论文标题
太阳耀斑加热，湍流抑制热传导
Solar Flare Heating with Turbulent Suppression of Thermal Conduction
论文作者
论文摘要
在太阳耀斑期间，血浆通常被加热至非常高的温度，并且通过热传导的能量重新分布是一种主要的机制，可以在整个耀斑的太阳大气中运输能量。通常使用Spitzer理论对热通量进行建模，该理论基于带有热通量的电子之间的局部库仑碰撞。但是，通常在耀斑期间，温度梯度变得足够陡峭，以至于碰撞平均自由路径超过温度梯度尺度的大小，因此热传导本质上是非本地的。此外，在原子发射线的非热宽度中可检测到的湍流角散射也可以起作用增加碰撞频率并抑制热通量。 Emslie＆Bian（2018）最近的工作扩展了Spitzer的热传导理论，以解释非本地性和湍流抑制。我们已将其用于热通量（这是具有内核函数的Spitzer通量的卷积）实施的理论表达，并将其进行了参数研究，以了解热传导的结果变化如何影响耀斑动力学，从而产生了辐射。我们发现，降低热通量的模型可以预测散装流量较慢，线条发射较少以及更长的冷却时间。通过比较由特定耀斑观察得出的具有多普勒速度和非热线宽度的模型预测的原子发射线的特征，我们发现，相对于Spitzer值在0.3至0.5之间的模型相对于spitzer值在0.3至0.5之间的模型最佳重现观察到的观察到的多普勒速度在广泛的温度范围内形成了跨发射线的多普勒速度。有趣的是，与观察到的非热线宽度最匹配的模型具有KAPPA型速度分布函数。
During solar flares plasma is typically heated to very high temperatures, and the resulting redistribution of energy via thermal conduction is a primary mechanism transporting energy throughout the flaring solar atmosphere. The thermal flux is usually modeled using Spitzer's theory, which is based on local Coulomb collisions between the electrons carrying the thermal flux and those in the background. However, often during flares, temperature gradients become sufficiently steep that the collisional mean free path exceeds the temperature gradient scale size, so that thermal conduction becomes inherently non-local. Further, turbulent angular scattering, which is detectable in nonthermal widths of atomic emission lines, can also act to increase the collision frequency and so suppress the heat flux. Recent work by Emslie & Bian (2018) extended Spitzer's theory of thermal conduction to account for both non-locality and turbulent suppression. We have implemented their theoretical expression for the heat flux (which is a convolution of the Spitzer flux with a kernel function) into the RADYN flare-modeling code and performed a parameter study to understand how the resulting changes in thermal conduction affect flare dynamics and hence the radiation produced. We find that models with reduced heat fluxes predict slower bulk flows, less intense line emission, and longer cooling times. By comparing features of atomic emission lines predicted by the models with Doppler velocities and nonthermal line widths deduced from a particular flare observation, we find that models with suppression factors between 0.3 to 0.5 relative to the Spitzer value best reproduce observed Doppler velocities across emission lines forming over a wide range of temperatures. Interestingly, the model that best matches observed nonthermal line widths has a kappa-type velocity distribution function.
