电离层加热中热自聚焦不稳定性的数值研究

The thermal self-focusing instability (TSFI) caused by ionospheric heating is an important mechanism for the large-scale field aligned irregularities (FAI) generating, and give a profound impact on the radio waves pass through, so that the research on which are meaningful for engineering and military application. However, the ionospheric modulation facilities or experimental records are less involved in middle-low latitude areas and the theoretical research previously have somewhat limitation all make the TSFI a difficult issue in the research of ionospheric nonlinear effects. The two-dimensional (2-D) slow change full-wave model describing the propagation of HF pump waves in inhomogeneous magnetized plasma are presented by the finite difference time domain (FDTD) method in this project, then the transport equations of electron temperature and plasma density and the 2D full wave model are nonlinearly coupled together to simulating the process of the excitation of the TSFI and the formation of large scale field inhomogeneous structure. The simulation results will be compared with the observation results of EISCAT heating experiments to verify the validity of the model and analyze the effect of incident parameters, ionosphere background parameters on the spatial distribution of the electric field of pump waves and the development of TSFI, furthermore, lay the foundation for exploring the approaches to improve the efficiency of ionospheric heating effectively.

电离层加热所激发的热自聚焦不稳定性可促使改变电离层结构的大尺度场向不均匀体产生，对经过该区域的无线电波产生深远的影响，具有十分重要的工程及军事应用价值。由于目前中低纬区域电离层调制设备及实验数据的相对匮乏，以往理论研究又各有所限，使得热自聚焦不稳定性成为电离层非线性效应研究中的一大难点。本项目拟用时域有限差分方法构建非均匀磁化电离层背景中的二维缓变全波解数值模型，并耦合电子密度及电子温度的输运方程对电离层加热过程中激发热自聚焦不稳定性并生成大尺度场向不均匀体的过程进行详细模拟，模拟结果将与欧洲EISCAT调制实验结果相比较，以验证模型的准确性；最后我们结合模拟结果及实验数据分析泵波入射参数、电离层背景等对泵波场强空间分布以及热自聚焦不稳定性发展的影响，为探索能够有效提升电离层加热效率的方法或途径奠定基础。

本课题采用时域有限差分方法构建了非均匀磁化电离层背景中的一维及二维‘慢’波全波解数值模型，并耦合电子密度及电子温度的输运方程对电离层调制过程中激发热自聚焦不稳定性并生成大尺度场向不均匀体的过程进行了详细模拟，并对特征波反射区域附近电子密度及电子温度的变化率进行采样后求取其功率谱密度并进行了深入分析，结果表明：当HF泵波的电场阈值达到或超过百毫伏每米的量级时，即可有效激发热自聚焦不稳定性并发展出大尺度电子密度及温度不均匀体，这些不均匀体内的密度耗空约为1%-10%，而电子温度剧烈增长，到达背景温度值的1.2-2.1倍；且在相当的加热条件下，背景电子温度越低、电子密度越小，加热效果越显著；电子密度及电子温度的扰动幅度随着加热时间的推移而逐渐减小，即扰动逐渐趋于饱和，且电子温度要快于电子密度达到饱和状态；热自聚焦不稳定性发展出的大尺度不均匀体满足幂律谱结构，谱指数随着加热的进行逐渐趋于稳定，白天与夜间的幂律谱指数区别不大，但电子密度与电子温度的幂律谱有一定的区别。本课题研究成果为后续继续探索能够有效提升电离层调制效率的方法或途径提供理论依据及仿真结果参考。