THE ROLE OF TORSIONAL ALFVÉN WAVES IN CORONAL HEATING
THE ROLE OF TORSIONAL ALFVÉN WAVES IN CORONAL HEATING
复制标题
扭转阿尔文波在日冕加热中的作用
DOI：
10.1088/0004-637x/712/1/494
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
K. Shibata
中科院分区：
文献类型：
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作者：
P. Antolin;K. Shibata
在日冕加热的背景下，在太阳大气中存在的众多磁流体动力学（MHD）波中，alfvsamn波受到了特别的关注。事实上，这些波构成了一种有吸引力的加热剂，因为它们能够在太阳大气的许多不同层上携带足够的能量来加热和维持日冕。然而，由于它们不可压缩的性质，这些波需要一种机制，如模式转换（导致激波加热）、相位混合、共振吸收或湍流级联，以加热等离子体。此外，它们的不可压缩性使得在太阳大气中探测它们非常困难。利用偏振、光谱学和成像仪器进行的新观测，如日本“日野”卫星上的仪器，或瑞典太阳望远镜上的Crisp分光偏振仪，或日冕多通道偏振仪，提供了强有力的证据，证明太阳日冕中存在高能阿尔夫萨芬波。为了评估alfvsamn波在日冕加热中的作用，本文通过模式转换机制模拟了受alfvsamn波加热的磁通管。使用1.5维MHD代码，我们进行了参数测量，改变了磁通管的几何形状（长度和膨胀），光球磁场，光球速度振幅和波的性质（单色或白噪声谱）。阿尔夫萨芬波加热产生热而稳定的日冕的机制被发现相当狭窄。与光球波振幅和磁场无关，日冕只能产生和维持长（80毫米）和厚（光球和日冕之间的面积比500毫米）的环路。超过光球速度振幅的临界值（通常是几km s−1），日冕就不能再维持很长一段时间，并且由于光波的巨大动量而坍塌。这些结果建立了一些限制，特别是对活跃区环路的阿尔夫萨芬波加热作为日冕加热机制。
In the context of coronal heating, among the zoo of magnetohydrodynamic (MHD) waves that exist in the solar atmosphere, Alfvén waves receive special attention. Indeed, these waves constitute an attractive heating agent due to their ability to carry over the many different layers of the solar atmosphere sufficient energy to heat and maintain a corona. However, due to their incompressible nature these waves need a mechanism such as mode conversion (leading to shock heating), phase mixing, resonant absorption, or turbulent cascade in order to heat the plasma. Furthermore, their incompressibility makes their detection in the solar atmosphere very difficult. New observations with polarimetric, spectroscopic, and imaging instruments such as those on board the Japanese satellite Hinode, or the Crisp spectropolarimeter of the Swedish Solar Telescope or the Coronal Multi-channel Polarimeter, are bringing strong evidence for the existence of energetic Alfvén waves in the solar corona. In order to assess the role of Alfvén waves in coronal heating, in this work we model a magnetic flux tube being subject to Alfvén wave heating through the mode conversion mechanism. Using a 1.5 dimensional MHD code, we carry out a parameter survey varying the magnetic flux tube geometry (length and expansion), the photospheric magnetic field, the photospheric velocity amplitudes, and the nature of the waves (monochromatic or white-noise spectrum). The regimes under which Alfvén wave heating produces hot and stable coronae are found to be rather narrow. Independently of the photospheric wave amplitude and magnetic field, a corona can be produced and maintained only for long (>80 Mm) and thick (area ratio between the photosphere and corona >500) loops. Above a critical value of the photospheric velocity amplitude (generally a few km s−1) the corona can no longer be maintained over extended periods of time and collapses due to the large momentum of the waves. These results establish several constraints on Alfvén wave heating as a coronal heating mechanism, especially for active region loops.