Collisions, magnetization, and transport coefficients in the lower solar atmosphere
Collisions, magnetization, and transport coefficients in the lower solar atmosphere
复制标题
太阳低层大气中的碰撞、磁化和输运系数
DOI：
10.1051/0004-6361/201220738
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发表时间：
2013
影响因子：
6.5
通讯作者：
P. Krstic
中科院分区：
文献类型：
--
作者：
J. Vranjes;P. Krstic
上下文。较低的太阳大气是一个本质上是多组分的碰撞环境，电子和质子的碰撞频率在108~1010赫兹范围内，这可能比这两个物种的陀螺频率高得多。不同物种之间的碰撞是海拔高度相关的，因为所有物种的密度和温度都不同。目标。我们的目标是为低太阳大气中最重要的物种提供一组可靠的碰撞频率、磁化强度、粘度和热导率的定量数据。手头有这样的数据对于任何旨在描述所考虑环境的真实属性的建模都是必不可少的。方法：研究方法。在所考虑的碰撞能量范围内的相关弹性和电荷转移截面现在被科学界所接受，因为对于可能在较低的太阳大气中发现的最重要的物种来说，这是前所未有的准确。它们以前是使用量子力学方法计算的，并通过实验室测量进行了验证。只有可靠的碰撞数据，才能得到准确的碰撞频率、粘度系数和导热系数。结果。我们描述了参数的高度依赖关系和带电粒子之间、带电粒子与中性粒子之间碰撞的不同物理性质。每种碰撞类型的主导区域都被清楚地识别出来。我们确定电子或离子或两者都不磁化的层。研究表明，在较低的大气中，质子在至少1000公里厚的一层中是不磁化的，即使是千高斯磁场也是如此，该磁场随高度呈指数下降。在这些层中，带电物种的动力学不受磁场的影响，这一事实被用在我们的建模中。对于离子未磁化的层，计算了粘度系数和导热系数。我们比较了粘度和摩擦力，并确定了每种现象的优势区域。结论。我们为低太阳大气中最重要的参数提供了最可靠的量化值，用于各种现象的分析建模和数值模拟，如波、粒子的输运和磁化，以及日冕物质抛射的触发机制。
Context. The lower solar atmosphere is an intrinsically multi-component and collisional environment with electron and proton collision frequencies in the range 10 8 10 10 Hz, which may be considerably higher than the gyro-frequencies for both species. Collisions between di erent species are altitude dependent because of the variation in density and temperature of all species. Aims. We aim to provide a reliable quantitative set of data for collision frequencies, magnetization, viscosity, and thermal conductivity for the most important species in the lower solar atmosphere. Having such data at hand is essential for any modeling that is aimed at describing realistic properties of the considered environment. Methods. The relevant elastic and charge transfer cross sections in the considered range of collision energies are now accepted by the scientific community as known with unprecedented accuracy for the most important species that may be found in the lower solar atmosphere. These were previously calculated using a quantum-mechanical approach and were validated by laboratory measurements. Only with reliable collision data one can obtain accurate values for collision frequencies and coe cients of viscosity and thermal conductivity. Results. We describe the altitude dependence of the parameters and the di erent physics of collisions between charged species, and between charged and neutral species. Regions of dominance of each type of collisions are clearly identified. We determine the layers within which either electrons or ions or both are unmagnetized. Protons are shown to be unmagnetized in the lower atmosphere in a layer that is at least 1000 km thick even for a kilo-Gauss magnetic field that decreases exponentially with altitude. In these layers the dynamics of charged species cannot be a ected by the magnetic field, and this fact is used in our modeling. Viscosity and thermal conductivity coe cients are calculated for layers where ions are unmagnetized. We compare viscosity and friction and determine the regions of dominance of each of the phenomena. Conclusions. We provide the most reliable quantitative values for most important parameters in the lower solar atmosphere to be used in analytical modeling and numerical simulations of various phenomena such as waves, transport and magnetization of particles, and the triggering mechanism of coronal mass ejections.