低纬电离层TEC起伏与相位闪烁的统计特征

穿过电离层不规则体传播后的无线电波,其振幅和相位出现快速随机起伏,即电离层闪烁.为了量化电离层不规则体和相位闪烁的强度,本文提出用TEC起伏δTEC作为特征参量,并用δTEC的标准差构建一种新指数σtec.文中证明指数σtec与相位闪烁指数完全等效.在电离层强闪烁期间,经常出现信号短暂失锁和周跳,导致TEC值突跳和不连续.为此,本文设计了一种周跳检测与校正的批处理算法,用于消除TEC值突跳.在此基础上,利用位于我国中南部电离层闪烁监测台网2012—2015年的观测数据,考察了GPS信号相位闪烁和不规则体的统计特征.结果表明,我国低纬电离层不规则体和相位闪烁与振幅闪烁随地方时和月份变化的特征类似,一天之中主要出现在日落后至黎明前,一年之中,春季不规则体出现最频繁、秋季次之,呈现春秋不对称性,冬夏季出现很少.此外,我们还比较分析了指数S4与σtec的联系,两者之间显著正相关表明,小于第一菲涅尔带尺度的小尺度不规则体和大于第一菲涅尔带尺度的大尺度不规则体一般同时存在.

Statistical feature of TEC fluctuations and phase scintillations in the low latitude ionosphere of China

Transionospheric radio waves propagating through the irregularities experience rapid random fluctuation in phase and/or amplitude of the signal at the receiver, termed scintillation, which can degrade GNSS services. Thus, investigation and prediction of this scintillation effect is very important. Various indices have been derived in order to quantify the scintillation. In this paper, the total electron content (TEC) fluctuation δTEC is used as a characteristic parameter and a new index is established by the standard deviation of TEC fluctuations and denoted by the symbol σ_tec. It is demonstrated that the index σ_tec and the phase scintillation index is fully equivalent. During strong ionospheric scintillations, the receiver signals often encounter loss-of-lock and cycle slips, which create jumps and discontinuities in the TEC time series. In order to obtain continuous TEC data in the condition of the disturbed ionosphere, a batch processing method is developed to detect and correct cycle slip. Based on the methods mentioned above, we investigate the statistical feature of the phase scintillations of GPS signals and irregularities by means of the observations from a scintillation observation network in the mid-south region of China during 2012-2015. The results show that the variation features of phase scintillation occurrence with local time and month are very similar to those of the amplitude scintillation occurrence. Phase scintillations occur mainly during the night, from post-sunset to pre-dawn sector. It is found that phase scintillations occur most frequently in spring, the second in autumn, and seldom in winter and summer, and an equinoctial asymmetry that phase scintillations occur more frequently in spring than in autumn is also found. Besides, A comparison of σ_tec and S4 indicates there is close relation between them, implying the co-existence of large and small scale irregularities in equatorial irregularity structures.