论文标题
在膨胀的太阳风中保护总波动
Conservation of Total Wave Action in the Expanding Solar Wind
论文作者
论文摘要
在移动等离子体中的波动动作的保护已众所周知，已有半个多世纪的历史。但是，当多个波模式传播并共存接近变性条件时（声速等于alfvén速度，即等离子体$β\ sim 1 $）。在这里，我们表明侵犯保护是由于波模式的转换造成的，并且在相互作用模式上求和的总波动仍然是保守的。尽管结果是一般的，但我们专注于MHD波，并确定三种独特的模式转换机制，即退化，线性模式转换和共振，并为模式转换过程提供直观的物理图片。我们将1D MHD模拟与扩展的框模型一起使用，以模拟扩展的太阳风中单色MHD波的非线性演化。仿真结果验证了理论。因此，对于太阳风中的波和湍流研究，总波动仍然是一个有趣的诊断。
The conservation of wave action in moving plasmas has been well-known for over half a century. However, wave action is not conserved when multiple wave modes propagate and coexist close to degeneration condition (Sound speed equals Alfvén speed, i.e. plasma $β\sim 1$). Here we show that the violation of conservation is due to wave mode conversion, and that the total wave action summed over interacting modes is still conserved. Though the result is general, we focus on MHD waves and identify three distinctive mode conversion mechanisms, i.e. degeneracy, linear mode conversion, and resonance, and provide an intuitive physical picture for the mode conversion processes. We use 1D MHD simulations with the Expanding Box Model to simulate the nonlinear evolution of monochromatic MHD waves in the expanding solar wind. Simulation results validate the theory; total wave action therefore remains an interesting diagnostic for studies of waves and turbulence in the solar wind.
