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A Particle-in-Cell Simulation Study on Harmonic Waves Excited by Electron Beams in Unmagnetized Plasmas

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Chinese Physics Letters 2016年第8期33卷 69-72页

作者：郭俊 College of Mathematics and Physics Qingdao University of Science and Technology State Key laboratory of space weather Chinese Academy of Sciences

The excitation of harmonic waves by an electron beam is studied with electrostatic simulations. The results suggest that the harmonic waves are excited during the linear stage of the simulation and are developed in the nonlinear stage. First, the Langmuir waves （LWs） are excited by the beam electrons. Then the coupling of the forward propagating LWs and beam modes will excite the second harmonic waves. The third harmonic waves will be produced if the lower velocity side of the beam still has a positive velocity gradient. The beam velocity decreases at the same time, which provides the energy for wave excitation. We find that it is difficult to excite the harmonic waves with the increase of the thermal velocity of the beam electrons. The beam electrons will be heated after waves are excited, and then the part of the forward propagating LWs will turn into electron acoustic waves under the condition with a large enough intensity of beam electrons. Moreover, the action of ions hardly affects the formation of harmonic waves.

关键词： in is of that on by

Irreversible rapid changes of magnetic field associated with the 2012 October 23 circular near-limb X1.8 Flare

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Research in Astronomy and Astrophysics 2016年第6期16卷 99-104页

作者： Dan-Dan Ye Chang Liu Haimin Wang space weather Research laboratory and Big Bear Solar Observatory New Jersey Institute of TechnologyUniversity Heights

It has been found that photospheric magnetic fields can change in accordance with restructuring of the three-dimensional magnetic field following solar eruptions. Previous studies mainly use vector mag- netic field data taken for events near the disk center. In this paper, we analyze the magnetic field evolution associated with the 2012 October 23 X1.8 flare in NOAA AR 11598 that is close to the solar limb, using both the 45 s cadence line-of-sight and 12 min cadence vector magnetograms from the Helioseismic and Magnetic Imager on board Solar Dynamics Observatory. This flare is classified as a circular-ribbon flare with spine-fan type magnetic topology containing a null point. In the line-of-sight magnetograms, there are two apparent polarity inversion lines （PILs）. The PIL closer to the limb is affected more by the projection effect. Between these two PILs there lie positive polarity magnetic fields, which are surrounded by negative polarity fields outside the PILs. We find that after the flare, both the apparent limb-ward and disk-ward negative fluxes decrease, while the positive flux in-between increases. We also find that the horizontal mag- netic fields have a significant increase along the disk-ward PIL, but in the surrounding area, they decrease. Synthesizing the observed field changes, we conclude that the magnetic fields collapse toward the surface above the disk-ward PIL as depicted in the coronal implosion scenario, while the peripheral field turns to a more vertical configuration after the flare. We also suggest that this event is an asymmetric circular-ribbon flare： a flux rope is likely present above the disk-ward PIL. Its eruption causes instability of the entire fan-spine structure and the implosion near that PIL.

关键词： Sun flares -- Sun magnetic field

Effect of Chorus Latitudinal Distribution on Evolution of Outer Radiation Belt Electrons

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Plasma Science and Technology 2009年第5期11卷 544-549页

作者：肖伏良李君求唐立军贺艺华厉江帆 School of Physics and Electronic Sciences Changsha University of Science and Technology State Key laboratory of space weather Chinese Academy of Sciences

Primary result on the impact of the latitudinal distribution of whistler-mode chorus upon temporal evolution of the phase space density （PSD） of outer radiation belt energetic electrons was presented. We evaluate diffusion rates in pitch angle and momentum due to a band of chorus frequency distributed at a standard Gaussian spectrum, and solve a 2-D bounce-averaged momentum-pitch-angle Fokker-Planck equation at L = 4.5. It is shown that chorus is effective in accelerating electrons and can increase PSD for energy of ～1 MeV by a factor of 10 or more in about one day, which is consistent with observation. Moreover, the latitudinal distribution of chorus has a great impact on the acceleration of electrons. As the latitudinal distribution increases, the efficient acceleration region extends from higher pitch angles to lower pitch angles, and even covers the entire pitch angle region when chorus power reaches the maximum latitude λm = 45°.

关键词： wave-particle interaction acceleration of energetic electrons whistler-modechorus latitudinal distribution

Ultralow frequency wave characteristics extracted from particle data:Application of IGSO observations

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Science China(Technological Sciences) 2017年第3期60卷 419-424页

作者： LI Li ZHOU XuZhi ZONG QiuGang CHEN XingRan ZOU Hong REN Jie HAO YiXin ZHANG XianGuo Institute of space Physics and Applied Technology Peking University College of Astronautics Nanjing University of Aeronautics and Astronautics State Key laboratory of space weather National Space Science CenterChinese Academy of Sciences

3 Summary and discussion In the generalized drift resonance theory[17],a characteristic signature of the ULF wave-particle interactions is the increasingly-tilted stripes in the particle energy *** phase difference ac... 详细信息

关键词： ultralow frequency waves wave-particle interactions drift resonance ULF wave characteristics

Three-dim ensional MHD simulation for the solar wind structure observed by Ulysses

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Chinese Science Bulletin 2001年第16期46卷 1352-1355页

作者： Shi Yong WeiFengSi Feng Xueshang Ye ZhanYin laboratory for space weather Center for Space Science and Applied ResearchChinese Academy of SciencesBejing 100080China

Ulysses has been the first spacecraft to explore the high latitudinal regions of the heliosphere till now. During its first rapid pole-to-pole transit from September 1994 to June 1995, Ulysses observed a fast speed flow with magnitude reaching 700—800 km/s at high latitudinal region except 20°area near the ecliptic plane where the velocity is 300—400 km/s. The observations also showed a sudden jump of the velocity across the two regions. In this note, based on the characteristic and representative observations of the solar magnetic field and K-coronal polarized brightness, the large-scale solar wind structure mentioned above is reproduced by using a three-dimensional MHD model. The numerical results are basically consistent with those of Ulysses observations. Our results also show that the distributions of magnetic field and plasma number density on the solar source surface play an important role in governing this structure. Furthermore, the three-dimensional MHD model used here has a robust ability to simulate this kind of large-scale wind structure.

关键词： Ulysses solar wind structure numerical simulation

Magnetohydrodynamics (MHD) numerical simulations on the interaction of the solar wind with the magnetosphere: A review

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Science China Earth Sciences 2013年第7期56卷 1141-1157页

作者： WANG Chi GUO XiaoCheng PENG Zhong TANG BinBin SUN TianRan LI WenYa HU YouQiu State Key laboratory of space weather Center for Space Science and Applied Research Chinese Academy of Sciences School of Earth and space Sciences University of Science and Technology of China

The magnetosphere is the outermost layer of the geospace, and the interaction of the solar wind with the magnetosphere is the key element of the space weather cause-and-effect chain process from the Sun to Earth, which is one of the most challenging scientific problems in the geospace weather study. The nonlinearity, multiple component, and time-dependent nature of the geospace make it very difficult to describe the physical process in geospace using traditional analytic analysis approach. Numerical simulations, a new research tool developed in recent decades, have a deep impact on the theory and application of the geospace. MHD simulations started at the end of the 1970s, and the initial study was limited to two-dimensional (2D) cases. Due to the intrinsic three-dimensional (3D) characteristics of the geospace, 3D MHD simulations emerged in the 1980s, in an attempt to model the large-scale structures and fundamental physical processes in the magnetosphere. They started to combine with the space exploration missions in the 1990s and make comparisons with observations. Physics-based space weather forecast models started to be developed in the 21st century. Currently only a few space-power countries such as USA and Japan have developed 3D magnetospheric MHD models. With the rapid advance of space science in China, we have developed a new global MHD model, namely PPMLR-MHD, which has high order spatial accuracy and low numerical dissipation. In this review, we will briefly introduce the global 3D MHD modeling, especially the PPMLR-MHD code, and summarize our recent work based on the PPMLR-MHD model, with an emphasis on the interaction of interplanetary shocks with the magnetosphere, large-scale current systems, reconnection voltage and transpolar potential drop, and Kelvin-Helmholtz (K-H) instability at the magnetopause.

关键词： solar wind magnetosphere MHD simulations

Shape and position of Earth's bow shock near-lunar orbit based on ARTEMIS data

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Science China Earth Sciences 2016年第8期59卷 1700-1706页

作者： LIU Ji SHI QuanQi TIAN AnMin Lü JianYong WU Hao WANG Ming FU SuiYan YANG YuChen ZONG QiuGang ZHANG Jiang FENG YongYong PU ZuYin School of space Science and Physics Shandong UniversityWeihai 264209China State Key laboratory of space weather Chinese Academy of SciencesBeijing 100190China Institute of space weather Nanjing University of Information Science and TechnologyNanjing 210044China School of Earth and space Sciences Peking UniversityBeijing 100871China

Earth's bow shock is the result of interaction between the supersonic solar wind and Earth's magnetopause. However, data limitations mean the model of the shape and position of the bow shock are based largely on near-Earth satellite data. The model of the bow shock in the distant magnetotail and other factors that affect the bow shock, such as the interplanetary magnetic field(IMF) B_y, remain unclear. Here, based on the bow shock crossings of ARTEMIS from January 2011 to January 2015, new coefficients of the tail-flaring angle a of the Chao model(one of the most accurate models currently available) were obtained by fitting data from the middle-distance magnetotail(near-lunar orbit, geocentric distance -20R_E>X>-50R_E). In addition, the effects of the IMF B_y on the flaring angle a were analyzed. Our results showed that:(1) the new fitting coefficients of the Chao model in the middle-distance magnetotail are more consistent with the observed results;(2) the tail-flaring angle a of the bow shock increases as the absolute value of the IMF B_y increases. Moreover, positive IMF B_y has a greater effect than negative IMF B_y on flaring angle. These results provide a reference for bow shock modeling that includes the IMF B_y.

关键词： Bow shock Interplanetary magnetic field(IMF) Magnetosphere Solar wind

Modeling the Earth's magnetosphere under the influence of solar wind with due northward IMF by the AMR-CESE-MHD model

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Science China Earth Sciences 2015年第7期58卷 1235-1242页

作者： WANG Juan DU AiMin ZHANG Ying ZHANG TieLong GE YaSong State Key laboratory of space weather Center for Space Science and Applied ResearchChinese Academy of Sciences Key laboratory of Earth and Planetary Physics Institute of Geology and Geophysics Chinese Academy of Sciences space Research Institute Austrian Academy of Sciences

We present a newly developed global magnetohydrodynamic(MHD) model to study the responses of the Earth's magnetosphere to the solar wind. The model is established by using the space-time conservation element and solution element(CESE) method in general curvilinear coordinates on a six-component grid system. As a preliminary study, this paper is to present the model's numerical results of the quasi-steady state and the dynamics of the Earth's magnetosphere under steady solar wind flow with due northward interplanetary magnetic field(IMF). The model results are found to be in good agreement with those published by other numerical magnetospheric models.

关键词： numerical simulation magnetosphere magnetohydrodynamic model adaptive mesh refinement technique the space-time conservation element and solution element method

Structure and evolution of magnetic fields associated with solar eruptions

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Research in Astronomy and Astrophysics 2015年第2期15卷 145-174页

作者： Haimin Wang Chang Liu space weather Research laboratory and Big Bear Solar Observatory New Jersey Institute of Technology University Heights

This paper reviews the studies of solar photospheric magnetic field evo- lution in active regions and its relationship to solar flares. It is divided into two top- ics, the magnetic structure and evolution leading to solar eruptions and rapid changes in the photospheric magnetic field associated with eruptions. For the first topic, we describe the magnetic complexity, new flux emergence, flux cancelation, shear mo- tions, sunspot rotation and magnetic helicity injection, which may all contribute to the storage and buildup of energy that trigger solar eruptions. For the second topic, we concentrate on the observations of rapid and irreversible changes of the photospheric magnetic field associated with flares, and the implication on the restructuring of the three-dimensional magnetic field. In particular, we emphasize the recent advances in observations of the photospheric magnetic field, as state-of-the-art observing facilities （such as Hinode and Solar Dynamics Observatory） have become available. The link- ages between observations, theories and future prospectives in this research area are also discussed.

关键词： Sun:flares—Sun:magnetic fields