD)simulation.The root mean square deviations between the reconstructed and MHD standoff distances do not exceed 0.2 RE(Earth radius)and the maximal difference equals 0.24 RE during the 25-minute interval around the southward turning.

Global Hybrid Simulation of Magnetic Reconnection in the Magnetosheath

A three-dimensional(3-D)global hybrid simulation is carried out for the generation and structure of magnetic reconnection in the magnetosheath due to interaction of an interplanetary Tangential Discontinuity(TD)with the bow shock and magnetosphere.Runs are performed for solar wind TDs possessing diFFerent initial half-widths.As the TD propagates through the bow shock toward the magnetopause,it is greatly narrowed by a two-step compression processes,a "shock compression" followed by a subsequent "convective compression".In cases with a relatively thin solar wind TD,3-D patchy reconnection is initiated in the transmitted TD,forming magnetosheath flux ropes.Multiple components of ion particles are present in the velocity distribution in the magnetosheath merging,accompanied by ion heating.For cases with a relatively wide initial TD,a dominant single X-line appears in the subsolar magnetosheath after the transmitted TD is narrowed.A shock analysis is performed for the detailed structure of magnetic reconnection in the magnetosheath.Rotational Discontinuity(RD)/TimeDependent Intermediate Shock(TDIS)are found to dominate the reconnection layer,which and some weak slow shocks are responsible for the ion heating and acceleration.

Solar wind transport into magnetosphere caused by magnetic reconnection at high latitude magnetopause during northward IMF: Cluster-DSP conjunction observations

An event of Cluster-Double Star conjunction observations of magnetic reconnec-tion at high latitude magnetopause nightside of both cusps and solar wind trans-port into magnetosphere caused by such reconnection process has been investi-gated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause nightside of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: (1) during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; (2) the direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; (3) reconnection can heat plasma more in par-allel direction than in perpendicular direction, to a level of about 4 keV; (4) with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; (5) by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magneto-sphere. This event presents further observational evidence for magnetic reconnec-tion at high latitude magnetopause nightside of both cusps as an important mech-anism of sol-ar w-ind transport into magnetosphere.

Simulation of turbulent magnetic reconnection in the smallscale solar wind

Some observational examples for the possible occurrence of the turbulent magnetic reconnection in the solar wind are found by analysing Helios spacecraft’s high resolution data. The phenomena of turbulent magnetic reconnections in small scale solar wind are simulated by introducing a third order accuracy upwind compact difference scheme to the compressible two-dimensional MHD flow. Numerical results verify that the turbulent magnetic reconnection process could occur in small scale interplanetary solar wind, which is a basic feature characterizing the magnetic reconnection in high-magnetic Replolds number (R(inM) = 2 000-10 000) solar wind. The configurations of the magnetic reconnection could evolve from a single X-line to a multiple X-line reconnection, exhibiting a complex picture of the formation, merging and evolution of magnetic islands, and finally the magnetic reconnection would evolve into a low-energy state. Its life-span of evolution is about one hour order of magnitude. Various magnetic and flow signatures are recorded in the numerical test for different evolution stages and along different crossing paths, which could in principle explain and confirm the observational samples from the Helios spacecraft. These results are helpful for revealing the basic physical processes in the solar wind turbulence.

磁云传播的动力学演化过程研究进展

磁云因其独特的磁场结构经常是重大灾害性空间天气的驱动源.近来从磁云的边界层结构、环向通量、大尺度结构等方面关于磁云传播的动力学演化过程的研究取得了一些进展.在磁云边界存在一个由于磁场重联而形成的边界层结构.在磁云传播过程中,这种发生在边界处的磁场重联可能会把磁云的磁场剥蚀掉,进而引起其磁通量绳结构环向通量的减少以及不对称.在磁云内部,经常会观测到多个子通量绳结构.这些特性各异的子通量绳可以通过磁场重联而合并,进而引起磁云磁结构的改变.关于磁云大尺度磁场拓扑位形的演化机制,除了较早提出的交换重联外,目前的研究表明在行星际空间中,磁云边界处的重联过程也可以将磁云闭合或半开放的磁场线打开或断开.尽管在相关研究中已经取得了较大进展,但关于磁云传播的动力学演化过程还有许多问题尚不清楚.在行星际小尺度磁通量绳边界也发现了边界层结构,那么磁云是否会因剥蚀而成为小尺度通量绳?磁云内子通量绳结构在相互作用中会不会引起某些不稳定性而导致整个通量绳系统的崩溃?这些问题的解决还有待于进一步的理论、观测和数值模拟研究.

地球远磁尾中的磁场重联——(Ⅱ)局部驱动力的影响

基于可压缩磁流体动力学模型,数值研究了由太阳风引起的局部驱动力对地球远磁尾中磁场重联的影响.结果表明,在远磁尾等离子体片中将发生强迫磁场重联,并形成磁岛和等离子体团.形成磁岛的特征时间很大于流动撕裂模不稳定性引起磁岛非线性饱和的特征时间.磁岛宽度随着磁Reynolds数S的增大而减小,随着尾瓣中等离子体压力与磁压之比值β_∞的降低而减小.认为太阳风引起的局部驱动力对地球远磁尾等离子体片中磁场重联的影响,可能不如流动撕裂模不稳定性那样显著.

EISCAT雷达观测到的极区电离层等离子体反常对流

综合分析EISCAT雷达与卫星当地测量数据 ,并利用磁层磁场模式对磁力线进行追踪 ,研究了发生在极光椭圆朝极盖边界附近电离层中 ,一例反常的背离太阳流动的强等离子体对流事件 ,及相关的太阳风 -磁层 -电离层耦合过程 .结果表明 ,磁暴期间IMFBz 指向南时观测到这一反常高速对流 ,及其相应的等离子体性态特征 。

Magnetic reconnection structures in the boundary layer of an interplanetary magnetic cloud

An interplanetary magnetic diffusion region was detected by WIND during 0735-0850 UT on May 15, 1997 when the front boundary layer of a magnetic cloud passed through the spacecraft about 190 earth radii upstream of the earth. The main signals of magnetic reconnection processes are: (i) Flow reversal was detected at about 0810 UT. The counter-streaming flows have the speeds of about 65 and 41 km/s, respectively, with an angle of about 140 degree between them. (ii) Hall magnetic field was detected. The Hall fields ?By and +By, perpendicular to the X-Z plane, with their magnitude up to ～7.0 nT, are superposed upon a guide field about 12 nT. (iii) Alfvenic fluctuations are obviously intensified inside the reconnection region; at the front boundary of the reconnection region, a slow-mode-like discontinuity was detected. (iv) Ions are heated intensively inside the reconnection region, with their temperature three times higher than that ahead of the boundary layer; electrons are also heated, with a little enhancement in their temperature. The above observations indicate that magnetic reconnection processes could take place in interplanetary space. Keywords solar wind - interplanetary magnetic clouds - magnetic reconnection

太阳风中小尺度磁通量管边界重联的统计研究

通过对WIND卫星1995—2005年的数据,利用程序筛选及人工识别两种不同方法确定的小尺度磁通量管进行比较,发现程序筛选法中41%的小尺度磁通量管有边界重联现象,与人工识别法确定的小尺度磁通量管的统计结果接近;通过人工识别和程序筛选两种方法确定的小尺度磁通量管的边界重联特征,包括磁场剪切角、磁场强度以及重联耗散区的持续时间等,也具有相同的统计趋势.结果表明,两种方法确定的小尺度磁通量管在重联特性上没有本质区别,因此采用这两种方法得到的数据作为样本来统计小尺度磁通量管前后边界重联事件.本文共确定了71个重联事件,统计结果显示有50个(70%)重联耗散区磁场的减小超过20%,47个(66%)磁场剪切角大于90°;多数重联事件的磁场剪切角大于90°,表明小尺度磁通量管边界中主要发生的是反平行重联.将小尺度磁通量管的前后边界重联分开进行统计,结果显示其前后边界重联的特征是相似的,与磁云前后边界存在差异的性质不同,这意味着太阳风中的小尺度磁通量管并不具有磁云这种大尺度磁通量管的膨胀特征.

行星际磁重联的观测与研究

近50多年来,磁重联的概念越来越多地被应用到空间物理领域中,用以解释地球磁层、太阳大气以及行星际空间等环境下发生的爆发性物理现象。从观测方面对当前行星际磁重联研究的现状做了概述。首先介绍了磁重联的理论模型,接着回顾了行星际磁重联观测研究的历史,随后介绍了当前行星际磁重联的证认方法及磁云边界层磁重联在观测上的研究现状及存在的问题,然后分别介绍了近些年来,单飞船及多飞船联合观测的结果,最后总结了行星际磁重联现象的特点以及一些尚未解决的问题。

Solar wind entry via flux tube into magnetosphere observed by Cluster measurements at dayside magnetopause during southward IMF

By analyzing hot ion and electron parameters together with magnetic field measurements from Cluster, an event of magnetopause crossing of the spacecraft has been investigated. At the latitude of about 40° and magnetic local time (MLT) of 13:20 during the southward interplanetary magnetic field (IMF), a transition layer was observed, with the magnetospheric field configuration and cold dense plasma features of the magnetosheath. The particle energy-time spectrograms inside the layer were similar to but still a little different from those in the magnetosheath, obviously indicating the solar wind entry into the magnetosphere. The direction and magnitude of the accelerated ion flow implied that reconnection might possibly cause such a solar wind entry phenomenon. The bipolar signature of the normal magnetic component BN in magnetopause coordinates further supported happening of reconnection there. The solar wind plasma flowed toward the magnetopause and entered the magnetosphere along the reconnected flux tube. The magnetospheric branch of the reconnected flux tube was still inside the magnetosphere after reconnection and supplied the path for the solar wind entry into the dayside magnetosphere. The case analysis gives observational evidence and more details of how the reconnection process at the dayside low latitude magnetopause caused the solar wind entry into the magnetosphere.

Magnetospheric Boundary Layer Structure and Dynamics as Seen From Cluster and Double Star Measurements

In this review,we discuss the structure and dynamics of the magnetospheric LowLatitude Boundary Layer(LLBL)based on recent results from multi-satellite missions Cluster and Double Star.This boundary layer,adjacent to the magnetopause on the magnetospheric side,usually consists of a mixture of plasma of magnetospheric and magnetosheath origins,and plays an important role in the transfer of mass and energy from the solar wind into the magnetosphere and subsequent magnetospheric dynamics.During southward Interplanetary Magnetic Field(IMF)conditions,this boundary layer is generally considered to be formed as a result of the reconnection process between the IMF and magnetospheric magnetic field lines at the dayside magnetopause,and the structure and plasma properties inside the LLBL can be understood in terms of the time history since the reconnection process.During northward IMF conditions,the LLBL is usually thicker,and has more complex structure and topology.Recent observations confirm that the LLBL observed at the dayside can be formed by single lobe reconnection,dual lobe reconnection,or by sequential dual lobe reconnection,as well as partially by localized cross-field diffusion.The LLBL magnetic topology and plasma signatures inside the different sub-layers formed by these processes are discussed in this review.The role of the Kelvin-Helmholtz instability in the formation of the LLBL at the flank magnetopause is also discussed.Overall,we conclude that the LLBL observed at the flanks can be formed by the combination of processes,(dual)lobe reconnection and plasma mixing due to non-linear Kelvin-Helmholtz waves.

New progress of Double Star-Cluster joint exploration and study

The magnetic reconnection of magnetosphere and the magnetospheric space storms (including magnetospheric substorm, magnetic storm, magnetospheric particle storm) has long been one of the most challenging subjects in the so-lar-terrestrial physics. The reconnection mechanism and global triggering process of the magnetospheric space storms are still unclear up to now. Based on the Double Star Program (DSP) and Cluster joint measurements, we have observed the solar wind density hole, the component magnetic field reconnection in the magnetopause, the structures of magnetic storm ring current, global and multi-scale driven and triggering processes of magnetospheric substorm. In this paper we will briefly introduce these results.

A review of recent studies on coronal dynamics: Streamers, coronal mass ejections, and their interactions

In this article I present a review of recent studies on coronal dynamics, including research progresses on the physics of coronal streamers that are the largest structure in the corona, physics of coronal mass ejections (CMEs) that may cause a global disturbance to the corona, as well as physics of CME-streamer interactions. The following topics will be discussed in depth: (1) acceleration of the slow wind flowing around the streamer considering the effect of magnetic flux tube curvature; (2) physical mechanism accounting for persistent releases of streamer blobs and diagnostic results on the temporal variability of the slow wind speed with such events; (3) force balance analysis and energy release mechanism of CMEs with a flux rope magnetohydrodynamic model; (4) statistical studies on magnetic islands along the coronal-ray structure behind a CME and the first observation of magnetic island coalescence with associated electron acceleration; and (5) white light and radio manifestations of CME-streamer interactions. These studies shed new light on the physics of coronal streamers, the acceleration of the slow wind, the physics of solar eruptions, the physics of magnetic reconnection and associated electron acceleration, the large-scale coronal wave phenomenon, as well as the physics accounting for CME shock-induced type II radio bursts.