Interactive database of cosmic ray anisotropy (DB-A10)

The worldwide neutron monitor network is a unique tool for obtaining with high accuracy the information on density variations, energy spectrum and anisotropy of comic rays at the Earth, outside its atmosphere and magnetosphere. These hourly averaged parameters were obtained over the whole period of cosmic ray monitoring by the ground level neutron monitor network (from 1957 till present) and are collected within the MySQL database. The Internet-project has developed for free access and supplying of cosmic ray density and anisotropy data in different formats.     

日侧外磁层ULF波调制EMIC波的MMS观测

磁层多尺度卫星(MMS-1)在日侧06:30 MLT(磁地方时,Magnetic Local Time)外磁层大于2Re(L为7.5～10.1)的范围内观测到多达21个波包的准周期性电磁离子回旋波(EMIC)事件.超低频(ULF)波和能量质子温度各向异性准周期性增强也被同步观测到.频率分析显示,ULF波的周期、质子各向...     

Effect of random nature of cosmic ray sources – Supernova remnants – on cosmic ray intensity fluctuations,anisotropy, and electron energy spectrum

The random nature of sources (the supernova remnants) leads to the fluctuations of cosmic ray intensity in space and time. We calculate the expected fluctuations in a flat-halo diffusion model for particles with energies from 0.1 to 10³ TeV. The data on energy spectra and anisotropy of very high energy protons, nuclei and electrons, and the astronomical data on supernova remnants, the potential sources of cosmic rays, are used to constrain the value of the cosmic-ray diffusion coefficient and its dependence on energy.     

HXMT卫星空间环境监测器及初步观测结果

硬X射线调制望远镜（HXMT）卫星是中国首个专门进行天文探测的空间科学实验卫星,运行于高度约550km、倾角约43°的低地球轨道.星载空间环境监测器为星上科学任务开展提供背景辐射实测资料.该监测器采用固体探测器望远镜系统和扇形阵列全新组合设计,可获取轨道空间高能质子和高能电子能谱、方向综合动态结果,给出更为全面的粒子辐射分布图像.初步探测结果显示,卫星运行轨道遭遇的带电粒子辐射集中分布在经度80°W-20°E,纬度0°-40°S的南大西洋异常区,粒子辐射在该区域表现出不同程度的方向差异分布,高能电子方向差异分布显著强于高能质子.2017年9月空间环境扰动期间,爆发的太阳质子事件并未对该轨道粒子辐射产生影响,而地磁活动导致该轨道穿越经度120°W-60°E,纬度40°-43°N的北美上空和经度60°-120°E,纬度43°-40°S的澳大利亚西南区域时遭遇增强粒子辐射影响,增强的粒子辐射表现出极强的方向分布.      

L'interaction entre le flot d'helium neutre d'origine interstellaire et l'heliosphere

Elastic collisions between neutral helium atoms from interstellar origin and protons from both the interstellar plasma in the heliospheric interface and the solar wind inside the heliosphere modify parameters of the helium gas. Upstream the heliopause, the helium atoms release momentum to the plasma, which results in a decrease of their bulk velocity, and remove energy from the plasma, which results in an increase of their temperature. Inside the heliosphere, the major part of the energy communicated by solar wind protons to helium atoms is transferred through scarce frontal collisions, which results in the creation of a hot tenuous He component in the downstream (with respect to the sun) region. The modification of the spatial He distribution function near the sun due to slightly deflected atoms is negligible in first approximation. Lastly, we emphasize that the collisional effect is probably insufficient to explain the high temperature of helium derived from photometric measurements of the interplanetary medium at 58.4 nm (16 000 K). By taking into account two other effects which are the light transfer in the He resonance line inside the focusing cone and a possible latitudinal anisotropy of the solar ionizing EUV flux, leading both to a lowering of the contrast of the cone, we show that the temperature discrepancy between H (8 000 K : spectral measurements : line width, Doppler shift) and He (16 000 K : photometric measurements) can be reasonably explained by the combined actions of these three effects : elastic collisions, light transfer at 58.4 nm inside the focusing cone, solar EUV flux latitudinal anisotropy.     

CME-geometry and cosmic-ray anisotropy observed by a prototype muon detector network

We analyze the cosmic-ray anisotropy observed by a prototype network of muon detectors during geomagnetic storms associated with coronal mass ejections (CMEs). The network currently consists of multidirectional surface muon detectors at Nagoya (Japan) and Hobart (Australia), together with a prototype detector at São Martinho (Brazil) which has been in operation since March, 2001. In this report, we analyze the anisotropy recorded in both the muon detector and neutron monitor (the Spaceship Earth) networks and find significant enhancements of cosmic-ray anisotropy during geomagnetic storms. Following the analysis by Bieber and Evenson [Bieber, J.W., Evenson, P. CME geometry in relation to cosmic ray anisotropy. Geophys. Res. Lett. 25 (1998) 2955–2958] for the neutron monitor data at 10 GeV, we also derive cosmic-ray density gradients from muon data at higher-energy (50 GeV), possibly reflecting the larger-scale geometry of CMEs causing geomagnetic storms. We particularly find in some events the anisotropy enhancement clearly starting prior to the storm onset in both the muon and neutron data. This is the first result of the CME-geometry derived from simultaneous observations of the anisotropy with networks of multidirectional muon detectors and neutron monitors.     

Cosmic ray anisotropies in the outer heliosphere

The observation of the directional distribution of energetic and cosmic ray particles has been done with the Voyager spacecraft over a long period. Since 2002, when the first flux enhancements of charged particles associated with the approach of Voyager 1 to the solar wind termination shock were observed, these anisotropy measurements have become of special interest. They play an important role to understand the magnetic field and shock structure and the basics of the modulation of cosmic ray and anomalous particles at and beyond the termination shock. They also serve as motivation to study the spatial behavior of galactic and anomalous cosmic ray anisotropies with numerical modulation models in order to illustrate how the radial anisotropy, at different energies, change from upstream to downstream of the termination shock. Observations made by Voyager 1 indicate that the termination shock is a complicated region than previously thought, hence the effects of the latitude dependence of the termination shock’s compression ratio and injection efficiency on the radial anisotropies of galactic and anomalous protons will be illustrated. We find that the magnitude and direction of the radial anisotropy strongly depends on the position in the heliosphere and the energy of particles. The effect of the TS on the radial anisotropy is to abruptly increase its value in the heliosheath especially in the A > 0 cycle for galactic protons and in both polarity cycles for anomalous protons. Furthermore, the global effect of the latitude dependence of the shock’s compression ratio is to increase the radial anisotropy for galactic protons throughout the heliosphere, while when combined with the latitude dependence of the injection efficiency this increase depends on modulation factors for anomalous protons and can even alter the direction of the radial anisotropy.     

太阳风中磁重联的可能性及其观测证据

本文利用美国行星际监测卫星IMP-H和IMP-J同时在弓激波上游的极佳时机(1976年1月21日—22日)探测的结果, 比较了两个卫星同时测得的离子脉冲(E≥125keV/Q, Q≥1)的计数率和各向异性.分析表明在IMP-H比IMP-J离地球远的四个事件a—d中, a和b事件时, IMP-H上测得的计数率大于IMP-J上计数率, 各向异性从太阳指向地球;c事件时, IMP-J上计数率大于IMP-H上的测量值, 各向异性从太阳指向地球;d事件时, IMP-J上计数率大于IMP-H上的相应值, 各向异性改变方向, 从地球指向太阳.它们可以用太阳风中扇形边界样的磁场反转形态磁重联产生的高能粒子的假说来满意地得到解释.      

宇宙弥漫X射线背景的各向异性

本文利用HEAO-1A2的2-60keV弥漫X射线资料,扣除了银河系起源的X弥漫背景影响,得到有关宇宙X背景的资料.在宇宙X背景的各向异性是由Compton-Getting效应引起的假设下,导出其各向异性度δ=(0.45±0.18)%,从而得到太阳系相对于2-60keV宇宙X背景“海”的运动速度V=(397±159)km/s.这个值与由微波背景观测资料得到的结论不矛盾.      

Relativistic proton production at the Sun in the 20 January 2005 solar event

Based on the concept of multiple acceleration of solar energetic particles (SEP) we analyzed the super-event of 20 January 2005 by the data of ground level, balloon and spacecraft observations. The main characteristics of relativistic solar protons (energy spectra, anisotropy directions and pitch-angle distributions) are derived and their dynamics during the event is studied. It is shown that the flux of relativistic solar protons may consist of two distinct components, the so-called prompt and delayed ones. Within a two-source model of particle generation, one of which is associated with an expanding magnetic loop, we solved the transport equation in energy phase space, including adiabatic losses simultaneously with the stochastic acceleration process, and calculate the expected spectra of the delayed component at the source. The confrontation of experimental spectra with theoretical ones shows that the delayed component may be correctly described by stochastic acceleration, but not the prompt component. The required acceleration efficiencies turned out to be rather high, so that, for this particular event, adiabatic cooling is practically negligible. Our results provide a new support to the existence of two populations of relativistic solar protons in some SEP events.     

27-day variations of the galactic cosmic ray intensity and anisotropy in the minimum of the 23rd solar activity cycle

We study the 27-day variations of the solar wind velocity, galactic cosmic ray (GCR) intensity and anisotropy in the last minimum epoch of solar activity (2007–2009, A < 0). The average amplitude of the 27-day variation of the galactic cosmic ray anisotropy (A27A) in the current minimum epoch of solar activity (2007–2009, A < 0) is lesser than in previous positive polarity period as it is expected from the drift theory. So, polarity dependence rule for the 27-day variation of the GCR anisotropy is fully kept. It is a universal principle for the amplitudes of the 27-day variation of the GCR anisotropy. At the same time, the average amplitude of the 27-day variation of the GCR intensity (A27I) remains at the same level as for previous minimum epoch 1995–1997 (A > 0) showing by the same token an violation of its polarity dependence rule established earlier. We assume that this phenomenon could be generally related with the well established 27-day variation of the solar wind velocity being in anti-correlation with the similar changes of the 27-day variation of the GCR intensity. Generally, a character of the heliolongitudinal asymmetry of spatial large-scale structure of the solar wind velocity (SWV) established in the recent minimum epoch, preferentially pronounces in the behavior of the 27-day variation of the GCR intensity than anisotropy. The formation of the 27-day variation of the GCR anisotropy preferentially takes place in a restricted disk like local vicinity in the helioequatorial region, whilst the 27-day variation of the GCR intensity is formed in the global three dimensional vicinity of the heliosphere.     

On transmissivity of low energy cosmic rays in disturbed magnetosphere

Access of low energy cosmic rays to any position on the Earth depends on the state of the magnetosphere. Anisotropy of cosmic rays, deduced from the neutron monitor network, must assume the variable transmissivity of the magnetosphere especially during the geomagnetic disturbances. We illustrate that computations based on different available models of geomagnetic field during selected strong geomagnetic disturbances in 2003 and 2004 imply different profiles of cut-off rigidities in time, different transmissivity functions and different asymptotic directions. Using of cosmic ray records by neutron monitors at middle and low latitudes during geomagnetically active periods, in addition to cosmic ray anisotropy in interplanetary space deduced from high and low energy cosmic ray ground based measurements, may be used for checking validity of geomagnetic field models.     

来自电离层的尾向流对近地磁场位形的影响

探测一号(TC-1)卫星的观测结果表明,尾向流能够拉伸近地磁尾的磁力线,从而导致磁场位形改变.尾向流具有垂直于磁场的速度分量,这种垂直磁场的速度分量会导致磁力线向尾向拉伸,磁场的结构由偶极型变为非偶极型.而随尾向流的终止,地向流的出现,磁场的结构由非偶极型变为偶极型,磁力线恢复原状.另外在磁场的结构由非偶极型变为偶极型的过程中,伴随磁能的释放热离子温度的迅速升高,温度由各向同性逐渐趋向各向异性.其次,观测结果显示来自电离层的尾向流对磁场By分量有重要的影响,能够引起磁场By分量的显著增强.上述分析结果表明来自电离层的尾向流对近地磁尾动力学过程有着重要的影响.      

Maps of hydrogen isotopes at low altitudes in the inner zone from sampex observations

The PET instrument aboard the SAMPEX satellite has provided us with long-term intra-calibrated observations of geomagnetically trapped protons and deuterons in the inner zone, suitable for use in constraining the low-altitude portions of radiation belt models being developed as successors to AP-8. These observations have been summarized elsewhere (Looper et al., 1996). Here we report a detection of geomagnetically-trapped tritium at energies from 14 to 35 MeV/nuc below L = 1.2, at about 1/8 the flux of deuterium previously reported at that location and at similar energy per nucleon. We also demonstrate the utility of the SAMPEX/PET observations for measuring the east-west anisotropy in the trapped particle flux at low altitudes, which is due to displacement of particle gyrocenters from the position of observation in a region of strong flux gradients. This anisotropy is implicitly ignored in omnidirectional radiation-flux models, but it can be important to mission planners considering how to distribute shielding over the surface of oriented spacecraft in low Earth orbit.     

地球磁鞘中磁场起伏特性的分布

本文利用行星际起伏通过激波后的变化的MHD模型, 具体讨论了地球磁鞘中磁场起伏特性在黄道面内的分布.主要结果是:(1)行星际磁场起伏的强度和各向异性在磁鞘中被显著放大;(2)行星际磁场基本位于黄道面内时, 磁鞘中磁场起伏特性(强度、相对起伏和各向异性等)呈现明显的晨一昏不对称性, 早晨侧(准平行激波)显著地高于黄昏侧(准垂直激波);(3)行星际磁场方向对磁场起伏特性在磁鞘中的分布有强烈的控制作用, 早晨侧响应灵敏, 黄昏侧反响不大.相对地讲, 黄昏侧的磁活动较之早晨侧稳定;(4)行星际磁场转南的增强将导致磁鞘中磁场起伏的最大区域自黄道面低纬向北极高纬移动, 南-北不对称性磁活动随之加强, 最强大致出现在磁场与黄道面相交成大约45°时, 而晨-昏不对称性的强弱程度则发生相反变化;(5)行星际磁场的相对起伏增加, 晨-昏不对称性反随之减弱.磁鞘中磁场起伏分布的特性与卫星观测大体符合, 是磁顶、边界层某些晨-管不对称性出现的可能起因之一.      

GA-A3DI-FDTD的PML吸收边界数值反射分析

研究一种减小三维交替方向隐式时域有限差分法ADI-FDTD(Alternating-Direction Implicit Finite-Difference Time-Domain)数值色散的新方法GA-A3DI-FDTD(Genetic Algorithm Artificial Anisotropy ADI-FDTD).首先对添加人工各向异性介质后的三维ADI-FDTD迭代公式进行变形,得到新的数值色散关系,再利用自适应遗传算法AGA(Adaptive Genetic Algorithm)得到需要添加的人工各向异性介质的相对介电常数.并以空心波导作为数值算例,分析了由不同目标函数得到的人工各向异性介质对计算精度以及PML(Perfectly Matched Layers)吸收边界数值反射产生的影响,同时分别与传统ADI-FDTD相比较.结果表明通过正确选择目标函数,得到更加合适的人工各向异性介质,可以在减小三维ADI-FDTD数值色散的同时,有效地抑制由于人工各向异性介质的添加所造成的PML吸收边界数值反射的增强.      

Electron temperature anisotropy effects on tearing mode in ion-scale current sheets

Recent two-dimensional (2-D) particle-in-cell (PIC) simulations have shown that there is a critical thickness of a current sheet, above which no significant saturation amplitude of the 2-D tearing (TI) mode can be expected. Here, we have introduced the initial electron temperature anisotropy (α_e0 = T_e⊥/T_e|| > 1), which is known to raise significantly the linear growth rates, and inspected if α_e0 > 1 can change the saturation level of the TI in a super-critical current sheet. Varying α_e0 and D (D: the current sheet half-thickness) systematically, we have found that while α_e0 boosts up the linear growth rate in both sub- and super-critical current sheets, macroscopic effects are obtained only in sub-critical current sheets, that is, energy transfer from the fastest growing short wavelength modes to longer wavelength modes are available only in the sub-critical regime. Since the critical thickness is a fraction of the ion inertial length, the tearing mode assisted by the electron temperature anisotropy alone, despite its significant boost in the linear growth rate, cannot be the agent for reconnection triggering in a current sheet of ion-scale thickness.     

The Compton–Getting effect of energetic particles with an anisotropic pitch-angle distribution

This paper presents a simulation of anisotropy measurements by the low-energy charged particle (LECP) experiment on Voyager 1 for cases when the particle pitch-angle distribution function in the solar wind plasma reference frame is not isotropic. The model includes both the Compton–Getting anisotropy and perpendicular diffusion anisotropy that possibly exists in the upstream region of the termination shock. The results show that the Voyager 1 data cannot rule out either the model with zero solar wind speed or the one with a finite speed on qualitative basis. The determination of solar wind speed using the Compton–Getting effect is affected by the assumption of the magnetic field direction and perpendicular diffusion anisotropy. Because the pitch-angle distribution anisotropy is so large, a small uncertainty in the magnetic field direction can produce very different solar wind speeds ranging from ∼0 to >400 km/s. In fact, if the magnetic field is chosen to be in the Parker spiral direction, which is consistent with the magnetometer measurement on Voyager 1, the derived solar wind speed is still close to the supersonic value. Only the two lowest-energy channels of the LECP instrument may give a definitive answer to the solar wind speed. However, because these channels contain a very high level of cosmic ray background, an uncertainty of just a few percent in the background can entirely hamper the estimate of solar wind speed.     

Effect of Interplanetary Transients on Cosmic Ray Anisotropic Variations

In the present work the cosmic ray intensity data recorded with ground-based neutron monitor at Deep River has investigated taking into account the associated interplanetary magnetic field and solar wind plasma data during 1981—1994.A large number of days having abnormally high/low amplitudes for successive number of five or more days as compared to annual average amplitude of diurnal anisotropy have been taken as high/low amplitude anisotropic wave train events(HAE/LAE).The amplitude of the diurnal anisotropy of these events is found to increase on the days of magnetic cloud as compared to the days prior to the event and it found to decrease during the later period of the event as the cloud passes the Earth.The High-Speed Solar Wind Streams(HSSWS)do not play any significant role in causing these types of events. The interplanetary disturbances(magnetic clouds)are also effective in producing cosmic ray decreases.Hαsolar flares have a good positive correlation with both amplitude and direction of the anisotropy for HAEs, whereas PMSs have a good positive correlation with both amplitude and direction of the anisotropy for LAEs. The source responsible for these unusual anisotropic wave trains in CR has been proposed.     

Study of the 27-day variations of the galactic cosmic ray intensity and anisotropy

We demonstrate that the general features of the radial and azimuthal components of the anisotropy of galactic cosmic rays can be studied by the harmonic analysis method using data from an individual neutron monitor with cut off rigidity <5 GV. In particular, we study the characteristics of the 27-day (solar rotation period) variations of the galactic cosmic ray intensity and anisotropy, solar wind velocity, interplanetary magnetic field strength and sunspot number. The amplitudes of the 27-day variations of the galactic cosmic ray anisotropy are greater, and the phases more clearly established, in A > 0 polarity periods than in A < 0 polarity periods at times of minimum solar activity. The phases of the 27-day variations of the galactic cosmic rays intensity and anisotropy are opposite with respect to the similar changes of the solar wind velocity in A > 0 polarity periods. No significant dependence of the amplitude of the 27-day variation of the galactic cosmic ray anisotropy on the tilt angle of the heliospheric neutral sheet is found. Daily epicyclegrams obtained by Chree’s method show that the 27-day variations of the galactic cosmic ray anisotropy during A > 0 polarity periods follow elliptical paths with the major axes oriented approximately along the interplanetary magnetic field. The paths are more irregular during A < 0 polarity periods.