GPS observations of medium-scale traveling ionospheric disturbances over Europe
GPS observations of medium-scale traveling ionospheric disturbances over Europe
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DOI：
10.5194/angeo-31-163-2013
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发表时间：
2013-01-01
影响因子：
1.9
通讯作者：
Tsugawa, T.
中科院分区：
文献类型：
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作者：
Otsuka, Y.;Suzuki, K.;Tsugawa, T.
利用从欧洲全球定位系统（GPS）接收网的800多个GPS接收器获取的总电子含量（TEC）图，首次揭示了欧洲上空中等尺度行波电离层扰动（MSTIDs）的二维结构。通过对2008年获取的TEC图进行统计分析，我们发现观测到的MSTIDs可分为两类：白天MSTID和夜间MSTID。白天MSTID在冬季频繁出现。在欧洲低纬度地区，其按月和按小时统计的最大出现率超过70%，而在高纬度地区约为45%。由于大多数白天MSTIDs向南传播，我们推测它们可能是由热层中的大气重力波引起的。夜间MSTIDs也在冬季频繁出现，但大多数向西南传播，这一方向与极化电场在产生夜间MSTIDs中起重要作用的理论相符。夜间MSTID的出现率呈现明显的纬度差异：在欧洲低纬度地区，按月和按小时统计的出现率最大值约为50%，而在高纬度地区很少观测到夜间MSTID。我们分别对由重力波和振荡电场引起的等离子体密度扰动进行了模型计算，以重现白天和夜间的MSTIDs。我们发现由重力波引起的TEC扰动不显示倾角依赖性，而由振荡电场引起的TEC扰动在低纬度地区具有较大振幅。TEC扰动振幅的这些倾角依赖性可能导致MSTID出现率的纬度变化。与先前的研究相比，我们讨论了夜间MSTID出现率的经度差异以及E区和F区的耦合过程。欧洲夜间MSTID出现率的季节变化与夜间MSTID出现的经度和季节变化可归因于Es层出现的变化这一理论不一致。
Two-dimensional structures of medium-scale traveling ionospheric disturbances (MSTIDs) over Europe have been revealed, for the first time, by using maps of the total electron content (TEC) obtained from more than 800 GPS receivers of the European GPS receiver networks. From statistical analysis of the TEC maps obtained 2008, we have found that the observed MSTIDs can be categorized into two groups: daytime MSTID and nighttime MSTID. The daytime MSTID frequently occurs in winter. Its maximum occurrence rate in monthly and hourly bin exceeds 70 % at lower latitudes over Europe, whereas it is approximately 45 % at higher latitudes. Since most of the daytime MSTIDs propagate southward, we speculate that they could be caused by atmospheric gravity waves in the thermosphere. The nighttime MSTIDs also frequently occur in winter but most of them propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs. The nighttime MSTID occurrence rate shows distinct latitudinal difference: The maximum of the occurrence rate in monthly and hourly bin is approximately 50 % at lower latitudes in Europe, whereas the nighttime MSTID was rarely observed at higher latitudes. We have performed model calculations of the plasma density perturbations caused by a gravity wave and an oscillating electric field to reproduce the daytime and nighttime MSTIDs, respectively. We find that TEC perturbations caused by gravity waves do not show dip angle dependencies, while those caused by the oscillating electric field have a larger amplitude at lower latitudes. These dip angle dependencies of the TEC perturbation amplitude could contribute to the latitudinal variation of the MSTID occurrence rate. Comparing with previous studies, we discuss the longitudinal difference of the nighttime MSTID occurrence rate, along with the E- and F-region coupling processes. The seasonal variation, of the nighttime MSTID occurrence rate in Europe, is not consistent with the theory that the longitudinal and seasonal variations of the nighttime MSTID occurrence could be attributed to those of the Es layer occurrence.