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

哨声模式合唱波是宇宙飞船在地球、木星、土星和天王星的磁层中观测到的电磁辐射，频率范围为0.05-0.8 Ω，其中Ω是当地的电子回旋频率。在地球上，合唱发射也被记录在地面上，合唱发射是在磁场扰动时观察到的，如磁暴和亚暴。合唱波包括短持续时间（<10- 1秒）的离散发射，频率通常随时间增加（升调），当连接到音频放大器时，听起来像黎明时的鸟鸣或蟋蟀的鸣叫。理论和模拟研究以及观测证据已经确定，在地磁扰动期间，通过回旋共振波-粒子与合唱波的相互作用来加速电子，是在地球外辐射带产生相对论性（>1 MeV）电子的一个关键机制。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，成功地模拟了具有升调的合唱发射的产生。我们发现，在模拟的合唱产生，一些共振电子被迅速激发的相对论转向加速（RTA）和超相对论加速（URA）的过程。RTA和URA是相干哨声模式波对共振电子的非线性波捕获的特殊形式，并构成了在磁化行星辐射带中产生相对论电子的可行机制。计算机模拟表明，由于升调的非线性波增长的合唱波的产生的关键成分。

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.