An investigation of ionospheric disturbances over South Africa during the magnetic storm on 15 May 2005

The effects of the 15 May 2005 severe geomagnetic storm on the South African ionosphere are studied using ground-based and satellite observations. Ionospheric disturbances have less frequently been investigated over mid-latitude regions. Recently, a number of studies investigated their evolution and generation over these regions. This paper reports on the first investigation of travelling ionospheric disturbances (TIDs) over mid-latitude South Africa. Using global positioning system (GPS)-derived total electron content (TEC) variations from the South African network of dual frequency GPS receivers, we were able to examine the effects of the disturbance on the TEC. During this storm, two TEC enhancements were observed at low- and mid-latitudes: the first enhancement was observed between 30–45°S geomagnetic latitudes associated with equatorward neutral winds and the passage of a TID, while the second TEC enhancement is associated with a second TID. In addition, the F-region critical frequency (foF2) values observed at two ionosonde stations show response features that differ from those of the TEC during the disturbance period. The dissimilarity between the TEC and the foF2 suggests that two competing drivers may have existed, i.e., the westward electric field and equatorward neutral wind effects.     

Ionospheric anomalies observed over South Korea preceding the Great Tohoku earthquake of 2011

We investigated the ionospheric anomalies observed before the Tohoku earthquake, which occurred near the northeast coast of Honshu, Japan on 11 March, 2011. Based on data from a ground-based Global Positioning System (GPS) network on the Korean Peninsula, ionospheric anomalies were detected in the total electron content (TEC) during the daytime a few days before earthquake. Ionospheric TEC anomalies appeared on 5, 8 and 11 March. In particular, the ionospheric disturbances on 8 March evidenced a remarkable increase in TEC. The GPS TEC variation associated with the Tohoku earthquake was an increase of approximately 20 total electron content units (TECU), observed simultaneously in local and global TEC measurements. To investigate these pre-earthquake ionospheric anomalies, space weather conditions such as the solar activity index (F10.7) and geomagnetic activity indices (the Kp and Dst indices) were examined. We also created two-dimensional TEC maps to visual the spatial variations in the ionospheric anomalies preceding the earthquake.     

Total electron content variations in equatorial anomaly region

Diurnal variations in the total electron content (TEC) at Makerere University (00°19′N, 32°40′E, Geo Dip −22°), Uganda, have been investigated using a NovAtel GSV400B GPS receiver for the year 2010. The highest TEC values occurred from 13h00 to 17h00 local time (LT) throughout the year, with the highest values being exhibited during equinoctial months. In addition, there was some correlation between this high TEC and the moderate storms that occurred in 2010. These high TEC values have been attributed to the solar EUV ionization coupled with the upward vertical ExB drift. Nighttime enhancements were also found to be seasonally dependant, attaining maximum values during equinoctial months. These results were also compared with modeled TEC values by the IRI-2007 model. The modeled values were in good agreement with the measured values except for these two points: (1) the model had a short-fall in predicting the nighttime enhancements; and (2) the model’s minimum TEC did not coincide with the measured minimum in most of the months. Observed TEC depletions were found to correlate with an increase in the S₄ index and have been identified as a manifestation of the plasma density depletions of the equatorial origin.     

Variability study of ionospheric total electron content at crest of equatorial anomaly in China from 1997 to 2007

The variation of TEC data at Wuhan station (geographic coordinate: 30.5°N, 114.4°E; geomagnetic coordinate: 19.2°N, 183.8°E) at crest of equatorial anomaly in China from January 1997 to December 2007 were analyzed. Variability with solar activity, annual, semiannual, diurnal and seasonal variation were also analyzed. The MSIS00 model and ISR model were used to analyze the possible mechanisms of the variabilities found in the results. The TEC data in 1997 and 2001 deduced from another crest station Xiamen (geographic coordinate: 24.4°N, 118.1°E; geomagnetic coordinate: 13.2°N, 187.4°E) were used to contrast. Analysis results show that long-term variations of TEC at Xiamen station are mainly controlled by the variations of solar activities. Typical diurnal variation behaves as a minimum of the TEC in the pre-dawn hours around 05:00–06:00LT and a maximum on the afternoon hours around 13:00–15:00LT. Some features like the semiannual anomaly and winter anomaly in TEC have been reported. The anomaly may be the result of common action of the electric field over the magnetic equatorial and the [O/N₂] at the crest station.     

基于ProE的航天器三维屏蔽与辐射剂量评估方法研究

为准确评估结构异常复杂的航天器内部遭遇的辐射剂量,本文将直线近似原理和ProE工程软件相结合,自主开发了一种新型的航天器三维屏蔽与辐射剂量评估方法。利用本方法对立方体、球、平板等简单几何体内部的屏蔽厚度和辐射剂量进行了分析计算,计算结果表明基于ProE的三维屏蔽与辐射剂量计算方法是可靠的。结构复杂程度相当于中等规模航天器的模型计算结果表明,本方法能够较高效的分析评估复杂航天器内部遭遇的屏蔽厚度和辐射剂量。
     

国产数字信号处理器在轨验证技术研究

文章通过研究某国产数字信号处理器（XX-DSP）体系结构、DSP地面测试方法和空间环境对DSP的典型影响,设计了一种针对国产DSP类器件的在轨验证方法。验证系统硬件平台采用1∶1热备份设计,提高系统可靠性;验证方法借鉴当前地面应用广泛的功能测试方法,覆盖DSP的全部功能单元;另外考虑空间环境中的电离总剂量效应和单粒子效应影响,对DSP的片内RAM和内部寄存器的单粒子翻转（SEU）进行统计,并最终给出单粒子翻转率,同时检测DSP单粒子锁定（SEL）;最后通过运行DSP典型应用算法——有限长单位冲激响应（FIR）滤波算法验证DSP的系统功能,全面考核国产DSP的空间环境适应性。     

Improved model of ionosphere variability and study for long-term statistical characteristics

Ionospheric variability is influenced by many factors, such as solar radiation, neutral atmosphere composition, and geomagnetic disturbances. Mainly characterized by the total electron content (TEC) and electron density, the climatology of the ionosphere features temporal and spatial changes. Establishing a multivariant regression model helps substantially in better understanding the ionosphere characteristics and their long-term variability. In this paper, an improvement of the existing ionosphere multivariate linear fitting regression model is proposed and investigated using data from both the ionosonde and the global ionosphere map (GIM) derived from ground-based Global Navigation Satellite System (GNSS) observations. The proposed method gives more consideration to the impact of the solar activity and adds modeling of the annual periodic fluctuations and half-year periodic fluctuations for the F10.7 index. The improved model is verified to have a better correlation with the real observations and can help reduce the calculation uncertainty. Moreover, the proposed model is used to evaluate the fitting accuracy of the GIMs produced by five authorized data analysis centers from the International GNSS Service (IGS). The results show that there is a fixing hole in the North America region for the GIM model where the correlation between the GIM and the proposed model always returns lower values compared to other places.     

A preliminary study of the single crest phenomenon in total electron content (TEC) in the equatorial anomaly region around 120°E longitude between 1999 and 2012

The diurnal variations in total electron content (TEC) in the equatorial ionisation anomaly (EIA) region are not always represented by two crests on both sides of the magnetic equator. Sometimes, only an obvious single crest is evident at equatorial and low latitudes. In this paper, we focus on analysis of the morphological features of the single crest phenomenon in TEC around 120°E longitude during geomagnetic quiet days (Kp < 4₋). The variations in TEC are also compared with morphological parameters (foF2 and hmF2) derived from the International Reference Ionosphere extended to Plasmasphere (IRI–Plas) model. Our results show that the single crest phenomenon occurs mainly on days with extremely low solar activity, while the corresponding F2 layer critical frequency showed obvious asymmetry, or even only a single peak.     

核电站工作场所中子能谱和周围剂量当量率测量

中子周围剂量当量是核电站辐射防护监测的主要对象之一,而中子周围剂量当量的评估强烈依赖中子的能量分布。利用自制的多球谱仪对秦山第三核电有限公司（TQNPC）重水反应堆安全壳内5个位置的中子能谱和周围剂量当量率进行了测量。该谱仪由1个³He正比计数器以及9个2.5～12英寸不同直径的聚乙烯球组成,响应函数通过MCNP程序计算,并利用标准²⁵²Cf中子源进行了校准和验证。通过测量的中子能谱,获得了不同工作区域的中子周围剂量当量率及其能量分布,并与中子周围剂量当量率仪和CR-39径迹蚀刻探测器的测量结果进行了比较,为核电站中子剂量的监测提供了相关参考数据。     

载人航天器舱内辐射环境及剂量分析

构建载人航天器模型,利用Geant4软件计算了银河宇宙射线中的质子穿过载人航天器后在水模体中的总吸收剂量以及次级粒子吸收剂量,并且统计了不同种类的次级粒子在水模体中的总数量分布。计算结果表明,次级粒子引起的辐射剂量所占比例为50%,且二次电子总数量达到了10~7量级。