1998年5月日冕三维结构的数值模拟

采用三维理想磙流体力学（MHD）模式，内边界条件把二维投影特征线边界方法推广应用到三维计算，有效地稳定了数值计算并保证稳态解的自洽性；初始猜解磁场由1935卡林顿周光球磁场观测数据得到，这样计算得到的1998年5月份期间日冕三维结构比较符合实际，计算结果表明：（1）计算得到的源表面非径向磁场量值在磁中性线附近不超过2μT，表明源表面磁场基本径向。（2）模拟得到的源表面径向磁场量值除了在磁中性线附近的区域外变化不大，这和观测一致。（3）由源表面磁场按平方反比的规律计算出1AU处磁场量值更接近观测值。（4）计算得到的日冕结构和观测定性一致，三维数值模拟结果表明，日冕的三维大尺度背景结构主要是由磁场决定的，在闭磁场处或者电流片附近，太阳风的密度高，速度低；在开场区，太阳风的密度低，速度高。     

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.      

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.      

基于MapReduce的CME参数识别模型并行计算技术

日冕物质抛射（Coronal Mass Ejection,CME）参数识别模型是太阳风预报过程的重要组成部分.在空间环境预报业务中,为提高太阳风预报的准确率,需要提高CME参数识别的精度.模型以计算任务串行的方式运行,运算效率低导致模型运算时间长,不能满足这种需求.CME参数识别模型的物理运算过程相互不独立,其在单节点上的运行方式不能满足并行化要求.基于MapReduce的并行计算框架,改进了CME参数识别模型的计算流程,提出CDMR（CME detection under MapReduce）方法,实现了CME参数识别模型的并行计算,并对比分析CME参数识别模型在串行计算和MapReduce并行计算下的运行时间,提高了模型的识别精度和计算效率.      

1998年5月2日日冕亮度观测图的数值研究

采用数值手段模拟了1998年5月2日日冕亮度观测图，计算模式改进为球坐标下系下特殊的二维理想磁流体（MHD）模型，即把（r,φ）坐标建立在SOHO观测日冕亮度的子午面上，消除了子午面极区的几何奇异性，根据SOHD日冕观测布置磁极子得到初始磁场位形，内边界条件采用自治的投影特征边界条件，计算迭代出稳态的多 磁场结构，得得到了与观测基本一致的亮度图，计算结果表明在太阳表面附近磁场位形对太阳凤等离子参数分布起控制作用。     

基于CPU/GPU的日冕偏振亮度并行计算模型

三维磁流体力学(MHD)数值模拟是用来研究日冕和太阳风最常用的方法之一, 其中将计算得到的日冕电子数密度转化为日冕偏振亮度(Polarization Brightness, PB)是与观测对比的重要方法. 由于待转换电子数据网格密度、PB数据网格密度和计算模型的复杂度, 使得日冕偏振亮度的计算比较耗时, 利用单CPU计算无法达到近实时转换日冕偏振亮度的要求, 从而影响了数值模拟的验证效率. 本文在CPU/GPU环境下, 利用CUDA编程技术, 提出了一个日冕偏振亮度并行计算模型. 实验结果表明, 该模型比CPU上的串行模型计算速度提高了31.86倍, 达到了近实时模拟与观测数据比对的计算要求.      

太阳风对流效应对CME渡越时间的影响

基于Gopalswamy预报日冕物质抛射（CME）渡越时间的经验模型,选取1996-2007年间52个与地磁效应Dst<-50nT相关的CME事件以及10个引起特大磁暴（Dst<-200nT）的CME事件,结合ACE卫星在1AU处的太阳风观测资料,分析背景太阳风对流效应对CME到达1AU处渡越时间预报的影响.对于52个CME事件,考虑太阳风对流效应的影响后,预报的标准偏差由16.5h降为11.4h,修正后的误差分布趋向于高斯分布,并且68%事件的预报误差小于15h.对于10个引起特大磁暴的CME事件,考虑太阳风对流效应的影响后,预报的标准偏差由10.6h降低到6.5h,其中6个事件的预报误差小于5h.研究结果表明,对于CME事件,考虑背景太阳风对流效应的影响可以降低预报CME渡越时间的标准偏差,说明太阳风对流效应对预报CME事件渡越时间具有重要作用.      

SIP-AMR-CESE模式对CR2055背景太阳风的模拟

使用三维太阳行星际自适应网格守恒元解元太阳风模型（SIP-AMR-CESE MHD）,模拟从太阳表面到地球轨道附近的太阳风.该模型使用六片网格技术,同时利用PARAMESH软件包实现网格自适应.在该模型的基础上,通过增加广义拉格朗日乘子（GLM）磁场散度误差消去方法,完善网格加密放粗判据,微调加速加热形式等方法,使模拟结果与观测更好地符合.另外,通过控制不同时刻的计算区域,显著提高了模型的计算效率.在此基础上,给出了模型改进后模拟得到的CR2055太阳风稳态解与观测的对比分析.      

两冕流间CME事件数值模拟的改进

通过偶极子场和六极子场适当叠加，改进猜解磁场，使猜解磁场在太阳南北极符号相反，然后采用理想磁流体力学方程组(MHD)，由猜解磁场与太阳风流动相互作用计算出稳态自洽解，得到定性上与观测比较接近的具有两个冕流的背景结构．在两个冕流间采用具有同心圆磁场位形的触发模型触发CME事件，研究CME的日冕传播特征．模拟结果表明，CME被约束在两冕流间传播，CME闭磁场位形和磁云横截面磁场位形相似，可以解释1AU处观测磁云的部分特征；在CME附近，存在压力和Lorentz力起主要作用的区域，这可以为分析1AU处CME事件的观测数据提供帮助．     

磁云边界层中的复合重联喷流观测分析

太阳风中的磁场重联通常与行星际日冕物质抛射有关.本文分析了1995年10月18日WIND飞船观测到的一例磁云前边界层中的复合重联喷流事件.该复合排空区由相邻两个不同方向的喷流构成，这两个喷流分别经过Walén关系的证认，符合行星际磁场重联排空区等离子体喷流的特征.结果表明，在磁云前端可能存在众多重联点，从而将磁云本体的磁场剥离，形成比单一重联喷流区更复杂的三维边界层结构.磁云边界层中可能发生多点多次重联，从而不表现出单点重联的排空区特征，这可能是行星际磁场重联排空区较少在ICME前端被观测到的原因之一.      

Relation between solar wind velocity and properties of its source region

Different kinds of coronal holes are sources of different kind of solar winds. A successful solar wind acceleration model should be able to explain all those solar winds. For the modeling it is important to find a universal relation between the solar wind physical parameters, such as velocity, and coronal physical parameters such as magnetic field energy. To clarify the physical parameters which control the solar wind velocity, we have studied the relation between solar wind velocity and properties of its source region such as photospheric/coronal magnetic field and the size of each coronal hole during the solar minimum. The solar wind velocity structures were derived by using interplanetary scintillation tomography obtained at Solar-Terrestrial Environment Laboratory, Japan. Potential magnetic fields were calculated to identify the source region of the solar wind. HeI 1083 nm absorption line maps obtained at Kitt Peak National Solar Observatory were used to identify coronal holes. As a result, we found a relation during solar minimum between the solar wind velocity and the coronal magnetic condition which is applicable to different kind of solar winds from different kind of coronal holes.     

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...     

Evolution of solar wind structures from 0.72 to 1 AU

Understanding the evolution of solar wind structures in the inner heliosphere as they approach the Earth is important to space weather prediction. From the in situ solar wind plasma and magnetic field measurements of Pioneer Venus Orbiter (PVO) at 0.72 AU (1979–1988), and of Wind/Advanced Composition Explorer (ACE) missions at 1 AU (1995–2004), we identify and characterize two major solar wind structures, stream interaction regions (SIRs) and interplanetary coronal mass ejections (ICMEs). The average percentage of SIRs occurring with shocks increases significantly from 3% to 24% as they evolve from 0.72 to 1 AU. The average occurrence rate, radial extent, and bulk velocity variation of SIRs do not change from 0.72 to 1 AU, while peak pressure and magnetic field strength both decrease with the radial evolution of SIRs. Within the 0.28 AU distance from the orbit of Venus to that of Earth, the average fraction of ICMEs with shocks increases from 49% to 66%, and the typical radial extent of ICMEs expands by about a fraction of 1.4, with peak pressure and magnetic field strength decreasing significantly. The mean occurrence rate and expansion velocity of ICMEs do not change from 0.72 to 1 AU.     

Characterization of the slow wind in the outer corona

The study concerns the streamer belt observed at high spectral resolution during the minimum of solar cycle 23 with the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO. On the basis of a spectroscopic analysis of the O VI doublet, the solar wind plasma parameters are inferred in the extended corona. The analysis accounts for the coronal magnetic topology, extrapolated through a 3D magneto-hydrodynamic model, in order to define the streamer boundary and to analyse the edges of coronal holes. The results of the analysis allow an accurate identification of the source regions of the slow coronal wind that are confirmed to be along the streamer boundary in the open magnetic field region.     

Synoptic magnetic field in cycle 23 and in the beginning of the cycle 24

The SOHO/MDI data provide the uniform time series of the synoptic magnetic maps which cover the period of the cycle 23 and the beginning of the cycle 24. It is very interesting period because of the long and deep solar minimum between the cycles 23 and 24. Synoptic structure of the solar magnetic field shows variability during solar cycles. It is known that the magnetic activity contributes to the solar irradiance. The axisymmetrical distribution of the magnetic flux (Fig. 3c) is closely associated with the ‘butterfly’ diagram in the EUV emission (Benevolenskaya et al., 2001). And, also, the magnetic field (B_∥) shows the non-uniform distributions of the solar activity with longitude, so-called ‘active zones’, and ‘coronal holes’ in the mid-latitude. Polar coronal holes are forming after the solar maxima and they persist during the solar minima. SOHO/EIT data in the emission of Fe XII (195 Å) could be a proxy for the coronal holes tracking. The active longitudinal zones or active longitude exist due to the reappearance of the activity and it is clearly seen in the synoptic structure of the solar cycle. On the descending branch of the solar cycle 23 active zones are less pronounced comparing with previous cycles 20, 21 and 22. Moreover, the weak polar magnetic field precedes the long and deep solar minimum. In this paper we have discussed the development of solar cycles 23 and 24 in details.     

Evolution of Dst index,cosmic rays and global temperature during solar cycles 20–23

We have studied conditions in interplanetary space, which can have an influence on galactic cosmic ray (CR) and climate change. In this connection the solar wind and interplanetary magnetic field parameters and cosmic ray variations have been compared with geomagnetic activity represented by the equatorial Dst index from the beginning 1965 to the end of 2012. Dst index is commonly used as the solar wind–magnetosphere–ionosphere interaction characteristic. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Because of this CMEs, coronal holes and the solar spot numbers (SSN) do not adequately reflect peculiarities concerned with the solar wind arrival to 1 AU. Therefore, the geomagnetic indices have some inestimable advantage as continuous series other the irregular solar wind measurements. We have compared the yearly average variations of Dst index and the solar wind parameters with cosmic ray data from Moscow, Climax, and Haleakala neutron monitors during the solar cycles 20–23. The descending phases of these solar cycles (CSs) had the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. They also had effects on cosmic rays variations. We show that long-term Dst variations in these solar cycles were correlated with the cosmic ray count rate and can be used for study of CR variations. Global temperature variations in connection with evolution of Dst index and CR variations is discussed.     

膨胀磁场和太阳风粒子相互作用三维数值模拟

采用三维模型,使用混合网格质点法HPIC(Hybrid Particle-in-Cell)对膨胀的磁场和太阳风相互作用过程进行数值模拟.研究了线圈产生的偶极子磁场在注入等离子体后和太阳风粒子的相互作用过程,并对以不同速度入射的等离子体引起的太阳风粒子的变化和磁场变化进行了比较.研究结果表明,偶极子磁场和太阳风作用时会产生弓形激波,此时磁压等于太阳风粒子的动压,当向线圈产生的偶极子磁场中注入高能等离子体时引起磁场膨胀,膨胀的磁场将会排斥太阳风粒子向外运动,从而引起弓形激波的变化,增大与太阳风相互作用的面积,并且粒子入射速度越大,磁场膨胀越明显,与太阳风相互作用愈强.      

Sunspot activity and cosmic ray modulation at 1 a.u. for 1900–2013

The descent of sunspot cycle 23 to an unprecedented minimum of long duration in 2006–2009 led to a prolonged galactic cosmic ray (GCR) recovery to the highest level observed in the instrumental era for a variety of energetic charged particle species on Earth, over a wide range of rigidities. The remarkable GCR increase measured by several ground-based, balloon-borne, and detectors on a satellite is described and discussed. It is accompanied by a decrease in solar wind velocity and interplanetary magnetic field at 1 a.u., reaching the lowest values since measurements of the solar wind began in October 1963; the solar polar field strength (μT) measured at the Wilcox Solar Observatory (WSO) is also significantly reduced compared to prior cycles since the start of the program in 1976, the polar field in the northern hemisphere reversed in June 2012 and again in February 2014, that in the southern hemisphere reversed in July 2013. If updates of WSO data confirm the second reversal in northern solar hemisphere, it would pose a serious challenge to the Dynamo Theory. The long-term change in solar behavior may have begun in 1992, perhaps earlier. The physical underpinnings of these solar changes need to be understood and their effect on GCR modulation processes clarified. The study discusses the recent phenomena in the context of GCR modulation since 1900. These happenings affected our empirical predictions for the key parameters for the next two sunspot cycles (they may be progressively less active than sunspot cycle 24) but it enhanced support for our prediction that solar activity is descending into a Dalton-like grand minimum in the middle of the twentyfirst century, reducing the frequency of the coronal mass ejections; they determine the space weather affecting the quality of life on Earth, radiation dose for hardware and human activities in space as well as the frequency of large Forbush decreases at 1 a.u.