太阳周期活动对低高度内辐射带高能质子的影响

利用NOAA-15卫星1998年到2011年近13年的高能质子全向通量观测资料, 分析了一个太阳活动周内, 低高度内辐射带高能质子通量的分布变化特性及其物理原因, 比较了观测结果与AP8模型的不同. 研究表明, 低高度内辐射带高能质子通量与太阳活动水平的反相关关系与磁壳参数L值及磁场B值有关; L值越低, B值越大的空间点, 其高能质子通量与太阳活动水平的反向相关性越明显. 高能质子通量随太阳活动水平的变化存在明显滞后现象, L值越高、 B值越小的空间点, 滞后现象就越明显, 滞后严重时可以达到一年左右的时间; 这种滞后现象反映出低高度内辐射带高能质子的源与损失达到平衡是一个中长期过程. 通过与AP8模型计算结果的比较分析可以看出, 利用AP8模型时, 仅考虑地磁场长期变化对质子通量的影响可能会夸大低高度内辐射带局部高能质子通量的增强.      

低高度内辐射带高能质子空间分布位形的研究

利用国际地磁参考场模式(IGRF模式)分析了1970-2000年低高度南大西洋负磁异常区位形的漂移与变化，给出了几个高度异常区中心位置磁场强度的变化和位置的变化。利用带电粒子的运动学方程，简要分析了低高度辐射带高能粒子的运动，得出在低高度，磁场是决定辐射带高能粒子空间强度与分布的决定性因素．低高度辐射带空间分布位形的变化特征应该与低高度南大西洋负磁异常区的变化特征基本一致．低高度南大西洋负磁异常区的特征可以作为低高度辐射带空间分布位形的一个初步判据。     

FY-3A观测的次南大西洋异常区形成机理

研究FY-3A卫星观测到的内辐射带质子通量分布,发现3～5MeV能道出现除南大西洋异常区以外的第二个异常区.该异常区是一个质子通量的次极值区,由于该质子通量极值区比主南大西洋异常区强度弱、面积小,因此称之为次南大西洋异常区.通过在主南大西洋异常区和次南大西洋异常区分别选取有代表性的样本点进行研究,发现内辐射带质子通量随投掷角近似呈正态分布,当投掷角在90°附近时,质子通量出现极大值;当投掷角大于120°或者小于60°时,质子通量几乎为零.此外,主南大西洋异常区质子通量在各个能道均为完全各向异性,次南大西洋异常区质子通量随着能道增高逐渐趋于各向同性.通过NOAA观测数据对此规律进行了验证,并由此解释了次南大西洋异常区的形成机理.      

FY-3A卫星与NOOA系列卫星高能带电粒子实测结果的比较

FY-3A卫星是运行于830 km高度的太阳同步轨道气象卫星,其搭载的空间环境监测器可观测3～300 MeV的高能质子和0.15～5.70 MeV的高能电子.FY-3A卫星在轨工作期间,太阳活动处于由谷年向峰年过渡期,空间环境非常平静,探测结果显示3～300 MeV的高能质子分布主要集中在南大西洋辐射带异常区,0.15～5.70 MeV的高能电子分布区域除南大西洋异常区外,还分布在南北两极高纬区域.FY-3A与NOAA卫星测量结果反映出带电粒子强度及分布区域随投掷角变化的空间各向异性特征.本文在充分考虑了带电粒子时间、空间分布差异以及比对探测器之间自身设计差异的前提下,经过归一化处理后,首次对两颗卫星同期探测结果进行相关性分析,验证了两颗卫星相同时空条件下高能带电粒子通量分布的一致性;说明FY-3A空间环境监测器不仅具备空间带电粒子辐射监测能力,且探测结果有效可靠,可用作辐射带环境数据源的组成部分,为发展新的模型,深入研究辐射带高能粒子的分布、起源和传输等提供新的观测依据.     

FY-3A卫星与NOAA系列卫星高能带电粒子实测结果的比较

FY-3A卫星是运行于830 km高度的太阳同步轨道气象卫星, 其搭载的空间环境监测器可观测3~300 MeV的高能质子和0.15~5.70 MeV的高能电子. FY-3A卫星在轨工作期间, 太阳活动处于由谷年向峰年过渡期, 空间环境非常平静, 探测结果显示3~300 MeV的高能质子分布主要集中在南大西洋辐射带异常区, 0.15~5.70 MeV的高能电子分布区域除南大西洋异常区外, 还分布在南北两极高纬区域. FY-3A与NOAA卫星测量结果反映出带电粒子强度及分布区域随投掷角变化的空间各向异性特征. 本文在充分考虑了带电粒子时间、空间分布差异以及比对探测器之间自身设计差异的前提下, 经过归一化处理后, 首次对两颗卫星同期探测结果进行相关性分析, 验证了两颗卫星相同时空条件下高能带电粒子通量分布的一致性; 说明FY-3A空间环境监测器不仅具备空间带电粒子辐射监测能力, 且探测结果有效可靠, 可用作辐射带环境数据源的组成部分, 为发展新的模型, 深入研究辐射带高能粒子的分布、起源和传输等提供新的观测依据.      

Polar卫星在低高度时表面正高电位的统计研究

基于Polar卫星1996-2008年的表面电压数据，研究了卫星在低轨区域出现正高电位（异常事件）与太阳活动的关系及其发生位置的磁地方时（MLT）分布.研究表明:太阳辐射与异常事件发生次数呈正相关，太阳活动越活跃，异常事件出现次数越多，但不会影响航天器表面电位；异常事件发生占比呈现明显季节性变化，在太阳活动高年，冬季和夏季次数较多，春季和秋季次数较少，在太阳活动低年，每月次数均维持在较低水平，而一个月内异常事件次数没有明显规律；在分布上南北半球表现出相似性，异常事件均不会发生在地磁纬度50°-60°区域，极区和昏侧发生次数较多，而不同的是异常事件在南半球发生得更多更集中；虽然太阳活动与航天器在低高度时表面出现正高电位的次数呈正相关，但即使在太阳活动峰年，航天器异常事件发生率也不超过10%.      

NeQuick模式在亚太地区扇区电离层参数f0F2的预测能力

利用亚洲、澳大利亚地区8个电离层观测台站的F2层临界频率f0F2的历史观测数据,考察了NeQuick模式预报电离层基本参数f0F2在亚太扇区的适应性.对比分析表明,此模式能比较好地预测各地的F2层临界频率,其绝对误差在南半球各站相对北半球各站较大,太阳活动高年相对太阳活动低年较大,春秋季相对夏冬季较大.其误差均方根在太阳活动高年相对太阳活动低年较大.      

基于CHAMP卫星观测数据对热层大气密度的经验正交分析

对2003年(太阳活动较高年)至2007年(太阳活动低年) CHAMP卫星的热层大气密度观测数据进行了经验正交函数(EOF)分析, 得到了400 km高度上白天平均大气密度ρ的太阳活动周变化与年度变化等不同变化分量. 研究结果表明, ρ受太阳活动影响较大, 其太阳周变化分量与F10.7指数变化之间的相关系数可高达94.5 %; ρ的太阳周变化分量随纬度增加而减小, 且在中高纬地区, 南半球的值明显大于北半球的值, 在低纬地区则出现基本对称的双峰分布, 即赤道质量密度异常(EMA)结构. 在ρ的年变化中, 呈现出明显的季节变化, 即夏季低冬季高; 同时ρ的年变化幅度随太阳活动增加而增强, 随纬度增加而增强. 将本文结果与经验模式NRLMSISE00在观测条件下的输出数据进行对比, 发现两者的太阳周变化与年变化分量基本一致, 但本文观测数据的太阳周成分随纬度变化略小, 年变化幅度略大, 且NRLMSISE00模式不能再现EMA结构. 研究结果对揭示热层气候学变化特征具有重要意义.      

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.      

基于SAMPEX卫星观测的南大西洋异常区高能质子动态分布特征

利用SAMPEX卫星1992年7月至2004年6月19～27MeV高能质子数据对南大西洋异常区的分布特征进行研究, 发现南大西洋异常区高能质子分布随高度及F_10.7的变化十分显著. 在540±25km高度上, 地磁较为平静时期南大西洋异常区高能质子微分通量随着F_10.7的增大而减小, 同时在F_10.7≥115sfu时减小趋势较为平缓. 对中等及以上磁暴进行统计分析发现, 磁暴期间南大西洋异常区高能质子微分通量和SYM-H指数的绝对值存在明显的反相关关系, 且地磁暴对南大西洋异常区高能质子微分通量存在明显的持续影响效应. 磁暴发生期间高能质子微分通量明显减少. 磁暴恢复相及其之后高能质子微分通量呈现较为显著的恢复过程.      

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.     

Space radiation environment in low earth orbit during influences from solar and geomagnetic events in December 2006

In low earth orbit, the SAA region is the dominant contributor to both proton environment and electron environment from the standpoint of radiation dose for spacecraft lifetime. However, the polar region and the horn region are sometimes strongly disturbed due to large solar and geomagnetic events. During large disturbances, enhancements in proton flux are measured in the polar region, which gives temporary more severe space radiation environment than that given in the SAA region. On the other hand, enhancements in electron flux are measured mainly in the horn region corresponding to the outer radiation belt, which are likely sources of high-energy electrons in the inner radiation belt. These short-term disturbances have another radiation hazard to spacecraft such as single event and electrostatic discharge.     

Recent space shuttle observations of the South Atlantic Anomaly and the radiation belt models.

Active instruments consisting of a tissue equivalent proportional counter (TEPC) and a proton and heavy ion detector (PHIDE) have been carried on a number of Space Shuttle flights. These instruments have allowed us to map out parts of the South Atlantic Particle Anomaly (SAA) and to compare some of its features with predictions of the AP-8 energetic proton flux models. We have observed that consistent with the generally observed westward drift of the surface features of the terrestrial magnetic field the SAA has moved west by about 6.9 degrees longitude between the epoch year 1970 of the AP-8 solar maximum model and the Space Shuttle observations made twenty years later. However, calculations indicate that except for relatively brief periods following very large magnetic storms the SAA seems to occupy the same position in L-space as in 1970. After the great storm of 24 March 1991 reconfiguration of the inner radiation belt and/or proton injection into the inner belt, a second energetic proton belt was observed to form at L approximately = 2. As confirmed by a subsequent flight observations, this belt was shown to persist at least for six months. Our measurements also indicate an upward shift in the L location of the primary belt from L = 1.4 to L = 1.5. In addition we confirm through direct real time observations the existence and the approximate magnitude of the East-West effect.     

Trapped proton fluxes measured on board LEO satellites in comparison with models

The proton fluxes from the low-Earth orbital satellites databases (NPOES-17 and CORONAS-F) were analyzed for the quiet geomagnetic period in April 2005. The satisfactory consent was found between the experimental and the AP8 model fluxes of the trapped protons with energy more than ∼10 MeV. At the same time, trapped proton fluxes with energy less than 10 MeV measured by LEO satellites were higher than the ones predicted by the AP8 model in the region of the SAA (drift shell L < 1.5).     

REM measurements aboard Mir during 1995

Measurements of the South Atlantic Anomaly (SAA) made with the Radiation Environment Monitor (REM) aboard Mir from November 1994 to February 1996 are presented. During this period an increase of the SAA radiation by ≈25% is observed, which coincides with a lowering of the radio solar flux. Radio solar flux is one of the parameters controlling the earth's atmospheric distribution and with it the absorption of inner radiation belt protons forming the SAA. Due to the altitude gradient of the atmospheric density, the proton fluxes in the SAA are anisotropic (loss cone, east-west effect). The measured distribution can be accounted for by basic models.     

On the spatial extent of the proton radiation belt from solar cell output variation of the Akebono satellite

Output current of silicon solar cells of Akebono satellite orbiting in the inner magnetosphere decreased from 13 A in 1989 to about 7 A in 2009, due to accumulated damage by energetic particles. A fair correlation between the monthly decrease rate of solar cell output current and trapped proton flux was found between 1989 and 1992, indicating that trapped energetic protons are responsible for the solar cell degradation. Simple variation from month to month was dominated by a fluctuation with one-year period and the correlation was not discernible after 1993. On the other hand, during orbiting the earth, another kind of decrease of output current emerged at low altitude above the sub-solar point, i.e., in the midst of sunlit condition. The decrease was larger in later years. The fact indicates more prominent temperature effect in the later years because of progress of the degradation. By removing data affected by the orbit condition above, variation from the same month in the previous year shows a clear oscillation due to orbit precession correlated with trapped energetic proton flux up to 1996. The amplitude of the annual variation oscillation tends to be larger than that expected from a degradation model based on energetic proton distribution of the NASA’s AP8 model. The larger oscillation amplitude suggests that the proton radiation belt was more sharply localized than given by the AP8 model throughout the early half of 1990s.     

利用质子强度变化对太阳质子事件进行短期预报方法初步研究

采用GOSE-10卫星4～9 MeV(P2),9～15 MeV(P3),15～40 MeV(P4),40～80 MeV(P5)能段上的质子通量数据,结合质子能谱,对太阳质子事件发生前各能谱参数的变化特征进行分析,详细介绍利用能谱参数的变化特征及能量E>10 MeV的质子通量数据对太阳质子事件进行预报的新方法,并运用这种方法对2002-2006年期间太阳质子事件进行了预报.预报结果显示,预报提前量最多达到100 h以上,对质子事件的报准率达97.5%,预报方法具备一定的有效性和实用性.