Geomagnetic pulsation over conjugate locations during geomagnetic storms and substorm

Geomagnetic data collected during magnetic storm over magnetically conjugate pair (according to IGRF 2000) of high latitude stations viz., Maitri (70° 45′ S, 11° 42′ E) and Tromso (69° 40′ N, 18° 56′ E) reveal that amplitudes of Pc6 pulsation characteristically differ. The amplitude obtained from horizontal magnetic field for the Pc6 pulsation frequency range between 0.6 and 1.6 mHz significantly differs in time corresponding to peak amplitude. The relative differences in its time of occurrence found to gradually increase around initial phase of storm and remain exactly out of phase at peak amplitude of storm. Thence, it is found to be in agreement in phase gradually until storm unwinds. This indicates that simultaneous amplitude of Pc6 pulsation at conjugate pair of stations and its time of occurrence could be a key factor to infer storm arrivals somewhat prior to its peak effects. The emphasize remains on prediction of storm arrivals only by utilizing ground based magnetometer observations. However, it is necessary to understand differences on the basis of weak, moderate, strong, and super strong cases and more exactly how they behave along the line of magnetic Meridian. Nevertheless, the analysis implies that geo-effective magnetic ejecta/clouds/CIRs/sheaths/CMEs/ICMEs giving rise to geomagnetic storm can be predicted ahead of its peak effects by having magnetometer data over conjugate locations.     

Comparative analysis of TEC disturbances over tropical cyclone zones in the North–West Pacific Ocean

In this paper, we study ionospheric total electron content (TEC) disturbances associated with tropical cyclones (TCs). The study relies on the statistical analysis of six cyclones of different intensity which occurred in the North–West Pacific Ocean in September–November 2005. We have used TEC data from the international network of two-frequency ground-based GPS receivers and NCEP/NCAR meteorological archive. TEC variations of different period ranges (02–20 and 20–60 min) are shown to be more intense during TC peaks under quiet geomagnetic conditions. The highest TEC variation amplitudes are registered when the wind speed in the cyclone and the TC area are maximum. The intensification of TEC disturbances is more pronounced when several cyclones occur simultaneously. We have revealed that the ionospheric response to TC can be observed only after the cyclone has reached typhoon intensity. The ionospheric response is more pronounced at low satellite elevation angles.     

Investigation of the relationship between ionospheric foF2 and earthquakes

Variations of the ionospheric F2 region critical frequency (foF2) have been investigated statistically before earthquakes during 1980–2008 periods in Japan area. Ionosonde data was taken from Kokubunji station which is in the earthquake preparation zone for all earthquakes. Standard Deviations and Inter-Quartile Range methods are applied to the foF2 data. It is observed that there are anomalous variations in foF2 before earthquakes. These variations can be regarded as ionospheric precursors and may be used for earthquake prediction.     

中性风对夜间低纬电离层参量的影响

利用一个改进的二维低纬电离层理论模式研究夜间中性风对低纬电离层多量的作用．模式计算结果表明：夜间中性风对低纬F层的影响与纬度、地方时有关．夜间低纬F层峰值电子浓度和峰高及其随时间的变化受中性风的影响与传统观点有所差异．低纬F层参量不只依赖于中性风的方向、强度,还与中性风场空间分布及时间变化率有关．中性风对低纬F层的影响值得重新认识．     

武汉站第23周电离层TEC与太阳及地磁活动的相关性分析

利用武汉电离层观测站1997-2007年电离层TEC资料, 采用连续小波变换和交叉小波以及小波相干方法, 分析了该站电离层TEC的周期变化特征以及与太阳和地磁活动之间的关系. 分析结果表明, 武汉站TEC变化的长期趋势主要随太阳活动的强弱而变化; 在局部时域上分别存在128～256d, 256～512d和512d～1024d的周期尺度, 且与同时期的太阳黑子数和地磁Dst指数的周期特征存在很好的对应关系; 太阳黑子数在512～1024d周期尺度上超前TEC变化约1/6个周期; 在准半年的周期尺度上武汉站TEC与地磁Dst指数几乎呈反相位变化, 但TEC对$Dst$指数的这种响应仅在太阳活动高年存在, 具体机理尚需进一步分析研究.     

MGEX北斗差分码偏差两种精确处理方法对比分析

差分码偏差是北斗卫星导航系统（BDS）在高精度定位和电离层建模中需精确处理的系统误差之一.利用MGEX发布的2017年全年和2018年6月的BDS卫星的差分码偏差数据,比较分析了DLR和CAS分别解算的BDS卫星差分码偏差的日解值、月平均值和稳定性的变化特性.分析结果表明,DLR与CAS估算的BDS卫星差分码偏差值差异不大,具有较好的一致性;2017年CAS估算的BDS卫星C2I-C6I差分码偏差稳定性略优于DLR,C2I-C7I差分码偏差稳定性与DLR相当,且均具有较高稳定性;2018年6月DLR C2I-C6I差分码偏差月平均值稳定性优于CAS;C2I-C7I差分码偏差的稳定性明显优于C2I-C6I差分码偏差,卫星差分码偏差月平均值稳定性优于日解值稳定性.     

华南地区电离层闪烁与TEC耗空的时间和空间分布统计分析

利用位于赤道异常区的深圳站（22.59°N,113.97°E）2011年1月至2012年12月及2015年1月至2015年12月监测到的GPS-TEC数据,统计分析华南地区电离层闪烁与TEC耗空同时出现、电离层闪烁单独出现和TEC耗空单独出现3种现象的时间和空间分布特性.结果表明：这3种现象均主要发生在春秋季节;闪烁与TEC耗空同时出现、闪烁单独出现和TEC耗空单独出现分别主要发生在纬度为19°-23°N,21°-24°N和24°-26°N的空间区域.探测到闪烁和TEC耗空同时出现、闪烁单独出现和TEC耗空单独出现的时间分别主要分布在20：00LT-22：00LT,21：00LT-23：00LT和22：30LT-23：30LT.闪烁与TEC耗空同时出现、闪烁单独出现和TEC耗空单独出现3种现象的时间和空间分布特性对应了华南地区不规则体和赤道等离子体泡（EPBs）从产生到消失的演变过程.     

Multi-station observation of ionospheric irregularities over South Africa during strong geomagnetic storms

This paper presents results pertaining to the response of the mid-latitude ionosphere to strong geomagnetic storms that occurred from 31 March to 02 April 2001 and 07–09 September 2002. The results are based on (i) Global Positioning Systems (GPSs) derived total electron content (TEC) variations accompanying the storm, (ii) ionosonde measurements of the ionospheric electrodynamic response towards the storms and (iii) effect of storm induced travelling ionospheric disturbances (TIDs) on GPS derived TEC. Ionospheric data comprising of ionospheric TEC obtained from GPS measurements, ionograms, solar wind data obtained from Advanced Composition Explorer (ACE) and magnetic data from ground based magnetometers were used in this study. Storm induced features in vertical TEC (VTEC) have been obtained and compared with the mean VTEC of quiet days. The response of the mid-latitude ionosphere during the two storm periods examined may be characterised in terms of increased or decreased level of VTEC, wave-like structures in VTEC perturbation and sudden enhancement in hmF2 and h′F. The study reveals both positive and negative ionospheric storm effects on the ionosphere over South Africa during the two strong storm conditions. These ionospheric features have been mainly attributed to the travelling ionospheric disturbances (TIDs) as the driving mechanism for the irregularities causing the perturbations observed. TEC perturbations due to the irregularities encountered by the satellites were observed on satellites with pseudo random numbers (PRNs) 15, 17, 18 and 23 between 17:00 and 23:00 UT on 07 September 2002.     

On radiation belt dynamics during magnetic storms

Temporal variations of the radiation belt particle during the magnetic storms are investigated using measurements by the low altitude satellite spectrometer. Along with several known effects, such as the outer radiation belt intensity decrease at the main phase, the radial diffusion with the particle acceleration and the recovery of the radiation belt during the recovery phase, some less known features were investigated, such as the dawn–dusk asymmetry of the radiation belt.     

GNSS电离层模型改正精度评估与分析

电离层时延误差是导航定位信号在空间传播路径上的主要误差源之一,因此全面了解GNSS电离层模型的改正精度具有一定现实意义.根据GPS,BDS和Galileo系统所采用的电离层修正模型,利用2014年电离层校正参数,以高精度全球电离层图为基准,评估分析了三大系统电离层时延的改正精度.结果表明:目前GNSS使用的几种电离层修正模型的改正率在65~75%左右;Galileo系统使用的第二版NeQuick模型与第一版NeQuick模型相比在修正精度上并无显著提高;GPS使用的Klobuchar 8参数模型在北半球25°-45°N的中纬度地区精度很高,但是在全球其他区域精度较低,分布性较差,而NeQuick模型全球改正率分布则较为平均且平滑.