太阳宁静区磁漏斗结构的扩展特征

On the Expansion of Coronal Funnels in the Quiet Sun

通过对观测的光球纵向磁场进行势场外推,重构了一个太阳宁静区光球以上的磁场结构。结果显示,在20Mm以下,开放磁力线呈现多个明显的小磁漏斗结构,这些小磁漏斗结构随高度扩展,并且在20Mm左右融合成大的漏斗结构。通过系统地研究磁漏斗结构横截面积随高度的变化趋势,发现太阳宁静区磁漏斗结构的截面积随高度近似线性扩展,磁漏斗结构在较低高度上(<20 Mm)扩展的速度比在较高高度上(>20Mm)扩展的速度要快。这一结果对太阳风起源和磁环中物质流动的二维数值模拟具有重要的意义。同时还发现,闭合磁力线的数目随高度以指数函数的形式减少。

Coronal funnels originated from chromospheric networks are key regions of solar wind origin and mass supply to large coronal loops. However, due to the lack of observational coronal magnetic field data, the geometrical and physical properties of coronal funnels can not be obtained through direct observations. Through applying force-free magnetic field extrapolation to a rectangu- lar quiet-Sun region based on the observational MDI magnetogram, the coronal magnetic field up to 40 Mm above the photosphere can be reconstructed. Below 20 Mm, there are over 10 small funnels originating from magnetic networks and expanding with height. The small funnels merge into two big funnels above 20 Mm. For the first time, the height variations of the funnels＇ cross section areas in the quiet Sun are studied using observational data. The result reveals that coronal funnels expand almost linearly with height above the photosphere in the quiet Sun region. The expansion factor is larger in the lower part of the solar atmosphere than in the upper part. This result has been discussed with regard to 2D modeling of solar wind origin and mass flows in coronal loops. It is also found that the number of closed magnetic field lines decreases exponentially with height.