Simultaneous Light-Radio Observations of Ionospheric E-region field-aligned irregularities

自1989年以来，MU雷达被广泛用于揭示电离层e区场向不规则（FAI）的精细结构。我们在e区FAI中发现了两种类型的FAI回波。一类是准周期性（QP）型，夏季在海拔100 km以上区域间歇性出现。另一种是连续型，在90 ~ 100 km高度区域时间上连续出现。虽然QP结构被认为是由大气重力波产生的，但其产生机制尚不确定。在本研究中，我们利用MU雷达（京都大学无线电大气科学中心）、频率捷变雷达（FAR） （SRI International）和多色气辉成像系统（MAIS）（日本东北大学）研究了e区FAI的空间结构。FAR位于MU雷达站以北约40公里的塔加。从1993年5月26日至1993年7月26日期间，在MU雷达和FAR之间进行了同步观测。在同一时期，MAIS位于东京大学的木户天文台进行了这项合作研究。本研究结果总结如下：(1) MU雷达与FAR同时观测发现，FAI的波浪形结构向南-西南或西南方向水平传播。回声区由西北向东南延伸。(2) MAIS和其他气辉观测在90 ~ 100 km高度区域显示了相似的波浪形结构。(3)通过对雷达观测和电离空仪的对比，发现FAI与散e层有较好的相关性。(4)提出了大气重力波对散发性e层的高度调制产生极化电场，从而产生FAI QP结构的模型。

Since 1989, the MU radar has been extensively utilized to reveal fine structures of the ionospheric E-region field-aligned irregularities (FAI). We found two types of FAI echoes in the E-region FAI.One is the quasi-periodic (QP) type which intermittently appears in the altitude region above 100 km in the summer months. The other is the continuous type which appear continuously in time in the altitude region of 90-100 km. Although the QP structure were thought to be generated by the atmospheric gravity waves, its generation mechanism were uncertain. In this study we have studied spatial structure of the E-region FAI by using the MU radar (Radio Atmospheric Science Center, Kyoto University), Frequency Agile Radar (FAR) (SRI International), and Multicolor Airglow Imaging System (MAIS) (Tohoku University). The FAR was located in Taga which is approximately 40 km north of the MU radar site. Simultaneous observation between the MU radar and FAR were conducted in the period from May 26,1993 until July 26,1993. The MAIS was located in Kiso observatory of Univ. Tokyo for this cooperative study in the same period. Results of this study is summarized as follows.(1) From simultaneous observations between the MU radar and FAR,it was found that wavelike structures of the FAI horizontally propagated toward south-southwest or southwest. The echoing regions were elongated from northwest to the southeast.(2) MAIS and other airglow observations revealed similar wavelike structures in the altitude region of 90-100 km.(3) From the comparison between the radar observations and the ionosonde in Shigaraki, good correlation between the FAI and the sporadic-E layr was found.(4) We have proposed a model that the QP structures of the FAI are generated by the polarization electric field which is produced by the altitude modulation of the sporadic-E layr by the atmospheric gravity waves.