声重波激发的赤道 Spread—F 不稳定性

EQUATORIAL SPREAD-F INITIATED BY ACOUSTIC-GRAVITY WAVES

本文导出了声重波扰动与赤道电离层扩展Ｆ层相互作用的基本方程，并对数值模拟结果进行了讨论．结果表明当声重波扰动与Ｋａｖｌｅｉｇｈ－Ｔａｙｌｏｒ不稳定性共同作用于赤道Ｆ层时，将导致大尺度波状结构的Ｓｐｒｅａｄ－Ｆ．其特征为以一定速度漂移的准周期不规则性，发展到后期伴有羽柱形状的ｂｕｂｂｌｅ（电子密度低区）产生．这种现状的ｂｕｂｂｌｅ可上升至Ｆ层顶部并发生倾斜．声重波波矢量的方向决定着羽柱的倾斜方向．这些结果与实验观测特征相符，说明声重波扰动不仅是大尺度Ｓａｒｅａｄ－Ｆ的触发源，而且对其整个形态发展过程起着重要的作用．

The basic equation discribing Spread--F instability with the existance of acousticgravity waves in the ionospheric F region are derived and the numerical simulationsfor certain cases are conducted. The results show that the Spread-F will occur inlarge-scale wavelike structures under the conbined action of acoustic-gravity wavesand the Rayleigh Taylor instability in the equatorial F region. This Spread-F is aquasi-periodic instability moving at certain velocity and at late;developing stage itwill form plumelike plasma density depletions (bubbles) which can rise well abovethe F peak and become tilt. The acoustic-gravity wave vector determines the tiltdirection of bubbles. All these results are in agreement with the main observationalcharacteristics. It is thought then that acoustic-gravity waves are not only one ofthe initial sources of large-scale Spread-F, but also play an important role on itswhole evolutions.