等温大气中的日冕阿尔芬速度I。全局属性
Coronal Alfven speeds in an isothermal atmosphere I. Global properties
摘要：
估算阿尔芬速度对于模拟日冕、研究日冕加热问题和理解日冕物质抛射（CME）的发生和传播都有重要意义。这里我们假设日冕处于磁流体静力平衡，并且由于等离子体β较低，可以使磁力与压力和重力解耦。然后描述的磁场由一个无力场，我们进行了统计研究的磁场强度与高度为四个不同的活动区域。假设沿每条场线的等离子体处于流体静力平衡。作为第一近似，假设日冕等离子体是等温的，具有恒定或随高度变化的重力。我们研究了具有环形电流分布的双极磁场，并将这种方法应用于与不同喷发事件相关的四个活动区。通过研究活动区上方磁场强度的整体性质，我们得出结论：（i）大部分磁通量集中在光球层50 μ m以内，（ii）大部分能量储存在150 μ m以下的日冕中，（iii）大部分磁场强度随高度的衰减，非线性无力场比势场慢.在等温大气中的阿尔芬速度值可以变化两个数量级（高达100000公里/秒）。阿尔芬速度的全局性质对磁位形的性质很敏感。对于具有高度扭曲的通量管的活动区域，阿尔芬速度在扭曲的通量束的典型高度处显著增加;在燃烧区域，平均阿尔芬速度高于5000 km/s，并且强烈偏离势场值。
英文摘要：
Estimating Alfven speeds is of interest in modelling the solar corona, studying the coronal heating problem and understanding the initiation and propagation of coronal mass ejections (CMEs). We assume here that the corona is in a magnetohydrostatic equilibrium and that, because of the low plasma beta, one may decouple the magnetic forces from pressure and gravity. The magnetic field is then described by a force-free field for which we perform a statistical study of the magnetic field strength with height for four different active regions. The plasma along each field line is assumed to be in a hydrostatic equilibrium. As a first approximation, the coronal plasma is assumed to be isothermal with a constant or varying gravity with height. We study a bipolar magnetic field with a ring distribution of currents, and apply this method to four active regions associated with different eruptive events. By studying the global properties of the magnetic field strength above active regions, we conclude that (i) most of the magnetic flux is localized within 50 Mm of the photosphere, (ii) most of the energy is stored in the corona below 150 Mm, (iii) most of the magnetic field strength decays with height for a nonlinear force-free field slower than for a potential field. The Alfven speed values in an isothermal atmosphere can vary by two orders of magnitude (up to 100000 km/s). The global properties of the Alfven speed are sensitive to the nature of the magnetic configuration. For an active region with highly twisted flux tubes, the Alfven speed is significantly increased at the typical height of the twisted flux bundles; in flaring regions, the average Alfven speeds are above 5000 km/s and depart strongly from potential field values.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
