运用一维太阳风MHD CE/SE模型预报行星际激波到达时间

在一维太阳风磁流体(MHD)数值模拟中, 应用时空守恒元和解元(Conservation Element/Solution Element, CE/SE)方法, 建立了一个行星际激波扰动传播模型(1D-MHD (CE/SE)模型), 用来预报行星际激波到达时间. 收集了1997年2月至2002年8月间的137个激波事件, 对激波到达地球轨道附近的传播时间进行了预测, 并将预报结果与STOA, ISPM, HAFv.2以及SPM模型所得结果进行比较. 对于相同的样本事件, 1D-MHD (CE/SE)模型给出的渡越时间平均绝对值误差并不大于其他4个模型, 且该模型预报的相对误差小于10 %的事件占25.6 %, 小于30 %的事件占69.3 %, 小于50 %的事件占87.6 %, 其预报精度与其他模型相比基本相当. 这表明该模型在空间天气的激波到达时间预报方面有潜在的应用价值.      

行星际激波传播至1AU的渡越时间预测

考虑了激波爆发源角宽度、能量、驱动时间、激波速度及其与背景太阳风之间的相互作用,利用流体力学扰动方程建立起一个激波扰动传播模型,用于研究激波从太阳传播到地球轨道附近(1 AU处)所需要的时间(渡越时间)问题.为印证扰动传播模型的适用性,利用1979-1989年间的27个激波事件,以及1997年2月到2000年1月间的68个激波事件,对激波到达地球轨道附近的渡越时间进行了预测,并将结果与STOA和ISPM预报模型结果进行了比较.实验表明,该模型在所有95个事件中,渡越时间相对误差小于10%的事件数占总事件数的25.26%;相对误差小于20%的占总事件数的50.53%;相对误差小于30%的占总事件的65.26%.      

1994年2月21日行星际激波引起的磁暴

利用Imp-8,Geotail和Goes-6等卫星资料,研究了1994年2月21日0900UT到达地球磁层的行星际激波引起的磁暴期间,从太阳风向磁层传输能量的有关问题.结果指出:（1）南向行星际磁场（IMF）的长持续时间不是太阳风向磁层输能的必要条件.南北振荡的,较强IMF也能产生显著的能量传输;（2）行星际扰动磁场通过弓激波和磁层顶后扰动磁能增加,增幅将近5倍;（3）在磁层内扰动磁场的Bz分量在1×10-4Hz附近显著被吸收.这一低频扰动磁场可能是磁暴期间导致氧离子和质子等环电流粒子向内扩散并被加速的原因之一.     

异常SSC事件的行星际原因分析

磁暴急始(SSC)是强烈太阳风动压或行星际激波与磁层相互作用的结果.通常SSC事件的上升时间在4～10 min,我们把上升时间超过15 min的SSC事件称为异常SSC事件.本文利用地磁SYM-H指数鉴别出了5个有地磁观测历史以来发生的上升时间大于15 min的异常SSC事件,并利用Wind,ACE,IMP 8,Goes,Geotail多点卫星太阳风观测数据和地磁观测数据,分析了异常SSC事件的行星际原因.结果表明,异常SSC事件通常都是强烈行星际扰动引起的,5个异常SSC事件有4个对应于行星际激波,有3个对应于多步太阳风动压跃变,有1个对应于行星际电场大幅度变化;由行星际激波产生的异常SSC事件,其上升时间依赖于行星际激波的方向,方向相对于日地连线越偏,上升时间越长;异常SSC事件上升时间与行星际磁场方向关系不明显.      

影响地球环境的太阳质子事件的时间过程

利用1966年以来的大量太阳耀斑以及相应质子事件的资料,分析研究了质子事件到达时间和极大时间同耀斑经度位置的统计关系.结果表明当耀斑位置处于经过地球的行星际大尺度场磁力线足点位置附近时,上述两种时间过程最短.这个结果支持了太阳耀斑粒子经日冕传播再向行星际空间传播的二阶段传播模型.      

夜侧极区电离层对流对行星际激波的响应

利用超级双子极光雷达网（Super Dual Aurora Radar Network,SuperDARN）高频雷达、北半球IMAGE地磁台链以及南极中山站的极光观测数据,研究电离层对流对2012年7月14日一个行星际激波扰动事件的响应.在18:10UT行星际激波到达地球并与磁层相互作用触发地磁急始和磁层亚暴,SuperDARN雷达观测到北半球夜侧极区电离层对流显著增强,观测视野覆盖黄河站的Hankasalmi雷达观测到从激波到达地球至18:33UT,电离层F层出现剧烈扰动,雷达回波数明显增多,并出现局部对流速度反转现象.18:33UT之后,观测到F层出现三块速度高达600m·s-1的逆阳运动不规则体.而与Hankasalmi雷达地磁共轭的南半球Kerguelen雷达探测到的回波主要来自E层,回波数量几乎无变化,但是Kerguelen雷达观测视野内的中山站全天空光学成像仪观测到极光活动显著增强.南北半球夜侧电离层观测结果的差异,主要是由于它们分别处于极夜和极昼.      

全晕CME与太阳质子事件的关系

日冕物质抛射（CME）是太阳质子事件的重要源头.CME的速度和源区位置是太阳质子事件产生的重要因素.通过统计最近5年全晕CME与太阳质子事件的关系发现,速度大且源区位置距离日面上连接地球磁力线足点近的全晕CME更易引发太阳质子事件,其中速度大于1200km…-1、角距离60°以内的样本引发太阳质子事件的概率最高.对3个未引发太阳质子事件的高速全晕CME进行了详细分析,发现CME的主体爆发方向和行星际磁场环境的变化也影响太阳质子事件的产生.因此,在太阳质子事件的实际预报中,综合CME爆发速度、源区位置、主体抛射方向和行星际环境等多个因素才能给出更准确的事件预报结果.      

基于集成学习的太阳质子事件短期预报方法

太阳质子事件是一种由太阳活动爆发时喷射并传播到近地空间的高能粒子引起的空间天气现象。这些高能粒子会对航天器和宇航员产生严重危害,对太阳质子事件进行准确的短期预报是航天活动灾害预防的重要内容。针对当前主要预报模型中普遍存在的高虚报率问题,提出了一种基于集成学习的太阳质子事件短期预报方法,利用第23个太阳活动周数据,建立了一种集成8种机器学习模型的太阳质子事件短期预报系统。实验结果表明,本文方法在取得了80.95%的报准率的同时,将虚报率降低至19.05%,相比现有的预报系统具有较为明显的优势。      

结合光球磁场特征物理量的质子事件短期预报

利用描述太阳活动区光球磁场复杂性和非势性特征的三个物理量(纵向磁场最大水平梯度|▽_hB_z |_m, 强梯度中性线长度L, 孤立奇点数目η)建立了质子事件短期预报模型, 验证了磁场特征物理量对质子事件短期预报的有效性. 目前已建立或使用的太阳质子事件短期预报模型中仍然没有正式将磁场特征物理量作为预报因子. 由于太阳质子事件是小概率事件, 其物理产生机制尚不完全清楚, 这些预报模型往往存在虚报率偏高或报准率偏低的问题. 本文试图将原有质子事件模型所用的传统因子与磁场特征物理量结合起来, 利用神经网络方法建立一个更为有效的质子事件短期预报模型. 利用1997--2001年的训练数据集1871个样本建立了输入层为传统预报因子的模型A以及输入层为传统预报因子和磁场特征物理量的模型B. 通过对2002--2003年973个样本的测试数据集进行模拟预报发现, 模型A与B在具有相同质子事件报准率的情况下, 模型B的虚报率明显降低. 这进一步验证了磁场特征物理量在质子事件短期预报中的作用, 进而可以加强对太阳质子事件的实际预报能力.      

电离层等效电流体系对行星际激波的响应研究

行星际激波是导致地球磁层-电离层系统发生扰动的重要原因之一,其可以通过对磁层-电离层系统电流体系的改变来影响地磁变化.本文采用全球三维磁流体力学数值模拟方法,分析了行星际激波作用下电离层等效电流体系的即时响应.模拟结果表明,在激波作用下伴随着异常场向电流对的产生,电离层在午前午后出现一对反向的等效电流涡.这对涡旋一边向极侧和夜侧运动,一边经历强度增强和减弱直至消失的过程.激波过后等效电流体系图像逐渐演化为激波下游行星际条件控制的典型图像.这个响应过程与行星际激波强度有关,激波强度越强,则反向的等效电流涡旋强度越大,寿命也就越短.      

Forecasting space weather: Predicting interplanetary shocks using neural networks

We are developing a system to predict the arrival of interplanetary (IP) shocks at the Earth. These events are routinely detected by the Electron, Proton, and Alpha Monitor (EPAM) instrument aboard NASA’s ACE spacecraft, which is positioned at Lagrange Point 1 (L1). In this work, we use historical EPAM data to train an IP shock forecasting algorithm. Our approach centers on the observation that these shocks are often preceded by identifiable signatures in the energetic particle intensity data. Using EPAM data, we trained an artificial neural network to predict the time remaining until the shock arrival. After training this algorithm on 37 events, it was able to forecast the arrival time for 19 previously unseen events. The average uncertainty in the prediction 24 h in advance was 8.9 h, while the uncertainty improved to 4.6 h when the event was 12 h away. This system is accessible online, where it provides predictions of shock arrival times using real-time EPAM data.     

Relationships between energetic storm particle events and interplanetary shocks driven by full and partial halo coronal mass ejections

We have analysed energetic storm particle (ESP) events in 116 interplanetary (IP) shocks driven by front-side full and partial halo coronal mass ejections (CMEs) with speeds $>$400 km s^?1during the years 1996–2015. We investigated the occurrence and relationships of ESP events with several parameters describing the IP shocks, and the associated CMEs, type II radio bursts, and solar energetic particle (SEP) events. Most of the shocks (57 %) were associated with an ESP event at proton energies $>$1 MeV.The shock transit speeds from the Sun to 1 AU of the shocks associated with an ESP event were significantly greater than those of the shocks without an ESP event, and best distinguished these two groups of shocks from each other. The occurrence and maximum intensity of the ESP events also had the strongest dependence on the shock transit speed compared to the other parameters investigated. The correlation coefficient between ESP peak intensities and shock transit speeds was highest (0.73 $\pm$ 0.04) at 6.2 MeV. Weaker dependences were found on the shock speed at 1 AU, Alfvénic and magnetosonic Mach numbers, shock compression ratio, and CME speed. On average all these parameters were significantly different for shocks capable to accelerate ESPs compared to shocks not associated with ESPs, while the differences in the shock normal angle and in the width and longitude of the CMEs were insignificant.The CME-driven shocks producing energetic decametric–hectometric (DH) type II radio bursts and high-intensity SEP events proved to produce also more frequently ESP events with larger particle flux enhancements than other shocks. Together with the shock transit speed, the characteristics of solar DH type II radio bursts and SEP events play an important role in the occurrence and maximum intensity of ESP events at 1 AU.     

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.     

Propagation of normal and faster CMEs in the interplanetary medium

We have analyzed 101 Coronal Mass Ejection (CME) events and their associated interplanetary CMEs (ICMEs) and interplanetary (IP) shocks observed during the period 1997–2005 from the list given by Mujiber Rahman et al. (2012). The aim of the present work is to correlate the interplanetary parameters such as, the speeds of IP shocks and ICMEs, CME transit time and their relation with CME parameters near the Sun. Mainly, a group of 10 faster CME events (V_INT > 2200 km/s) are compared with a list of 91 normal events of Manoharan et al. (2004). From the distribution diagrams of CME, ICME and IP shock speeds, we note that a large number of events tends to narrow towards the ambient (i.e., background) solar wind speed (∼500 km/s) in agreement with the literature. Also, we found that the IP shock speed and the average ICME speed measured at 1 AU are well correlated. In addition, the IP shock speed is found to be slightly higher than the ICME speed. While the normal events show CME travel time in the range of ∼40–80 h with a mean value of 65 h, the faster events have lower transit time with a mean value of 40 h. The effect of solar wind drag is studied using the correlation of CME acceleration with interplanetary (IP) acceleration and with other parameters of ICMEs. While the mean acceleration values of normal and faster CMEs in the LASCO FOV are 1 m/s², 18 m/s², they are −1.5 m/s² and −14 m/s² in the interplanetary medium, respectively. The relation between CME speed and IP acceleration for normal and faster events are found to agree with that of  and  except slight deviations for the faster events. It is also seen that the faster events with less travel time face higher negative acceleration (>−10 m/s²) in the interplanetary medium up to 1 AU.     

Three-dimensional global simulation of multiple ICMEs’ interaction and propagation from the Sun to the heliosphere following the 25–28 October 2003 solar events

This study performs simulations of interplanetary coronal mass ejection (ICME) propagation in a realistic three-dimensional (3D) solar wind structure from the Sun to the Earth by using the newly developed hybrid code, HAFv.2+3DMHD. This model combines two simulation codes, Hakamada–Akasofu–Fry code version 2 (HAFv.2) and a fully 3D, time-dependent MHD simulation code. The solar wind structure is simulated out to 0.08 AU (18 Rs) from source surface maps using the HAFv.2 code. The outputs at 0.08 AU are then used to provide inputs for the lower boundary, at that location, of the 3D MHD code to calculate solar wind and its evolution to 1 AU and beyond. A dynamic disturbance, mimicking a particular flare’s energy output, is delivered to this non-uniform structure to model the evolution and interplanetary propagation of ICMEs (including their shocks). We then show the interaction between two ICMEs and the dynamic process during the overtaking of one shock by the other. The results show that both CMEs and heliosphere current sheet/plasma sheet were deformed by interacting with each other.     

The influence of interplanetary shocks on solar protons measured in the stratosphere.

Since the beginning of the 22nd solar cycle twenty solar proton events were observed by the regular balloon measurements of cosmic rays. Temporal changes of intensities and energy spectra of solar protons with energy 100-500 MeV were obtained. The strong influence of interplanetary shock waves on the proton flux characteristics near the Earth was observed. Possible effects of solar proton transport in the vicinity of shock fronts are discussed to explain the observational data.     

基于Green函数法的太阳高能粒子行星际扩散过程模拟

统计分析了自1976-2017年期间记录到的217次SEP(Solar Energetic Particle)事件的日冕足点经度位置,其分布特征符合日冕横向分布的东西效应,同时基于两相传输模型及其Green函数解,对发生在不同日冕足点的四次SEP事件进行了模拟研究.模拟与观测结果表现一致,表明该模型能够较好地模拟发生在...     

Corotating interplanetary streams and associated ionospheric disturbances at Venus and Earth

During the summer of 1979, solar coronal structure was such that a sequence of recurrent regions produced a corresponding sequence of corotating solar wind streams, with pronounced downstream signatures. One of these stream events passed Earth on July 3, and was observed later at Venus late on July 11th, with similar characteristics. Corresponding in-situ measurements at Earth from the Atmospheric Explorer-E satellite and at Venus from the Pioneer Venus Orbiter are examined for evidence of comparable perturbations of the planetary ionospheres. The passage of the stream shock front is found to be associated with pronounced fluctuations in n(0⁺) which appear as pronounced local depletion of ion concentrations in both ionospheres. The ionosphere disturbances appear to be closely associated with large variations in the solar wind momentum flux. The implied local ionospheric depletions observed at each planet are interpreted to be the consequence of plasma redistribution, rather than actual depletions of plasma.     

Viewing radiation signatures of solar energetic particles in interplanetary space

A current serious limitation on the studies of solar energetic particle (SEP) events is that their properties in the inner heliosphere are studied only through in situ spacecraft observations. Our understanding of spatial distributions and temporal variations of SEP events has come through statistical studies of many such events over several solar cycles. In contrast, flare SEPs in the solar corona can be imaged through their radiative and collisional interactions with solar fields and particles. We suggest that the heliospheric SEPs may also interact with heliospheric particles and fields to produce signatures which can be remotely observed and imaged. A challenge with any such candidate signature is to separate it from that of flare SEPs. The optimum case for imaging high-energy (E > 100 MeV) heliospheric protons may be the emission of π⁰-decay γ-rays following proton collisions with solar wind (SW) ions. In the case of E > 1 MeV electrons, gyrosynchrotron radio emission may be the most readily detectible remote signal. In both cases we may already have observed one or two such events. Another radiative signature from nonthermal particles may be resonant transition radiation, which has likely already been observed from solar flare electrons. We discuss energetic neutrons as another possible remote signature, but we rule out γ-ray line and 0.511 MeV positron annihilation emission as observable signatures of heliospheric energetic ions. We are already acquiring global signatures of large inner-heliospheric SW density features and of heliosheath interactions between the SW and interstellar neutral ions. By finding an appropriate observable signature of remote heliospheric SEPs, we could supplement the in situ observations with global maps of energetic SEP events to provide a comprehensive view of SEP events.