基于电离层暴时f_0F_2经验模型Kalman滤波短期预报

利用时间累积地磁指数印ap(T),建立了强地磁扰动条件下电离层f0F2与月中值相对偏差经验模型.该经验模型只在春秋季节和夏季特强地磁扰动条件ap(T)>100,即时间累积地磁指数大于100时达到理想精度.尝试利用气象预报中常用的Kalman滤波方法对模型的系数进行实时修正,以提高预报精度,并对长春站1986-1995年近一个太阳周f0F2数据进行提前一小时预报试验.冬季预报均方根误差为0.76MHz,春秋季节为0.68MHz,夏季为0.61MHz.在特强地磁扰动条件下,预测误差在0.87～1.43MHz之间.该预报方法同时与包含暴时修正模型STORM的国际参考电离层IRI2001进行了比较,展示了Kalman滤波方法实时修正模型系数的能力和良好的应用前景.     

太阳活动低年广州地区地磁扰动与电离层闪烁的统计特征分析

基于肇庆地磁台的地磁监测数据和广州气象卫星地面站建立的华南地区GPS电离层闪烁监测网的监测数据, 统计分析了2008年7月至2010年7月太阳活动低年期间广州地区地磁扰动与电离层闪烁的关系. 用肇庆台地磁水平分量H的变化量换算出肇庆地磁指数K, 以此来代表广州地区地磁扰动情况.分析结果表明, 磁暴/强地磁扰动对广州地区电离层闪烁的发生总体表现为抑制作用, 电离层闪烁主要发生在低K值期间, 而在K ≥ 4时电离层闪烁的发生呈下降趋势. 电离层闪烁发生率随季节和地磁活动的变化规律表现在, 春季的弱闪烁发生率、夜间中等以上闪烁发生率和夏季中等以上闪烁的发生率明显与地磁活动指数K相关, 即随$K$指数的增大而减小; 在秋季和冬季闪烁发生率与K指数变化无明显关系. 同时还综合分析了地磁与太阳活动的变化对电离层活动的影响, 广州地区闪烁主要发生在太阳活动较低的磁静日期间.      

Modeling and observations of the north–south ionospheric asymmetry at low latitudes at long deep solar minimum

Using the physics based model SUPIM and FORMOSAT-3/COSMIC electron density data measured at the long deep solar minimum (2008–2010) we investigate the longitude variations of the north–south asymmetry of the ionosphere at low latitudes (±30° magnetic). The data at around diurnal maximum (12:30–13:30 LT) for magnetically quiet (Ap ? 15) equinoctial conditions (March–April and September–October) are presented for three longitude sectors (a) 60°E–120°E, (b) 60°W–120°W and (c) 15°W–75°W. The sectors (a) and (b) have large displacements of the geomagnetic equator from geographic equator but in opposite hemispheres with small magnetic declination angles; and sector (c) has large declination angle with small displacement of the equators; vertical E × B drift velocities also have differences in the three longitude sectors. SUPIM investigates the importance of the displacement of the equators, magnetic declination angle, and E × B drift on the north–south asymmetry. The data and model qualitatively agree; and indicate that depending on longitudes both the displacement of the equators and declination angle are important in producing the north–south asymmetry though the displacement of the equators seems most effective. This seems to be because it is the displacement of the equators more than the declination angle that produces large north–south difference in the effective magnetic meridional neutral wind velocity, which is the main cause of the ionospheric asymmetry. For the strong control of the neutral wind, east–west electric field has only a small effect on the longitude variation of the ionospheric asymmetry. Though the study is for the long deep solar minimum the conclusions seem valid for all levels of solar activity since the displacement of the equators and declination angle are independent of solar activity.     

The response of the ionosphere over Ilorin to some geomagnetic storms

The effects of some geomagnetic storms on the F2 layer peak parameters over Ilorin, Nigeria (Lat. 8:53°N, Long. 4.5°E, dip angle, −2.96°) have been investigated. Our results showed that the highest intensity of the noon bite-out occurred during the March equinox and lowest during the June Solstice on quiet days. Quiet day NmF2 disturbances which appeared as a pre-storm enhancement, but not related to the magnetic storm event that followed were observed at this station. These enhancements were attributed to the modification of the equatorial electric field as a result of injection of the Auroral electric field to the low and equatorial ionosphere. For disturbed conditions, the morphology of the NmF2 on quiet days is altered. Daytime and nighttime NmF2 and hmF2 enhancements were recorded at this station. Decreases in NmF2 were also observed during the recovery periods, most of which appeared during the post-noon period, except the storm event of May 28–29. On the average, enhancements in NmF2 (i.e. Positive phases) are the prominent features of this station. Observations from this study also indicate that Dst, Ap and Kp which have been the most widely used indices in academic research in describing the behavior of geomagnetic storms, are not sufficient for storm time analysis in the equatorial and low latitude ionosphere.     

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.      

X级以上耀斑与地磁效应关系研究

统计研究了2010年1月至2012年12月期间所有与耀斑爆发相伴生的日冕物质抛射(CME) 引发的地磁暴事件. 结果表明, 对于CME源区其主要分布在日面 45°E-45°W, 占总数的78.95%, 且西半球比东半球多, 即源区位于西半球的CME易产生地磁效应; X级耀斑与地磁效应的关联性更高, 60.0%的 X级耀斑在其爆发后的2～3天内观测到地磁暴, 而其他级别的耀斑与地磁效应的关联性低得多, 均不足10%; 通过对此期间日面爆发的所有X级耀斑研究分析后发现, 对于源区位于日面东经45°E-45°W 的X级耀斑, 若在其爆发过程中没有大尺度日面扰动, 则无伴生CME且后续产生地磁效应的可能性很低. 由此提出一种通过分析日面观测数据进行地磁暴预报的方法.      

基于MRPs/NPUPF的地磁/加速度计测量的姿态估计新方法

针对现有基于地磁/加速度计的姿态估计算法存在状态误差协方差阵的奇异值和需要准确已知当地地磁矢量的问题,提出了一种新的姿态估计基本方法。该方法采用修正罗德里格参数(MRPs)表示系统动态,消除了采用四元数法导致的状态误差协方差阵的奇异值问题;根据地磁场缓变的特性,将地磁矢量作为平稳过程加入到状态变量中,使得姿态估计不再需要准确已知当地地磁矢量。针对大初始误差和有色噪声对基本方法的影响,通过引入模型误差预测(NPF)和无迹粒子滤波(UPF)方法对其进行改进,提出了基于模型预测无迹粒子滤波(NPUPF)的地磁/加速度计的姿态估计新方法。仿真结果表明,NPUPF方法可在大初始误差和非高斯条件下实现高精度的姿态估计,提高了基于地磁/加速度计的姿态估计方法的可靠性和实用性。
     

高维寻优ICP算法及其在地磁辅助导航中的应用

利用地磁场特征进行辅助导航是目前组合导航技术的重要研究方向.地磁导航可采用基于ICP算法的匹配定位来限制推算定位或惯性系统时间增长带来的位置误差.ICP算法使用的前提是初始误差较小,当初始误差较大时,最近点的计算容易落入伪目标点,导致该算法不再适用.针对ICP算法的这种缺陷,本文利用地磁场特征量的高维特性,提出在最近点...     

World grid of cosmic ray vertical cut-off rigidity for the last decade

Cosmic ray cut-off rigidity tables and maps over the world concerning the epochs 2010, 2015 and the current one 2020 have been constructed. These maps display the effective cut-off rigidity in every five degrees in latitude and in longitude at the altitude of 20 km above the surface of the international reference ellipsoid. The values of the geomagnetic cut-off rigidity were calculated in every 5° in latitude and in every 15° in longitude applying the well-known method of particle trajectory calculations resulted from the theory of the particle motion in the Earth's magnetic field. The applied software employed the 12th Generation of the International Geomagnetic Reference Field (IGRF 12) and trajectories were calculated at 0.01 GV intervals in order to determine the vertical cut-off rigidity for each location. Beyond the use of the calculated cut-off rigidity values as a basic reference of charged particle access to different geographical locations during quiet and/or more intense geomagnetic periods, these results can be used for a long- term forecasting of the geomagnetic conditions variations.     

Effects of variations of geomagnetic field on VLF waves induced by beating of two HF waves

Beat wave (BW) high frequency (HF) ionospheric heating experiments were conducted to generate very low frequency (VLF) waves. The VLF waves were registered with a VLF receiver located ～15?km east of the European Incoherent Scatter (EISCAT) heating facility in Tromsø, Norway. A fluxgate magnetometer was used to monitor auroral electrojet current, and ionospheric conditions were measured using a Dynasonde. Correlation coefficients between VLF amplitudes and the deviation of geomagnetic north–south components were calculated. Experimental results show that strong and positive correlation exists the majority of the time, but sometimes no correlation or even a negative correlation occurred. This is consistent with similar past experiments that took place with exclusively AM generation. These results therefore support the conclusion that BW generation of VLF waves is no different than with AM, likely occurring in the D or lower E ionospheric region.