The solar energetic particle(SEP)event is a kind of hazardous space weather phenomena,so its quantitative forecast is of great importance from the aspect of space environmental situation awareness.We present here a se...The solar energetic particle(SEP)event is a kind of hazardous space weather phenomena,so its quantitative forecast is of great importance from the aspect of space environmental situation awareness.We present here a set of SEP forecast tools,which consists of three components:(1)a simple polytropic solar wind model to estimate the background solar wind conditions at the inner boundary of 0.1 AU(about 20 R⊙);(2)an ice-cream-cone model to estimate the erupted coronal mass ejection(CME)parameters;and(3)the improved Particle Acceleration and Transport in the Heliosphere(i PATH)model to calculate particle fluxes and energy spectra.By utilizing the above models,we have simulated six realistic SEP events from 2010 August 14 to 2014 September 10,and compared the simulated results to the Geostationary Operational Environmental Satellites(GOES)spacecraft observations.The results show that the simulated fluxes of>10 Me V particles agree with the observations while the simulated fluxes of>100 Me V particles are higher than the observed data.One of the possible reasons is that we have adopted a simple method in the model to calculate the injection rate of energetic particles.Furthermore,we have conducted the ensemble numerical simulations over these events and investigated the effects of different background solar wind conditions at the inner boundary on SEP events.The results imply that the initial CME density plays an important role in determining the power spectrum,while the effect of varying background solar wind temperature is not significant.Naturally,we have examined the influence of CME initial density on the numerical prediction results for virtual SEP cases with different CME ejection speeds.The result shows that the effect of initial CME density variation is inversely associated with CME speed.展开更多
Kinematic properties of coronal mass ejections （CMEs） suffer from projection effects,and it is expected that the real velocity should be larger and the real angular width should be smaller than the apparent values.S...Kinematic properties of coronal mass ejections （CMEs） suffer from projection effects,and it is expected that the real velocity should be larger and the real angular width should be smaller than the apparent values.Several attempts have been taken to correct the projection effects,which however led to an inflated average velocity probably due to the biased choice of CME events.In order to estimate the overall influence of the projection effects on the kinematic properties of the CMEs,we perform a forward modeling of real distributions of CME properties,such as the velocity,the angular width,and the latitude,by requiring their projected distributions to best match observations.Such a matching is conducted by Monte Carlo simulations.According to the derived real distributions,we found that （1） the average real velocity of all non-full-halo CMEs is about 514 km s-1,and the average real angular width is about 33°,in contrast to the corresponding apparent values of 418 km s-1 and 42.7° in observations;（2） For the CMEs with the angular width in the range of 20°-120°,the average real velocity is 510 km s-1 and the average real angular width is 43.4°,in contrast to the corresponding apparent values of 392 km s-1 and 52° in observations.展开更多
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05:35 UT爆发的CME-EUV波(Coronal Mass Ejections...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05:35 UT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EUV1/STEREOB195 A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247 km.s^(-1),数值模拟得到的EUV波速度为245 km·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.展开更多
Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal fie...Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal field at the solar surface is the same or very close to that of a central dipole. The characteristic plasma β (the ratio between gas pressure and magnetic pressure) is taken to be so small (β = 10-4) that the magnetic field is close to being force-free. The system as a whole is then let evolve quasi-statically with a slow increase of either the annular magnetic flux or the axial magnetic flux of the rope, and the total magnetic energy of the system grows accordingly. It is found that there exists an energy threshold: the flux rope sticks to the solar surface in equilibrium if the magnetic energy of the system is below the threshold, whereas it loses equilibrium if the threshold is exceeded. The energy threshold is found to be larger than that of the corresponding fully-open magnetic field by a factor of nearly 1.08 irrespective as to whether the background field is completely closed or partly open, or whether the magnetic energy is enhanced by an increase of annular or axial flux of the rope. This gives an example showing that a force-free magnetic field may have an energy larger than the corresponding open field energy if part of the field lines is allowed to be detached from the solar surface. The implication of such a conclusion in coronal mass ejections is briefly discussed and some comments are made on the maximum energy of force-free magnetic fields.展开更多
通过两种不同方法对太阳高能粒子(Solar Energetic Particles,SEP)通量初始时刻进行研究,一种是数值模拟方法,即数值模拟中取第一颗粒子出现的时刻来确定,另一种是观测背景方法,即通过太阳高能粒子通量随时间变化的背景值与上升值的拐...通过两种不同方法对太阳高能粒子(Solar Energetic Particles,SEP)通量初始时刻进行研究,一种是数值模拟方法,即数值模拟中取第一颗粒子出现的时刻来确定,另一种是观测背景方法,即通过太阳高能粒子通量随时间变化的背景值与上升值的拐点时刻来确定.Kahler(2013)定义的SEP时间尺度TO(the onset time from CME launch to SEP onset,从CME爆发时刻到SEP初始时刻的时间段)、TR(the rise time from onset to half the peak intensity(0.5Ip),从SEP初始时刻的上升时间直到半峰值时刻)、TD(the duration of the SEP intensity above 0.5Ip,SEP强度高于半峰值的持续时间)都与SEP通量初始时刻相关.将CME驱动激波作为源,利用粒子输运方程,对SEP传播进行数值模拟.然后对描述SEP时间尺度的TR、TO的数值模拟值与观测进行对比,发现两者吻合很好,即TR随CME速度和宽度增加而增加.由于TO影响的因素较为复杂,并没有很好的规律性.另外,当源位置经度距离观测者较远的时候,影响时间尺度TR,TO的因素较多.因此,用不同方法确定的SEP通量初始时刻对TR,TO的影响不大;当源位置经度距离观测者较近的时候,观测背景方法下的数值模拟与观测更加符合.展开更多
Observations from multiple spacecraft show that there are energy spectral ＂breaks＂ at 1-10 MeV in some large CME-driven shocks. However, numerical models can hardly simulate this property due to high computational e...Observations from multiple spacecraft show that there are energy spectral ＂breaks＂ at 1-10 MeV in some large CME-driven shocks. However, numerical models can hardly simulate this property due to high computational expense. The present paper focuses on analyzing these energy spectral ＂breaks＂ by Monte Carlo particle simulations of an isolated CME-driven shock. Taking the 2006 Dec 14 CME-driven shock as an example, we investigate the formation of this energy spectral property. For this purpose, we apply different values for the scattering time in our isolated shock model to obtain the highest energy ＂tails,＂ which can potentially exceed the ＂break＂ energy range. However, we have not found the highest energy ＂tails＂ beyond the ＂break＂ energy range, but instead find that the highest energy ＂tails＂ reach saturation near the range of energy at 5 MeV. So, we believe that there exists an energy spectral ＂cut off＂ in an isolated shock. If there is no interaction with another shock, there would not be formation of the energy spectral ＂break＂ property.展开更多
日冕物质抛射(coronal mass ejection,CME)是一种由太阳的剧烈活动所引发的空间天气现象,如何针对特定的CME/太阳风暴事件了解其日冕/行星际传播及演化过程,预报是否以及何时到达地球轨道,预测近地空间太阳风状态相应的变化,是空间天气...日冕物质抛射(coronal mass ejection,CME)是一种由太阳的剧烈活动所引发的空间天气现象,如何针对特定的CME/太阳风暴事件了解其日冕/行星际传播及演化过程,预报是否以及何时到达地球轨道,预测近地空间太阳风状态相应的变化,是空间天气科学界一直关注的重要课题之一.CME通常携带巨大的能量,当其到达地球附近空间时,会造成地球附近空间环境的剧烈扰动,从而引发一系列的灾害性空间天气现象,例如地磁暴.为了能够更好地运用太空资源和发展空间科学,避免遭受由CME引发的灾害性空间天气的损害,对CME的准确预报的能力就显得尤为重要.对CME传播过程进行数值模拟是研究CME演化过程和提高CME预报准确性的重要方法.本文主要介绍了利用数值模拟方法对CME传播过程的最新研究进展.首先总结了用于CME传播数值模拟的各种模型,包括背景太阳风模型、CME初始化模型、日冕磁场重建模型等,总结了各种模型在CME传播模拟过程中的应用及研究进展.然后介绍了关于CME偏转方面的模拟研究进展,包括CME在日冕和行星际空间中不同的偏转特征.接着介绍了CME间的相互作用及其模拟研究的最新动态.最后提出了CME传播过程模拟研究方向亟待解决的若干问题,并对其发展方向和前景进行展望.展开更多
In a solar flare or coronal mass ejection （CME）, observations of the subse- quent interplanetary shock provide us with strong evidence of particle acceleration to energies of multiple MeV, even up to GeV. Diffusive ...In a solar flare or coronal mass ejection （CME）, observations of the subse- quent interplanetary shock provide us with strong evidence of particle acceleration to energies of multiple MeV, even up to GeV. Diffusive shock acceleration is an efficient mechanism for particle acceleration. For investigating the shock structure, the energy injection and energy spectrum ofa CME-driven shock, we perform a dynamical Monte Carlo simulation of the CME-driven shock that occurred on 2006 December 14 using an anisotropic scattering law. The simulated results of the shock＇s fine structure, par- ticle injection, and energy spectrum are presented. We find that our simulation results give a good fit to the observations from multiple spacecraft.展开更多
Solar eruptions,primarily manifested as solar flares,filament eruptions and coronal mass ejections,represent explosive releases of magnetic energy stored in the solar corona,with the potential to drive severe space we...Solar eruptions,primarily manifested as solar flares,filament eruptions and coronal mass ejections,represent explosive releases of magnetic energy stored in the solar corona,with the potential to drive severe space weather.The initiation of solar eruptions remains an open question,leading to various theoretical models that are inferred from observations.However,these models are subjects of debate due to the absence of direct measurements of the three-dimensional(3D)magnetic fields in the corona.Numerical simulations,based on solving magnetohydrodynamics(MHD)equations that govern the macroscopic dynamics of solar corona,serve as a touchstone for testing these theoretical models.One early proposed model suggested that eruptions could be triggered by reconnection within a single sheared magnetic arcade,which is known as the tether-cutting reconnection model,but it was never confirmed through 3D MHD simulations until very recently.Consequently,two models have gained more popularity:one involving the eruption of a twisted magnetic flux rope(MFR)due to ideal instability(or loss of equilibrium),and the other known as the breakout eruption,which requires a quadrupolar configuration with a delicately located magnetic null point.Other mixed mechanisms,involving both ideal instability and reconnection,are also proposed in association with localized magnetic flux emergence.Now with the validation of the tether-cutting model,the fundamental mechanisms are boiled down to two types of models,one primarily based on the ideal instability of a pre-existing MFR,and the other based on the reconnection of sheared field lines with or without an MFR.Recently,the modelling of the birth of solar eruption using observed data-based MHD simulations has advanced rapidly,becoming a crucial research tool in the study of the initiation mechanisms.These realistic modellings reveal a higher level of complexity compared to all currently available theories and idealized models.展开更多
基金supported by the National Science Foundation of China(No.42074224)the Key Research Program of the Chinese Academy of Sciences,grant No.ZDRE-KT-2021-3Pandeng Program of National Space Science Center,Chinese Academy of Sciences。
文摘The solar energetic particle(SEP)event is a kind of hazardous space weather phenomena,so its quantitative forecast is of great importance from the aspect of space environmental situation awareness.We present here a set of SEP forecast tools,which consists of three components:(1)a simple polytropic solar wind model to estimate the background solar wind conditions at the inner boundary of 0.1 AU(about 20 R⊙);(2)an ice-cream-cone model to estimate the erupted coronal mass ejection(CME)parameters;and(3)the improved Particle Acceleration and Transport in the Heliosphere(i PATH)model to calculate particle fluxes and energy spectra.By utilizing the above models,we have simulated six realistic SEP events from 2010 August 14 to 2014 September 10,and compared the simulated results to the Geostationary Operational Environmental Satellites(GOES)spacecraft observations.The results show that the simulated fluxes of>10 Me V particles agree with the observations while the simulated fluxes of>100 Me V particles are higher than the observed data.One of the possible reasons is that we have adopted a simple method in the model to calculate the injection rate of energetic particles.Furthermore,we have conducted the ensemble numerical simulations over these events and investigated the effects of different background solar wind conditions at the inner boundary on SEP events.The results imply that the initial CME density plays an important role in determining the power spectrum,while the effect of varying background solar wind temperature is not significant.Naturally,we have examined the influence of CME initial density on the numerical prediction results for virtual SEP cases with different CME ejection speeds.The result shows that the effect of initial CME density variation is inversely associated with CME speed.
基金supported by the National Basic Research Program of China(No.2011CB811402)the National Natural Science Foundation of China (Grant Nos.11025314,10403003,10933003 and 10673004)
文摘Kinematic properties of coronal mass ejections （CMEs） suffer from projection effects,and it is expected that the real velocity should be larger and the real angular width should be smaller than the apparent values.Several attempts have been taken to correct the projection effects,which however led to an inflated average velocity probably due to the biased choice of CME events.In order to estimate the overall influence of the projection effects on the kinematic properties of the CMEs,we perform a forward modeling of real distributions of CME properties,such as the velocity,the angular width,and the latitude,by requiring their projected distributions to best match observations.Such a matching is conducted by Monte Carlo simulations.According to the derived real distributions,we found that （1） the average real velocity of all non-full-halo CMEs is about 514 km s-1,and the average real angular width is about 33°,in contrast to the corresponding apparent values of 418 km s-1 and 42.7° in observations;（2） For the CMEs with the angular width in the range of 20°-120°,the average real velocity is 510 km s-1 and the average real angular width is 43.4°,in contrast to the corresponding apparent values of 392 km s-1 and 52° in observations.
基金Supported by the National Natural Science Foundation of China
文摘Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal field at the solar surface is the same or very close to that of a central dipole. The characteristic plasma β (the ratio between gas pressure and magnetic pressure) is taken to be so small (β = 10-4) that the magnetic field is close to being force-free. The system as a whole is then let evolve quasi-statically with a slow increase of either the annular magnetic flux or the axial magnetic flux of the rope, and the total magnetic energy of the system grows accordingly. It is found that there exists an energy threshold: the flux rope sticks to the solar surface in equilibrium if the magnetic energy of the system is below the threshold, whereas it loses equilibrium if the threshold is exceeded. The energy threshold is found to be larger than that of the corresponding fully-open magnetic field by a factor of nearly 1.08 irrespective as to whether the background field is completely closed or partly open, or whether the magnetic energy is enhanced by an increase of annular or axial flux of the rope. This gives an example showing that a force-free magnetic field may have an energy larger than the corresponding open field energy if part of the field lines is allowed to be detached from the solar surface. The implication of such a conclusion in coronal mass ejections is briefly discussed and some comments are made on the maximum energy of force-free magnetic fields.
文摘通过两种不同方法对太阳高能粒子(Solar Energetic Particles,SEP)通量初始时刻进行研究,一种是数值模拟方法,即数值模拟中取第一颗粒子出现的时刻来确定,另一种是观测背景方法,即通过太阳高能粒子通量随时间变化的背景值与上升值的拐点时刻来确定.Kahler(2013)定义的SEP时间尺度TO(the onset time from CME launch to SEP onset,从CME爆发时刻到SEP初始时刻的时间段)、TR(the rise time from onset to half the peak intensity(0.5Ip),从SEP初始时刻的上升时间直到半峰值时刻)、TD(the duration of the SEP intensity above 0.5Ip,SEP强度高于半峰值的持续时间)都与SEP通量初始时刻相关.将CME驱动激波作为源,利用粒子输运方程,对SEP传播进行数值模拟.然后对描述SEP时间尺度的TR、TO的数值模拟值与观测进行对比,发现两者吻合很好,即TR随CME速度和宽度增加而增加.由于TO影响的因素较为复杂,并没有很好的规律性.另外,当源位置经度距离观测者较远的时候,影响时间尺度TR,TO的因素较多.因此,用不同方法确定的SEP通量初始时刻对TR,TO的影响不大;当源位置经度距离观测者较近的时候,观测背景方法下的数值模拟与观测更加符合.
基金supported by the Xinjiang Natural Science Foundation(No.2014211A069)funded by the Key Laboratory of Solar Activity of NAOC,the Key Laboratory of Modern Astronomy and Astrophysics(Nanjing University)Ministry of Education,and the China Scholarship Council(CSC)
文摘Observations from multiple spacecraft show that there are energy spectral ＂breaks＂ at 1-10 MeV in some large CME-driven shocks. However, numerical models can hardly simulate this property due to high computational expense. The present paper focuses on analyzing these energy spectral ＂breaks＂ by Monte Carlo particle simulations of an isolated CME-driven shock. Taking the 2006 Dec 14 CME-driven shock as an example, we investigate the formation of this energy spectral property. For this purpose, we apply different values for the scattering time in our isolated shock model to obtain the highest energy ＂tails,＂ which can potentially exceed the ＂break＂ energy range. However, we have not found the highest energy ＂tails＂ beyond the ＂break＂ energy range, but instead find that the highest energy ＂tails＂ reach saturation near the range of energy at 5 MeV. So, we believe that there exists an energy spectral ＂cut off＂ in an isolated shock. If there is no interaction with another shock, there would not be formation of the energy spectral ＂break＂ property.
文摘日冕物质抛射(coronal mass ejection,CME)是一种由太阳的剧烈活动所引发的空间天气现象,如何针对特定的CME/太阳风暴事件了解其日冕/行星际传播及演化过程,预报是否以及何时到达地球轨道,预测近地空间太阳风状态相应的变化,是空间天气科学界一直关注的重要课题之一.CME通常携带巨大的能量,当其到达地球附近空间时,会造成地球附近空间环境的剧烈扰动,从而引发一系列的灾害性空间天气现象,例如地磁暴.为了能够更好地运用太空资源和发展空间科学,避免遭受由CME引发的灾害性空间天气的损害,对CME的准确预报的能力就显得尤为重要.对CME传播过程进行数值模拟是研究CME演化过程和提高CME预报准确性的重要方法.本文主要介绍了利用数值模拟方法对CME传播过程的最新研究进展.首先总结了用于CME传播数值模拟的各种模型,包括背景太阳风模型、CME初始化模型、日冕磁场重建模型等,总结了各种模型在CME传播模拟过程中的应用及研究进展.然后介绍了关于CME偏转方面的模拟研究进展,包括CME在日冕和行星际空间中不同的偏转特征.接着介绍了CME间的相互作用及其模拟研究的最新动态.最后提出了CME传播过程模拟研究方向亟待解决的若干问题,并对其发展方向和前景进行展望.
基金supported by the National Natural Science Foundation of China (Grant No. 10921303)the National Basic Research Program of the Ministry of Science and Technology (MOST Grant No. 2011CB 811401)
文摘In a solar flare or coronal mass ejection （CME）, observations of the subse- quent interplanetary shock provide us with strong evidence of particle acceleration to energies of multiple MeV, even up to GeV. Diffusive shock acceleration is an efficient mechanism for particle acceleration. For investigating the shock structure, the energy injection and energy spectrum ofa CME-driven shock, we perform a dynamical Monte Carlo simulation of the CME-driven shock that occurred on 2006 December 14 using an anisotropic scattering law. The simulated results of the shock＇s fine structure, par- ticle injection, and energy spectrum are presented. We find that our simulation results give a good fit to the observations from multiple spacecraft.
基金supported by the National Natural Science Foundation of China(Grant No.42174200)the Guangdong Basic and Applied Basic Research Foundation(Grant No.2023B1515040021)+1 种基金the Shenzhen Science and Technology Innovation Program(Grant No.RCJC20210609104422048)the Shenzhen Key Laboratory Launching Project(Grant No.ZDSYS20210702140800001)。
文摘Solar eruptions,primarily manifested as solar flares,filament eruptions and coronal mass ejections,represent explosive releases of magnetic energy stored in the solar corona,with the potential to drive severe space weather.The initiation of solar eruptions remains an open question,leading to various theoretical models that are inferred from observations.However,these models are subjects of debate due to the absence of direct measurements of the three-dimensional(3D)magnetic fields in the corona.Numerical simulations,based on solving magnetohydrodynamics(MHD)equations that govern the macroscopic dynamics of solar corona,serve as a touchstone for testing these theoretical models.One early proposed model suggested that eruptions could be triggered by reconnection within a single sheared magnetic arcade,which is known as the tether-cutting reconnection model,but it was never confirmed through 3D MHD simulations until very recently.Consequently,two models have gained more popularity:one involving the eruption of a twisted magnetic flux rope(MFR)due to ideal instability(or loss of equilibrium),and the other known as the breakout eruption,which requires a quadrupolar configuration with a delicately located magnetic null point.Other mixed mechanisms,involving both ideal instability and reconnection,are also proposed in association with localized magnetic flux emergence.Now with the validation of the tether-cutting model,the fundamental mechanisms are boiled down to two types of models,one primarily based on the ideal instability of a pre-existing MFR,and the other based on the reconnection of sheared field lines with or without an MFR.Recently,the modelling of the birth of solar eruption using observed data-based MHD simulations has advanced rapidly,becoming a crucial research tool in the study of the initiation mechanisms.These realistic modellings reveal a higher level of complexity compared to all currently available theories and idealized models.
