磁拱脚点缓慢运动引起的磁场演化和日冕加热

Heyvaerts和Priest最近提出了一个线性无力场演化的简化模型来定量计算磁拱脚点做缓慢的剪切运动所引起的日冕加热。由于他们在能量的计算中漏掉了一些二阶项,并且保留了导致位移无界的磁场的线性演化项,本文对他们的工作进行了修正,同时还对脚点运动引起的磁拱无力场演化进行了进一步探讨。本文主要结果如下:(1)得到的加热效率(即耗散能量在光球供给能量中所占比例)比Heyvaerts和Priest所得结果大。(2)磁拱无力场的无耗散线性演化是不可能的。(3)由磁场位形具体说明了非线性无力场发生磁力线重联的可能性,并指出最容易发生磁力线重联的高度大约为一个磁拱宽度。

The Evolution and Heating of the Coronal Arcade in Response to the Slow Motion of its Footpoints

In order to study quantitatively the magnetic heating of the corona due to the slow photospberic motion, Heyvaerts and Priest developed a "mixing time" theory to calculate the evolution of a magnetic arcade. In the present work the second order perturbation of the force free field is considered consistently with the frozen equation and solved completely. The heating efficiency (the ratio of the heating energy to the energy supplied by the photosphere) is found to be much greater than theirs. Since the linear part of the perturbed magnetic field, which was retained by Heyvaerts and Priest, leads to infinite displacements, it should be dropped, implying that the linear evolution of the force free magnetic arcade is impossible. There exists a maximum concentration of the magnetic fields lines of the sheared field at a height about the same order of magnitude as the width of the arcade, where the magnetic reconnection is more likely to set in.