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A study on the dynamic spectral indices for SEP events on 2000 July 14 and 2005 January 20

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Research in Astronomy and Astrophysics 2020年第3期20卷 129-135页

作者： Ming-Xian Zhao Gui-Ming Le Key laboratory of space weather National Center for Space WeatherChina Meteorological Administration.Beijing 100081China

We have studied the dynamic proton spectra for the two solar energetic particle(SEP)events on2000 July 14(hereafter GLE59)and 2005 January 20(hereafter GLE69).The source locations of GLE59 and GLE69 are N22 W07 and N12 W58 *** fluxes>30 Me V have been used to compute the dynamic spectral indices of the two SEP *** results show that spectral indices of the two SEP events increased more swiftly at early times,suggesting that the proton fluxes>30 Me V might be accelerated particularly by the concurrent flares at early times for the two SEP *** the GLE69 with source location at N12 W58,both flare site and shock nose are well connected with the Earth at the earliest ***,only the particles accelerated by the shock driven by eastern flank of the CME can propagate along the interplanetary magnetic field line to the Earth after the *** the GLE59 with source location at N22 W07,only the particles accelerated by the shock driven by western flank of the associated CME can reach the Earth after the *** results also show that there was slightly more than one hour during which the proton spectra for GLE69 are softer than that for GLE59 after the flares,suggesting that the shock driven by eastern flank of the CME associated with GLE69 is weaker than the shock driven by the western flank of the CME associated with *** results support that quasi-perpendicular shock has stronger potential in accelerating particles than the quasi-parallel *** results also suggest that only a small part of the shock driven by western flank of the CME associated with the GLE59 is quasi-perpendicular.

关键词： Sun:flares-Sun coronal mass ejections(CMEs)-Sun particle emission-Sun solarterrestrial relations

Large scale current systems developed from substorm onset:Global MHD results

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Science China(Technological Sciences) 2018年第3期61卷 389-396页

作者： TANG BinBin WANG Chi State Key laboratory of space weather National Space Science Center Chinese Academy of Sciences

We investigate the large-scale substorm current systems developed from its onset in an idealized substorm event simulated by global magnetohydrodynamic(MHD) models. Mainly three current systems(loops) are revealed:(1) the classical substorm current wedge, which is composed by the disputed cross-tail current in the magnetotail, the nightside westward electrojet in the high-latitude ionosphere and a pair of region 1 field-aligned currents(FAC);(2) the partial-ring current system, which is braced by two region 2 FACs; and(3) the meridional current system, which is formed by an equatorial radial current(outward/inward in the morning/evening sector), and region 1 and region 2 FACs at its two ends. The region 2 FAC connects with region 1 FAC by a latitudinal horizontal current at each morning/evening ionosphere to complete Loops 2 and 3. A quantitative study shows the significant enhancement of these current systems during the substorm expansion phase, while Loop 1 dominates, which can reach a magnitude of ~1 MA. Empirical relations among the ionospheric currents and the related magnetotail currents are established based on the simulation results, implying that the substonn current systems are not evolved locally or separately, but must be viewed from a global perspective. This knowledge of large-scale substorm current system would deepen our understanding of the substorm development and could be validated by observations in the future.

关键词： magnetospheric physics substorm current system magnetohydrodynamic(MHD) simulation

GPU-accelerated computing of three-dimensional solar wind background

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Science China Earth Sciences 2013年第11期56卷 1864-1880页

作者： FENG XueShang ZHONG DingKun XIANG ChangQing ZHANG Yao SIGMA weather Group State Key Laboratory for Space Weather Center for Space Science and Applied ResearchChinese Academy of Sciences

High-performance computational models are required to make the real-time or faster than rea^-time numerical prediction of adverse space weather events and their influence on the geospace environment. The main objective in this article is to explore the application of programmable graphic processing units （GPUs） to the numerical space weather modeling for the study of solar wind background that is a crucial part in the numerical space weather modeling. GPU programming is realized for our Solar-Interplanetary-CESE MHD model （SIP-CESE MHD model） by numerically studying the solar corona/interplanetary so- lar wind. The global solar wind structures are obtained by the established GPU model with the magnetic field synoptic data as input. Meanwhile, the time-dependent solar surface boundary conditions derived from the method of characteristics and the mass flux limit are incorporated to couple the observation and the three-dimensional （3D） MHD model. The simulated evolu- tion of the global structures for two Carrington rotations 2058 and 2062 is compared with solar observations and solar wind measurements t^om spacecraft near the Earth. The MHD model is also validated by comparison with the standard potential field source surface （PFSS） model. Comparisons show that the MHD results are in good overall agreement with coronal and interplanetary structures, including the size and distribution of coronal holes, the position and shape of the streamer belts, and the transition of the solar wind speeds and magnetic field polarities.

关键词： space weather modeling SIP-CESE MHD model GPU computing

A New Hybrid Numerical Scheme for Two-Dimensional Ideal MHD Equations

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Chinese Physics Letters 2012年第9期29卷 101-104页

作者： ZHOU Yu-Fen FENG Xue-Shang SIGMA weather Group State Key Laboratory for Space WeatherCenter for Space Science and Applied ResearchChinese Academy of SciencesBeijing 100190

We present a new hybrid numerical scheme for two-dimensional(2D)ideal magnetohydrodynamic(MHD)equations.A simple conservation element and solution element(CESE)method is used to calculate the flow variables,and the unknown first-order spatial derivatives involved in the CESE method are computed with a finite volume scheme that uses the solution of the derivative Riemann problem with limited reconstruction to evaluate the numerical flux at cell interface *** show the validation and capacity of its application to 2D MHD problems,we study several benchmark *** results verify that the hybrid scheme not only performs well,but also can retain the solution quality even if the Courant number ranges from close to 1 to less than 0.01.

关键词： scheme element verify

An improved CESE method and its application to steady-state coronal structure simulation

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Science China Earth Sciences 2014年第1期57卷 153-166页

作者： ZHOU YuFen FENG XueShang SIGMA weather Group State Key Laboratory for Space Weather Center for Space Science and Applied ResearchChinese Academy of Sciences

This paper presents an improved space-time conservation element and solution element(CESE)method by applying a non-staggered space-time mesh system and simply improving the calculation of flow variables and applies it to magnetohydrodynamics(MHD)*** improved CESE method can improve the solution quality even with a large disparity in the Courant number(CFL)when using a fixed global marching ***,for a small CFL(say<0.1),the method can significantly reduce the numerical dissipation and retain the solution quality,which are verified by two benchmark *** meanwhile,comparison with the original CESE scheme shows better resolution of the improved scheme ***,we demonstrate its validation through the application of this method in three-dimensional coronal dynamical structure with dipole magnetic fields and measured solar surface magnetic fields as the initial input.

关键词： improved CESE scheme numerical dissipation steady-state coronal structure

Spatial Distribution and Anisotropy of Energetic Particles Accelerated by Shock Waves: Focused Transport Model

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Chinese Physics Letters 2013年第1期30卷 235-238页

作者： ZUO Ping-Bing FENG Xue-Shang SIGMA weather Group State Key Laboratory of Space WeatherCenter for Space Science and Applied ResearchChinese Academy of SciencesBeijing 100190

The focused transport equation(FTE)contains the necessary physics of shock acceleration but avoids the limitation of small pitch-angle anisotropy inherent in the cosmic ray transport *** present a focused transport model based on FTE to investigate the spatial distribution and anisotropy of energetic particles accelerated by shock waves from pickup *** is found that in the upstream of the shock,the accelerated particles are highly anisotropic,but in the downstream it is approximately *** intensity spike is formed across the *** simulation results are qualitatively consistent with the observations of the termination shock particles by two Voyager spacecraft in the vicinity of the termination shock.

关键词： equation. shock anisotropy

Characteristics of the boundary layer of magnetic clouds and a new definition of the cloud boundary

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Science China(Technological Sciences) 2003年第1期46卷 19-32页

作者：魏奉思刘睿范全林冯学尚 SIGMA weather Group Laboratory for Space Weather Center for Space Science and Applied Research Chinese Academy of Sciences Beijing 100080 China

Based on the analysis of the boundaries of 70 magnetic clouds from 1967 to 1998, and relatively complete spacercraft observations, it is indicated that the magnetic cloud boundaries are boundary layers formed through the interaction between the magnetic clouds and the ambient medium. Most of the outer boundaries of the layers, with relatively high proton temperature, density and plasma β, are magnetic reconnection boundaries, while the inner boundaries, with low proton temperature, proton density and plasma β, separate the main body of magnetic clouds, which has not been affected by the interaction, from the boundary layers. The average time scale of the front boundary layer is 1.7 h and that of the tail boundary layer 3.1 h. It is also found that the magnetic probability distribution function undergoes significant changes across the boundary layers. This new definition, supported by the preliminary numerical simulation in principle, could qualitatively explain the observations of interplanetary magnetic clouds, and could help resolve the controversy in identifying the boundaries of magnetic clouds. Our concept of the boundary layer may provide some understanding of what underlies the observations, and a fresh train of thought in the interplanetary dynamics research.

关键词： interplanetary, magnetic cloud boundary, magnetic reconnection.

Dependence of large SEP events with different energies on the associated flares and CMEs

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Research in Astronomy and Astrophysics 2017年第12期17卷 41-52页

作者： Gui-Ming Le Xue-Feng Zhang Key laboratory of space weather National Center for Space WeatherChina Meteorological Administration School of Computer Science Anhui University of Technology

To investigate the dependence of large gradual solar energetic particle（SEP） events on the associated flares and coronal mass ejections（CMEs）, the correlation coefficients（CCs） between peak intensities of E 〉 10 MeV（I10）, E 〉 30 MeV（I30） and E 〉 50 MeV（I50） protons and soft X-ray（SXR） emission of associated flares and the speeds of associated CMEs in the three longitudinal areas W0–W39, W40–W70（hereafter the well connected region） and W71–W90 have been *** correlation analysis shows that CCs between SXR emission and peak intensities of SEP events always reach their largest value in the well connected region and then decline dramatically in the longitudinal area outside the well connected region, suggesting that they may contribute to the production of SEPs in large SEP events. Both classical and partial correlation analyses show that SXR fluence is a better parameter describing the relationship between flares and SEP events. For large SEP events with source location in the well connected region, the CCs between SXR fluence and I10, I30 and I50 are0.58±0.12, 0.80±0.06 and 0.83±0.06 respectively, while the CCs between CME speed and I10, I30 and I50 are 0.56±0.12, 0.52±0.13 and 0.48±0.13 respectively. The partial correlation analyses show that in the well connected region, both CME shock and SXR fluence can significantly affect I10, but SXR peak flux makes no additional contribution. For E 〉 30 MeV protons with source location in the well connected region, only SXR fluence can significantly affect I30, and the CME shock makes a small contribution to I30, but SXR peak flux makes no additional contribution. For E 〉 50 MeV protons with source location in the well connected region, only SXR fluence can significantly affect I50, but both CME shock and SXR peak flux make no additional contribution. We conclude that these findings provide statistical evidence that for SEP events with source locations in the well connected region, a CME shock is only an effect

关键词： Sun:coronal mass ejections(CMEs) Sun:flares (Sun:)particle emission

Cause of winter gravity wave spectrum saturation

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Science China Earth Sciences 2005年第10期48卷 1802-1808页

作者： WU Yongfu XU Jiyao laboratory for space weather Center for Space Science and Applied Research Chinese Academy of Sciences Beijing 100080 China Laboratory for Space Weather Center for Space Science and Applied Research Chinese Academy of Sciences Beijing 100080 China

This paper utilizes horizontal velocity measurements observed from 19 chaff rockets and nearly simultaneous temperature measurements collected from 19 falling sphere rockets to study the cause of winter gravity wave spectrum saturation. Results suggest that strong hori-zontal velocity shears larger than 0.04 s?1 are observed to be present at various heights near the winter mesopause. On one single chaff rocket flight, an extremely strong horizontal velocity shear as high as 0.33 s?1 is observed at 87.4 km and is believed to be the strongest value ever meas-ured in the mesosphere. These strong horizontal velocity shears, together with Brunt-V?is?l? frequency squared obtained from the temperature profile, act collectively to yield two dynamical instability regions of Richardson number smaller than 1/4, suggesting that the saturated gravity wave spectrum observed by the chaff rockets in winter is a result of dynamical instability.

关键词： winter spectrum, strong shear, dynamical instability, spectrum saturation.