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FAI回波类型，一种是准周期(QP)型，夏季间歇性地出现在海拔100公里以上的地区。另一种是连续型，在时间上连续出现在海拔90-100公里范围内。虽然QP结构被认为是由大气重力波产生的，但其产生机制尚不清楚。在这项研究中，我们利用京都大学无线电大气科学中心的MU雷达、SRI国际的频率捷变雷达(FAR)和东北大学的多色气辉成像系统(MAIS)研究了E区FAI的空间结构。FAR位于塔加，在MU雷达站以北约40公里处。在1993年5月26日至1993年7月26日期间，对MU雷达和FAR进行了同步观测。MAIS位于伊利诺伊大学基索天文台。东京为这一合作研究同期。主要研究结果如下：(1)MU雷达与FAR的同步观测发现，FAI的波状结构沿水平方向向西南偏南或西南方向传播。(2)MAIS和其他气辉观测在90-100公里的高度区域发现了相似的波状结构。(3)将FAI与重力波对零星-E层进行了比较，发现FAI与零星-E层有很好的相关性。(4)我们提出了FAI的QP结构是由大气重力波对零星-E层的高度调制所产生的极化电场产生的。

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.