arXiv 1206.27062012-06-13astro-ph.SR

日冕边缘碰撞重联等离子体的自组织

Self-Organization of Reconnecting Plasmas to Marginal Collisionality in the Solar Corona

S. Imada, E. G. Zweibel

备注：: accepted for publication in The Astrophysical Journal, 33 pages, 12 figures
DOI：: 10.1088/0004-637X/755/2/93

摘要：

我们探讨了Uzdensky（2007）和Cassak等人（2008）的建议，即由磁重联加热的日冕环应该自组织到边缘碰撞状态。我们用一维流体动力学计算讨论了他们的冕环动力学模型。我们假设存在许多电流片，具有厚度分布，但是只有比离子趋肤深度薄的电流片可以快速重新连接。这种假设自然会导致密度依赖的加热速率，其由等离子体主动调节。本文报道了9个日冕环流体动力学的数值模拟结果，其中加热率的绝对值不同，但它们的密度依赖性是相同的。我们发现两个制度的行为，取决于加热速率的幅度。在加热幅度低于阈值的情况下，回路处于稳定平衡。典型的日冕环的上部和密度较低的部分是无碰撞加热和传导冷却的。当加热幅度高于阈值时，平衡无碰撞加热所需的低层大气的传导通量驱动蒸发流，该蒸发流淬灭快速重连，最终冷却并排空回路，直到循环再次开始。这个循环的关键要素是重力和加热函数的密度依赖性。存在一些额外的因素，包括来自回路顶部的压力驱动流，其携带大的焓通量并且在降低密度方面起重要作用。我们发现，平均而言，系统的密度是接近的边际碰撞值。

英文摘要：

We explore the suggestions by Uzdensky (2007) and Cassak et al. (2008) that coronal loops heated by magnetic reconnection should self-organize to a state of marginal collisionality. We discuss their model of coronal loop dynamics with a one-dimensional hydrodynamic calculation. We assume that many current sheets are present, with a distribution of thicknesses, but that only current sheets thinner than the ion skin depth can rapidly reconnect. This assumption naturally causes a density dependent heating rate which is actively regulated by the plasma. We report 9 numerical simulation results of coronal loop hydrodynamics in which the absolute values of the heating rates are different but their density dependences are the same. We find two regimes of behavior, depending on the amplitude of the heating rate. In the case that the amplitude of heating is below a threshold value, the loop is in stable equilibrium. Typically the upper and less dense part of coronal loop is collisionlessly heated and conductively cooled. When the amplitude of heating is above the threshold, the conductive flux to the lower atmosphere required to balance collisionless heating drives an evaporative flow which quenches fast reconnection, ultimately cooling and draining the loop until the cycle begins again. The key elements of this cycle are gravity and the density dependence of the heating function. Some additional factors are present, including pressure driven flows from the loop top, which carry a large enthalpy flux and play an important role in reducing the density. We find that on average the density of the system is close to the marginally collisionless value.

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