分层大气中的MHD模式转换
MHD mode conversion in a stratified atmosphere
摘要：
在声速和阿尔文速度相等的区域中的模式转换是一个复杂的过程，已经用解析和数值方法进行了研究，并且已经在观测中看到。为了进一步理解这一过程，我们建立了一个简单的一维模型，并研究波通过这个系统的传播使用的分析和数值技术相结合。模拟在重力分层大气中进行，具有均匀的，垂直磁场的等温和非等温的情况下。对于非等温的情况下，温度曲线被选择来模仿在过渡区遇到的陡峭的温度梯度。在所有的模拟中，慢波被驱动的上边界，从而传播从低β到高β等离子体的模式转换区域。此外，进行了详细的分析研究，我们预测的振幅和相位的入射波的传输和转换的组件，因为它通过模式转换区域。这些分析预测与数值结果的比较显示出良好的一致性，让我们有信心在这两种技术。这些知识可以用来帮助确定观测到的波类型，并深入了解日冕加热可能涉及哪些模式。
英文摘要：
Mode conversion in the region where the sound and Alfven speeds are equal is a complex process, which has been studied both analytically and numerically, and has been seen in observations. In order to further the understanding of this process we set up a simple, one-dimensional model, and examine wave propagation through this system using a combination of analytical and numerical techniques. Simulations are carried out in a gravitationally stratified atmosphere with a uniform, vertical magnetic field for both isothermal and non-isothermal cases. For the non-isothermal case a temperature profile is chosen to mimic the steep temperature gradient encountered at the transition region. In all simulations, a slow wave is driven on the upper boundary, thus propagating down from low-beta to high-beta plasma across the mode-conversion region. In addition, a detailed analytical study is carried out where we predict the amplitude and phase of the transmitted and converted components of the incident wave as it passes through the mode-conversion region. A comparison of these analytical predictions with the numerical results shows good agreement, giving us confidence in both techniques. This knowledge may be used to help determine wave types observed and give insight into which modes may be involved in coronal heating.
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