地震及非震源引起的电离层ELF嘶声波动研究

ELF hiss waves in upper ionosphere and plasmasphere can resonate with energetic electrons in the Earth’s radiation belt, leading to precipitation of energetic electrons into the atmosphere, which is regarded as a most important mechanism of energetic particle loses, so it has received increasing attention in recent years. Recent satellite observations also show that electromagnetic perturbations induced both by earthquake activities also more easily occur at the ELF hiss frequency band. However the generation mechanism and propagation characteristics of ELF hiss induced by earthquake and non-earthquake sources are still not fully understood. In this project, we will combine the multipoint satellite conjugate observations, numerical modeling and theoretical works together, to investigate the generation and propagation characteristics of hiss waves induced both by earthquake and non-earthquake sources. Firstly, based on observations of low earth orbit satellites, we will focus on the variations of ELF hiss waves under the different geomagnetic field perturbations and during earthquake periods. Secondly, based on the conjugate observations of low to medium-high earth orbit satellites, we will simulate how chorus waves propagate in the magnetosphere, enter into ionosphere and evolve into ionospheric hiss waves, by using a three-dimensional ray tracing code. Additionally, using the wave-particle interaction theory, we will investigate the ELF waves and energetic particles distributions related with earthquake activities. The expected results will contribute to a better understanding about the generation mechanism and propagation characteristics of ELF hiss, and more importantly, will lay a good foundation for extracting earthquake precursors from satellite observations.

电离层/等离子体层的ELF嘶声通过与辐射带能量电子相互作用，可导致能量电子沉降，是辐射带能量电子的重要损失机制，日益成为研究热点。现有卫星观测证实地震在ELF频段上也可激发类似嘶声的电磁扰动。然而目前对来自于地震和非震源的两类ELF嘶声的产生机制，传播特征尚不完全清楚。本项目将结合多点卫星观测和理论模拟，研究地震及非震源引起的ELF嘶声的传播特征及产生机制。首先利用低轨卫星观测，研究电离层/等离子体层空间内嘶声在不同空间天气背景以及在地震前后的传播特征。然后利用低轨至中高轨卫星的多点共轭观测和3D射线追踪理论模拟，综合研究合声波演化成嘶声这一近年被观测证实的新产生机制。另外开展嘶声与能量粒子相互作用研究，探讨地震前兆信号中ELF波与能量粒子变化之间的联系。本项目的实施不仅使我们能更加深入地了解嘶声的产生机制和传播过程，而且还为提取地震空间电磁前兆信息提供重要的科学依据。

电离层/等离子体层的ELF嘶声通过与辐射带能量电子相互作用，可导致能量电子沉降，是辐射带能量电子的重要损失机制，日益成为研究热点。现有卫星观测证实地震在ELF频段上也可激发类似嘶声的电磁扰动，然而目前对来自于地震和非震源的两类ELF嘶声的产生机制，传播特征尚不完全清楚。本项目结合地球低轨道卫星，中高轨道卫星的联合观测事件和理论模拟，研究了地震及非震源引起的ELF嘶声的传播特征及产生机制。研究发现电离层非震源引起的ELF嘶声有向地球方向传播和离开地球方向两种。统计特征总体反映出了地震上空的ELF 300- 800 Hz辐射主要离开地球方向传播。统计研究发现电离层嘶声在日侧的观测总是比夜侧的强，在不同地磁条件下电离层嘶声与地磁扰动具有强烈的相关性，在高地磁扰动条件下所有频段的功率谱密度值都得到了增强，ELF嘶声波强度周期性的在每年7月份达到最低值，在1月份达到了最大值，嘶声的强度在夏天高于冬天。为了探索电离层ELF嘶声的源头，开展了低轨道卫星与高轨道卫星共轭观测多点之间的射线传播模拟，研究结果发现嘶声当传播角度达小于70度的射线能够穿越到电离层并传播到低轨道卫星位置，当嘶声射线的传播角大概在50到70度能够从低轨道卫星传播到中高轨道卫星。电离层嘶声的产生源可能有三种：较高轨道空间产生的等离子体嘶声下传到电离层高度，形成电离层嘶声被低轨道卫星记录到； 大气层产生产生的闪电事件也可能是电离层嘶声的产生源，通常闪电触发的嘶声表现在 2 kHz以下；低轨道卫星空间本身等离子体不稳定性也可能产生嘶声波动。然而经过近半世纪的卫星观测研究，电离层嘶声的产生机制依然尚未真正揭开，仍旧是学界研究热点，本项目的实施使我们能更加深入地了解嘶声的产生机制和传播过程，也为我们进一步提取地震电磁异常提供了良好的科学参考。