三种典型化学物质释放变态电离层的数值模拟研究

电离层人工变态会影响短波通信及卫星通信，对空间物理研究具有重要意义.基于中性气体扩散方程、离子化学反应方程及等离子体扩散方程，模拟了三种典型化学物质（氢气H₂、二氧化碳CO₂和三氟溴甲烷CF₃Br）经点源和多源释放后导致的电离层三维扰动变化，并利用自适应变步长的三维数字射线追踪技术讨论了化学释放变态电离层对不同频率短波传播的影响.结果表明:点源释放时产生的"空洞"在水平面上沿磁场线方向的轴长略大于其垂直方向；在释放量及释放高度相同的前提下，H₂扩散最快，CF₃Br扩散最慢，但就t=100 s时电子密度最大相对变化率而言，CF₃Br最大，CO₂次之，H₂最小；CF₃Br释放形成的"空洞"垂直范围最小，开始发生穿透现象所需的短波频率最高；H₂扰动下"空洞"边界的电子密度梯度最小，射线聚焦点明显偏高，聚焦效应最弱；多源释放产生类抛物线管状的电离层"空洞"结构，射线的传播路径更加多样，此时仍有聚焦效应出现，且聚焦点随射线频率增加而升高，聚焦效应减弱.

Numerical simulation of ionospheric modification by three representative chemical releases

Artificial ionospheric modification can disturb the short-wave communications and satellite communications. In this paper, on the basis of neutral gas diffusion equation, chemical reaction equation and plasma diffusion equation, the ionospheric disturbances caused by three representative chemicals (H₂, CO₂, CF₃Br) are simulated with a 3D dynamics model. The short wave propagation in disturbed ionosphere is also investigated with a 3D digital ray tracing method. The results show that single-point releases generate ellipse-like ionospheric holes, and a slightly larger scale is found along magnetic field than vertical direction in the hole's horizontal plane. With the same amount of substance and same release altitude, H₂ diffuses fastest and CF₃Br diffuses slowest, but as for the maximum relative change rate of electron density at t=100 s, CF₃Br corresponds to the highest rate while H₂ corresponds to the lowest. The release of CF₃Br results in the smallest vertical range of ionospheric hole, so the ray firstly penetrating the hole is at a higher frequency than that of CO₂ and CF₃Br. The release of H₂ results in the smallest electron density gradient at the hole's boundary among three chemicals, so the altitude of ray focus point is always higher than that of CO₂ and CF₃Br, indicating the weakest focus effect. Multipoint releases generate parabola-like tubular holes and lead to more diverse ray paths as well as ray focus effect. The altitude of focus point elevates with higher ray frequency, which is consistent with the single-point release condition.