Time-dependent hydrogen ionisation in 3D simulations of the solar chromosphere. Methods and first results
Time-dependent hydrogen ionisation in 3D simulations of the solar chromosphere. Methods and first results
复制标题
太阳色球层 3D 模拟中随时间变化的氢电离。
DOI：
10.1051/0004-6361:20066123
复制
发表时间：
2006
影响因子：
6.5
通讯作者：
S. Wedemeyer
中科院分区：
文献类型：
--
作者：
J. Leenaarts;S. Wedemeyer
上下文在太阳色球层条件下，氢电离度大大偏离统计平衡。因此，对这一大气层的现实描述必须考虑到随时间变化的非平衡效应。目标。通过改进相关物理学的数值处理，推进太阳色球层数值模拟的现实性，将提供更现实的模型，这对解释现有和未来的观测至关重要。方法.在三维辐射（磁）流体动力学程序CO5BOLD中，推广并实现了一种求解氢粒子数速率方程的近似方法。该方法基于具有六个能级和固定辐射率的模型原子。它已经在一维模拟中进行了广泛的测试。扩展的方法已被用来创建一个三维模型，从上层对流区延伸到色球层。结果氢的电离度在我们的随时间变化的模拟相当于相应的平衡值高达500公里以上的光学深度单位。在这个高度以上，非平衡电离度在时间和空间上是相当恒定的，并且倾向于处于由热传播冲击波设定的值。氢能级布居数和电子密度也比统计平衡时的相应值恒定得多。相比之下，平衡电离度的变化超过20个数量级之间的热，冲击区域和冷，非冲击区域。结论.该模拟首次在3D中显示，色球氢电离度和电子密度无法在平衡状态下计算。我们的模拟可以为详细的辐射传输计算提供这些量的现实值。
Context. The hydrogen ionisation degree deviates substantially from statistical equilibrium under the conditions of the solar chromosphere. A realistic description of this atmospheric layer thus must account for time-dependent non-equilibrium effects. Aims. Advancing the realism of numerical simulations of the solar chromosphere by improved numerical treatment of the relevant physics will provide more realistic models that are essential for interpretation of existing and future observations. Methods. An approximate method for solving the rate equations for the hydrogen populations was extended and implemented in the three-dimensional radiation (magneto-)hydrodynamics code CO5BOLD. The method is based on a model atom with six energy levels and fixed radiative rates. It has been tested extensively in one-dimensional simulations. The extended method has been used to create a three-dimensional model that extends from the upper convection zone to the chromosphere. Results. The ionisation degree of hydrogen in our time-dependent simulation is comparable to the corresponding equilibrium value up to 500 km above optical depth unity. Above this height, the non-equilibrium ionisation degree is fairly constant over time and space, and tends to be at a value set by hot propagating shock waves. The hydrogen level populations and electron density are much more constant than the corresponding values for statistical equilibrium, too. In contrast, the equilibrium ionisation degree varies by more than 20 orders of magnitude between hot, shocked regions and cool, non-shocked regions. Conclusions. The simulation shows for the first time in 3D that the chromospheric hydrogen ionisation degree and electron density cannot be calculated in equilibrium. Our simulation can provide realistic values of those quantities for detailed radiative transfer computations.