基于宽带sferic全波反演法的D层局部扰动研究

The high power, broadband electromagnetic waves radiated from lightning return strokes are called radio atmospherics or sferics for short. Their major energy distributes in extremely low frequency (ELF, 3Hz-3000Hz), very low frequency (VLF, 3kHz-30kHz) and low frequency (LF, 30kHz-300kHz) wavebands. Therefore, sferics are mostly reflected by the D region and are always used for D region detection. However, in the current study of D region based on ELF/VLF/LF, it is difficult to quantitatively and directly measure the localized disturbances. In this research project, we propose a plan for the direct measurement of D region disturbances. Specifically speaking, we treat lightning return strokes as transmitting antennas and sferic receivers as receiving antennas, use the full wave iterative inverse algorithms of computational electromagnetics to process broadband sferic signals which are recorded by sferic recorders located in multiply azimuthal directions to the disturbed region, and thus quantitatively compute the three dimensional electron density profile of the disturbed region in the background ionosphere. Based upon these results, we would deeply explore the interactions between the D region and all kinds of possible disturbance triggering sources including volcano eruption, earthquakes, energetic particle precipitation, strong lightning heating or other nature phenomena by combining the data of triggering sources and energy coupling models.

由雷电回击辐射的高功率宽带电磁波称为天电（radio atmospherics，简称sferics）。它们的主要能量分布在超低频（3Hz-3000Hz）、甚低频（3kHz-30kHz）和低频（30kHz-300kHz）波段，大部分被D层反射，常常用于D层探测。然而在目前基于超低频、甚低频和低频电磁波的D层研究中，人们还难以定量的直接测量D层的局部扰动。在本课题中，我们提出一种直接测量D层局部扰动的方案。具体来讲，我们把雷电回击作为发射天线，sferic接收器作为接收天线，用计算电磁学中的全波迭代反演算法处理D层扰动区多个方位角上的接收器所记录的宽带sferic信号，定量计算出背景电离层中局部扰动区域电子密度的三维剖面。在此计算的基础上，我们通过结合可能的D层扰动源数据和相应的能量耦合模型，深入研究D层和各种扰动触发机制如火山喷发、地震、高能粒子沉降、强雷电持续加热等自然现象的相互作用过程。

雷电回击辐射的高功率宽带电磁波称为天电(radio atmospherics，简称sferics)。它们的主要能量分布在超低频(3Hz-3000Hz)、甚低频(3kHz-30kHz)和低频(30kHz-300kHz)波段，大部分被D层反射，所以常常用于D层探测。在本研究课题中，我们建立各向异性电离层多频率天电传播模型，用于D层磁化冷等离子体参数的反演。具体来讲，我们首先建立任意各向异性分层介质模型，通过二维谱域积分的方式计算格林函数，同时在谱域完成地球弯曲表面影响的校正，这样得到的空域格林函数已经包含了地球弯曲表面的影响。然后建立单轴个各向异性分层介质中三维快速正演计算模型，通过双共轭梯度和快速傅里叶变换加速方法实现嵌入在单个分层中任意各向异性散射体的正散射快速计算。最后建立任意各向异性散射体三维反演模型，一次反演出任意各向异性散射体的所有介质参数。这几方面的研究成果给D层等离子体参数的直接反演奠定了基础，同时为D层背景剖面或者扰动区电子密度变化各种触发机制如火山喷发、高能粒子沉降等深入研究提供有效参考。