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arXiv 1206.2114astro-ph.SR
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太阳大气中的阿尔文反射和混响

Alfvén Reflection and Reverberation in the Solar Atmosphere

P. S. Cally

备注：
Accepted by Solar Physics
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摘要：

阿尔文速度[a]随高度单调增加的磁大气常被用来模拟太阳大气，至少在几个太阳半径范围内。一个常见的例子是等温大气中均匀的垂直或倾斜的磁场，其阿尔文速度是指数的。我们解决了这种大气中的内反射问题，包括时间谐波和瞬态波。人们发现，可以设计一个数学边界条件，对应于完美的吸收在无穷远，并使用这一点，许多大气中，a（x）是解析和无界目前没有内反射谐波阿尔文波。然而，除了某些特殊情况，这种解决方案是伴随着一个尾流，这可能被认为是一种反射。对于初始值问题，谐波源突然打开（并可选地关闭），也有一个相关的瞬态，通常随时间衰减为O（t-1）或O（t-1 ln t），取决于驱动器的相位。与稳态谐波解不同，瞬态反射很弱。由有限持续时间的p模式训练驱动的日冕中的阿尔文波预计会留下这样的瞬变。

英文摘要：

Magneto-atmospheres with Alfvén speed [a] that increases monotonically with height are often used to model the solar atmosphere, at least out to several solar radii. A common example involves uniform vertical or inclined magnetic field in an isothermal atmosphere, for which the Alfvén speed is exponential. We address the issue of internal reflection in such atmospheres, both for time-harmonic and for transient waves. It is found that a mathematical boundary condition may be devised that corresponds to perfect absorption at infinity, and, using this, that many atmospheres where a(x) is analytic and unbounded present no internal reflection of harmonic Alfvén waves. However, except for certain special cases, such solutions are accompanied by a wake, which may be thought of as a kind of reflection. For the initial-value problem where a harmonic source is suddenly switched on (and optionally off), there is also an associated transient that normally decays with time as O(t-1) or O(t-1 ln t), depending on the phase of the driver. Unlike the steady-state harmonic solutions, the transient does reflect weakly. Alfvén waves in the solar corona driven by a finite-duration train of p-modes are expected to leave such transients.

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