Influence of meteors on the mesosphere studied by the cooperative radar/lidar

本研究利用京都大学的MU雷达对流星尾迹进行观测，以研究流星流量和中间层动力学参数。同时进行了激光雷达和气辉成像仪的观测，并对结果进行了比较，以阐明中间层和中间层顶区成分变化的机制。特别是，零星钠层是关注的主要目标之一。从大量的同步观测中，我们发现了以下几点。从高灵敏度的MU雷达观测来看，流星流量不受主要流星流活动的影响。然而，如果高度、方向或流星回波强度有限，则可能存在显著的时间变化。中层顶附近钠浓度的时间变化是惯性重力波，其周期大于数小时，向下传播缓慢.零星的钠层有时伴随着局部温度升高或风切变。特别是水平风的垂直切变与零星钠层的出现有很强的相关性。流星流量与零星钠层之间没有显著的相关性.在钠激光雷达和气辉成像仪的合作观测中，观测到气辉层内频繁的大气重力事件，阐明了中层顶小尺度重力波的气候特征和结构.在1998年11月预测的流星风暴前一天左右，MU雷达观测到了狮子座明亮流星（火球）的强烈活动。然而，通过光学测量没有发现对中间层顶区域的显著影响。

In this study, meteor trails have been observed by the MU radar of Kyoto University, in order to investigate meteor flux and mesospheric dynamical parameters. Simultaneous lidar and airglow imager observations have been carried out and results are compared, in order to clarify the mechanism of variations of constituents in the mesosphere and mesopause region. Especially, sporadic sodium layer is focused as one of the main targets. From plenty of simultaneous observations, the following findings have been revealed.1. The meteor flux was not influenced by the major meteor stream activity, from the MU radar observation with a high sensitivity. However, if height, direction, or meteor echo strength is limited there could be a significant temporal variation.2. The temporal variation of sodium density around the mesopause with slow downward progression with a period larger than several hours was confirmed to be inertia gravity waves.3. The sporadic sodium layer was sometimes accompanied by localized temperature increase or wind shear. Especially, there was a strong correlation between the vertical shear of horizontal wind and occurrence of sporadic sodium layers. No significant correlation was found between the meteor flux and sporadic sodium layer.4. During the cooperative observation of sodium lidar and airglow imager, atmospheric gravity events were frequently observed in the airglow layer by the imagers, which have clarified climatologies and structures of small scale gravity waves in the mesopause region.5. Strong activity of bright Leonid meteors (fireballs) were observed by the MU radar about one day prior to the predicted meteor storm in November 1998. However, no significant influence on the mesopause region was found by the optical measurement.