Pitch angle diffusion as seen by CRRES

Lifetimes and pitch angle distributions of radiation belt electrons injected into the slot region are determined from CRRES/MEA particle flux measurements. The dominant loss mechanism is presumed to be pitch angle scattering due to whistler waves, for which a theoretical formulation is available. The empirical lifetimes are compared to those from recent calculations, which rely on model whistler wave parameters. CRRES measurements of cyclotron-frequency electric fields are also presented and compared to the wave model.     

A model for stochastic acceleration of electrons during geomagnetic storms

The theory of resonant diffusion is extended to fully relativistic plasmas, and we examine resonant interactions between electrons and electromagnetic R mode (whistler) and L-mode (EMIC) waves. Resonant diffusion curves are constructed for plasma parameters representative of the Earth's storm time magnetosphere, both inside and outside the plasmapause. EMIC waves can resonate with electrons > 1 MeV, but the energies remain nearly constant along the diffusion curves. Storm-time EMIC waves can induce rapid pitch—angle scattering, but the waves are ineffective for stochastic acceleration of elections. Substantial energy change can occur along the diffusion curves for interactions between resonant electrons and whistler—mode waves, especially in regions of low plasma density. Specifically, whistlers can accelerate electrons from energies near 100 keV to above 1 MeV outside the plasmapause. A model is proposed comprising energy diffusion by whistler-mode chorus and pitch-angle scattering by EMIC waves to account for the gradual acceleration of electrons over the region 4 ≤ L ≤ 6 during the recovery phase of a geomagnetic storm.     

2008年4月24日行星际激波事件相关联的超热电子90°投掷角的增强

利用测试粒子数值模拟的方法研究了与STEREO-A卫星观测到的2008年4月24日行星际激波事件相关联的超热电子90°投掷角的增强.根据激波到达前给定时刻超热电子的观测分布,拟合得到不同投掷角的初始分布函数;在给定的激波参数下,采用时间向后的方法计算特定能道上激波下游超热电子的投掷角分布.由于超热电子具有较高的共振频率,模拟采用的磁场湍流谱包含了低能电子发生共振的耗散区.对以215.76,151.67,106.63,eV为中心的三个能道进行了模拟.结果表明,不同能道上超热电子在激波下游的投掷角分布均在90°投掷角附近出现峰值,呈现出明显的90°投掷角增强,这与观测结果符合得很好.可以认为在激波对电子的加速过程中,电子与湍流耗散区的共振对90°投掷角的增强具有重要作用.      

Spatial coherence and electromagnetic wave generation during electron beam experiments in space

A two-dimensional electromagnetic simulation model is used to investigate the production of whistler waves in connection with electron beam experiments in space. The spectrum is observed to peak near 0.7 ω_e, and the conversion efficiency of beam energy to whistler waves is about 5 × 10⁻⁵. The whistlers can be trapped in a density trough extending out from the spacecraft and experience ducted propagation.     

New aspects of whistler waves driven by an electron beam studied by a 3-D electromagnetic code

We have restudied electron beam driven whistler waves with a 3-D electromagnetic particle code. In the initialisation of the beam-plasma system, “quiet start” conditions were approached by including the poloidal magnetic field due to the current carried by beam electrons streaming along a background magnetic field. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, (2) the parallel phase velocity of the whistler wave is smaller than that of the beam mode, and (3) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is involved in the generation of the whistler waves.     

左旋寻常的极光千米波与辐射带高能电子相互作用的参数化研究

参数化研究了在L=4.5外辐射带区域左旋寻常（Left-hand Ordinary mode, L-O模）的极光千米波与高能电子的相互作用，定量计算了左旋寻常的极光千米波在不同峰值频率、传播角分布和纬度分布条件下的弹跳平均投掷角扩散系数、动量扩散系数和投掷角–动量交叉扩散系数。计算结果表明，动量扩散系数一般比投掷角扩散系数大100倍左右，说明动量扩散在L-O模与电子间的相互作用中起主导作用。随着传播角范围的改变，扩散系数均未发生明显变化，这说明L-O模与电子相互作用的扩散系数对传播角范围的依赖性很小。此外，扩散系数会因为L-O模纬度分布的改变而发生剧烈变化，该结果与之前得到的纬度分布对右旋奇异的极光千米波的影响是一致的。通过参数化研究结果表明，适当条件下，L-O模可能会显著影响外辐射带高能电子的动力学过程。      

Effect of spectral distribution of energetic electrons on wave-particle interaction and precipitated energy input

The precipitated energy flux as affected by the presence of parallel electric field and geomagnetic field distortions have been obtained using a complete kinetic treatment of pitch angle scattering by whistler waves. Four different energy spectra have been used to show that the precipitated energy flux depends on the spectral details of the interacting electron ensemble.     

Propagation of upstream protons in the near-earth solar wind

The propagation of energetic protons (35–1600 keV) from the Earth's magnetosphere to the ISEE-3 spacecraft located about 240 earth radii (R_E) upstream in the solar wind is used as a tool to study the interaction between these protons and the solar wind. In this preliminary study we present proton pitch angle distributions seen at different times during the development of upstream events that occur in relatively quiet interplanetary conditions. In general a highly anisotropic sunward flow is seen at the beginning of the events. During the course of the events pitch angle distributions may vary between streaming along the field lines (peaked around 0° pitch angle), a uniform intensity between 0° and 90°, and a peaked distribution around a preferred pitch angle that is often near 90°.     

Appearance of VLF and ELF-noises in topside ionosphere under the action of high power radio wave from data of satellite intercosmos-24

Results of a satellite experiment are presented on detection of VLF and ELF-waves excited by irradiation of the night ionosphere F-region by the field of a nonmodulated high-power radio wave. The excited VLF and ELF-waves have been detected at the topside ionosphere heights h=500–1000 km in the frequency bands 8 kHz相似文献   

Conical ion distributions at one earth radius — observations from the acceleration region?

Thermal ion measurements from the Retarding Ion Mass Spectrometer (RIMS) on Dynamics Explorer 1 (DE 1) in the night side auroral region were surveyed for evidence of ion acceleration. The RIMS measurements showed evidence for ion acceleration in the 2–10,000 km altitude range, with ion distributions peaked near 90°, and with temperatures of 1 to 10 eV. Two illustrations of the RIMS data for such observations are given here. The conical distributions are found at the low latitude edge of the auroral region, just outside the plasmapause. In the first example, the three major ion species (H+, He+, and O+) show evidence of acceleration. The angular distributions are peaked at different pitch angles, indicating that the different species have been accelerated at different altitudes. The H+ flux is higher than the O+ flux in this first example, in the RIMS energy range (0–50 eV). This is apparently typical of the RIMS observations on the night side. In the second example, only O+ is transversely accelerated.     

HF wave activity in the low and middle-altitude polar cusp

We reported the results of our investigations of wave activity in high-frequency range performed on board CLUSTER spacecraft in the middle-altitude cusp region, around 5 R_E during August and September 2002. Our analysis was mainly based on the registration gathered by the WHISPER instrument (Waves of HIgh frequency and Sounder for Probing of Electron density by Relaxation). For a better understanding of the processes of wave-particle interaction and in order to understand the general plasma conditions in the cusp region, we also included in our analysis the data registered by the STAFF (Spatio-Temporal Analysis of Field Fluctuation experiment) instrument and the CIS (Ion Spectrometry experiment) instrument. These observations were carried out during different geomagnetic activity; under quiet conditions and during magnetic storm period. The space plasma is characterised by the ratio of plasma frequency to electron gyrofrequency, in this case, the local plasma frequency was, mainly, a little greater than the electron plasma, but it was also frequently observed that these two characteristic frequencies were not very different from one another. The whistler waves, electron-cyclotron waves, electron-acoustic waves and Langmuir waves have been detected when the spacecraft was crossing the middle-altitude cusp region. We suggested that the majority of those waves were generated by electron beams. For a better understanding the plasma conditions in the low and middle-altitude cusp region the past FREJA wave data results are used to describe typical wave activity detected in the low-altitude cusp region. The aim of this paper is to discuss, on the basis of a few chosen representative examples, the property of typical high wave activity detected in the lower part of cusp region.     

Sources and losses of ring current ions: An update

The cleft ion fountain has been identified as a prodigious source of upflowing suprathermal ionospheric plasma. Modeling efforts have traced the path of these ions from the polar ionosphere along trajectories where the ions are energized to keV energies and deposited in the near earth plasma sheet. Mass and energy dispersion of these ions accounts in a natural way for the observed variation in heavy ion content of the plasma sheet. Observations of ion composition in the plasma sheet by the AMPTE and ISEE spacecraft establish that ionospheric ions dominate in the near earth plasma sheet but solar wind ions become significant tailward. The heavy ion content of the plasma sheet increases with both solar cycle and magnetic activity. Direct injection of ionospheric ions into the ring current has been observed in the outer plasmasphere. Several mechanisms for the direct injection of ions from the plasmasphere and ionosphere into the ring current have appeared. Estimation of ionospheric source strengths and residence times have led to an estimate of the magnetospheric densities that would result solely from an ionospheric outflow populating the magnetosphere. Estimated densities were quite reasonable even without inclusion of a solar wind source of ions. Ring current ions decay primarily via charge exchange with the hydrogen geocorona, however, the roles of pitch angle diffusion and Coulomb collisions in this decay process are being clarified.

Modeling and observations of ENA by the 1SEE1 spacecraft has led to a re-affirmation of the dominant role of charge exchange in ring current decay. Ion cyclotron waves contribute to ring current decay in the dusk bulge region. The role of low frequency. (< 1 Hz) ion cyclotron waves in the plasmasphere is still unclear. Other wave modes may be responsible for the pitch angle diffusion and subsequent loss of ring current ions. Coulomb collisional energy losses from ring current O⁺ to thermal electrons are sufficient to power SAR arcs and represent an energy sink for ring current O⁺ within the plasmasphere. Coulomb collisions may be important for decay of low energy (< 10 KeV) ring current ions in the plasmasphere.     

Counterstreaming hydrogen and oxygen ions observed in the magnetosphere on ISEE-1

Counterstreaming ions or ions travelling simultaneously both parallel and antiparallel to the magnetic field direction have been briefly noted in the literature but have not been studied previously in depth. We have studied over 60 counterstreaming ion (CSI) events observed on the ISEE-1 satellite. They were found to occur at altitudes of about 2 to 8 Earth radii on L shells of about 5 to 12 in the evening-to-morning sector from about 1700 - 0900 LT. Often both oxygen and hydrogen ions at a number of energy levels are counterstreaming but some events show only either oxygen or hydrogen ions involved. One particularly interesting event shows only counterstreaming oxygen ions with 417 eV energy; oxygen ions of lower energy (215 eV) and above (630–17000 eV) and all the hydrogen ions between 215–17000 eV energy have lower fluxes and/or nearly isotropic pitch angle distributions. This event correlates well with wave activity in the 17–100 Hz band and is also accompanied by 200 eV downgoing and 400 eV upgoing electrons. Details of this event and the other counterstreaming events are presented.     

GEOS-2卫星S329和S301实验所得对流图象的综合分析与比较

本文对GEOS-2卫星S329电子枪实验和S301冷等离子体电子浓度实验所得对流图象进行了综合分析比较.比较是通过Volland半经验模式将对流电场与等离子体层顶相联系的.两种观测都表明对流电场的西旋与K_p有关,并说明Volland模式在一级近似下较好地描述了同步轨道附近的对流情况.两种实验在高地磁活动时等离子体层顶大小方面有矛盾处.这种矛盾的可能原因是高磁扰日时等离子体层顶附近动力过程的复杂性.此外,S329实验所得的对流电场之晨昏不对称性也是值得注意的现象.      

Volland对流电场模型的实验参数

本文将几个地面和卫星观测结果结合起来给出Volland对流电场模型的实验参数.结果能很好地与GEOS-2卫星所测得的等离子体层顶运动特征、STARE雷达测得的Harang不连续性的运动及近年来探测的磁层电离层电场相吻合.文章指出只要Volland电场模型的参数由实验确定后, 将更有助于磁层和电离层物理的研究.      

磁层中哨声波与电子的相互作用

哨声波与磁层中电子的非线性相互作用,导致电子投掷角降低,沉降到低电离层,引起局部电离增强,而诱发Trimpi效应。本文讨论波-粒子相互作用的过程,并利用超粒子法进行了计算机模拟。计算结果指出共振不仅与电子的速度有关,而且与电子初始拉莫尔相位角有关;计算得到了相互作用时共振电子相位聚焦效应、非共振电子相位聚束效应及电子速度-相位空间中的不均匀振荡等一些结果。同时,也给出了波-电子相互作用引起的沉降电子能量通量随时间的变化和沉降电子的能量分布。      

Nightside plasmapause positions observed by DE-1 as a function of geomagnetic indices: Comparison with whistler observations and model calculations

We have analysed 28 plasmapause crossings made by the DE1 satellite in the night local time sector (from January to March 1982). Different signatures obtained by the Retarding Ion Mass Spectrometer instrument (RIMS) have been used for this analysis. The observed plasmapause positions (Lpp) have been organized as a function of geomagnetic indices. They are compared with the empirical relationship deduced by Carpenter and Parks (1973) from whistler observations. Moreover, the dependence of Lpp versus K_p has been inferred from model calculation using K_p dependent electric and magnetic fields derived from McIlwain's (1974) E3H electric field model and M2 magnetic field model respectively. Stationary models, as well as time dependent ones, have been used to determine the positions of the plasmapause. The results of the model calculations are compared to the observations.     

哨声模波通过低纬电离层传播的某些特征

本文采用IGRF(1980)模型进行了哨声模三维射线跟踪计算, 研究了夜间哨声通过低纬电离层传播的射线与波法的特征.着重讨论了形成非导管哨声可透射路径的条件、射线的聚焦效应及射线的低纬截止.数值计算得到路径终纬度截止约在倾角纬度10.7°N.      

无碰撞电流片哨声波不稳定性

通过数值求解文献[4]中物理模型A得到的一般形式的色散关系,讨论了无碰撞电流片低频波不稳定性问题.结果表明,哨声波能被无碰撞电流片直接激发.在中性片上(z/di=0),在较宽的波数范围内,斜哨声波是可以传播的,但它基本上是稳定的.在离子惯性区内(z/di<1,电子惯性区外),斜传播的哨声波是不稳定的.在离子惯性区边缘(z/di=1),斜传播的哨声波仍然是不稳定的,增长率更大,不稳定的波频率范围更高.此外,朝向中性片方向传播(kzdi<0)的哨声波比离开中性片方向传播(kzdi>0)的哨声波有更大的增长率.     

Ion cyclotron waves observed near the plasmapause

Pc2 electromagnetic ion cyclotron waves at 0.1 Hz, near the oxygen cyclotron frequency, have been observed by ISEE-1 and -2 between L = 7.6 − 5.8 on an inbound near equatorial pass in the dusk sector. The waves occurred in a thick plasmapause of width ⋍ 1 R_e and penetrated ⋍ 1 R_e into the plasmasphere. Wave onset was accompanied by significant increases in the thermal (0–100 eV) He⁺ and the warm (0.1–16 keV/e) O⁺ and He⁺ heavy ion populations. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by multicomponent cold plasma propagation theory are identified in the wave data. The results are considered an example of wave-particle interactions occurring during the outer plasmasphere refilling process at the time of the substorm recovery phase.