太阳风高速流能流分布

根据Ylysses观测,比较完整地计算了高纬行星际空间太阳风能流分布．计算表明,行星际空间的高速流能流密度约为2．1×10-3J·m-2·s-1（日心距离r＝1AU）,主要来自于太阳风离子所携带的动能流（占58％）和克服太阳引力的势能流（占39％）．要驱动高速流,需要在日冕底部高速流源区（日心距离r=1Rs）向外输出到太阳风的能流密度为7．1×102J·m-2·s－1·分析表明,由日冕底部向外可能输出两种形式的能流,其中一种具有较短的耗散长度,被耗散在很短的空间区域（～1—2Rs）,使日冕温度迅速提高。另一种储藏在连续向外传播的太阳风中,不断耗散用以加速太阳风（＞2Rs）．     

太阳风质子束流密度的径向变化

利用Helios2飞船的数据,对太阳风速度分布中质子束流部分与整个质子的密度之比随日心距离的变化做了分析.为了排除碰撞因素的影响,有针对性地分析了太阳风高速流(600相似文献   

日冕边界条件与太阳风共转相互作用

本文根据第二十太阳周太阳风数据的统计分析结果,用太阳风二维理想流体模型探讨近太阳区的不同边界条件太阳风与共转相互作用对1AU处太阳风各参数影响,得到共转相互作用不能引起太阳风速度和马赫数的反相扰动,推断在太阳风加速区温度扰动对太阳风的影响最大,而在太阳风传播区速度扰动对太阳风的影响最大.      

一个基于观测的太阳风背景模型

建立由太阳光球磁场和日冕偏振亮度等观测约束的单流体太阳风模型,包括日冕和太阳风的等离子体密度、速度和磁场,温度还有待于以后处理.这里采用高山观测台(HAO)MKⅢ的日冕偏振亮度(pB)在1.36Rs上的观测概图,根据Guhathakurta在1996年发展的日冕电子密度反演模型确定日冕的电子密度分布.同时采用Wilcox太阳观测台(WSO)的光球磁场视向分量的观测概图作为底部边界,根据Zhao等在1994年发展的水平电流-电流片(HCCS)模型得到全球磁场.Phillips在1995年及McComas在2003年分别用Ulysses第一次和第二次跨极飞行的观测发现,归一化到1 AU的太阳风动量流密度除了在10°～30°的纬度范围内略低以外几乎不变.根据这一结论,结合已经得到的密度数据,就可以得到日冕和太阳风的速度.将上面的模型应用于1918卡林顿自转周稳态太阳风的研究,结果与太阳活动极小期的观测基本相符,但是与观测相比较低速高密度区偏大,因此密度模型还有待改进.      

利用多卫星观测CIR事件演变的统计分析

根据2007-2009年STEREO-BEHIND (STB)和ACE卫星的行星际磁场和太阳风数据, 基于冕洞高速流从太阳向外匀速径向传输假设, 讨论了随着STB和ACE卫星与太阳之间的夹角从0°增大至70°时, 冕洞发出的高速太阳风形成的相互作用区(CIR)依次扫过STB和ACE卫星的时间差特性, 并统计分析了两颗卫星观测到的CIR参数的变化特征. 结果显示, 可以利用STB对CIR事件的观测来预测这个CIR事件到达ACE的理论时间, 时间误差均值和最大值分别为0.217d和0.952d, 时间误差的产生与STB和ACE卫星观测到的CIR速度大小的不同有关, 用速度差异矫正后, 时间误差的平均值和最大值可分别减小为0.194d 和0.489d; STB和ACE卫星观测的CIR事件太阳风速度最大值的线性相关系数达到了0.84, STB和ACE卫星观测到的CIR事件对特征物理量中速度、质子温度的变化最小, 而质子密度及总压力的变化最大. 分析结果表明, STB和ACE卫星观测到的CIR事件有很强的相似性, STB卫星的CIR观测可以作为ACE卫星观测CIR事件特征的参考, 从而为地球空间环境扰动预报提供依据.      

日冕三维太阳风模拟

COIN-TVD MHD模型是近年发展起来的能有效实现日冕–行星际三维太阳风模拟的模型.本文利用此模型针对日冕区三维太阳风进行研究,为了模拟日冕太阳风的加热加速,对模型中的体积加热项做了调整.在磁流体模拟中,减小磁场散度的误差是关键问题之一,在调整体积加热项后应用扩散法、八波法、扩散八波法,对2199卡林顿周的背景太阳...     

0.3AU和1AU之间高速太阳风的加速和加热机制

本文应用Helios飞船在0.3AU和1AU之间的高速太阳风质子和磁流涨落观测, 同时考察了包括各种可能的加速和加热效应的高速太阳风动量方程和质子能量方程.分析表明在碰撞为主的等离子体条件下导出的经典粘性系数表式明显地不适用于太阳风等离子体;在0.3AU和1AU之间主要加速力是热压梯度力和Alfven波压力, 背景磁场的洛伦兹力可忽略;在减速方面, 除了太阳重力外, 还需存在其它减速机制, 才能使太阳风动量平衡.看来唯有粘性能同时满足减速和加热这两种要求.      

上游太阳风中高能电子向同步轨道区的传输

通常认为，同步轨道区的电子通量增加是由于磁暴或者上游太阳风高速流的扰动所引起．近来的观测表明，起源于太阳活动的行星际高能电子也是引起同步轨道电子通量增加的重要原因之一．Zhao等在研究2000年7月14日太阳剧烈活动时发现，同步轨道区相对论电子通量巨幅增加时没有观察到上游太阳风高速流的扰动，并且磁暴发生在电子通量事件之后．采用解析磁场模型和实际磁场模型(T96模型)模拟来自太阳的相对论电子在磁尾中的运动特性．计算结果表明，当行星际磁场南向时，进入到磁尾的行星际相对论电子可以从较远的磁尾区域运动到同步轨道区域．这一研究结果从理论上论证了起源于太阳活动的高能电子可以对同步轨道区相对论电子通量的增加产生重要的作用．     

球坐标系六片网格下三维定态行星际太阳风模拟

采用二阶MacCormack差分格式, 利用稳态的磁流体(MHD)方程组在球坐标系六片网格下模拟研究了行星际太阳风. 六片网格系统能有效避免极区奇性和网格收敛性. 迭代按径向方向推进求解, 很大程度上减少了计算量, 节约了计算时间. 内边界条件根据太阳与行星际观测确定, 比较测试了5种内边界条件, 模拟给出了1922卡林顿周的背景太阳风结构. 几种内边界条件所得模拟结果与行星际观测基本吻合. 太阳风速度采用McGregor 等的经验公式给出, 磁场由水平电流片(HCCS)模型得到, 密度和温度分别根据动量守恒和气压守恒得到, 研究表明采用这样的边界条件模拟结果最佳.      

二维太阳风速度结构与日球电流片

本文分析了第1733—1742Carrington周的太阳耀斑、行星际闪烁(IPS)、太阳风及K-日冕资料,对二维太阳风速度结构进行了综合研究。结果表明:速度的大尺度分布、高速区、速度梯度、经度不均匀性和边界形状等方面相对于太阳赤道面都是不对称的;通过对理想的和实际的电流片以及飞船测量的磁场和速度比较,可以看到电流片附近大体上为低速区,但不存在简单的对应关系;扰动太阳风对背景太阳风的二维速度结构有显著的影响;理想电流片与实际电流片之间也存在较大的差距。      

多种观测数据驱动的三维行星际太阳风MHD模拟

三维磁流体力学（MHD）数值模拟是行星际太阳风研究的重要手段.本文发展了一种由多种观测数据驱动的三维行星际太阳风MHD数值模型.模型的计算区域为0.1AU到1AU附近，使用Lax-Friedrich差分格式在六片网格系统中进行数值求解.边界条件中磁场使用GONG台站观测的光球磁图外推获得，密度通过LASCO观测的白光偏振亮度反演得到，速度根据以上两种观测数据并利用一种基于人工神经网络技术（ANN）的方法得到，温度通过自洽方法根据磁场和密度导出.利用该模型模拟了第2062卡灵顿周（CR2062）时期的行星际太阳风，模拟结果显示出丰富的观测特征，并与OMNI以及Ulysses的实际观测值符合得较好.该模型可用于提供接近真实的行星际太阳风，有助于提高空间天气预报的精度.      

Density of discontinuities in the heliosphere

The spatial distribution of MHD discontinuities in the solar wind has been studied, based on the long time observations by the magnetometer onboard Ulysses. We emphasize the critical importance of the method whereby events are selected; some previous work is critically reviewed in this respect. Our analysis supports earlier observations that the density of discontinuities decreases with increasing distance from the Sun. It is suggested, however, that the distribution of the discontinuity normals should be revised, retaining only those discontinuities for further study that have reliable normals. This study shows that the vast majority of well defined discontinuities has a small magnetic field component parallel to the discontinuity normal. Given the large number of discontinuities in the Ulysses data set there is a statistically sufficient number for further study. It is also shown in this paper that for the subset of well defined discontinuities the determination of the normal vector using Minimum Variance Analysis and the cross-product technique are equally valid.     

Exploring the global shock scenario at multiple points between sun and earth: The solar transients launched on January 1 and September 23, 1978

We revisit the transient interplanetary events of January 1 and September 23, 1978. Using in-situ and remote sensing observations at locations widely separated in longitudes and distances from the Sun, we infer that in both cases the overall shock surface had a very fast “nose” region with speeds >900 and >1500 km⁻¹ in the January and September events, respectively, and much slower flank speeds (∼600 km⁻¹ or less), suggesting a shock surface with a strong speed gradient with heliospheric longitude. The shock-nose regions are thus likely efficient acceleration sites of MeV ions, even at 1 AU from the Sun. Our 3D magnetohydrodynamics modeling suggests that a 24° × 24° localized disturbance at 18 solar radii injecting momentum 100 times the background solar wind input over 1 h can produce a disturbance in semi-quantitative agreement with the observed shock arrival time, plasma density and velocity time series in the January 1978 event.     

Radio sounding of the solar wind acceleration region with spacecraft signals

Data from coronal radio-sounding experiments carried out on various interplanetary spacecraft are used to derive the empirical radial dependence of solar wind velocity and density at heliocentric distances from 3 to 60 solar radii for heliolatitudes below 60° and for low solar activity. The radial dependencies of solar wind power and acceleration are derived from these results. Summaries of the radial behavior of characteristic parameters of the solar wind turbulence (e.g., the spectral index and the inner and outer turbulence scales), as well as the fractional density fluctuation, are also presented. These radio-sounding results provide a benchmark for models of the solar wind in its acceleration region.     

Saturn kilometric radiation as a monitor for the solar wind?

Since the Voyager mission it is known that Saturn Kilometric Radiation (SKR) is strongly influenced by external forces, i.e., the solar wind and in particular the solar wind ram pressure. Recent studies using Cassini data essentially confirmed these findings for particular periods during the first Cassini orbit of Saturn. The data coverage of SKR by the Cassini/RPWS experiment for the period of six months prior to Saturn Orbit Insertion (July 1, 2004) is rather continuous, whereas there are gaps in the solar wind plasma data. The strong correlation of SKR with the solar wind may provide an indication on the variations of the solar wind plasma, specifically during the gap periods. These periods lacking solar wind data are substituted by Ulysses solar wind data which have been propagated over ∼4 AU, applying magnetohydrodynamic propagation models. Cross correlation studies showed that Ulysses solar wind data can be taken as a substitute for missing Cassini data. The use of SKR as monitor for solar wind variations is discussed. With the present set of observations the SKR proxy lacks significant reliability.     

In situ observations of magnetic field fluctuations

It is well known that the irregularities of the magnetic field are intimately related to the motion of charged particles. Although transport theories need the spatial and time variations of the magnetic field as input, in situ observations are very limited. Ulysses observations have provided a major step forward by entering the unexplored high latitude regions of the heliosphere, the knowledge of which is vital to interpret particle flux measurements, even at the ecliptic. We analyze the magnetic field data of Ulysses during the mission to study the waves and discontinuities in the heliosphere at different locations, covering a total sunspot cycle. Various tools are employed, including power spectral and structure function analysis. A remarkable difference was found between the fluctuations in the fast and slow solar wind. We argue that the latitudinal extent of the high speed solar wind contributes significantly to the latitudinal variation of the transport parameters, which should also affect the 11 (and 22) year modulation cycle.     

Solar neutron events as a tool to study particle acceleration at the Sun

The Sun provides unique opportunities to study particle acceleration mechanisms using data from detectors placed on the Earth’s surface and on board spacecrafts. Particles may gain high energies by several physical mechanisms. Differentiating between these possibilities is a fundamental problem of cosmic ray physics. Energetic neutrons provide us with information that keeps the signatures of the acceleration site. A summary of some representative solar neutron events observed on the Earth’s surface, including associated X and γ-ray observations from spacecrafts is presented. We discuss evidence of acceleration of particles by the Sun to energies up to several tens of GeV. In addition, a recent solar neutron event that occurred on September 7th 2005 and detected by several observatories at Earth is analyzed in detail.     

磁场强度对日冕定态结构的影响

以二维ＭＨＤ模型及时变方法为基础,内外边界完整的设影特征线边界条件,考察了太阳日冕大气的定态结构随偶极场强度的变化情况。模拟结果表明：随着偶极场强度的增加,磁场对太阳风的约束增强,低纬闭磁场打开程度减少,高纬与低纬区速度差增加,并且在阿尔文马赫数为１的点附近达到最大,速度过度区变陡;随着日心距离增加,低纬区宽度减小,速度过渡区变陡,可定性解释Ｕｌｙｓｓｅｓ飞船的新观测事实。     

Hybrid simulations of the O ion escape from Venus: Influence of the solar wind density and the IMF x component

As an initial effort to study the evolution of the Venus atmosphere, the influence of the solar wind density and the interplanetary magnetic field (IMF) x component (the x-axis points from Venus towards the Sun) on the O⁺ ion escape rate from Venus is investigated using a three-dimensional quasi-neutral hybrid (HYB-Venus) model. The HYB-Venus model is first applied to a case of the high-density (100 cm⁻³) solar wind interaction with Venus selected from the Pioneer Venus Orbiter observations to demonstrate its capability for the study. Two sets of simulations with a wide range of solar wind densities and different IMF x components are then performed. It is found that the O⁺ ion escape rate increases with increasing solar wind density. The O⁺ ion escape rate saturates when the solar wind density becomes high (above 100 cm⁻³). The results also suggest that the IMF x component enhances the O⁺ ion escape rate, given a fixed IMF component perpendicular to the x-axis. Finally, the results imply a higher ion loss rate for early-Venus, when solar conditions were dramatically different.