电离层中ELF辐射源向下传播衰减理论分析

利用大功率高频（HF）电波调制加热电离层可在电离层中有效形成辐射源，并用于辐射ELF电磁波.本文基于磁流体力学的基本方程通过对电离层中极低频（ELF）辐射源的辐射场分析，获得ELF电磁波在电离层中传播的色散关系式，建立电离层中的ELF辐射源向下传播衰减模型.并依据建立的传播衰减模型，分析不同纬度地区传播衰减的差异，以及传输频率和背景电离层参数对传播衰减的影响.

Theoretical Analysis of Downward Propagation Attenuation of ELF Radiation in Ionosphere

Sources and resultant radiations of extremely low frequency (ELF) electromagnetic waves can be effectively generated via modulated heating of the ionosphere by powerful high-frequency (HF) waves.With fundamental equations of magneto-hydrodynamics,the radiation field of the ELF radiation source in the ionosphere is derived.The dispersion relation of ELF waves propagating in the ionosphere is then obtained and the downward propagation attenuation model is established.According to this model,the differences of propagation attenuation in distinct latitudes and influences of transmitting frequency and ambient ionospheric parameters on propagation attenuation are analyzed.It is shown that the relative attenuation rate is raised with increase of the geomagnetic inclination and firstly rises and then falls with increase of the transmission frequency,resulting in an optimal transmission frequency value at which the relative attenuation rate reaches minimum.With enhancement of electron density or electron temperature,the relative attenuation rate rises and its growth rate drops.