电离层TEC日落阶段涨落异常增强现象研究

重点报道了一种TEC信距测量的夜间抖动异常现象，分析了这种现象的观测特征，指出了夜间GPS伪距观测是的异常抖动，特别是日落后时段GPS伪距观测量的散开十分严重的乐是个别的偶然现象，在考察了周围环境之后初步排除了这种现象是由周围地物引起的可能性，而进一步与电离层不均匀体（Spread-F)的特征，特别是它发生率最大的地方时进行比较，认为这是一种电离层效应，由大尺度的电离层不规则结构造成的散射很可能是这种夜间散开的主要原因。本文仅就单站GPS观测资料认证了这种夜间强烈抖动的存在，分析了北京上空电离层中发生的不均匀体或各种扰动对GPS信号的可能影响及其观测特征，指出了夜间GPS伪距观测量的异常抖动，特别是日落后时段GPS伪距观测量的散开十分严重的现象，可以用于电离层不规则结构的研究。由于GPS设备比较简便，数据量大，精度高，适用于各种环境等特点，我们发展的单站数据分析方法可能会对研究电离层TEC夜间涨落异常增加现象，包括地域，时间上的统计特性比较有利。

THE ABNORMAL FLUCTUATIONS OF GPS PSEUDO-RANGE MEASUREMENTS AFTER LOCAL SUNSET

Using GPS signals to deduce the ionospheric TEC as a tool to study the ionospheric physical processes has been widely conducted. For a duel frequency GPS receiver, both pseudo-range and phase measurements are used. Phase measurement is not sensitive to so-called multi-path effect so it is less affected by scattered or reflected signals and is more useful in determining the exact TEC value, including the signals' scintillation due to the fast fluctuations of electron density.In this paper, an observational phenomenon is introduced to show that the pseudo-range fluctuates asymmetrically day and night. During the nighttime, especially, one to three hours after the local sunset, fluctuations of pseudo-range values often appear and last for several hours. The magnitudes of these fluctuations are much larger than that observed at daytime. Some examples are given and their observational features are analyzed. Both examinations of the environments around the receiver and the asymmetrical features of the phenomenon itself show that these fluctuations can not be produced by any ground objects, but instead, may be due to some ionospheric structures.By comparing with the theoretical and observational characteristics of ionospheric Spread-F at mid- and low latitudes, particularly with its occurring time after local sunset, it is suggested that the nighttime fluctuations of GPS pseudo-range measurements is a kind of multi-path effects, which is produced due to the scattering of GPS signals by large scaled ionospheric structures such as Spread-F. Thus, GPS may provide a way to study the ionospheric irregularities.