太阳高能粒子观测特征经向分布统计

基于多卫星联合观测数据,筛选了2006年12月至2017年10月期间122个太阳高能粒子（SEP）事件及其伴随的日冕物质抛射（CME）,分析了SEP事件属性随相对经度的变化、与CME属性之间相关性的经向分布以及与Fe/O比值的关联.研究结果显示:低Fe/O类事件的峰值通量I_p通常更高,伴随CME更大,但通量上升速度较慢,且其D_u（持续时间）和I_p与CME速度呈现更强的相关性;SEP特征时间T_O（CME爆发至SEP事件爆发）与T_R（SEP事件爆发至半峰值）随相对经度增加而增大,D_u与I_p随相对经度增加而减小,通量上升斜率K在±90°范围内自东向西递减;SEP事件属性与伴随CME属性的相关性随相对经度的改变有明显变化,在磁连接好的位置,T_O与CME速度等属性呈现负相关,T_R与CME速度等属性呈现正相关,D_u,I_p与CME速度之间的相关性更强.研究结果进一步表明,SEP事件观测属性既与CME参数相关,同时又具有很强的经度依赖性,在磁连接越好的位置卫星观测到的SEP事件强度越高,SEP观测参数受CME的影响越大,这对大型SEP事件的预报很有意义.此外,高Fe/O类SEP事件与CME相关性的减弱暗示了耀斑加速、种子粒子源等因素的影响.      

太阳高能粒子事件上升时间统计研究

选取1997-2006年共66个较大的缓变型太阳高能粒子(SEP)事件, 分析了不同条件下太阳高能粒子通量廓线上升时间与源区日面经向分布之间的相关关系, 研究了日冕物质抛射(CME)和耀斑在SEP上升阶段的作用特点.统计结果表明,大SEP事件的源区主要分布在太阳西半球, 特别是磁足点东西两侧45°范围内; 在高速太阳风条件下, 低能通道的通量上升时间与日面相对经度有较好的相关性,即离磁足点越远, 上升时间越长,而高能通道相关性则不明显; 全晕状CME产生的SEP事件对应的上升时间与源区位置没有明显的相关性, 而部分晕状CME伴随的SEP事件则与二次拟合曲线符合很好.分析表明,在缓变型SEP事件的通量上升阶段, 耀斑加速过程起着重要作用,这在部分晕状CME伴随的SEP事件中尤为显著.      

缓变型太阳高能粒子事件特征时间及其经向分布

利用SOHO,STEREO高能粒子观测数据,对2011-2014年30个通量短时间内显著增强的缓变型太阳高能粒子（SEP）事件的两个特征时间（局地爆发时间,起始释放时间）及其经向分布进行统计分析.研究结果显示,多颗卫星同时观测到的SEP事件伴随的日冕物质抛射（CME）角宽明显较一般事件大,且基本都为Halo CME;不同卫星观测到的粒子通量局地增强时间差与卫星位置经度差明显线性正相关且东西不对称;局地爆发时间和起始释放时间相对于耀斑时间的延迟与卫星相对经度正相关;卫星所有能量通道的两个特征时间极差与卫星相对经度呈现较好的正相关,这表明不同能量SEP释放的时间跨度具有明显经度差异;高低能释放时间差与CME速度正相关.这些结论表明,SEP事件的两个特征时间具有明显的经向依赖性,并都与CME速度相关.      

应用BP神经网络针对高通量质子事件的通量数值预报

质子事件的爆发与太阳软X射线辐射有着很强的相关性,利用GOES卫星的1～8 (A)波段和0.5～4 (A)波段的软X射线数据,选取一些特征参量验证该相关性并应用到质子事件短期预报中.在当前质子事件传输物理机制不完全明确的情况下,在现有的预报质子事件有无的模型基础上,利用BP神经网络,根据软X射线通量水平等预测事件质子峰值通量水平,再对训练后的网络进行检验,检验预测所得结果与实际探测值误差小于一个量级,具备一定实用意义.      

质子辐射带辐射中心区域模型

利用AP-8和CRRESPRO质子辐射带模式数据库, 比较了二者在磁赤道面上计算结果 的差异并给出其差异原因. 利用AP-8模式数据库数据, 建立起质子辐射带函数形式的辐射中心区域模式, 包括各能道全向微分通量峰值所对应的L值(L_c) 随能量E的变化模式以及各能道全向微分通量峰值J_max随能量E的变化模式. 利用RBSP A卫星REPT望远镜在磁赤道面上的高能质子观测数据, 分别与 AP-8模式、CRRESPRO模式及本文所得辐射中心区域模式计算结果进行比较, 发现在78.9, 102.6和208MeV三个能道上, RBSP A卫星观测所得各能道全向微分 通量明显偏大, 而L_c与AP-8或本文辐射中心模式所得结果基本一致; RBSP A卫星也观测到CRRESPRO Quiet模式所得的隐性第二质子辐射带结构.      

太阳质子耀斑X射线辐射特征及质子事件警报

太阳质子耀斑X射线辐射特征的研究, 为太阳质子事件的警报提供一个重要的途径和方法。本文分析了第21周太阳活动峰年(1977—1986)期间质子耀斑和相应的GOES和SMM卫星观测的X射线辐射资料, 结果表明:大部分质子耀斑的硬X射线峰值流量F_HX≥104s/c;积分流量F₀≥106counts;硬X射线辐射到达峰值时间T_R≥100s;持续时间T_D≥103s;X光子最高能量E_x≥300keV;平均能谱指数√r≤3.5;高能时延T_L≥10s。利用这些X射线暴的特征参数, 对第21周峰年大质子事件作警报检验, 结果是:报准率为94％, 虚报率为40％。      

影响卫星故障的空间天气分析

基于美国国家地球物理数据中心(NGDC) 2384例和中国19颗卫星的263例卫星故障信息, 结合1963-2012年小时平均的多种空间环境数据, 定量分析了三种卫星故障发生期间的空间要素特征, 探讨单粒子锁定(SEU)、表面充电致静电放电(ESD)和内部深层充电所致电子引起的电磁脉冲(ECEMP)与空间天气事件的可能联系, 得出以下主要结论. (1)大部分SEU和ECEMP发生于空间天气平静时, 但在其前后3日内地磁活动达到了磁暴水平, 相对来说比例最大的发生在Dst_min之后第3日 (48～72h). (2) ESD受地磁活动和高能电子通量影响明显. 与磁暴、相对论电子通量增强事件的季节性相对应, 两分点附近ESD和ECEMP的发生率高; 93.6% 的 ESD发生前后72h内地磁活动达到磁暴水平, 故障发生时间均匀分布在 Dst_min前0～48h 和后0～24h; 54.9%的ESD 发生时处于地磁暴期(Dst <-30nT), 以-50～-30nT的小磁暴水平居多; 40.6%的ESD发生于高能电子通量高水平期(≥ 103pfu, 1pfu =1cm-2·s-1·sr-1), 81.9%的ESD发生前后72h 内高能电子通量峰值≥ 103pfu, 发生率最高时段为电子通量峰值前 48～72h. (3)高能电子对中国同步轨道卫星的SEU影响明显, 42.5% 故障发生 时高能电子通量≥ 103pfu, 故障在峰值前48～72h和峰值后48～72h 的发生概率相当, 约为23.0%. (4)同步轨道卫星SEU受太阳质子事件的影响相对较大, 22.5%的中国同步轨道卫星故障发生前后72h内发生了太阳质子事件, 季节性不明显.      

VLF相位突然异常与太阳X射线事件相关性的分析

本文通过实测的VLF信号的SPA事件的数据和太阳X射线爆发通量密度之间的相关分析,建立了它们之间的数值关系.由于在SPA事件时,电离层高度的变化与太阳X射线爆发的通量密度之间的相关性很好,可以利用SPA事件的数据来估算太阳X射线爆发的强度.因为大气的吸收,在地面上不能直接观测X射线强度.作为一个实例,用推出的数值关系,计算了1982年6月3日的一次SPA事件,并与X射线爆发的数据作了比较.      

质子事件上升时间及峰值强度的统计研究

在耀斑已基本确定为质子耀斑的情况下, 为了对即将到达地球的太阳质子作出半定量的粗略预报(警报), 即估计从观测到光学耀斑开始, 需经多长时间质子通量将到达峰值;峰值强度有多大。为此, 我们收集了1967年5月—1972年12月约五年半期间国外发表的比较系统的质子事件资料, 以及相应的太阳耀斑和太阳射电资料。      

地球同步轨道高能电子通量预报方法研究

统计分析了GOES卫星测量得到的E > 2MeV能道电子通量与地磁Ap指数及太阳风数据的关系, 构建了基于径向基函数RBF的神经网络模型框架, 对GOES-12卫星所处的地球同步轨道高能电子通量进行提前1天的预报, 其对2008-2010年数据预测的效果较好. 另外, 发现在GOES-12卫星观测的E >2MeV能道高能电子达到108 cm-2·d-1·sr-1以上时, FY-2D卫星的测量数据同时达到108 cm-2·d-1·sr-1以上的比例达到90%左右. 通过对FY-2D卫星E >2MeV能道电子通量与GOES卫星E>2MeV电子通量的相关性分析, 建立了FY-2D卫星高能电子预报模型, 预报结果与实测通量符合较好.      

Modeling solar proton access to geostationary spacecraft with geomagnetic cutoffs

Solar energetic particle (SEP) cutoffs at geosynchronous orbit are sensitive to moderate geomagnetic activity and undergo daily variations due to the day–night asymmetry of the magnetosphere. At geosynchronous orbit, cutoff rigidity also has a large directional dependence, with the highest cutoff rigidity corresponding to ions arriving from magnetic east and lowest cutoff rigidity corresponding to ions incident from the west. Consequently, during geomagnetically quiet periods, the SEP flux observed by an eastward facing particle detector is significantly lower than observed by a westward facing particle detector. During geomagnetically disturbed periods the cutoff is suppressed allowing SEPs access well inside of geosynchronous, so that the east–west SEP flux ratio approaches unity. Variations in the east–west SEP flux ratio observed by GOES Energetic Particle Sensors (EPS) have recently been reported by Rodriguez et al. (2010). In NOAA’s operational processing of EPS count rates into differential fluxes, the differential flux is treated as isotropic and flat over the energy width of the channel. To compare modeled SEP flux with GOES EPS observations, the anisotropy of the flux over the EPS energy range and field of view must be taken into account. A technique for making direct comparisons between GOES EPS observations and SEP flux modeled using numerically computed geomagnetic cutoffs is presented. Initial results from a comparison between modeled and observed flux during the 6–11 December 2006 SEP event are also presented. The modeled cutoffs reproduce the observed flux variations well but are in general too high.     

A comparison of two different types of geosynchronous satellite measurements during the 1989 solar proton events.

The proton telescope aboard the GOES-7 satellite continuously records the proton flux at geosynchronous orbit, and therefore provides a direct measurement of the energetic protons arriving during solar energetic particle (SEP) events. Microelectronic devices are susceptible to single event upset (SEU) caused by both energetic protons and galactic cosmic ray (GCR) ions. Some devices are so sensitive that their upsets can be used as a dosimetric indicator of a high fluence of particles. The 93L422 1K SRAM is one such device. Eight of them are on the TDRS-1 satellite in geosynchronous orbit, and collectively they had been experiencing 1-2 upset/day due to the GCR background. During the large SEP events of 1989 the upset rate increased dramatically, up to about 250 for the week of 19 Oct, due to the arrival of the SEP protons. Using the GOES proton spectra, the proton-induced SEU cross section curve for the 93L422 and the shielding distribution around the 93L422, the calculated upsets based on the GOES satellite data compared well against the log of measured upsets on TDRS-1.     

强磁暴、能量粒子暴与热层大气密度涨落之间的相关关系

利用1997-2007年由GOES8, GOES11和GOES12星载高能粒子探测器在地球同步轨道高度上所探测到的高能质子和高能电子通量探测数据以及高度560km左右星载大气密度探测器所得的热层大气密度探测数据, 统计分析了强地磁扰动、高能粒子通量跃变和热层大气密度涨落之间的相关关系, 初步获得强地磁扰动期间, 地球同步轨道(外辐射带外环)均出现了增幅大于三个数量级的高能质子通量(尤其是E>1MeV)强增强现象, 随后热 层大气密度强烈上涨, 表明三者之间是正相关关系. 在时间上地球同步轨道高能质子通量强增强现象先于日均Ap值(地磁活动程度)上涨约一天左右, 而热层大气密度强涨落现象又明显滞后于强地磁扰动事件.      

Relative fluxes of shock and prompt peaks in SEP event time profiles

Peak fluxes are an important property of gradual solar energetic particle (SEP) event time profiles from both astro/heliophysical and applications perspectives. However, the peak flux in an event may occur at the event onset, or at the time of the interplanetary shock arrival (the ESP or energetic storm particles). This makes an important difference in the interpretation of the peak flux, and in any attempts to characterize or model it. This paper describes a study of SEP data sets from ACE, IMP-8 and GOES toward determining the relative properties of these peak fluxes for protons with energies near 1, 10, and 50 MeV. The results suggest that for gradual events with both peaks, the ESP peak often dominates at 1 MeV energies and is dominant about half the time at 10 MeV. Moreover, the prompt peak fluxes can be used to estimate the shock peak (ESP event) up to days ahead, especially in the lower energy range.     

两个临近脉冲型太阳能量电子事件的观测与拟合

WIND飞船在2010年11月15日观测到两个临近的脉冲型太阳能量电子事件, 这两个事件在1AU处呈现出不同类型的通量-时间曲线. 事件一的通量表现出快速上升及快速下降的特性; 事件二则表现为缓慢上升, 更缓慢下降, 事件二的持续时间是事件一的5～17倍. 以往的解释认为事 件二中的电子在行星际受到了更强的散射. 本文引入等腰三角形的释放函数并 求解电报方程, 利用得到的解对1AU处的观测进行拟合. 根据最佳拟合结果 反推两事件在太阳上的释放函数和在行星际传播的平均自由程, 发现造成两事 件在1AU处能谱和通量-时间曲线形状不同的原因是太阳上电子 加速过程的不同而非行星际散射. 结合SOHO卫星的白光观测, 发现两事件可能 与一个CME (日冕物质抛射)相关, 并进一步推测了这两个太阳电子事件可能 的加速图像.      

2009年2月13日EUV波现象数值研究

结合STEREO卫星的观测和三维磁流体力学数值模拟方法, 采用WSO (Wilcox Solar Observatory)磁场数据和势场源表面模型建立日冕初始磁场, 并在日面活动区加上时变的压强扰动, 对2009年2月13日05:35UT爆发的CME-EUV波(Coronal Mass Ejections-Extreme Ultraviolet wave, 日冕物质抛射-远紫外波)事件进行研究. 从COR1/STEREO-A图像判断, 此次CME前沿速度约340km·s-1, 角宽度约60°; 分析EUVI/STEREO-B 195 ?的差分图像, 可以看到, 环形亮环波前从活动区向四周传播, 亮环波前后面是日冕暗化区, 取四个方向的波前位置进行线性拟合可知, 该EUV波速度为247km·s-1, 数值模拟得到的EUV波速度为245km·s-1, 将计算结果采用IDL可视化后可以看到明显的亮环和暗区结构, 数值模拟结果与卫星观测相一致, 表明该EUV波现象是快磁声波.      

Comparing proton fluxes of central meridian SEP events with those predicted by SOLPENCO

We have developed an operational code, SOLPENCO, that can be used for space weather prediction schemes of solar energetic particle (SEP) events. SOLPENCO provides proton differential flux and cumulated fluence profiles from the onset of the event up to the arrival of the associated traveling interplanetary shock at the observer’s position (either 1.0 or 0.4 AU). SOLPENCO considers a variety of interplanetary scenarios where the SEP events develop. These scenarios include solar longitudes of the parent solar event ranging from E75 to W90, transit speeds of the associated shock ranging from 400 to 1700 km s⁻¹, proton energies ranging from 0.125 to 64 MeV, and interplanetary conditions for the energetic particle transport characterized by specific mean free paths. We compare the results of SOLPENCO with flux measurements of a set of SEP events observed at 1 AU that fulfill the following four conditions: (1) the association between the interplanetary shock observed at 1 AU and the parent solar event is well established; (2) the heliolongitude of the active region site is within 30° of the Sun–Earth line; (3) the event shows a significant proton flux increase at energies below 96 MeV; (4) the pre-event intensity background is low. The results are discussed in terms of the transit velocity of the shock and the proton energy. We draw conclusions about both the use of SOLPENCO as a prediction tool and the required improvements to make it useful for space weather purposes.     

Cone model-based SEP event calculations for applications to multipoint observations

The problem of modeling solar energetic particle (SEP) events is important to both space weather research and forecasting, and yet it has seen relatively little progress. Most important SEP events are associated with coronal mass ejections (CMEs) that drive coronal and interplanetary shocks. These shocks can continuously produce accelerated particles from the ambient medium to well beyond 1 AU. This paper describes an effort to model real SEP events using a Center for Integrated Space weather Modeling (CISM) MHD solar wind simulation including a cone model of CMEs to initiate the related shocks. In addition to providing observation-inspired shock geometry and characteristics, this MHD simulation describes the time-dependent observer field line connections to the shock source. As a first approximation, we assume a shock jump-parameterized source strength and spectrum, and that scatter-free transport occurs outside of the shock source, thus emphasizing the role the shock evolution plays in determining the modeled SEP event profile. Three halo CME events on May 12, 1997, November 4, 1997 and December 13, 2006 are used to test the modeling approach. While challenges arise in the identification and characterization of the shocks in the MHD model results, this approach illustrates the importance to SEP event modeling of globally simulating the underlying heliospheric event. The results also suggest the potential utility of such a model for forcasting and for interpretation of separated multipoint measurements such as those expected from the STEREO mission.