太阳风中非线性离子波研究的解析方法Ⅱ

本文从MHD方程组出发，推导了太阳风磁化等离子体中非线性静电离子声波孤立子传播的非线性控制方程，考虑电子捕获效应，使用解析方法得到了扰动位势的精确解，应用得到的精确解讨论了各种等离子体参数情况下孤立子形成的条件。     

太阳风中非线性离子波研究的解析方法Ⅰ

本文从MHD方程组出发，推导了太阳风磁化等离子体中非线性静电离子声波孤立于传播的非线性控制方程，从而得到了扰动位势的解析解。讨论了各种等离子体参数情况下孤立于形成的条件。     

Multi-scale pressure-balanced structures in the solar wind observed by WIND

This work detects multi-scale, from hour to seconds, pressure-balanced structures (PBSs) in the solar wind based on the anti- correlation between the plasma thermal pressure and the magnetic pressure measured by WIND at 1 AU on April 5th, 2001. In our former research based on Cluster measurements, we showed the anti-correlation between the electron density and the magnetic field strength in multi-scales, and we supposed these structures may be pressure-balanced structures. Thus, in this work we aim to prove our speculation by the direct evidence on pressure measurements. Different from our previous work, we apply the WIND measurements this time, for they have both the magnetic pressure and the plasma pressure which Cluster could not offer. We use the wavelet cross-coherence method to analyze the correlation between the plasma pressure (P th ) and the magnetic pressure (P B ), and also the electron density (N e ) and the magnetic field strength (B) on various scales. We observe the anti-correlation between P th and P B distributed at different temporal scales ranging from 1000 s down to 10 s. This result directly indicates the existence of pressure- balanced structures (PBSs) with different sizes in the solar wind. Further, We compare the wavelet cross correlation spectrum of P th -P B and N e -B. We notice that the two spectra are similar in general. Thus this result confirms that the relation between P th -P B and N e -B are consistent with each other in the PBSs we study. Moreover, we compare the power spectrum density (PSD) of relative N e fluctuation with our previous work based on Cluster measurements. The two spectra show similar trend with Komolgorov’s -5/3 as their slopes. This may imply the similarity of the structures observed by both WIND and Cluster spacecrafts. Finally, we discuss the possible formation mechanisms for these multi-scale pressure-balanced structures. Our result is important to support the existence of multi-scale PBSs from one-hour scale down to one-minute, and is helpful to understand the role of compressive fluctuation in the solar wind turbulence dominated by Alfvénic cascading.     

Observations of thermospheric vector wind over Yellow River Station during auroral substorm events

Strong disturbances associated with auroral substorms originate from the ionosphere–magnetosphere owing to the effects of the solar wind, and the wind field in the ionosphere is related to such substorm activity. Here, we describe the analysis of four auroral substorm events, for which we employed an all-sky Fabry–Perot interferometer to observe the two-dimensional horizontal wind field and combined the results with data from an all-sky charge-coupled device imager, a fluxgate magnetometer installed at Yellow River Station, and the Super Dual Auroral Radar Network. The results demonstrate that, during auroral substorms, the vector wind field is related closely to variations in the ion drift and geomagnetic field. Moreover, we observed a changing wind field of approximately 300 m/s in response to variations in the electric and magnetic fields (likely caused by ion drag) and a disturbance of about 200 m/s that we attribute to the interaction of Joule heating and ion drag.     

太阳风中非线性离子波研究的解析方法Ⅲ

本文是文[1]的继继续与深入，基于所导出的太阳风磁化等离子体中非线性静电离子声波孤立子传播的非线性控制方程，考虑电子捕获效应，使用解析方法得到了扰动位势的精确解，并讨论了等离子体参数变化对孤立子形成的影响。与以前结果比较，区别于以前的等离子体背景情况，发现在适当的等离子体背景下控制方程允许有45度附近方向传播的大振幅离子孤立波．但大振幅孤波主要是在垂直于磁场方向如太阳风方向附近形成，这与Heliosl，2卫星观测结果相吻合。     

Magnetic Storm Effects in the Auroral Ionosphere Observed with EISCAT Radar -Two Case Studies

Storm-time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pressure and the IMF Bz component. Strong hard particle precipitation occurred in the initial phase for both storma,associated with high solar wind dynamical pressure. During the recovery phase of the storms, some strong particle precipitation was neither concerned with high solar wind pressure nor southward IMF Bz. Severe negative storm effects depicted by electron density depletion appeared in theF-region during the main and recovery phase of both storms, caused by intensive electric field-related strong Joule/frictional heating when IMF was largely southward. The ion temperature behaved similarly in E- and F-region, but the electron temperature did quite different, with a strong increase in the lower E-region relating to plasma instability excited by strong electric field and a slight decrease in the F-region probably concerning with a cooling process. The field-aligned ion velocity was high and apparently anticorrelated with the northward component of the ion convection velocity.     

等离子体非线性手性:有螺统计及可积结构

在等离子体湍流,如太阳风中产生的螺旋现象和谐振现象具有典型的非线性行为特征.等离子湍流在不同条件下可以有不同的动力学特征,容许存在各种非线性结构.本文主要讨论了等离子湍流中由单手性主导的湍动涡模态和(近)可积结构(如呼吸子):前者可以通过扩展磁流体统计模型的某种统计解来说明;而对于等离子湍流中是否存在可积结构,本文通过对水波、等离子体和玻色-爱因斯坦凝聚的类比分析来加以推断.本文以呼吸子可能有贡献为例说明,将采样频谱中有限频率部分视为线性波的分析不一定准确.     

太阳风离子在月面的反射过程及对月面电场的影响

为探究月表磁异常区对太阳风离子产生反射的原理, 基于嫦娥二号卫星携带太阳风离子探测器的探测数据, 用单粒子模拟法反演太阳风离子运动, 并分析离子入射角和反射角的分布. 实验结果表明： 太阳风离子先被月壤向各方向大范围散射, 再被月面电场向天顶方向加速; 太阳风中, 月面有45~75 V电势, 该正电势对月面反射的太阳风离子有显著影响.     

A comparative study on 3-D solar wind structure observed by Ulysses and MHD simulation

Ulysses, which was a joint NASA/ESA probe to studythe sun and launched in October of 1990, has been thefirst spacecraft to explore the high latitudinal regions ofheliosphere till now[1]. One of its main scientific purposeswas to observe the latitudinal structures of solar wind pa-rameters, such as velocity, density, mass flux, magneticfield, etc.[1―4]. During its first rapid pole-to-pole transitcovering heliographic latitudes of ±80° from September of1994 to June of 1995, Ulysses observ…     

Alfvénic waves with sufficient energy to power the quiet solar corona and fast solar wind

Energy is required to heat the outer solar atmosphere to millions of degrees (refs 1, 2) and to accelerate the solar wind to hundreds of kilometres per second (refs 2-6). Alfvén waves (travelling oscillations of ions and magnetic field) have been invoked as a possible mechanism to transport magneto-convective energy upwards along the Sun's magnetic field lines into the corona. Previous observations of Alfvénic waves in the corona revealed amplitudes far too small (0.5?km?s(-1)) to supply the energy flux (100-200?W?m(-2)) required to drive the fast solar wind or balance the radiative losses of the quiet corona. Here we report observations of the transition region (between the chromosphere and the corona) and of the corona that reveal how Alfvénic motions permeate the dynamic and finely structured outer solar atmosphere. The ubiquitous outward-propagating Alfvénic motions observed have amplitudes of the order of 20?km?s(-1) and periods of the order of 100-500?s throughout the quiescent atmosphere (compatible with recent investigations), and are energetic enough to accelerate the fast solar wind and heat the quiet corona.     

Responses of properties in the plasma sheet and at the geosynchronous orbit to interplanetary shock

On July 22, 2004, the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock front （i.e., southward turning）. When the shock impinged on the magnetosphere, the magnetospheric plasma convection was abruptly enhanced in the central plasma sheet, which was directly observed by both the TC-1 and Cluster spacecraft located in different regions. Simultaneously, the Cluster spacecraft observed that the dawn-to-dusk electric field was abruptly enhanced. The variations of the magnetic field observed by TC-1, Cluster, GOES-10 and GOES-12 that were distributed in different regions in the plasma sheet and at the geosynchronous orbit are obviously distinct. TC-1 observations showed that the magnetic intensity kept almost unchanged and the elevation angle decreased, but the Cluster spacecraft, which was also in the plasma sheet and was further from the equator, observed that the magnetic field was obviously enhanced. Simultaneously, GOES-12 located near the midnight observed that the magnetic intensity sharply increased and the elevation angle decreased, but GOES-10 located in the dawn side observed that the magnetic field was merely compressed with its three components all sharply increasing. Furthermore, the energetic proton and electron fluxes at nearly all channels observed by five LANL satellites located at different magnetic local times （MLTs） all showed impulsive enhancements due to the compression of the shock. The responses of the energetic particles were much evident on the dayside than those on the nightside. Especially the responses near the midnight were rather weak. In this paper, the possible reasonable physical explanation to above observations is also discussed. All the shock-induced responses are the joint effects of the solar wind dynamic pressure pulse and the magnetic field southward turning.     

The correlations of ions density with geomagnetic activity and solar dynamic pressure in cusp region

A statistical study of the properties of ions (O , He and H ) measured by the Cluster-II in cusp region as a function of the solar wind dynamic pressure and geomagnetic index Kp respectively was made dur-ing the summer and fall of 2001-2003. The main results are that: (1) O ion density responds in a sig-nificant way to geomagnetic index Kp, and He ion density is not correlated with geomagnetic index Kp, both of them have a significant positive correlation with solar wind dynamic pressure; (2) H ion density is also observed to increase with solar wind dynamic pressure, and not correlated with geomagnetic index Kp.     

Three-dimensional MHD simulation for the solar wind structure observed by Ulysses

Ulysses has been the first spacecraft to explore the high latitudinal regions of the heliosphere till now. During its first rapid pole-to-pole transit from September 1994 to June 1995, Ulysses observed a fast speed flow with magnitude reaching 700—800 km/s at high latitudinal region except 20°area near the ecliptic plane where the velocity is 300—400 km/s. The observations also showed a sudden jump of the velocity across the two regions. In this note, based on the characteristic and representative observations of the solar magnetic field and K-coronal polarized brightness, the large-scale solar wind structure mentioned above is reproduced by using a three-dimensional MHD model. The numerical results are basically consistent with those of Ulysses observations. Our results also show that the distributions of magnetic field and plasma number density on the solar source surface play an important role in governing this structure. Furthermore, the three-dimensional MHD model used here has a robust ability to simulate this kind of large-scale wind structure.     

Observation and simulation of flux rope structures at the dayside magnetopause

The signatures of flux ropes with obvious core magnetic field are detected by Cluster Ⅱ at the dayside magnetopause during 11:00--11:15 UT on Mar. 2, 2001. The similar characteristics can be found from the magnetic fiel dvariations recorded by the four spacecrafts (Cluster Ⅱ C1--C4). All the three (-/ ) bipolar signatures in the BN component are accompanied with enhancements of BM and magnetic field strength B in the boundary normal coordinates (LMN coordinates). A MHD simulation with two dimensions and three components is performed to explore the reconnection process driven by the incoming flow of solar wind at the dayside magnetopause. The numerical results can illustrate the recurrent formation of magnetic structures with a core magnetic field. The time history of the magnetic field B and three components Bx, By and Bz at a given point of the current sheet can reproduce the observational features of the events mentioned above.     

地球外太空的奥秘:一个巨大的动力辐射区域

2010年,作者在地球外太空发现一个以磁口(cusp)为中心的巨大的动力辐射区域.这个新辐射区域纵深可达10.5Re;在7-8Re高度上,其尺度在纬线和经线方向上可分别达到6Re和＞10Re;当人造卫星穿越该区域时,测得的电磁涨落强度与高能带电粒子强度都有数量级的增加.本文对此进行了综述分析,认为这是太空时代最关键和最...     

Magnetic storm effects in the auroral ionosphere observed with EISCAT radar—Two case studies

Storm-time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pressure and the IMFB _z component. Strong hard particle precipitation occurred in the initial phase for both storms, associated with high solar wind dynamical pressure. During the recovery phase of the storms, some strong particle precipitation was neither concerned with high solar wind pressure nor southward IMFB _z. Severe negative storm effects depicted by electron density depletion appeared in theF-region during the main and recovery phase of both storms, caused by intensive electric field-related strong Joule/frictional heating when IMF was largely southward. The ion temperature behaved similarly inE-andF-region, but the electron temperature did quite different, with a strong increase in the lowerE-region relating to plasma instability excited by strong electric field and a slight decrease in theF-region probably concerning with a cooling process. The field-aligned ion velocity was high and apparently anticorrelated with the northward component of the ion convection velocity. Foundation item: Supported by the National Natural Science Foundation of China (49674241) and the Research Fund for the Doctoral Program of Higher Education Biography: LIU Hui-xin (1974-), female, Ph.D. candidate. Research direction: polar ionospheric behaviors during magnetic storms.     

特高压直流输电线路离子流作用下人体电场效应分析

利用Comsol有限元仿真软件建立特高压直流输电线路和人体的三维模型,主要分析了输电线路产生的静电场和离子流作用下产生的合成电场两种情况下人体电场效应;以及在不同的风速下合成电场对人体电场效应。结果表明:在合成电场下:人体周围、人体内部以及头部的电场最大值均是静电场情况下的2.7倍左右,说明离子流作用下增加的电场是不可忽略的;并且对人体产生更大的作用。不同的风速情况下人体周围、人体内部以及头部的电场是不同的;风速逐渐增大,其电场值逐渐减小,说明在风速作用下,人体周围的离子流发生了变化并减小;且也减小了合成电场的大小,进而对人体的作用也变小。根据国际非电离辐射防护委员会(international commission on non-ionizing radiation protection,ICNIRP)导则限值对比分析,静电场和合成电场下人体内部电场最大值均超过普通民众限值和专业人员限值;而两种情况下的人体头部电场最大值在普通民众限值内,但是对于长期居住在特高压直流输电线路周边的居民会有一定的健康风险;因此在实际建设中需采取一定的降低电磁暴露防护措施或者避免穿越居民区。     

冕流波及其冕震学应用研究综述

本文综述了我们近两年来在冕流波(Streamer Waves)现象研究方面的进展。冕流波是由日冕物质抛射(CME)和冕流结构相互作用所激发的、沿等离子体片向外传播的波动过程,是迄今发现的最大尺度的日冕波动现象。冕流波被解释为由冕流等离子体片片状结构所支持的快体积扭曲模式。基于这一理解,我们结合有关的太阳风速度和数密度方面的观测限制,发展了一种新的冕震学方法,可利用波动参数的观测结果推断冕流等离子体片区域在3-10太阳半径范围的阿尔芬速度和磁场强度的径向剖面。我们还在第23太阳活动周内找到了8例较好的CME-冕流摆动事件,其中5例被认定为冕流波事件。比较这些事件发现,导致冕流波激发的CME都具有很高的喷发速度和角宽度,CME与冕流大都从侧面发生相互作用,且作用的最初位置大都位于C2视场的底部或下方,所有正面CME均伴有耀斑现象。这些共同观测特征为我们理解冕流波的激发条件提供了线索。     

磁暴非线性起源的四种孤子机制

引起磁暴的主要原因是太阳耀斑等产生的太阳风,本文基于磁暴起源的非线性机制,讨论了四种孤子模型：1．已知的Alfven波及相应的变形kd方程。2．Langmuir波及其方程与相关的非线性Schrodinger方程。3．一般的离子声波和磁流体动力学波的kdV方程。4．太阳风粒子密度的非线性Dirac方程,各种原因导致的这些方程都有孤子解。它们的起因和脉冲性可以为磁暴的预报提供一种理论基础。     

Solar wind dynamic pressure and electric field as the main factors controlling Saturn's aurorae

The interaction of the solar wind with Earth's magnetosphere gives rise to the bright polar aurorae and to geomagnetic storms, but the relation between the solar wind and the dynamics of the outer planets' magnetospheres is poorly understood. Jupiter's magnetospheric dynamics and aurorae are dominated by processes internal to the jovian system, whereas Saturn's magnetosphere has generally been considered to have both internal and solar-wind-driven processes. This hypothesis, however, is tentative because of limited simultaneous solar wind and magnetospheric measurements. Here we report solar wind measurements, immediately upstream of Saturn, over a one-month period. When combined with simultaneous ultraviolet imaging we find that, unlike Jupiter, Saturn's aurorae respond strongly to solar wind conditions. But in contrast to Earth, the main controlling factor appears to be solar wind dynamic pressure and electric field, with the orientation of the interplanetary magnetic field playing a much more limited role. Saturn's magnetosphere is, therefore, strongly driven by the solar wind, but the solar wind conditions that drive it differ from those that drive the Earth's magnetosphere.