Abstract: Collisinal Rayleigh-Tailor instability in the ionospheric F region of low and mid-latitudes is discussed. Emphasis is put on the effects of thebackground neutral wind to the growth rate of the instability. A set of equations governing the R-T instability in this region is established with electric field and neutral wind included and the linear growth rate is deduced. The results show that the growth rate decreases as increasing latitude. For latitudes higher than 30 degree, normal neutral wind alone can no longer make the growth rate keeping positive values even under most favorable conditions, unless there is an eastward electric field. This indicates that the electric field may take an important role in local R-T instability evolution in mid-latitudes. Seasonal variations of the growth rate is also discussed using certain electron density profile model.

Key words: Spread-F, R-T instability, mid-latitude Spread-F

摘要： 讨论了中低纬度电离层F区中有碰撞的Rayleigh-Taylor不稳定性的线性增长率，着重考察背景中性风对增长率的影响，首先建立了适合于描述中低纬地区R-T不稳定性的基本方程，其中包括背景中性风和电场。在此基础上导出了色散关系和不稳定性增长率γ。结果表明，γ随纬度增加而逐渐减小，虽然东西方向和垂直向下的中性风分量有利于不稳定性增长，但在比30度更高的纬度，正常的背景中性风很难使γ为正值，除非存在合适的东西方向电场，亦即电场在中纬度Spread F的形成方面起着重要的作用。文中还根据比较合乎实际的电离层电子密度分布模式估算了线性增长率γ的季节变化。

关键词: 扩展F, 瑞利-泰勒不稳定性, 中纬扩展F