Empirical models of terrestrial trapped radiation.

A survey of empirical models of particles (electrons, protons and heavier ions) of the Earth's radiation belts developed to date is presented. Results of intercomparison of the different models as well as comparison with experimental data are reported. Aspects of further development of radiation condition modelling in near-Earth space, including dynamic model developing are discussed.     

基于数据网格化方法的低轨辐射带建模技术

地球辐射带中的高能带电粒子是引起航天器材料和器件性能退化甚至失效的主要空间环境因素.因此,航天器设计中所采用的辐射带模型的准确程度对于航天器的生存能力和航天任务的完成质量至关重要.在利用我国自主辐射带高能粒子探测数据进行的辐射带建模中,探测数据的空间网格化是一项非常重要的工作.介绍了我国辐射带探测数据的情况,以及辐射带建模的方法和步骤;重点研究了不同插值方法在低地球轨道(LEO)空间辐射带建模数据网格化中的应用,并开展了误差分析.研究结果表明:在各种常用的插值方法中,反距离加权法、自然邻点法和最近邻点法适合工程化应用.其中,反距离加权法生成的数据网格对粒子通量的反演结果精度最高,该方法采用低阶距离时得到的反演结果更为合理.      

Specification of the Earth’s plasmasphere with data assimilation

In this paper we report on initial work toward data assimilative modeling of the Earth’s plasmasphere. As the medium of propagation for waves which are responsible for acceleration and decay of the radiation belts, an accurate assimilative model of the plasmasphere is crucial for optimizing the accurate prediction of the radiation environments encountered by satellites. On longer time-scales the plasmasphere exhibits significant dynamics. Although these dynamics are modeled well by existing models, they require detailed global knowledge of magnetospheric configuration which is not always readily available. For that reason data assimilation can be expected to be an effective tool in improving the modeling accuracy of the plasmasphere. In this paper we demonstrate that a relatively modest number of measurements, combined with a simple data assimilation scheme, inspired by the ensemble Kalman filtering data assimilation technique does a good job of reproducing the overall structure of the plasmasphere including plume development. This raises hopes that data assimilation will be an effective method for accurately representing the configuration of the plasmasphere for space weather applications.     

Reanalysis of radiation belt electron phase space density using various boundary conditions and loss models

Data assimilation is becoming an increasingly important tool for understanding the near Earth hazardous radiation environments. Reanalysis of the radiation belts can be used to identify the electron acceleration mechanism and distinguish local acceleration from radial diffusion. However, for any practical applications we need to determine how reliable is reanalysis, and how significant is the dependence of the results on the assumptions of the code and choice of boundary conditions. We present the sensitivity of reanalysis of the radiation belt electron phase space density (PSD) to the assumed location of the outer boundary, using the VERB code and a Kalman filter. We analyze the sensitivity of reanalysis to changes in the electron-loss throughout the domain, and the sensitivity to the assumed boundary condition and its effect on the innovation vector. All the simulations presented in this study for all assumed loss models and boundary conditions, show that peaks in the phase space density of relativistic electrons build up between 4.5 and 6 R_E during relativistic electron flux enhancements in the outer radiation belt. This clearly shows that peaks build up in the heart of the electron radiation belt independent of the assumptions in the model, and that local acceleration is operating there. The work here is also an important step toward performing reanalysis using observations from current and future missions.     

Quiet time distribution of plasma pressure in the inner earth's magnetosphere

Trapped particles of the radiation belts provide a considerable part of plasma pressure at low L-shells. The evaluations of this part during quiet times can be made on the basis of existing trapped radiation models. The radial profiles of plasma pressure at 1.2 < L < 7 were obtained by using the empirical AP8MAX model of trapped radiation (L < 6.6) and the theoretical model of the distribution of the proton fluxes in the Earth's radiation belts (L < 7) developed on the basis of the numerical solution of the radial diffusion equation with dissipation processes. The calculations were compared with AMPTE/CCE data. The contribution of quiet-time plasma pressure profile producing the quiet-time ring current to D_st-variation was obtained about 15 nT which is comparative with the magnetic field disturbances during weak and moderate magnetic storms (D_st = −40 ≈ −100 nT).     

An investigation of the spatial variations of the energetic trapped electrons at low altitudes

We have analyzed the trapped electron data (0.19–3.2 MeV) taken by the Japanese OHZORA satellite operated at 350–850 km altitude in polar orbit during 1984–1987 near solar minimum. The electron observations reveal all the global attributes of the quiet-time electron radiation belts, such as the South Atlantic Anomaly, the electron “slot”, and the outer radiation belt regions. The electron data are in general agreement with the NASA AE-8 electron model, but there are differences, particularly with respect to distinctive local-time variations in the slot region. In this paper, we present results from analyses of variations of the electron pitch angle distributions with local time, L-shell and altitude.     

Geomagnetic transmission disturbances and heavy-ion fluences observed in low Earth orbit during the solar energetic particle events of October 1989.

The large solar energetic particle (SEP) events and simultaneous large geomagnetic disturbances observed during October 1989 posed a significant, rapidly evolving space radiation hazard. Using data from the GOES-7, NOAA-10, IMP-8 and LDEF satellites, we determined the geomagnetic transmission, heavy ion fluences, mean Fe ionic charge state, and effective radiation hazard observed in low Earth orbit (LEO) for these SEPs. We modeled the geomagnetic transmission by tracing particles through the combination of the internal International Geomagnetic Reference Field (IGRF) and the Tsyganenko (1989) magnetospheric field models, extending the modeling to large geomagnetic disturbances. We used our results to assess the radiation hazard such very large SEP events would pose in the anticipated 52 degrees inclination space station orbit.     

Results from the ESA SREM monitors and comparison with existing radiation belt models

The Standard Radiation Environment Monitor (SREM) is a simple particle detector developed for wide application on ESA satellites. It measures high-energy protons and electrons of the space environment with a 20° angular resolution and limited spectral information. Of the ten SREMs that have been manufactured, four have so far flown. The first model on STRV-1c functioned well until an early spacecraft failure. The other three are on-board, the ESA spacecraft INTEGRAL, ROSETTA and PROBA-1. Another model is flying on GIOVE-B, launched in April 2008 with three L-2 science missions to follow: both Herschel and Planck in 2008, and GAIA in 2011). The diverse orbits of these spacecraft and the common calibration of the monitors provides a unique dataset covering a wide range of B-L* space, providing a direct comparison of the radiation levels in the belts at different locations, and the effects of geomagnetic shielding. Data from the PROBA/SREM and INTEGRAL/IREM are compared with existing radiation belt models.     

基于NOAA卫星数据的辐射带质子投掷角分布研究

利用NOAA-12卫星数据对空间环境平静时期太阳同步轨道处辐射带质子投掷角分布进行了研究. 根据投掷角分布的经验公式,计算出90°投掷角的质子方向强度和各向异性指数n. 质子投掷角分布按n的取值范围可分为三类,即90°峰值分布、平顶分布和蝴蝶形分布. 观测证实,对于辐射带质子,三种分布类型均存在并且具有明显的空间区域特征. 在内辐射带边缘地区90°峰值分布占主要优势;在外辐射带高L值区域,90°峰值分布明显减少,平顶分布和蝴蝶形分布逐渐增多. 针对90°峰值分布,研究了质子强度各向异性的区域分布特征,对于内辐射带区域,n值随L值的增大而增大,对于外辐射带,n值表现为逐渐下降的趋势. 为了研究质子投掷角分布对磁地方时的依赖关系,分析了能量为250～800keV的质子在两个不同磁地方时范围的投掷角分布规律. 结果显示,在内辐射带,质子强度的投掷角分布相对稳定,随磁地方时的变化并不显著;而在外辐射带的高L值区域,质子强度的投掷角分布随磁地方时变化明显,与磁地方时之间有明显的依赖关系.      

质子辐射带辐射中心区域模型

利用AP-8和CRRESPRO质子辐射带模式数据库, 比较了二者在磁赤道面上计算结果 的差异并给出其差异原因. 利用AP-8模式数据库数据, 建立起质子辐射带函数形式的辐射中心区域模式, 包括各能道全向微分通量峰值所对应的L值(L_c) 随能量E的变化模式以及各能道全向微分通量峰值J_max随能量E的变化模式. 利用RBSP A卫星REPT望远镜在磁赤道面上的高能质子观测数据, 分别与 AP-8模式、CRRESPRO模式及本文所得辐射中心区域模式计算结果进行比较, 发现在78.9, 102.6和208MeV三个能道上, RBSP A卫星观测所得各能道全向微分 通量明显偏大, 而L_c与AP-8或本文辐射中心模式所得结果基本一致; RBSP A卫星也观测到CRRESPRO Quiet模式所得的隐性第二质子辐射带结构.      

Charged particles on the Earth–Jupiter–Europa spacecraft trajectory

Charged particle fluxes on the trajectory of future Russian space research mission to Jupiter and its satellite Europa are investigated. The existing experimental data and models of Jupiter’s main magnetic field and radiation belts are summarized. Preliminary results of computations of energetic particle fluxes and radiation doses for each stage of the flight are given. Special attention is paid to estimation of radiation conditions in Europa’s orbit and on its surface; influence of the satellite on spatial distribution of the fluxes of charged particles of various energies is studied.     

Near-Earth radiation model deficiencies as seen on CRRES.

The Space Radiation (SPACERAD) experiments on the Combined Release and Radiation Effects Satellite (CRRES) gathered 14 months of radiation particle data in an 18 degrees inclination orbit between 350 km and 36000 km from July 1990 to October 1991. When compared to the NASA radiation belt models AP8 and AE8, the data show the proton model (AP8) does not take into account a second belt formed after major solar flare/shock injection events, and the electron model (AE8) is misleading, at best, in calculating dose in near-Earth orbits. The second proton belt, although softer in energy than the main proton belt, can produce upsets in proton sensitive chips and would produce significant dose in satellites orbiting in it. The MeV electrons observed on CRRES show a significant particle population above 5 MeV (not in the AE8 model) which must be included in any meaningful dose predictions for satellites operating between L-shells of 1.7 and 3.0 RE.     

The physics of the FLUKA code: Recent developments

FLUKA is a Monte-Carlo code able to simulate interaction and transport of hadrons, heavy ions and electromagnetic particles from few keV (or thermal neutron) to cosmic ray energies in whichever material. The highest priority in the design and development of the code has always been the implementation and improvement of sound and modern physical models. A summary of the FLUKA physical models is given, while recent developments are described in detail: among the others, extensions of the intermediate energy hadronic interaction generator, refinements in photon cross sections and interaction models, analytical on-line evolution of radio-activation and remnant dose. In particular, new developments in the nucleus–nucleus interaction models are discussed. Comparisons with experimental data and examples of applications of relevance for space radiation are also provided.     

Development of Operational Space Weather Prediction Models

In this report, we summarize the needs of space weather models, and recommend that developing operational prediction models, rather than transitioning from research to operation, is a more feasible and critical way for space weather services in the near future. Operational models for solar wind speed, geomagnetic indices, magnetopause, plasma sheet energetic electrons, inner boundary of ion plasma sheet, energetic electrons in outer radiation belt, and thermospheric density at low Earth orbit, have been developed and will be introduced briefly here. Their applications made a big progress in space weather services during the past two years in China.      

Inner radiation belt source of helium and heavy hydrogen isotopes

Nuclear interactions between inner zone protons and atoms in the upper atmosphere provide the main source of energetic H and He isotopes nuclei in the radiation belt. This paper reports on the specified calculations of these isotope intensities using various inner zone proton intensity models (AP-8 and SAMPEX/PET PSB97), the atmosphere drift-averaged composition and density model MSIS-90, and cross-sections of the interaction processes from the GNASH nuclear model code. To calculate drift-averaged densities and energy losses of secondaries, the particles were tracked in the geomagnetic field (modelled through IGRF-95) by integrating numerically the equation of the motion. The calculations take into account the kinematics of nuclear interactions along the whole trajectory of trapped proton. The comparison with new data obtained from the experiments on board RESURS-04 and MITA satellites and with data from SAMPEX and CRRES satellites taken during different phases of solar activity shows that the upper atmosphere is a sufficient source for inner zone helium and heavy hydrogen isotopes. The calculation results are energy spectra and angular distributions of light nuclear isotopes in the inner radiation belt that may be used to develop helium inner radiation belt model and to evaluate their contribution to SEU (single event upset) rates.     

辐射带AP9模式在南大西洋异常区的系统性量化评估

针对目前辐射带AP9模式量化评估不够系统的问题，基于F_10.7指数确定高、中、低太阳活动水平，以三种太阳活动水平条件下NOAA-15观测的140~500MeV的全向质子通量为参考数据，以南大西洋异常区为对比区域，定义边界吻合度和大小量级差为评估指标，将辐射带AP9模式分别与AP8模式和参考数据进行对比，对AP9模式进行系统性量化评估.结果表明，AP8和AP9模式均能重构出南大西洋异常区，但AP8模式重构的南大西洋异常区轮廓与观测结果更为吻合.平均而言，AP8和AP9模拟结果均比观测值高，AP8比AP9更接近观测值.太阳活动水平越低，AP9与观测之间的差距越小.      

MONITORING OF ENERGETIC PARTICLE ENVIRONMENT INSIDE THE CHINA-BRAZIL EARTH RESOURCE SATELLITE

On 14 October 1999, the Chinese-Brazil earth resource satellite (CBERS-1) was launched in China. On board of the satellite there was an instrument designed at Peking University to detect the energetic particle radiation inside the satellite so the radiation fluxes of energetic particles in the cabin can be monitored continuously. Inside a satellite cabin, radiation environment consists of ether penetrated energetic particles or secondary radiation from satellite materials due to the interactions with primary cosmic rays.Purpose of the detectors are twofold, to monitor the particle radiation in the cabin and also to study the space radiation environment The data can be used to study the radiation environment and their effects on the electronics inside the satelhte cabin. On the other hand, the data are useful in study of geo-space energetic particle events such as solar proton events, particle precipitation and variations of the radiation belt since there should be some correlation between the radiation situation inside and outside the satellite.The instrument consists of two semi-conductor detectors for protons and electrons respectively. Each detector has two channels of energy ranges. They are 0.5-2MeV and ≥2MeV for electrons and 5-30MeV and 30-60MeV for protons. Counting rate for all channels are up to 104/(cm2@s)and power consumption is about 2.5 W. There are also the additional functions of CMOS TID (total integrated dose) effect and direct SEU monitoring. The data of CBMC was first sent back on Oct. 17 1999 and it's almost three years from then on. The detector has been working normally and the quality of data is good.The preliminary results of data analysis of CBMC not only reveal the effects of polar particle precipitation and radiation belt on radiation environment inside a satellite, but also show some important features of the geo-space energetic particle radiation.As one of the most important parameters of space weather, the energetic charged particles have great influences on space activities and ground tech nology. CBMC is perhaps the first long-term on-board special equipment to monitor the energetic particle radiation environment inside the satellite and the data it accnmulated are very useful in both satellite designing and space research.     

A skeptic's view of PLR effects in the magnetosphere

A critical appraisal is made of the hypothesis that power-line harmonic radiation can influence the Earth's radiation belts by triggering intense magnetospheric emissions which in turn resonantly scatter trapped electrons into the atmospheric loss cone. While such triggering may indeed occur, a combination of theoretical arguments supplemented by an indepth analysis of OGO-5 satellite data is employed to show that triggered waves comprise at best a small fraction of the total magnetospheric wave population. Previous claims to the contrary have been either based on erroneous statistical arguments or biased by the limited sample of ducted waves detectable by ground based receivers. The totality of satellite data is consistent with a predominantly natural origin for the two classes of electromagnetic waves (chorus and plasmaspheric hiss) which are known to interact strongly with energetic radiation belt electrons.     

23rd solar cycle: Solar activity parameters and associated Forbush decreases

We report Forbush decreases (FD) in cosmic ray intensity from January 1996 to December 2008, the whole Solar Cycle 23rd. Statistical analysis is done for only 152 events for which associated solar flare position, flare classes, and Coronal Mass Ejections (CME) speed are given. We applied FD parameters taken from the Forbush Effects and Interplanetary Disturbances databases maintained by the Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radiowave Propagation (IZMIRAN), obtained by processing the data of the worldwide neutron monitor network using the global survey method (GSM) (A. Belov et al., 2018). For the said number of events, we examine their effect on interplanetary space and the decrease of the galactic cosmic rays (GCR) near Earth. We found that the 11–20° latitudinal belt shows more FD- associated flare events than the other latitudinal belts, and on this belt, the Southern hemisphere is more active. The results reveal that FDs and solar flares are well correlated. Statistical analysis is carried out for the magnitude of the CR decrease with solar and geomagnetic parameters.     

Dynamics of the low altitude secondary proton radiation belt

At the interface between the upper atmosphere and the radiation belt region, there exists a secondary radiation belt consisting mainly of energetic ions that have become neutralized in the ring current and the main radiation belt and then re-ionized by collisions in the inner exosphere. The time history of the proton fluxes in the 0.64 – 35 MeV energy range was traced in the equatorial region beneath the main radiation belts during the three year period from 21 February 1984 to 26 March 1987 using data obtained with the HEP experiment on board the Japanese OHZORA satellite. During most of this period a fairly small proton flux of −1.2 cm⁻² s⁻¹ sr⁻¹ was detected on geomagnetic field lines in the range 1.05 < L < 1.15. We report a few surprisingly deep and rapid flux decreases (flux reduction by typically two orders of magnitude). These flux decreases were also long in duration (lasting up to three months). We also registered abrupt flux increases where the magnitude of the proton flux enhancements could reach three orders of magnitude with an enhancement duration of 1–3 days. Possible reasons for these unexpected phenomena are discussed.