垂直无碰撞激波的离子加速机制

利用一维全粒子模拟得到的垂直无碰撞激波的位形,通过试验粒子方法研究了不同初始能量粒子的激波加速机制.将与激波相互作用的离子分成反射和直接穿过两类,发现只有被激波反射的离子可被激波明显加速,其中初始能量较小的反射离子通过激波冲浪机制加速,而初始能量较大的离子通过激波漂移加速机制加速.同时激波厚度还对离子被加速过程有重要影响.     

垂直无碰撞激波中多离子波动和He2+加热

应用一维混合模拟方法数值研究了高Alfven－Mach数垂直无碰撞激波中He²⁺的运动及其加热机制．结果表明，在激波面处将会产生向下游传播的多离子波动，它对He²⁺加热有着重要影响．He²⁺的加热过程可能包含两个阶段，由于质子温度各向异性激发的质子回旋波和镜波先使He²⁺加热，而He²⁺与多离子波动相互作用进一步使He²⁺加热到更高的温度．     

Collisionless electrons in a thin high Mach number shock: dependence on angle and β

It is widely believed that electron dynamics in the shock front is essentially collisionless and determined by the quasistationary magnetic and electric fields in the shock. In thick shocks the electron motion is adiabatic: the magnetic moment is conserved throughout the shock and v²₁ ∝ B. In very thin shocks with large cross-shock potential (the last feature is typical for shocks with strong electron heating), electrons may become demagnetized (the magnetic moment is no longer conserved) and their motion may become nonadiabatic. We consider the case of substantial demagnetization in the shock profile with the small-scale internal structure. The dependence of electron dynamics and downstream distributions on the angle between the shock normal and upstream magnetic field and on the upstream electron temperature is analyzed. We show that demagnetization becomes significantly stronger with the increase of obliquity (decrease of the angle) which is related to the more substantial influence of the inhomogeneous parallel electric field. We also show that the demagnetization is stronger for lower upstream electron temperatures and becomes less noticeable for higher temperatures, in agreement with observations. We also show that demagnetization results, in general, in non-gyrotropic down-stream distributions.     

Shocks and sheaths in the heliosphere

This paper compares three kinds of shocks and sheaths; the bow shock and magnetosheaths of planets, interplanetary coronal mass ejection (ICME) shocks and sheaths, and the termination shock and heliosheath. We compare the energy balance across these shocks, fluctuations in the sheaths, asymmetries, and shock evolution. All three shocks and sheaths display asymmetries imposed by outside magnetic fields. Energy balance is often achieved through reflection of ions of the shocks, but in some cases no reflected ions are observed. The shocks may have similar small scale fluctuations which drive density changes in the sheaths.     

Injection and acceleration of H+ and He2+ at Earth’s bow shock

We have performed a number of one-dimensional hybrid simulations (particle ions, massless electron fluid) of quasi-parallel collisionless shocks in order to investigate the injection and subsequent acceleration of part of the solar wind ions at the Earth’s bow shock. The shocks propagate into a medium containing magnetic fluctuations, which are initially superimposed on the background field, as well as generated or enhanced by the electromagnetic ion/ion beam instability between the solar wind and backstreaming ions. In order to study the mass (M) and charge (Q) dependence of the acceleration process He²⁺ is included self-consistently. The upstream differential intensity spectra of H⁺ and He²⁺ can be well represented by exponentials in energy. The e-folding energy E_c is a function of time: E_c increases with time. Furthermore the e-folding energy (normalized to the shock ramming energy E_p) increases with increasing Alfvén Mach number of the shock and with increasing fluctuation level of the initially superimposed turbulence. When backstreaming ions leave the shock after their first encounter they exhibit already a spectrum which extends to more than ten times the shock ramming energy and which is ordered in energy per charge. From the injection spectrum it is concluded that leakage of heated downstream particles does not contribute to ion injection. Acceleration models that permit thermal particles to scatter like the non-thermal population do not describe the correct physics.     

Upstream whistler-mode waves at planetary bow shocks: A brief review

Upstream whistler-mode waves appear to be present in front of all collisionless shocks. Because the whistler-mode group velocity exceeds its phase velocity over the frequency range in which the phase velocity increases with frequency, interesting alterations of polarization and frequency spectrum occur in the observer's reference frame. Landau resonance also plays a role in the wave properties. The source of these waves is the shock but the mechanism for wave generation is not yet understood.     

弓激波前内透射离子动力学横场流电磁不稳定性

本文研究了地球弓激波前内透射离子动力学横场流不稳定性.电子速度分布函数采用平顶形式.对包含电磁效应的完整色散方程进行了数值求解.结果表明,增长率峰值比采用电子Maxwellian速度分布情形的值要大得多.同时在高速离子横场流和近乎垂直传播情况下,在色散方程中需要计入与电子贡献有关的含高阶Bessel函数的项.     

Investigation of hot Flow Anomaly structure observed near the Earth’s bow shock

The work is dedicated to investigation of Hot Flow Anomaly (HFA), formed at the front of Earth’s bows hock. Using Interball-Tail data we estimated orientation of the current sheet that was a cause of the anomaly. From the ion energy-time spectrogram we divided the anomaly into several regions. The motional electric fields near the HFA were estimated with 3D model of Earth’s bow shock. In accordance with previous investigations of HFA’s formation conditions these fields were directed towards the current sheet on both sides of it. We also provided the picture of HFA’s motion along the bow shock and calculated its speed. Analyzing ions’ bulk velocities within the HFA we found that the anomaly is expanding. This conclusion was supported by estimation of thermal and magnetic pressure balance. Ion energy-time spectrogram shows that anomaly is a complicated structure consisting of two parts—leading and trailing. Comparison of ion velocity distributions, magnetic field data and ion energy-time spectrogram provides better understanding of the phenomena and indicated the region that is the source of thermal and convective energy inside HFA.     

地球弓激波前的低频磁流体波

一、引言 在地球弓激波前存在着低频磁流体波。这种低频磁流体波是太阳风在地球弓激波上的反射粒子和太阳风粒子之间相互作用产生的。根据人造卫星的观测资料可以得到,在地球弓激波前,Pc3-4脉动频率范围内的低频磁流体波的主频率和行星际磁场强度     

地球弓激波及其与行星际激波相互作用

给定地球轨道附近的行星际条件和地球弓激波的几何位形,本文分析向阳侧弓激波强度参数沿激波阵面的分布,以及行星际激波与弓激波的相互作用.对于弓激波阵面相对日地连线轴对称的情形,得到如下结论：（1）弓激波强度参数分布相对由行星际磁场和日地连线构成的基准面对称,各激波强度参数的最大值出现在基准面上.磁压比在垂直激波线一侧较大,而气压比在平行激波点一侧较大,导致总压比相对日地连线大致呈轴对称分布.（2）随着行星际磁场与日地连线夹角的增大,弓激波强度参数的最大值有所减小,且位置朝远离日下点方向偏移;但气压比和总压比的分布基本上不受影响.（3）行星际激波透过弓激波之后,切向磁场比更接近于1,但总磁场跳变幅度增大.（4）透过弓激波之后,行星际准垂直激波的总磁场比更接近于1,准平行激波的总磁场比则反之.     

等离子体片中能量离子的空间分布--Cluster/RAPID观测数据分析

本文根据Cluster卫星上的粒子成像质谱仪（RAPID）探测器在穿越地球等离子体片过程中的观测数据,统计研究了等离子体片中能量离子能量密度的空间分布（氢离子能量范围从40keV到1500keV,氦离子和氧离子从10keV到1500keV）,并且给出了离子能量密度在不同地磁活动时期随GSE Z向分布的剖面.研究表明能量离子的能量密度以及能量密度的梯度与地磁活动指数Kp之间存在近似线性的关系.观测结果表明形成这种分布变化的主要原因是在地磁活动期间在电流片附近离子能量密度的增加,特别是其中的重离子成分增加更为显著.本文通过一个简化的电流片模型的数值计算,定性地研究了形成能量离子空间分布的机理.计算表明重离子在电流片中可以获得更多的能量,电流片加速可能是形成能量密度分布变化的一种可能的机制.     

Ion dynamics associated with substorm dipolarization fronts

We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts(DFs) in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS spacecraft in the near-Earth magnetotail(~?10 Re). We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic(LSK) simulation results. The LSK simulation reproduced the sudden ion energy flux enhancement concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure.     

Alfvèn波与慢激波的相互作用

本文分析了斜入射波矢与背景磁场和激波法线共面时,一维小幅度Alfvèn波干扰下,慢激波的稳定性问题;论证了Alfvèn波在慢激波上的射线反射和折射规律;并就日冕慢激波情形进行了具体的数值计算。结果表明,除非上游法向流速接近上游法向Alfvèn波波速,在上述斜入射的Alfvèn波干扰下,慢激波总是稳定的。日冕慢激波是这种稳定性的一个例子;日冕慢激波的存在,能使起源于日冕向行星际空间传播（不管它起源于日冕慢激波之内或外）的Alfvèn波的法向能流密度增大。     

Negative ions in the auroral mesosphere during a PCA event around sunset

This is a study of the negative ion chemistry in the mesosphere above Tromsø using a number of EISCAT observations of high energy proton precipitation events during the last solar maximum, and in particular around sunset on 23 October, 1989. In these conditions it is possible to look at the relative importance of the various photodetachment and photodissociation processes controlling the concentration of negative ions. The data analysed are from several UHF GEN11 determinations of the ion-plasma ACF together with the pseudo zero-lag estimate of the ‘raw’ electron density, at heights between 55 km and 85 km, at less than 1 km resolution. The power profiles from the UHF are combined with the 55-ion Sodankylä model to obtain consistent estimates of the electron density, the negative ion concentrations, and the average ion mass with height. The neutral concentrations and ion temperature are given by the MSIS90 model. These parameters are then used to compare the calculated widths of the ion-line with the GEN11 determinations. The ion-line spectrum gives information on the effects of negative ions below 70 km where they are dominant; the spectral width is almost a direct measure of the relative abundance of negative ions.     

Energy conversion and magnetic reconnection in space plasmas: Role of nonlinear kinetic processes and structures

Dynamics of plasma systems in space involves processes of large-scale energy conversion. Like in conventional gas dynamics, the conversion can occur on shocks. However, in collisionless magnetized plasma systems, quite different nonlinear structures may be responsible for energy conversion. Those are anisotropic kinetic current sheets. It is demonstrated that observations at the Earth’s magnetopause provide evidence of long-term existence of such structures.     

内日球子午面瞬态激波的传播特性

采用日球子午面内的二维三分量MHD模型,研究瞬态激波的传播特性,着重分析日球 电流片（HCS）、日球等离子体片（HPS）和低速流结构对激波传播的影响．结果表明,HCS 和HPS对激波传播几乎没有影响,而跨越HCS和HPS的低速流则显著改变激波的传播特性. 低 速流对激波的反射,导致激波扰动源一侧的激波速度加快、强度增强,低速流对激波透射的 阻碍作用导致激波扰动源异侧的激波滞后、强度减弱,但激波阵面的纬度跨度有所加宽．在 激波穿越过后,低速流区朝激波传播方向弯曲并受到骚扰,使得激波下游出现复杂的扰动结 构;对于激波扰动源同侧的激波下游,反射波与该处等离子体的相互作用同样会导致较为复 杂的扰动出现.     

高纬日侧电离层离子上行的地磁活动依赖性研究

本文对比分析了太阳活动高、低年期间高纬日侧顶部电离层离子上行随地磁活动水平的变化特征.按地磁活动水平,将DMSP卫星在太阳活动高年（2000-2002年,F13和F15）及太阳活动低年（2007-2009年,F13;2007-2010年,F15）期间的SSIES离子漂移速度观测数据分为三组：地磁平静期（Kp<3）,中等地磁扰动期（3 ≤ Kp < 5）和强地磁活动期（Kp ≥ 5）,分别统计分析了高纬日侧顶部电离层离子上行特征的时空分布.对比分析发现：（1）太阳活动低年期间,高纬日侧电离层离子上行发生率以及上行速度峰值均是太阳活动高年的2倍多,而离子上行通量峰值只有高年的1/6-1/4;（2）在相同太阳活动条件下,地磁活动水平对日侧电离层离子上行发生率峰值的影响并不明显,但对离子上行发生率的空间分布有着显著的控制作用：电离层离子上行高发区随地磁活动向低纬度扩展,并在强地磁活动期间呈现饱和的趋势;（3）日侧顶部电离层等离子体似乎存在两个效率相当的上行区域,一个位于极尖/极隙区纬度附近,离子可沿开放磁力线上行进入磁尾;另一个位于晨侧亚极光区附近,离子沿闭合磁力线上行,有可能进入日侧等离子体层边界层.     

行星际中间激波

在行星际空间可能存在由各类激波连接而成的混合激波,其组成部分的连接方式和时间演化遵循“慢激波-导灭激波-中间激波-导生激波-快激波”链式规则.中间激波将作为混合激波的必要组成部分,出现在日球电流片的附近,其阵面凹向太阳.上述结论已初步为观测证实,并对行星际激波的三维特性有着重要影响.     

Generation and evolution of interplanetary slow shocks

It is well known that most MHD shocks observed within 1 AU are MHD fast shocks. Only a very limited number of MHD slow shocks are observed within 1 AU. In order to understand why there are only a few MHD slow shocks observed within 1 AU, we use a one-dimensional, time-dependent MHD code with an adaptive grid to study the generation and evolution of interplanetary slow shocks (ISS) in the solar wind. Results show that a negative, nearly square-wave perturbation will generate a pair of slow shocks (a forward and a reverse slow shock). In addition, the forward and the reverse slow shocks can pass through each other without destroying their characteristics, but the propagating speeds for both shocks are decreased. A positive, square-wave perturbation will generate both slow and fast shocks. When a forward slow shock (FSS) propagates behind a forward fast shock (FFS), the former experiences a decreasing Mach number. In addition, the FSS always disappears within a distance of 150R_⊙ (where R_⊙ is one solar radius) from the Sun when there is a forward fast shock (with Mach number \geq1.7) propagating in front of the FSS. In all tests that we have performed, we have not discovered that the FSS (or reverse slow shock) evolves into a FFS (or reverse fast shock). Thus, we do not confirm the FSS-FFS evolution as suggested by Whang (1987).     

Solar-terrestrial storm of November 18–20, 2003. 1. Near-Earth disturbances in the solar wind

The structure, configuration, dynamics, and solar sources of the near-Earth MHD disturbance of the solar wind on November 20, 2003, is considered. The disturbances of October 24 and November 22 after flares from the same AR 10484 (10501) are compared. The velocity field in the leading part of the sporadic disturbance is for the first time studied in the coordinate system stationary relative to the bow shock. A possible scenario of the physical processes in the course of this solar-terrestrial storm is discussed in comparison with the previously developed scenario for the storm of July 15, 2000. It has been indicated that (1) the near-Earth disturbance was observed at the sector boundary (HCS) and in its vicinities and (2) the disturbance MHD structure included: the complicated bow shock, wide boundary layer with reconnecting fields at a transition from the shock to the magnetic cloud, magnetic cloud with a magnetic cavity including packed substance of an active filament, and return shock layer (supposedly). It has been found out that the shock front configuration and the velocity field are reproduced at an identical position of AR and HCS relative to the Earth on November 20 and 24. It has been indicated that the maximal magnetic induction in the cloud satisfied the condition B _m = (8πn ₁ m _p)^1/2(D ? NV₁), i.e., depended on the dynamic impact on the cloud during all three storms [Ivanov et al., 1974]. When the disturbance was related to solar sources, the attention has been paid to the parallelism of the axes of symmetry of the active filament, transient coronal hole, coronal mass ejection, zero line of the open coronal field (HCS), and the axis of the near-Earth magnetic cloud: the regularity previously established in the scenario of the storm of July 15, 2000 [Ivanov et al., 2005]. It has been indicated that the extremely large B _m value in the cloud of October 20 was caused by a strong suppression of the series of postflare shocks reflected from the heliospheric streamer.