Enhanced phase mixing of Alfvén waves propagating in stratified and divergent coronal structures
Enhanced phase mixing of Alfvén waves propagating in stratified and divergent coronal structures
复制标题
在分层和发散的日冕结构中传播的阿尔文波的增强相位混合
DOI：
10.1051/0004-6361:20078218
复制
发表时间：
2007
影响因子：
6.5
通讯作者：
Smith P
中科院分区：
文献类型：
--
作者：
Smith P
目的通过对具有不同磁场发散的重力层状日冕结构中传播的简谐Alfvén波的增强位相混合的解析和数值研究，探索太阳日冕加热之谜.方法推导出修正的解析解来模拟Alfvén波在发散和层状日冕结构中传播的耗散.结果给出了描述发散和层状日冕结构中Alfvén波增强位相混合的正确解析解。这些结果表明，增强的位相混合机制可以使Alfvén波在不到以前解析解所预测高度的一半的高度上被耗散。在发散和层状日冕结构中，只有当磁层高度与密度层高度之比时，才会产生增强的位相混合效应。0.1 GHz简谐Alfvén波在1 mm的强发散分层日冕结构中传播的增强相位混合，通过产生1J·m~(-2)s~(-1)的粘性加热通量，可以满足活动区的加热要求。这种配置中的Alfvén波在20 mm内完全消散，这比在均匀磁场中进行标准相位混合所产生的Alfvén波要低6倍。这导致加热长度标度，定义为Alfvén波Poynting通量已经消散的高度，被降低6倍，到活动区密度标度高度的一半以下。利用修正的解析解发现，对于给定的波频，通过在强发散磁场中增强位相混合来产生10 mm的加热长度标度，所需的剪切粘度比在均匀磁场中的标准位相混合所需的剪切粘度低8个数量级。研究还发现，利用经典布拉金斯基粘性，在强发散磁场中，可观测到的S-1阿尔芬波的增强位相混合可以在密度标度高度1 mm内产生加热长度标尺。因此，如果相位混合发生在强发散磁场中，则没有必要在电晕中调用反常粘度。这项研究表明，增强的相位混合作为太阳日冕(一种分层和发散介质)中的Alfvén波消散机制的重要性被严重低估。
AimsWe explore the solar coronal heating enigma by an analytical and numerical study of the enhanced phase mixing of harmonic Alfvén waves propagating in gravitationally stratified coronal structures of varying magnetic field divergence.MethodsCorrected analytical solutions are derived to model the dissipation of Alfvén waves propagating in divergent and stratified coronal structures. These analytical solutions are validated and further explored using a newly developed 2.5D visco-resistive linear MHD code.ResultsCorrected analytical solutions describing the enhanced phase mixing of Alfvén waves in divergent and stratified coronal structures are presented. These show that the enhanced phase mixing mechanism can dissipate Alfvén waves at heights less than half that is predicted by the previous analytical solutions. In divergent and stratified coronal structures, the enhanced phase mixing effect occurs only when the ratio of the magnetic and density scale heights, . The enhanced phase mixing of 0.1 Hz harmonic Alfvén waves propagating in strongly divergent, Mm, stratified coronal structures, Mm, can fulfill of an active region heating requirement, by generating viscous heating fluxes of J m-2s-1. The Alfvén waves in this configuration are fully dissipated within 20 Mm, which is six times lower than would occur as a result of standard phase mixing in uniform magnetic fields. This results in the heating length scale, , defined as the height at which of the Alfvén wave poynting flux has dissipated, being lowered by a factor of six, to less than half of an active region density scale height. Using the corrected analytical solutions it was found that, for a given wave frequency, the generation of a heating length scale of Mm, by enhanced phase mixing in strongly divergent magnetic fields, requires a shear viscosity eight orders of magnitude lower, than required by standard phase mixing in uniform magnetic fields. It was also found that the enhanced phase mixing of observable, rads s-1, Alfvén waves, in strongly divergent magnetic fields, Mm, can generate heating length scales within a density scale height, Mm, using classical Braginskii viscosity. It is therefore not necessary to invoke anomalous viscosity in corona, if phase mixing takes place in strongly divergent magnetic fields. This study shows that the importance of enhanced phase mixing as a mechanism for dissipating Alfvén waves in the solar corona (a stratified and divergent medium), has been seriously underestimated.
登录
查看更多内容
磁化等离子体中的粘度：物理解释
影响因子：
--
作者：
J. V. Hollweg
通讯作者：
J. V. Hollweg
影响因子：
8.8
作者：
Marie JP;Zittoun R;Thevenin D
通讯作者：
Thevenin D
影响因子：
--
作者：
M. Ruderman;M. Goldstein;D. Roberts;A. Deane;L. Ofman
通讯作者：
M. Ruderman;M. Goldstein;D. Roberts;A. Deane;L. Ofman
阿尔文波相位混合作为快磁声波源
影响因子：
2.8
作者：
V. Nakariakov;B. Roberts;K. Murawski
通讯作者：
K. Murawski
多离子太阳风等离子体波束加热二维混合模型
影响因子：
--
作者：
L. Ofman;A. Viñas
通讯作者：
A. Viñas