通过建立自然坐标系确定磁云边界方法的探讨

通常卫星探测到的关于行星际空间磁场的数据都是在GSE坐标系(地心太阳黄道坐标系)里表示出来的．磁云是行星际日冕物质抛射事件的一个重要子集,它们的边界认证一直是磁云研究中感兴趣的问题之一．通过讨论坐标系转换确定磁云边界的方法,由磁云的磁通量管特征建立磁云自然坐标系,然后把行星际空间的磁场转换到磁云自然坐标系里．在磁云自然坐标系里磁云作为一个磁通量管的结构能够清晰地显示出来．结合磁云的等离子体特征就可以比较容易地把磁云和背景太阳风分辨出来,即确定了磁云的边界．     

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.     

空间日冕观测进展

近年来Ｙｏｈｋｏｎ,ＳＯＨＯ和Ｕｌｙｓｓｅｓ等飞船的上天大大提高了日冕观测的范围和精度。如ＳＯＨＯ上的ＬＡＳＣＯ使日冕可观测范围扩展到１．１－３０Ｒ并有分光能力;Ｕｌｙｓｓｅｓ则可以取得黄道面外各纬度处的太阳风实地观测数据。这些资料为日冕物态研究提供了大量有用信息：Ｙｏｈｋｏｈ的软Ｘ射线观测发现了大尺度冕环重联的证据;     

日冕物质抛射

评述了近几年来冕物抛射研究的新进展,包括Ｙｏｈｋｏｈ、ＳＯＨＯ、ＷＩＮＤ、Ｕｌｙｓｓｅｓ、Ｇｅｏｔａｉｌ和ＰＯＬＡＲ等飞船最近取得的观测结果,并由典型事件探计日冕物质抛射与太阳活动、行星际扰动和地球空间环境变化之间的关系。进而介绍日冕物质抛射形成机制和传播过程的主要理论模型和数值模拟结果,提出今后日冕物质抛射研究中一些值得注意的问题。     

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.     

行星际磁通量绳尺度的幂律谱分布

利用最小二乘法拟合了1995年1月至2001年9月Wind卫星观测到的行星际磁通量绳。根据拟合所得磁通量绳的直径,分析了行星际磁通量绳在这段时间内的发生率随磁通量绳直径D变化的关系,发现磁通量绳的发生率P(D)随直径D的变化可近似以幂律形式表示为:P(D)≈64D-0.768。行星际磁通量绳的发生率相对其直径的幂律分布表明所有行星际磁通量绳很可能是同一类现象且有共同的源,即它们都是太阳上日冕物质抛射的行星际对应物,只不过小尺度的磁通量绳对应较小的日冕物质抛射。最后,对行星际磁通量绳、日冕物质抛射和太阳耀斑的可能关系做了讨论。     

日冕和行星际空间辐射机制

In this paper, the new models of the generation mechanism of the observed solar corona type II radio burst and the interplanetary type III radio emission are presented. The synchrotron-maser theory of type II solar is proposed. The electrostatic waves with frequencies close to twice the plasma frequency can be excited,and can naturclly change into electromagnetic waves when they propagate in a plasma in which the plasma density decreases spatially.Emission of electromagnetic waves with frequencies close to the plasma frequency and/or its second harmonic have been frequently observed in solar corona and interplanetary space. In the pass a number of theories have been suggested to explain the generation mechanism of the observed radiation.     

中尺度磁绳结构的行星际观测

由磁绳结构主导、平均尺度约二、三十个小时的行星际磁云是日冕物质抛射在行星际膨胀、传播的体现。最近，Moldwin等人报道在太阳风中还观测到一些尺度在几十分钟的小尺度磁绳结构，并认为太阳风中的磁绳结构在尺度分布上可能具有双峰特征，在全面检视了WIND卫星(1995年-2000年)和ACE卫星(1998年-2000年)的观测资料后，发现了在行星际太阳风中一些尺度为几个小时的中尺度磁绳结构，利用初步整理的其中28个中尺度磁绳结构事件，认为太阳风中的磁绳结构在尺度分布上可能是连续的，这对行星际太阳风中磁绳结构物理起源的研究可能提出重要的物理限制。     

漫谈粒子和宇宙（七）：太阳等离子体漫谈

等离子体天体物理学是研究宇宙间最广泛存在的物质状态规律的科学。太阳最外层大气日冕的温度约达到一二百万度,高温下的太阳物质呈现高温等离子体状态;地球电离层是处于温度相对较低的等离子体状态。人造地球卫星以及太阳系深空探测表明,行星际空间并非真空,而是存在着来自日冕的连续微粒辐射——太阳风,它是因日冕膨胀而形成的连续向外发出的、伸向遥远的太阳系空间的等离子体流。等离子体物理过程在许多日地物理现象中,诸如太阳耀斑、黑子、日冕物质抛射、日珥、太阳风等研究中起重要作用,探索日地空间物理过程的规律是认识与之有关的空间现象的关键。     

Prediction of Space Weather Using an Asymmetric Cone Model for Halo CMEs

Halo coronal mass ejections (HCMEs) are responsible of the most severe geomagnetic storms. A prediction of their geoeffectiveness and travel time to Earth’s vicinity is crucial to forecast space weather. Unfortunately, coronagraphic observations are subjected to projection effects and do not provide true characteristics of CMEs. Recently, Michalek (Solar Phys. 237, 101, 2006) developed an asymmetric cone model to obtain the space speed, width, and source location of HCMEs. We applied this technique to obtain the parameters of all front-sided HCMEs observed by the SOHO/LASCO experiment during a period from the beginning of 2001 until the end of 2002 (solar cycle 23). These parameters were applied for space weather forecasting. Our study finds that the space speeds are strongly correlated with the travel times of HCMEs to Earth’s vicinity and with the magnitudes related to geomagnetic disturbances.     

SWAN: A study of Solar Wind Anisotropies on SOHO with Lyman alpha sky mapping

On board the SOHO spacecraft poised at L1 Lagrange point, the SWAN instrument is mainly devoted to the measurement of large scale structures of the solar wind, and in particular the distribution with heliographic latitude of the solar wind mass flux. This is obtained from an intensity map of the sky Lyman emission, which reflects the shape of the ionization cavity carved in the flow of interstellar H atoms by the solar wind. The methodology, inversion procedure and related complications are described. The subject of latitude variation of the solar wind is shortly reviewed: earlier Lyman results from Prognoz in 1976 are confirmed by Ulysses. The importance of the actual value of the solar wind mass flux for the equation of dynamics in a polar coronal hole is stressed. The instrument is composed of one electronic unit commanding two identical Sensor Units, each of them allowing to map a full hemisphere with a resolution of 1°, thanks to a two-mirrors periscope system. The design is described in some details, and the rationale for choice between several variants are discussed. A hydrogen absorption cell is used to measure the shape of the interplanetary Lyman line and other Lyman emissions. Other types of observations are also discussed : the geocorona, comets (old and new), the solar corona, and a possible signature of the heliopause. The connexion with some other SOHO instruments, in particular LASCO, UVCS, SUMER, is briefly discussed.     

Waiting Time Distribution of Coronal Mass Ejections

Inspired by the finding that the large waiting time of solar flares presents a power-law distribution, we investigate the waiting time distribution (WTD) of coronal mass ejections (CMEs). SOHO/LASCO CME observations from 1996 to 2003 are used in this study. It is shown that the observed CMEs have a similar power-law behavior to the flares, with an almost identical power-law index. This strongly supports the viewpoint that solar flares and CMEs are different manifestations of the same physical process. We have also investigated separately the WTDs of fast-type and slow-type CMEs and found that their indices are identical, which imply that both types of CME may originate from the same physical mechanism.     

The dynamics of velocity fluctuations in the solar wind – I. Coronal mass ejections

In this paper we present a simple, analytic model for the dynamical evolution of supersonic velocity fluctuations at the base of the ambient solar wind. These fluctuations result in the formation of dense working surfaces that travel down the wind. It is shown how the initial parameters of the fluctuations (velocity, density and duration) are related to the characteristics of the working surfaces far from the Sun (for instance at the Earth). We apply the model to the evolution of the coronal mass ejections in the IP medium, finding that the model is in good agreement with satellite observations of these phenomena, thus providing physical insight into their dynamical evolution. Our model may contribute to future 'space weather forecasting' on the Earth, based on detailed satellite monitoring of the solar corona.     

行星际闪烁(IPS)单站观测对太阳风速度的诊断

借助于弱散射理论和模式拟合方法，单站行星际闪烁观测可以诊断太阳风速度，本文讨论了太阳风参数和射电源角尺度对闪烁谱的影响，以及太阳风速度的积分效应，结果表明，闪烁谱的特征是与视线上距太阳最近处的太阳风速度直接相关的。     

地磁感应电流行星际起因及其电网效应的初步分析

利用2004至2005年在广东岭澳监测到的地磁感应电流(Geomagneticily Induced Current,GIC)事件,分析了其对应的太阳驱动源和行星际太阳风结构,重点研究了GIC事件的行星际起因及效应,并利用小波变换对强GIC事件进行频谱分析.研究结果表明:(1)绝大多数GIC事件由全晕状日冕物质抛射(Coronal Mass Ejection,CME)主导驱动,其行星际起因则包含激波鞘层、磁云或多重行星际太阳风结构.(2)针对强GIC事件(2004-11-09)发现GIC事件强度前期的变化与磁云边界层相关,而后期的强度变化主要是磁云本身引起.(3)GIC在电力系统中相当于准直流,其能量体现在两个时间段,前期较弱属于脉冲类型,后期强度较大;关于GIC引起变压器温升的累积时间,相比GIC事件的前期,后期的累积时间更长,对电力系统以及设备的影响更为严重.(4)通过相关性分析,SYM-H指数和dBx/dt与GIC的相关性明显强于其它地磁指数与GIC的相关性.     

Are CME-Related Dimmings Always a Simple Signature of Interplanetary Magnetic Cloud Footpoints?

Coronal dimmings are often present on both sides of erupting magnetic configurations. It has been suggested that dimmings mark the location of the footpoints of ejected flux ropes and, thus, their magnetic flux can be used as a proxy for the flux involved in the ejection. If so, this quantity can be compared to the flux in the associated interplanetary magnetic cloud to find clues about the origin of the ejected flux rope. In the context of this physical interpretation, we analyze the event, flare, and coronal mass ejection (CME) that occurred in active region 10486 on 28 October 2003. The CME on this day is associated with large-scale dimmings, located on either side of the main flaring region. We combine SOHO/Extreme Ultraviolet Imaging Telescope data and Michelson Doppler Imager magnetic maps to identify and measure the flux in the dimming regions. We model the associated cloud and compute its magnetic flux using in situ observations from the Magnetometer Instrument and the Solar Wind Electron Proton Alpha Monitor aboard the Advance Composition Explorer. We find that the magnetic fluxes of the dimmings and magnetic cloud are incompatible, in contrast to what has been found in previous studies. We conclude that, in certain cases, especially in large-scale events and eruptions that occur in regions that are not isolated from other flux concentrations, the interpretation of dimmings requires a deeper analysis of the global magnetic configuration, since at least a fraction of the dimmed regions is formed by reconnection between the erupting field and the surrounding magnetic structures.     

太阳日冕物质抛射特性的模糊分类研究

应用模糊集理论对日冕物质抛射（CME）特性进行分类研究，根据CME形态特性和特征因子之间的关系，重点阐明构造每个特性的隶属函数和确定权重因子的基本原理与方法，通过数据处理，对CME特性进行聚类分析，结果表明，模糊分类方法要优于传统的统计分析，对于CME特性按重要性分类，为空间环境的预报提供了一个具有实用价值的方法。