中层顶附近Fe和Na层变化的特征时间比较

Comparison of Mesospheric Fe and Na Layers' Variation Characteristic Times

采用特征分析方法计算中层大气Fe和Na层的化学特征时间,同时计算了它们被流星烟粒吸附和被垂直输运的特征时间．结果表明, (1)在Fe层数密度峰值高度附近,其EA化学特征时间为数日,远大于传统定义的数分钟; (2)比较Fe的输运特征时间(w=1 m／s)和化学特征时间,得出在84 km以下化学过程占优势,而在84km以上,垂直输运过程占主导地位,与Na层结果相同; (3)通过将各自化学特征时间与垂直输运和流星烟粒吸附的特征时间比较,以及考察流星金属注入率对Fe和Na原子分布的影响,发现最有可能使Fe和Na层下边沿截止高度重合的原因是流星烟粒的吸附效应．

The chemical lifetime of the mesospheric ferrum and sodium layers is calculated using the EigenAnalysis （EA） method. For comparison, their meteoric smoke adsorption lifetime and vertical transportation lifetime are also computed. The results show that （1） at the altitudes around the peak number density of Fe layer, the EA chemical lifetime for Fe atom is several days, much longer than the traditionally defined chemical lifetime for Fe of several minutes, （2） below 84km chemical process prevails whereas above that height, vertical process dominates, and （3） among the four of meteoric injection process, chemical process, vertical transportation process, and meteoric smoke adsorption process, the most possible one that can make the cutoff heights of Fe and Na layers to be identical is meteoric smoke adsorption.