突发钠层的时间和空间变化性研究

Among the various properties of the atmospheric sodium layer, within 80-130km, the sporadic sodium layer (SSL) continues to attract the attention in recent years. The term “SSL” refers to thin layers (full width at half maximum, FWHM ∼ 1-4 km) of relatively high concentrations of Na atoms that appear and disappear on the topside of the normal Na layer, thus the main characteristics of SSLs are high peak density, narrow peak width, and short developing time. However, the formation mechanism of SSL remains an open question. One of the key problem related with it is the distinction between the temporal and spatial variation of SSL, which is difficult for the observation from a single lidar station. Note that the lidargram represents the time history of the vertical distribution of sodium over the lidar location, which should incorporate the temporal variations as well as the advection. In this project, we will establish a mobile Na lidar to achieve the co-observations of SSLs in different horizontal scales, through the combination of mobile Na lidar and the other fixed Na lidars. It will help us to distinguish between temporal and spatial variations of SSLs.The aim of the project is to investigate the temporal and spatial variations of SSLs, and understand the formation mechanism of the SSLs, as well as the role of gravity waves in the dynamical process within the mesospheric metal layer.

突发钠层现象是大气金属层（80-130km）在极狭窄的高度范围和较短时间迅速增加至同一高度整夜平均背景钠密度数倍以上的一种现象,其形成的机制目前仍有争论，而其中一个关键的因素就在厘清突发钠层时间和空间的变化性，而这是单站激光雷达观测的手段很难实现的。为此，我们通过建设可移动的高时空精度钠激光雷达，结合现有的固定激光雷达台站，针对突发钠层现象进行研究，通过合理配置移动站和固定站的水平距离，实现对突发钠层事件的时空变化的区分。研究突发钠层时间和空间变化的这一基础问题，探讨中纬度地区突发钠层的形成机制以及重力波在中层顶金属层动力学过程中的影响。

突发钠层现象是大气金属层（80-130km）在极狭窄的高度范围和较短时间迅速增加至同一高度整夜平均背景钠密度数倍以上的一种现象,其形成的机制目前仍有争论，而其中一个关键的因素就在厘清突发钠层时间和空间的变化性。本项目利用2011年-2018年合肥和武汉钠层的激光雷达观测数据，分析提取出19个共同观测到的突发钠层和低热层增强钠层（统称增强钠层）案例，进行分类后对两地增强钠层的相关性和形成机制进行了研究。总体上讲，长时间的增强钠层案例（超过2小时）两地间的相似度很高，这是由于某些大尺度机制的作用；短时间的增强钠层案例（小于2小时）两地间相关度较低，这是由于两地本地特征（动力学过程和化学过程）不同；合肥和武汉有时间延迟的3个案例显示出存在远距离输运过程的可能性。

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