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Generation of chorus emissions and acceleration of relativistic electrons associated with magnetic storms

与磁暴相关的合唱发射和相对论电子加速的产生

基本信息

批准号：
17340146
负责人：
OMURA Yoshiharu
金额：
$ 10.18万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2005
资助国家：
日本
起止时间：
2005 至 2007
项目状态：
已结题

项目摘要

Whistler-mode chorus waves are eletromagnetic emissions that have been observed by spacecraft in the magmetospheres of Earth, Jupiter, Saturn, and Uranus, with frequencies in the range 0.05-0.8 Ω, where Ωis the local electron gyrofrequency. At Earth chorus emissions have also been recorded on the ground Chorus emissions am observed at the time of magnetic field disturbance such as magnetic storms and suhstorms. Chorus waves comprise discrete emissions of short duration (<10-1sec), with frequency typically increasing in time (rising tones), and, when connected to an audio amplifier, sound like bird song at dawn or chirping crickets. Theoretical and modeling studies and observational evidence have established electron acceleration by gyroresonant wave-particle interaction with chorus waves as a key mechanism for generating relativistic (>1 MeV) electrons in the Earth's outer radiation belt during geomagnetically disturbed periods. After nearly four decades of chorus wave observations and numerical studies, only recently have computer simulations been performed that successfully model the generation of chorus emissions with a rising tone. We have found that in the simulation of chorus generation, some resonant electrons are rapidly energized by the processes of relativistic turning acceleration (RTA) and ultra-relativistic acceleration (URA). RTA and URA are particular forms of nonlinear wave trapping of resonant electrons by coherent whistler-mode waves and constitute viable mechanisms for the generation of relativistic electrons in the radiation belts of magnetized planets. The computer simulations reveal that nonlinear wave growth due to the rising tone is the key ingredient in the generation of chorus waves.

哨声模式合唱波是由宇宙飞船在地球、木星、土星和天王星的岩浆层中观测到的电磁发射，频率范围在0.05-0.8 Ω，其中Ωis为本地电子回旋频率。在地球上，也记录了地面上的合唱发射，在磁场扰动（如磁暴和超级风暴）时观测到合唱发射。合唱波由持续时间短（<10-1秒）的离散发射组成，频率通常随时间增加（上升音调），当连接到音频放大器时，听起来像黎明时分的鸟鸣或蟋蟀的啁啾。理论和模型研究以及观测证据已经证明，在地磁扰动期间，地球外辐射带产生相对论电子（bbb1mev）的关键机制是回旋共振波-粒子与合唱波相互作用所产生的电子加速。经过近四十年的合唱波观测和数值研究，直到最近才进行了计算机模拟，成功地模拟了带有上升音调的合唱发射的产生。我们发现在合唱产生的模拟中，一些共振电子在相对论性转向加速（RTA）和超相对论性加速（URA）过程中被快速激发。RTA和URA是共振电子被相干哨声模波非线性俘获的特殊形式，为磁化行星辐射带中相对论性电子的产生提供了可行的机制。计算机模拟结果表明，由升音引起的非线性波增长是合唱波产生的关键因素。