太阳抵近探测计划——观测位置的新突破

太阳抵近探测计划(SCOPE)旨在突破高温和强辐射防护、长距离运载、远距离轨道控制和先进载荷等一系列极限技术,将探测器投送至距太阳中心仅有5个太阳半径的位置上,深入太阳大气层进行探测,研究太阳附近极亮、极热的深空探测“无人区”,在全新的位置上对太阳进行超近距离原位探测和遥感观测,针对磁场和等离子体结构实现空间分辨率优于0.1"的观测。探测器将穿越太阳爆发磁重联电流片,显微观测太阳爆发磁结构,原位探测磁重联电流片、日冕物质抛射与激波以及各类带电粒子,以推动揭示太阳爆发理论机理。探测器将在最靠近太阳的区域显微监测和探测日冕中尺度小于0.1"的纳耀斑、光球中尺度小于0.06"的磁场和速度场结构及其演化特征,确认日冕加热机制;探测太阳风重离子电荷态,确认太阳起源及加速机制。探测器还将在最接近太阳的区域内与原位探测日冕磁场,显微观测太阳极区磁场和等离子体结构和演化特征;揭示太阳附近尘埃分布特征,进入无尘埃区,确定太阳系尘埃盘内边界。困扰太阳物理界近百年的两个科学难题,即太阳爆发机理难题和日冕加热与太阳风加速机理难题,随着该计划的顺利实施将被破解;在最接近日心的位置处实现日冕磁场,包括太阳极区磁场原位探测“0到1”的突破也将实现。本文将介绍SCOPE的背景、科学目标和预期产出、有效载荷以及卫星平台关键技术。

日地L5太阳探测工程概述

南京大学联合中国气象局、上海航天技术研究院等单位共同建议的日地L5太阳探测工程——“羲和二号”,将在国际上首次发射一颗人造探测器至日地系统第5个拉格朗日点,通过精测矢量磁场、揭示三维爆发和精准预警预报,解答“活动区磁场的产生演化及其与太阳爆发的物理联系”和“太阳爆发的传播规律及其与灾害性空间天气的关系”这2个太阳物理和空间天气领域亟待解决的重大科学和应用问题。本文重点阐述“羲和二号”的科学与应用目标,简要介绍其科学载荷和初步方案。联合日地连线方向上的太阳探测,“羲和二号”的实施将开启我国太阳立体探测时代,拓展人类对太阳爆发机制的理解,为空间天气预警预报带来革命性突破。

珠峰地面太阳光谱观测

利用国际标准高精度太阳光谱仪在2020—2021年期间对珠峰周边地面进行为期一年的太阳光谱观测研究。结果显示珠峰地面瞬时太阳光谱及其积分值(总辐射)频频超过大气层顶部光谱和太阳常数,夏至珠峰当地正午太阳光谱峰值达2.211 W/(m^(2)·nm)。珠峰地面观测光谱积分值比海平面高出约15%。观测期间最高日平均光谱峰值达1.121 W/(m^(2)·nm)。珠峰地面月均太阳光谱相对均匀,变化幅度小。最高月均太阳光谱出现在3月份,主要原因是下雪引起地表高反射。全年观测发现珠峰地面太阳总辐照度中紫外线B占0.26%,紫外线A占5.33%,可见光占49.58%,红外线占44.83%。为对比高海拔和低海拔太阳光谱特征,在2021年夏季同步观测珠峰和北京太阳光谱。利用全球气溶胶监测网络相关数据,研究大气气溶胶和水汽总量对珠峰和北京太阳光谱的影响。

西藏太阳光谱全年变化特征

精确观测地面太阳光谱能为反演大气环境、利用太阳能资源、保护植物生态等提供实地数据。对比目前卫星和地面观测结果显示由于海拔高、空气稀薄等因素西藏是地球上瞬时太阳辐照度最强的地区之一,观测西藏太阳光谱变化特征对研究强辐射环境下人类健康、生态变迁、太阳能利用等诸多领域具有独特的意义。2020年—2021年利用德国RAMSES-ACC-VIS光谱仪和加拿大SolarSIM-G高精度光谱仪对西藏五个高海拔地区(拉萨、林芝、那曲、日喀则、定日)进行了为期一年的太阳光谱观测研究。首次获得了西藏多地完整一年的太阳光谱实地数据,记录了每隔一分钟全天太阳紫外线、光合有效辐射和红外辐射光谱变化特征。分析研究了西藏各地全年日平均太阳光谱特征,发现全年日均最高光谱峰值1.12 W·m^(-2)·nm^(-1)出现在波长477.30 nm处。研究了西藏典型高原拉萨地区太阳光谱随季节性的变化特征,分析了其二分二至光谱辐照度变化区间,发现拉萨夏至日均光谱辐照度比冬至高约一倍多,夏至光谱峰值1.13 W·m^(-2)·nm^(-1),冬至0.43 W·m^(-2)·nm^(-1)。西藏日喀则全年太阳光谱变化浮动比拉萨的小,各节气光谱变化范围比较集中,夏至和冬至光谱峰值之差比拉萨的小。研究了西藏各地太阳光谱年平均辐照度特征,发现日喀则和珠峰平地年平均太阳光谱辐照度非常接近,两地光谱峰值均约为0.83 W·m^(-2)·nm^(-1);拉萨年均光谱峰值约为0.73 W·m^(-2)·nm^(-1),略低于日喀则和定日;那曲年均光谱曲线最低,峰值仅为0.53 W·m^(-2)·nm^(-1)。太阳光谱年均值和太阳能资源不同地区分布特征对西藏高原开发利用太阳能资源具有重要的应用价值。为了比较西藏高原与内地平原太阳光谱特征,同步观测研究了高海拔拉萨(3693 m)和低海拔北京(32 m)的晴天太阳光谱。2021年6月3日两地均为晴天,分析了两地当地正午太阳光谱特征,发现拉萨正午全波段光谱积分值比北京高约20%,比大气质量AM0的仅低5%左右;当日正午拉萨光谱峰值达1.83 W·m^(-2)·nm^(-1),北京为1.41 W·m^(-2)·nm^(-1);当日正午拉萨太阳紫外光谱积分值比北京高约15%。

等离子体波改变太阳成分

日冕是由炽热而稀薄的等离子体构成的光晕,围绕着太阳向外延伸,通常被太阳表面或光球层的强光所掩盖,但在日蚀期间可见。日冕中的化学元素含量与太阳其他部分不同。意大利国家天体物理研究所(INAF)的Mariarita Murabito及其同事进行的测量表明。

基于CEEMD-SSWT对太阳南北半球Rieger-type周期的不对称性分析

CEEMD(Complete Ensemble Empirical Mode Decomposition)是近年提出的一种自适应滤波算法,SSWT(Synchrosqueezed Wavelet Transform)是目前的一种高分辨率时频分析算法.采用CEEMD对太阳黑子日面积数据进行预滤波处理,再利用SSWT进行太阳南北半球Rieger-type周期不对称性分析,实现对太阳周期信号更精确的提取.研究结果表明:(1)虽然整个北半球的活动强度要高于南半球,但其整个13个活动周的Rieger-type周期信号的平均周期尺度却是极其相近的;(2)南北半球的太阳活动强度明显不对称,但在大部分活动周中,在太阳活动的极大期也是南北半球太阳活动不对称性最弱的时期;(3)太阳活动的强度与太阳的Rieger-type周期信号平均周期没有明显的相关关系,并不是在每个活动周中太阳活动强度越高的半球,所对应的半球Rieger-type周期信号的平均周期就一定越小,活动强度越低所对应的半球Rieger-type周期信号的平均周期就一定越大;(4)Rieger-type周期通常出现在太阳活动的极大期附近,但在某些活动周中Rieger-type周期会呈现多次波动,也会出现在太阳活动的上升期或下降期.

Application and prospect of the fluid cooling system of solar arrays for probing the Sun

The Solar Close Observations and Proximity Experiments(SCOPE)mission,which has been proposed by the Yunnan Observatories,Chinese Academy of Sciences,aiming to operate at a distance of 5 to 10 solar radii from the Sun,plans to complete the in situ detection of the solar eruption process and observation of the magnetic field structure response.The solar flux received by the satellite ranges from 10^(3) to 10^(6) Wm^(-2),which poses challenges for thermal management of the solar arrays.In this work,the solar array cooling system of the Parker Solar Probe is discussed,the developments of the fluid loop technique are reviewed,and a research plan for a next-generation solar array cooling system is proposed.This paper provides a valuable reference for novel thermal control systems in spacecraft for solar observation.

太阳黑子本影振荡的多波段观测

基于多波段的观测数据,研究了黑子本影振荡在太阳大气不同高度或温度的振荡特征.目标黑子发生在2017年9月15日,位于活动区12680.多波段的观测数据包括AIA(Atmospheric Imaging Assembly)的极紫外成像及IRIS(Interface Region Imaging Spectrograph)的紫外光谱和成像.在太阳黑子的本影位置,AIA 1700Å光变曲线的振荡周期约为(4.2±0.8)min,而AIA 1600Å、171Å和193Å光变曲线的振荡周期约为(2.8±0.3)min.IRIS的Mg II h和k谱线及远紫外成像(2796Å)都表现为(3.1±0.5)min的准周期振荡,而谱线Si IV 1393.76Å的振荡周期约为(2.9±0.4)min.观测结果说明黑子本影的振荡周期随着太阳大气高度的升高而逐渐减小.较短的周期可认为是3 min振荡,很可能与黑子本影上方的慢磁声波有关,它起源于温度极小区并向上传播到日冕.较长的周期可解释为光球的5 min振荡,与太阳的P模振荡有关.

A Comprehensive Classification and Analysis of Geomagnetic Storms Over Solar Cycle 24

A geomagnetic storm is a global disturbance of Earth?s magnetosphere,occurring as a result of the interaction with magnetic plasma ejected from the Sun.Despite considerable research,a comprehensive classification of storms for a complete solar cycle has not yet been fully developed,as most previous studies have been limited to specific storm types.This study,therefore,attempted to present complete statistics for solar cycle 24,detailing the occurrence of geomagnetic storm events and classifying them by type of intensity(moderate,intense,and severe),type of complete interval(normal or complex),duration of the recovery phase(rapid or long),and the number of steps in the storm?s development.The analysis was applied to data from ground-based magnetometers,which measured the Dst index as provided by the World Data Center for Geomagnetism,Kyoto,Japan.This study identified 211 storm events,comprising moderate(177 events),intense(33 events),and severe(1 event)types.About 36%of ICMEs and 23%of CIRs are found to be geoeffective,which caused geomagnetic storms.Up to four-step development of geomagnetic storms was exhibited during the main phase for this solar cycle.Analysis showed the geomagnetic storms developed one or more steps in the main phase,which were probably related to the driver that triggered the geomagnetic storms.A case study was additionally conducted to observe the variations of the ionospheric disturbance dynamo(Ddyn)phenomenon that resulted from the geomagnetic storm event of 2015July 13.The attenuation of the Ddyn in the equatorial region was analyzed using the H component of geomagnetic field data from stations in the Asian sector(Malaysia and India).The variations in the Ddyn signatures were observed at both stations,with the TIR station(India)showing higher intensity than the LKW station(Malaysia).

Physics-informed Neural Network for Force-free Magnetic Field Extrapolation

In this paper,we propose a physics-informed neural network extrapolation method that leverages machine learning techniques to reconstruct coronal magnetic fields.We enhance the classical neural network structure by introducing the concept of a quasi-output layer to address the challenge of preserving physical constraints during the neural network extrapolation process.Furthermore,we employ second-order optimization methods for training the neural network,which are more efficient compared to the first-order optimization methods commonly used in classical machine learning.Our approach is evaluated on the widely recognized semi-analytical model proposed by Low and Lou.The results demonstrate that the deep learning method achieves high accuracy in reconstructing the semianalytical model across multiple evaluation metrics.In addition,we validate the effectiveness of our method on the observed magnetogram of active region.

Nonlinear Coupling of Kinetic Alfvén Waves and Ion Acoustic Waves in the Inner Heliosphere

We study the nonlinear coupling of kinetic Alfvén waves with ion acoustic waves applicable to the Earth’s radiation belt and near-Sun streamer belt solar wind using dynamical equations in the form of modified Zakharov systems.Numerical simulations show the formation of magnetic field filamentary structures associated with density humps and dips which become turbulent at later times,redistributing the energy to higher wavenumbers.The magnetic power spectra exhibit an inertial range Kolmogorov-like spectral index value of-5/3 for k_(⊥)ρ_(i)<1 followed by a steeper dissipation range spectra with indices~-3 for the radiation belt case and~-4 for the nearSun streamer belt solar wind case,here k_(⊥)andρ_(i)represent the wavevector component perpendicular to the background magnetic field and the ion thermal gyroradius,respectively.Applying quasilinear theory in terms of the Fokker-Planck equation in the region of wavenumber turbulent spectra,we find the particle distribution function flattening in the superthermal tail population which is the signature of particle energization and plasma heating.

Long-term Variation of the Solar Polar Magnetic Fields at Different Latitudes

The polar magnetic fields of the Sun play an important role in governing solar activity and powering fast solar wind.However,because our view of the Sun is limited in the ecliptic plane,the polar regions remain largely uncharted.Using the high spatial resolution and polarimetric precision vector magnetograms observed by Hinode from 2012 to 2021,we investigate the long-term variation of the magnetic fields in polar caps at different latitudes.The Hinode magnetic measurements show that the polarity reversal processes in the north and south polar caps are non-simultaneous.The variation of the averaged radial magnetic flux density reveals that,in each polar cap,the polarity reversal is completed successively from the 70°latitude to the pole,reflecting a poleward magnetic flux migration therein.These results clarify the polar magnetic polarity reversal process at different latitudes.

基于注意力机制和不确定性损失的太阳磁图超分

为了全面了解太阳活动规律,需要连续观测时长覆盖多个太阳活动周的、高质量数据.太阳磁图是研究太阳活动的重要数据,连续、长时间和高空间分辨率的太阳磁图能够提供更精细的太阳磁场演化信息,有助于更准确地预报太阳活动和空间天气事件.因此,提出一种基于深度学习的超分率算法,对MDI(Michelson Doppler Imager)磁图进行超分,取得与日震和磁成像仪(Helioseismic and Magnetic Imager,HMI)磁图一致的分辨率,从而能够获得持续时长将近两个太阳活动周的高质量太阳磁图数据库.为了引导网络学习磁图中有效的特征信息,将注意力机制引入到网络中,学习注意力权重图.此外,采用了不确定性损失作为模型训练的损失函数,该方法能够对于带有磁场变化的纹理和边缘分配更大的权重,同时不增加网络参数和计算量.实验证明,提出的算法显著提高了超分太阳磁图的质量,在峰值信噪比(Peak Signal-to-Noise Ratio,PSNR:33.3168)、结构相似性(Structure Similarity Index Measure,SSIM:0.8754)、相关性(Correlation Coefficient,CC:0.9323)和均方根误差(Root Mean Square Error,RMSE:21.8544)等指标上取得了最优的结果.

Solar energetic particles intensity variations associated with a tilted-dipole 3D corotating interaction region

The effect of a tilted-dipole three-dimensional corotating interaction region(CIR)on the transport and acceleration of solar energetic particles(SEPs)is studied.In this work,we discussed how the particle intensity longitudinal and radial dependence might be influenced by the background structures.Moreover,we investigate how the spectral index distribution is modulated by the CIR structure We use the focused transport equation(FTE)to describe the propagation and acceleration of SEPs in a tilt-dipole 3D CIR,generated by the high-resolution 3D magnetohydrodynamic(MHD)model.The forward stochastic differential method is used to solve the FTE.The protons with theE~(-4.4)spectrum from 0.5 to 15 MeV are injected uniformly at the heliographic equator of 0.15 AU.Physical quantities are extracted along each interplanetary magnetic field(IMF)line to show the results.In the tilted-dipole CIR background,if injected from the solar equator at the inner boundary,particles in the slow flow are transported to higher latitudes due to the extension of the IMF lines to higher latitudes.The longitudinal patterns of the particles are dominated by the density of IMF lines.The focusing effect modulates the longitudinal variation of the particle intensity and gives rise to new longitudinal intensity peaks.The adiabatic effect largely increases the intensity fluctuation along the longitude.The structure of the solar wind can also lead to the difference of the indexαin the empirical functionI_(max)=kR~(-α),describing the radial variation of peak intensity according to our simulation.Under the influence of the CIR structure,the indexαvaries from 1.9 to 3.4 at 0.3-1.0 AU.The variation of the solar wind speed should be considered when estimating the radial dependence of the SEP peak intensity.The spectra indices rise near the CIR boundaries and drop near the stream interface(SI).The adiabatic effect makes the spatial variability of the spectral index larger.The spectral index could be similar at different radial distances in the CIR structure.

An improved non-uniform fast Fourier transform method for radio imaging of coronal mass ejections

Radioheliographs can obtain solar images at high temporal and spatial resolution,with a high dynamic range.These are among the most important instruments for studying solar radio bursts,understanding solar eruption events,and conducting space weather forecasting.This study aims to explore the effective use of radioheliographs for solar observations,specifically for imaging coronal mass ejections(CME),to track their evolution and provide space weather warnings.We have developed an imaging simulation program based on the principle of aperture synthesis imaging,covering the entire data processing flow from antenna configuration to dirty map generation.For grid processing,we propose an improved non-uniform fast Fourier transform(NUFFT)method to provide superior image quality.Using simulated imaging of radio coronal mass ejections,we provide practical recommendations for the performance of radioheliographs.This study provides important support for the validation and calibration of radioheliograph data processing,and is expected to profoundly enhance our understanding of solar activities.

亮桥与冕环关系的研究进展

亮桥是太阳黑子内部一种常见的结构,通常在亮桥区域会产生一系列的爆发活动,并对黑子演化产生影响。利用太阳动力学天文台(Solar Dynamics Observatory,SDO)搭载的大气成像阵列(Atmospheric Imaging Assembly,AIA)极紫外成像数据和日震学与磁场成像仪(Helioseismic and Magnetic Imager,HMI)视向磁图和矢量磁图,通过统计大数据样本,表明亮桥与冕环之间的抑制特征具有一定的普遍性。冕环缺失区域主要位于亮桥锚定点附近的本影-半影边界上,在该区域,随着亮桥的演化和形态的改变,冕环也表现出显现和消失现象。通过分析HMI磁图数据,亮桥锚定区通常伴随着极性相反的小尺度磁场结构,可以推断亮桥锚定点区域的磁力线与周围相反极性的小尺度磁场结构相连,并形成短程闭合磁环,由于磁环的长度较短,无法延伸到日冕层,因此在日冕层无法观测到冕环。根据研究结果,提出了亮桥与冕环关系模型,用来解释亮桥与冕环之间的磁连接性,这个模型可以解释许多与亮桥相关的物理过程。

西藏多点太阳光谱观测研究

西藏高海拔强太阳辐射为高原大气提供了热源,驱动着东亚大气环流和全球气候变化的“蝴蝶效应”。对该地区地面太阳光谱特征的同步观测能为地面大气环境变化、生态环境变化和太阳能资源利用等研究提供有效的实地数据。利用国际标准高精度太阳光谱仪RAMSES-ACC-VIS和SolarSIM-G,在2020―2021年期间对西藏拉萨、林芝、那曲、日喀则和珠峰地区进行了太阳光谱实地观测,首次同步观测了西藏高海拔地区多点全波段(波长280~2500nm)太阳光谱,研究了西藏多点太阳光谱辐照度的空间分布特征,并对西藏高海拔地区太阳光谱的吸收和散射等消光因素做了定性分析。研究发现在西藏五个观测地区中日喀则和珠峰地区全年平均太阳光谱辐照度最强,两地年均光谱峰值达0.83 W/(m^(2)·nm)以上;拉萨太阳光谱峰值仅次于日喀则和珠峰地区,年均峰值约0.73 W/(m^(2)·nm);那曲地区年均太阳光谱辐照度低于拉萨,峰值约0.53 W/(m^(2)·nm);林芝太阳光谱最低。在太阳光谱辐照度的空间分布特征方面,研究发现冬至日西藏光谱空间分布基本遵循纬向地带性规律,辐射强度随纬度升高而递减,而夏至日西藏各地因雨季原因纬向地带性规律不明显。

太阳短曝光图像的选帧算法仿真研究

太阳短曝光图像对太阳研究具有重要的科研意义。目前太阳望远镜通常采用斑点成像技术达到减轻大气湍流引起的图像变形、扭曲而获得高分辨率太阳图像的目的。斑点成像技术中经常使用帧选择算法遴选出太阳短曝光图像进行重建。为了获得更高质量的重建帧,始终需要找到更好的方法来评价观测太阳短曝光图像的质量,因此质量评价方法是否得当直接影响后续图像重建帧的选择。从多种质量评价方法的仿真实验结果得出,基于梯度相似性的无参考图像质量评价方法能够对太阳短曝光图像质量评价有着较好的结果,从而提高太阳短曝光图像的选帧效率。

太阳极紫外光谱探测的历史与展望

围绕国际一流科学目标,发展顶级探测设备是中国太阳物理位列国际先进行列的立足点。70多年的空间太阳探测历程中,极紫外波段探测发挥了极其重要的作用,极紫外观测设备也几乎成为了太阳探测卫星的必备载荷之一。中国在极紫外探测,尤其是光谱探测方面的基础非常薄弱,导致相关科学研究几乎全部依赖国外数据,从而严重制约了中国太阳物理学科的发展。本文根据太阳极紫外探测的特点,系统分析了国外光谱探测的历史、现状以及未来发展趋势,并归纳了三类主要探测方式,即全日面积分光谱探测、低速光谱成像探测、快速光谱成像探测的当前水平,包括其技术方案及取得的部分科学成果。在此基础上,提出中国太阳极紫外光谱探测“三步走”的发展思路,并对每一步的科学目标、指标需求和候选探测方案提出建议。同时,展望了在太阳极紫外成像探测方面开展创新性尝试的思路。

太阳高能粒子强度与日冕物质抛射及其Ⅱ型射电暴的关系

本文选取了第24太阳活动周2010年1月至2014年9月期间的快速、大角宽日冕物质抛射(CME)事件,结合不同约束条件下Richardson(2014)太阳高能粒子(SEP)强度经验模型输出结果,分析了CME属性、先行CME(pre-CME)、Ⅱ型射电暴等观测特征对SEP强度的影响,探讨了SEP事件的产生及其强度与这些特征的关系.主要结论如下:1)快速CME前13 h内是否存在pre-CME对模型预测效果和快速CME是否产生SEP事件有明显影响,但pre-CME的数量对模型输出结果没有明显改善.2)相比于无Ⅱ型射电暴伴随的快速CME而言,伴随Ⅱ型射电暴的CME爆发产生SEP事件的误报占比明显更低(42%),以此为约束条件,可更加突显大SEP事件(如峰值≥0.01 pfu/Me V)的模型预测值与观测值的关联;如果考虑射电增强,则SEP事件的误报占比可进一步下降至29.4%,模型预测效果显著提升.3)Ⅱ型射电暴的起始频率和结束频率对误报占比的影响不大,以此作为条件约束对模型预测效果提升不明显.4)如考虑Ⅱ型射电暴的细分类型作为模型约束条件,伴随多波段Ⅱ型射电暴的CME比单一波段事件具有更好的模型预测效果,如m-DH-kmⅡ型射电暴事件,具有较低的误报占比(35.4%),准确率较高.研究结果显示,除了CME的速度和角宽参数外,pre-CME、Ⅱ型射电暴及其增强、多波段类型等特征作为CME产生SEP事件的约束条件,SEP预测强度与观测强度具有较好的一致性,可以获得较优的模型预测效果.这也进一步表明了伴随有pre-CME、多波段Ⅱ型射电暴及其增强的快速大角宽CME更容易产生SEP事件,这些特征可作为SEP-rich类CME的辨别信号.