Butterfly distribution of Earth’s radiation belt relativistic electrons induced by dayside chorus

Previous theoretical studies have shown that dayside chorus can produce butterfly distribution of energetic electrons in the Earth’s radiation belts by preferentially accelerating medium pitch angle electrons, but this requires the further confirmation from high-resolution satellite observation. Here, we report correlated Van Allen Probes data on wave and particle during the 11–13 April, 2014 geomagnetic storm. We find that a butterfly pitch angle distribution of relativistic electrons is formed around the location L = 4.52, corresponding to the presence of enhanced dayside chorus. Using a Gaussian distribution fit to the observed chorus spectra, we calculate the bounce-averaged diffusion rates and solve two-dimensional Fokker-Planck equation. Numerical results demonstrate that acceleration by dayside chorus can yield the electron flux evolution both in the energy and butterfly pitch angle distribution comparable to the observation, providing a further evidence for the formation of butterfly distribution of relativistic electrons driven by very low frequency (VLF) plasma waves.     

Correlated observations linking loss of energetic protons to EMIC waves

Electromagnetic ion cyclotron (EMIC) emission is an efficient mechanism for scattering loss of energetic protons. Here, we report an event that provides both in-situ observation of energetic proton differential fluxes in the inner magnetosphere and precipitation of protons at ionospheric altitudes. During the 7–8 September 2015 geomagnetic storm the Van Allen Probes observed strong EMIC waves around L = 5 and a distinct decrement in fluxes of tens of keV protons around pitch angles 0°–45°. Meanwhile, precipitating protons at ionospheric altitudes were found to significantly enhanced (by several orders of magnitude), measured by NOAA 18 and 19 when they magnetically linked to the Van Allen Probe-A. By solving the Fokker-Planck diffusion equation, we show that EMIC waves can efficiently produce loss of energetic protons within about 2 h in the pitch angle range of ∼ 0°–45°, comparable to the satellite observations.

     

Dynamic variations of the outer radiation belt during magnetic storms for 1.5–6.0 MeV electrons

The CME’s structure of solar wind (interplanetary magnetic field) is different from CIR’s. The two processes in which plasma and solar wind energy are injected into the Earth’s inner magnetosphere are not the same. So, the variations of energetic electrons flux in the radiation belts are different between the storms associated with CMEs and CIRs. By using data from SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer) satellite, we have investigated the dynamic variations of the outer radiation belt for 1.5–6.0 MeV electrons during 54 CME-driven storms and 26 CIR-driven recurrent storms. According to the superposed epoch analysis, for CME- and CIR-driven storms, when the Dst index reaches the minimum, the locations of the outer boundary move to L=4 and L=5.5, respectively. In the recovery phases, the locations of the outer boundary of the outer radiation belt are generally lower than and slightly higher than those before CME- and CIR-driven storms, respectively. We have found that the logarithmically decaying 1/e cut-off L-shell is a satisfying indicator of the outer boundary of the outer radiation belt. Furthermore, our study shows that the logarithmically decaying 1/e cut-off latitude is dependent on the Kp index in the main phases of CME- and CIR- driven storms, while in the recovery phases, there is no obvious correlation. In addition, it has been shown that the locations of the peak electron flux are controlled by the minimum Dst index in the main phases of CME-driven storms. The influences of multiple storms on the electron flux of outer radiation belt have also been investigated.

     

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

Interaction between ultralow frequency (ULF) waves and charged particles plays an important role in the acceleration of particles in the Van Allen radiation belts. The strong wave-particle interaction predicts an energy-dependent observational signature of particle flux variations during different stages of the ULF wave evolution. In this paper, we find that the energetic particle data newly available from an IGSO spacecraft are quite consistent with theoretical predictions, which enables the application of a best-fit procedure to quantitatively extract key parameters of the ULF waves from the particle data. The general agreement between observations and the best-fit results validates the scenario of wave-particle drift resonance within the entire ULF life span, and provides a new technique to understand the ULF wave characteristics in the absence of electromagnetic field data. We also examine the minor differences between observations and the best-fit results, and propose that the differences may result from a longitudinal dependence of the ULF wave power to be considered in a future study.     

Compression-related EMIC waves drive relativistic electron precipitation

With coordinated observations of the NOAA 15 satellite and OUL magnetometer station in Finland, we report that the electromagnetic ion cyclotron(EMIC) waves which were stimulated by the compression of the magnetosphere drive relativistic electron precipitation in geoquiescence on 1 Jan 2007. After an enhancement of solar wind dynamic pressure(SWDP), a dayside Pc1 pulsation was observed by the OUL station. Such a Pc1 pulsation is caused by an EMIC wave which propagates from the generation source to lower altitudes. Simultaneously, the NOAA 15 satellite registered an enhancement of precipitating electron count rates with energies 3 Me V within the anisotropic zone of protons. This phenomenon is coincident with the quasi-linear theoretical calculation presented in this paper. Our observations suggest that after a positive impulse of solar wind, the compression-related EMIC waves can drive relativistic electrons precipitation and play a pivotal role in the dynamic of radiation belts.     

The HEPD particle detector of the CSES satellite mission for investigating seismo-associated perturbations of the Van Allen belts

CSES(China Seismo-Electromagnetic Satellite) is a mission developed by CNSA(Chinese National Space Administration) and ASI(Italian Space Agency), to investigate the near-Earth electromagnetic, plasma and particle environment, for studying the seismo-associated disturbances in the ionosphere-magnetosphere transition zone. The anthropogenic and electromagnetic noise,as well as the natural non-seismic electromagnetic emissions is mainly due to tropospheric activity. In particular, the mission aims to confirming the existence of possible temporal correlations between the occurrence of earthquakes for medium and strong magnitude and the observation in space of electromagnetic perturbations, plasma variations and precipitation of bursts with highenergy charged particles from the inner Van Allen belt. In this framework, the high energy particle detector(HEPD) of the CSES mission has been developed by the Italian LIMADOU Collaboration. HEPD is an advanced detector based on a tower of scintillators and a silicon tracker that provides good energy and angular resolution and a wide angular acceptance, for electrons of 3–100 Me V, protons of 30–200 Me V and light nuclei up to the oxygen. CSES satellite has been launched on February 2~(nd), 2018 from the Jiuquan Satellite Launch Center(China).     

高空高能带电粒子流

本文介绍高空高能电子研究进展,揭示接近宇宙空间的高能电子形成机制,高空高能带电粒子流和地震活动性之间的关系。指出在震中地区,地震形成过程中发射电磁辐射是高能带电粒子流和地震活动性之间存在关系的重要原因。     

Magnetospheric chorus wave instability induced by relativistic Kappa-type distributions

We study the field-aligned propagating magnetospheric chorus wave instability using a fully relativistic wave growth formula,the previously developed relativistic Kappa-type(KT) distribution and the regular Kappa distribution of energetic electrons.We demonstrate that the peak growth rate using the nonrelativistic Kappa simulation is higher than that using either the relativistic KT or the Kappa simulation at/above 100 keV, because the significant relativistic effect yields a reduction in the relativistic anisotropy. The relativistic anisotropy Arel basically decreases as the thermal parameter θ2 increases, allowing the peak growth by relativistic KT or Kappa distribution to stay at the lower frequency region. The growth rates tend to increase with the loss-cone parameter l because the overall anisotropy increases. Moreover, at high energy ~1.0 MeV, both the growth rate and the upper cutoff frequency become smaller as l increases for the relativistic KT calculation because the significant relativistic effect reduces both the resonant anisotropy and the number of the hot electrons, which is in contrast to the relativistic and nonrelativistic Kappa distribution calculations because the less relativistic or non-relativistic effect enhances the resonant anisotropy as l increases. The above results can be applied to the whistler-mode wave instability in the outer radiation belts of the Earth, the Jovian inner magnetosphere and other astrophysical plasmas where relativistic electrons often exist.     

The mid-high latitude whistler mode chorus waves observed around substorm onsets

Using the data of LFEW/TC-2, we studied the dawn side chorus around substorm onsets during a strong geomagnetic storm in November 2004. During this storm, LFEW/TC-2 observed 14 dawnside chorus events. Nine of them were associated with substorms and occurred within 40 min around the substorm onsets. The frequencies of waves have a very good correlation with the half equatorial electron cyclotron frequencies. Chorus can be excited in the region near magnetic equatorial plane and then propagate to the mid and high latitudes. When the wave frequencies reach the local lower hybrid frequencies, chorus can be reflected due to the lower hybrid resonance. The time delay between the chorus and its echo is about 28 min. Previous observations show that the chorus can propagate at most to the magnetic latitudes of 40°. LFEW/ TC-2 found for the first time that the chorus in space could propagate to the magnetic latitude of 70°. Since most of the previous chorus observations are made close to the magnetic equatorial plane, our results are important for the studies of excitation and propagation of whistler mode wave, and relevant relativistic electron acceleration in the magnetosphere. Supported by the National Natural Science Foundation of China (Grant Nos. 40621003, 40523006, 40704028, 40604018), 973 Program of China (Grant No. 2006CB806305), and the Specialized Research Fund for State Key Laboratories of China.     

Influence of wave normal angle on gyroresonance between chorus waves and outer radiation belt electrons

In this paper,using a Gaussian distribution of wave normal angle X=tan,and considering contributions of harmonic resonances n up to±5,we analyze the effect of normal angle on diffusion coefficients induced by gyroresonance between chorus waves and electrons with energies 0.1 and 1.0 MeV on the dayside and nightside at L=4.5.When pitch angle e>10°,for 0.1and 1.0 MeV electrons on the dayside and nightside,diffusion coefficients of five orders(2,1,0,1,2)decrease with increasing normal angle peak,leading to the total diffusion coefficients decreasing with increasing peak.When e<10°,for 1.0MeV electrons on the dayside and 0.1 MeV electrons on the dayside and nightside,the positive order diffusion coefficients are generally smaller than the same negative order ones;in the meanwhile,diffusion coefficients of orders(2,1,2)are very small,the dominant order n=1 diffusion coefficients change very little,hence the total diffusion coefficients almost remain unchanged.However,for 1.0 MeV electrons on the nightside,diffusion coefficients of orders(2,1,2)which are larger than those of the order(1)resonance increase with increasing peak,hence the total diffusion coefficients increase with increasing peak.The current results show that the wave normal angle plays an important role in the quantitative analysis of gyroresonance between chorus waves and electrons in the outer radiation belt.     

An analysis of the correlation between the fluxes of high-energy electrons and low-middle-energy electrons in the magnetosphere

The variation of the flux of energetic electrons in the magnetosphere has been proven to be strongly related to the solar wind speed. Observations of GEO orbit show that the flux of low-energy electrons is not only modulated by the solar wind speed, but, if a time delay is added, is also positively correlated to the flux of high-energy electrons. This feature provides a possible method to forecast the flux of high-energy electrons in GEO orbit. In this study, the correlations of the fluxes between the high-energy electrons and low-middle-energy electrons obtained at different L values and in different orbits are investigated to develop the application of this feature. Based on the analysis of long–term data observed by NOAA POES and GOES, the correlations between the fluxes of high-energy electrons and low–middle–energy electrons are good enough at different L values and in different orbits in quiet time, but this correlation is strongly affected by CME–driven geomagnetic storms.     

Particle bursts in the inner radiation belt related to global lightning activity

Particle bursts (PBs), the phenomena characterized by short-term increases of particle counting rates (CRs), were observed by space-borne radiation belt particle detectors. With the electron CR data obtained by National Oceanic and Atmospheric Administration (NOAA)-18 satellite, the occurrence of PBs in the inner belt (1?L?2 and B?20.5 μT) were derived for years 2006–2011. The monthly occurrence number of PBs exhibits a strong maximum in northern summer (May–August). In association with global lightning data, the seasonal occurrence of PBs is found to be consistent with the lightning activity, especially if only lightning flashes at latitudes >20° are taken into account. The positive correlation between PBs and mid-latitude lightning discharges indicates the role of lightning-induced whistler waves, and is consistent with the expected pitch-angle scattering by wave-particle interactions. The contribution of lightning is so significant that it forms a non-negligible seasonal background of PBs. If one connects PBs to seismoelectromagnetic emissions (SEME) in attempt to find the earthquake precursor, the lightning background needs to be considered with great care.     

东濮凹陷文南—刘庄地区沙二下亚段浅湖风暴沉积

风暴沉积是一种特殊的事件沉积,反映了区域特定时期的古地理环境和古气候变化。通过区域古地理研究和精细地层对比,探讨了东濮凹陷文南—刘庄地区沙二下亚段沉积时期浅湖风暴沉积证据及特征,在此基础上总结了风暴沉积模式。结果表明:沙二下亚段沉积时期湖盆沉积层序主要受气候条件控制,气候频繁变化导致风暴沉积广泛分布、多期发育;风暴沉积主要发育在湖侵体系域和高水位体系域,沉积早期发育在深水区,而到沉积晚期分布范围扩大;风暴沉积一般发生在每期砂组的边界附近,作为短期、等时的一种事件沉积,可以用来作为层序划分的辅助标志;研究区风暴沉积模式主要有I类和II类两种;I类风暴沉积为类深水风暴沉积,发育A—D段沉积的类鲍马序列层序,但粒度要较深水风暴沉积细得多,多见于漫湖沉积环境相对深水区;II类风暴沉积不发育I类风暴的B和D段沉积;风暴流在风暴停止时越靠近湖盆中央,其沉积特征就越类似深水风暴沉积,反之则越类似II类风暴沉积。     

Analysis of magnetotail flux rope events by ARTEMIS observations

Three earthward flowing magnetic flux ropes observed in the duskside plasma sheet at geocentric solar magnetospheric coordinate X~–55 Re by P1 and P2 of acceleration,reconnection,turbulence and electrodynamics of moon’s interaction with the sun mission during 13:00–15:00 UT on July 3,2012,were studied.The morphologies of the flux ropes were studied in detail based on Grad-Shfranov reconstruction method and electronic pitch angle distribution data.It is found that(1)the flux rope cross-sectional dimensions are 1.0 Re×0.78 Re,1.3 Re×0.78 Re,and 2.5 Re×1.25 Re,respectively.The magnetic field lines were asymmetric about the center with field line compression on both sides of the current sheet at the leading region;(2)the electron energy flux data presented asymmetry with larger electron flux and lower temperature in the precursor region.The flux ropes were blocked by the resistance of compressed particle density in the front central plasma sheet and the enhanced magnetic field on its sides;and(3)it is found that the flux rope has a layered structure.From inside out,event 1 can be divided into three regions,namely electronic depletion core region,closed field line region,and the caudal area possible with fields connected with the ionosphere.It suggests that the flux ropes cannot merge with the tail magnetic field lines near the lunar orbit.Especially,the flux rope asymmetrical shape reflects the different reconnection processes that caused it on both sides of the magnetic structure.The events shown in this paper support the multiple X-line magnetic reconnection model for flux ropes with in situ observations.     

Suprathermal particle events observed by WIND spacecraft in interplanetary space during 1995–1999 and their classification

Fifty-five suprathermal particle events were selected from WIND observations between 1995 and 1999. Based on systematic analysis on the observational characteristics of these events a two-parameter (the rising time and the flux ratio of electrons to protons in each event) classification method was proposed to classify these events. The three classified classes are (1) impulsive electron events with the flux ratio of electrons to protons being bigger than 1 and rising time being shorter than 200 min, (2) impulsive proton events with the flux ratio being smaller than 1 and rising time being shorter than 200 min, and (3) gradual proton events with the flux ratio being smaller than 1 and the rising time being longer than 200 min. In the past, “impulsive solar electron events” were under intense research. However, because the selection standards of their velocity dispersions or pitch-angle distributions were inadequate, statistical surveys of selected events were different from each other and even some conclusions were not consistent with the theory, for example, the relation of type-III solar radio bursts to the “impulsive solar electron events”. The first class of impulsive electron events are associated with type-III radio bursts and with clear velocity dispersions; therefore they ought to originate from the Sun. The second class of the events, which have short continuance time and usually are not associated with type-III radio bursts and without velocity dispersion, are still far away from interplanetary shocks and most of them do not one-to-one correspond to corrotating interacting regions (CIRs); such events are possible results of local interplanetary magnetic field reconnection or electromagnetic disturbances. Finally, about 2/3 gradual proton events of the third class occur with interplanetary shocks, the delay times of which are almost equal to the rising time. Some of these events can be understood as particle accelerations by shocks. Supported by the National Natural Science Foundation of China (Grant Nos. 10425312, 40574065 and 10333030), and the Major State Basic Research Development Program of China (973 program) (Grant No. 2006CB806302), and the Chinese Academy of Sciences (Grant No. KJCX2-YW-T04)     

Ultra low frequency waves impact on radiation belt energetic particles

One of the most fundamental important issues in the space physics is to understand how solar wind energy transports into the inner magnetosphere. Ultra low frequency (ULF) wave in the magnetosphere and its impact on energetic particles, such as the wave-particle resonance, modulation, and particle acceleration, are extremely important topics in the Earth’s radiation belt dynamics and solar wind—magnetospheric coupling. In this review, we briefly introduce the recent advances on ULF waves study. Further, we will explore the density structures and ion compositions around the plasmaspheric boundary layer (PBL) and discuss its possible relation to the ULF waves.     

高辐射通量空间相干X射线管(英文)

针对光栅X射线相位衬度成像技术中如何获取高辐射通量和高空间相干的台式X射线源的问题,研制一种桌面X射线源.与传统X射线源不同,其阳极采用平行深沟道阵列的结构靶,灯丝发出的电子经加速聚焦后作用于结构靶,产生高辐射通量的一维相干X射线,其焦斑呈平行线阵列结构分布.将这种X射线管用于基于光栅的X射线相衬成像系统的光源,利用5步相移法得到了新鲜鸡翅的X射线相衬图像照片.     

诸城盆地早白垩世砂岩主量元素地球化学特征及其对物源区构造环境的制约

诸城盆地作为早白垩世伸展盆地,与其东南侧胶南造山带之间的耦合关系一直以来仍缺少相关研究。基于野外地质考察、砂岩碎屑组分统计及主量元素特征分析,探讨了早白垩世诸城盆地的物源方向、莱阳群砂岩的地球化学组成、物源区风化特征及大地构造背景。结果表明:诸城盆地莱阳群砂岩地球化学类型主要为铁砂岩和杂砂岩,其源岩具有长英质火成岩或中性岩特点;砂岩的化学蚀变指数(45~58)、化学风化指数(47~69)、斜长石蚀变指数(58~73)和化学组分变化指数(0.86~1.02)体现了源区风化作用很弱的特征;Dickinson分类图解及古流向指示砂岩源区主要为盆地东南侧的胶南造山带,砂岩的地球化学组成、风化特征等共同说明早白垩世时期胶南造山带经历了快速隆升事件;结合前人关于该地区岩浆岩地球化学特征,胶南造山带的本次快速隆升是岩石圈减薄作用的结果,因而诸城盆地的快速沉降与胶南造山带的隆升是相互耦合的。上述结果一方面从地球化学角度证实了胶南造山带早白垩世时期经历了快速隆升事件,另一方面也说明了诸城盆地原型是伸展断陷盆地,二者均是华北东部岩石圈减薄作用的产物。