电离层谷区不均匀体的地区特性和产生机制研究

Investigating the occurrence and evolution characteristics, and generation mechanisms of ionospheric valley region irregularities (VRI) is very important for the study of ionospheric plasma instability processes, and may provide crucial electric field measurement which plays an important role in ionospheric dynamics. The project will use the experimental observations of ionospheric field aligned irregularities performed by the Sanya VHF coherent radar, to investigate the local time and seasonal variations of VRI. Analysis on the single/multi layer structures and periodical variations of VRI echo intensity provides a chance to reveal the regional features of VRI in the Chinese low latitude region. Combined with the high-time resolution ionogram measurements, the project will investigate how the disturbance and polarization associated with the ionospheric E and F region irregularities, and the background ionospheric conditions affect the generation and evolution of VRI, and study what source energy drives the instability processes responsible for the generation of VRI. Further, using the radar multi beam steering measurements in geomagnetic east-west, together with the 3D interferometry, the project will investigate the spatial structures, movements and beam-dependant appearance of VRI, and perform a comparison with the EAR and Gadanki radar VRI observations. This will help to understand the possible mechanisms responsible for the latitudinal occurrence of VRI.

分析研究电离层谷区不均匀体的区域发生特征、运动演化过程和产生机制，对认识电离层不稳定性过程有着重要的学术意义，同时也可为电离层动力学研究提供关键的电场信息。本项目拟利用三亚VHF相干雷达对电离层谷区不均匀体开展系统的实验观测与研究，分析谷区不均匀体随地方时和季节变化，不均匀体回波的单层/多层形态以及回波强度随时间短周期变化的规律，给出我国低纬谷区不均匀体的地区特性。结合雷达与频高图加密等观测，分析电离层E区、F区不均匀体有关的扰动和极化过程以及电离层背景条件变化对谷区不均匀体形成和演化的影响，揭示驱使不同地方时电离层谷区不稳定性发生的可能能量源。利用相干雷达多波束扫描和三维空间干涉观测，分析谷区不均匀体的空间结构形态和运动特征，考察谷区不均匀体东西向波束观测的差异性及其原因，通过与邻近经纬度的EAR和Gadanki雷达观测对比分析，探讨谷区不均匀体发生的纬度范围及其可能的影响机理。

本项目利用三亚空间环境观测站的VHF相干散射雷达和电离层测高仪等自主设备，发展了三亚VHF雷达不同高度电离层不均匀体多波束扫描和空间干涉探测分析方法，对我国低纬电离层谷区不均匀体开展了系列实验观测和研究，取得如下科学认识：（1）我国低纬夜间/日落后谷区不均匀体的发生率和回波强度远大于白天；（2）发现夜间谷区不均匀体常伴随E区不均匀体减弱与同时的F区等离子体泡产生，提出赤道等离子泡分裂产生的极化电场抑制和触发低纬不同高度不均匀体的机制；（3）首次在远离磁赤道的北半球低纬也探测到白天谷区不均匀体，伴随同时的中间等离子体层现象，证实了白天谷区不均匀体与150 km密度层的直接关联，暗示白天谷区不均匀体出现的磁纬边界可能在13度；（4）发现日落前底部类型不均匀体薄层现象，不能用日落等离子体漩涡这一传统机制来解释，提出重力波风场驱使的等离子体梯度漂移不稳定性可能产生日落前不均匀体薄层。对白天的谷区不均匀体和底部类型不均匀体薄层现象,国际上至今仍缺乏完整合理的解释，将开展进一步研究。