太阳异极性磁区的相互入侵

我们在文1]的启发下,计算了磁中性线附近异极性磁区相互入侵(或挤压)引起的等离子体动力学问题。气体初态取用流行的宁静太阳光球色球大气模型,即非等温的密度指数变化的重力分层大气。采用Lagrangian格式数值求解自洽的MHD方程,这可使入侵力学变得直观明显——磁场随流体而运动。我们的新结果是入侵流动在光球低层产生出强的水平磁场(即强的横向场),但光球高层和色球低层的磁结构却变化不大,有力地支持了文13]提出的光球色球里可能出现磁流体力学间断面的概念。入侵确实在磁中性线附近建立了电流片,但这电流片主要在光球低层,其量级和观测一致。另外还显示垂直下降运动也可能导致异极磁区的入侵。尽管在MHD~1方程里包含了电阻耗散和热传导流,但计算证明它们对入侵力学影响不大,热传导的作用只是使气体温度分布逐渐趋于宁静太阳分布(尽管高度变了)。

The Mutual Intrusion of Opposite Magnetic Polarities in a Solar Active Region

In developing further the ideas of a previous paper, we studied the plasma dynamics in connection with the mutual intrusion of opposite magnetic polarities in a solar active region. To describe the initial gas steady state we adopt the well-known Harvard-Smithsonian model for quiet photosphere and chromosphere, that is, a gravity-stratified atmosphere with a non-homo-genious temperature distribution and an exponentially declining law of gas density. In order to solve the self-consistent MHD equations numerically, a Lagrangian algorithm is used whichmakes the intrusion dynamics intuitive and clear at a glance-the magnetic field moving withgas flow. Our new results are: 1) a strong horizontal magnetic field (or transverse field) in the lower photosphere is created during the process of intrusion while the magnetic feature in the higher photosphere and lower chromosphere remains more or less unchanged. This new point strongly supports the suggestion offered by reference 13] that there could be an MHD jump in the solar photosphere-chromosphere. 2) a current sheet limited within the lower photosphere is built up by the intrusion. The current density may reach up to 105-106 c.g.s units which is in agreement with the solar observations. 3) a vertical denscending flow can lead to the mutual intrusion of opposite polarities. 4) although the resistive dissipation and thermocondu-ctive flow are included in the MHD equations, they have little effect on the intrusion dynamics. The only effect is, the gas temperature distribution will gradually changes into one for solar quiet atmosphere with a new overall altitude.