太阳磁场外推方法的研究与应用

Magnetic field is the key problem of solar physics, most of the activities of Sun closely relate to solar magnetic field. It is is very meaningful for understanding the activities and essence of Sun to study solar magnetic field. Since the property of spatial magnetic field is the most important property, thus, the study of the spatial magnetic field and the structure of spatial magnetic field is very important. Previous studies shown that there were evident changes of photospheric magnetic field and the distributions of magnetic field lines before/after solar flare, however most of these studies were studied basing on the photospheric magnetic field and monochromatic image of corona. At present, the reliable measurements of the magnetic field have been restricted to the photosphere..the study of the spatial magnetic field is mainly based on field extrapolation using the photospheric magnetic field as boundary condition. Field extrapolation is under development and there are some problems need to be resolved for the theory of field extrapolation, especially, for nonlinear force-free extrapolation. At the same time, studies based on magnetic extrapolation have also found that there were some changes before/after solar flare. For example, current, free energy, topology of magnetic field and so on. This study basing on high quality magnetograms use nonlinear force-free extrapolation to study the properties of spatial magnetic field, hence to study the relations between magnetic field and solar flare. In this study, the large sample of magnetograms observed at Huai Ruo Station will be used as the photospheric boundary for extrapolation, then the problems, differences and consistence among extrapolated fields can be studied systematically, also it is hoped to get some statistical results and conclusions about the relation between the properties of spatial magnetic field and solar activities.

磁场是太阳物理的核心问题，大部分太阳活动都和磁场有密切的联系。磁场的空间性质（即，磁场强度空间分布，磁场连接性，磁场非势性等）是太阳磁场的一个重要方面，因此研究磁场的空间性质与结构对理解太阳活动有着重要意义。研究发现太阳耀斑爆发前后，光球磁场和磁力线的空间分布有着明显的变化，此类研究多基于光球磁场观测和日冕单色像。目前，太阳空间磁场研究多是以太阳光球磁场为边界条件，基于理论模型的磁场外推。磁场外推理论尚未完善正在逐步发展过程中，尚有期待解决的问题，尤其是对于非线性无力场。同时，磁场外推研究发现，太阳爆发前后，空间电流分布、磁场自由能、磁场拓扑结构有明显变化。本项目以光球矢量磁场为边界条件，利用多种非线性无力场外推得到磁场。研究不同外推方法中存在的问题与异同，并进一步研究太阳活动区磁场与太阳耀斑爆发活动的关系。本项目基于怀柔大样本光球活动区矢量磁场，进行磁场外推，得到统计上的结果与结论。

太阳物理的核心问题是磁场，太阳活动现象都和磁场有密切的联系。磁场的空间性质（即，磁场强度空间分布，磁通的扩散，磁场连接性，磁场非势性等）是太阳磁场的一个重要方面，因此研究磁场的空间性质与结构对理解太阳活动有着重要意义。近年来，研究发现太阳耀斑爆发前后，光球磁场和磁力线的空间分布有着明显的变化，此类研究多基于光球磁场观测和日冕单色像。目前，太阳空间磁场研究多是以太阳光球磁场为边界条件，基于理论模型的磁场外推可以得到空间磁场。最近磁场外推研究发现，太阳爆发前后，空间电流分布、磁场自由能、磁场拓扑结构有变化。本项目以光球矢量磁场为边界条件，利用非线性无力场外推得到磁场，进一步研究太阳活动区磁场与太阳耀斑爆发活动的关系。本项目基于怀柔光球活动区矢量磁场，进行磁场外推。对于项目的实施，我们先对怀柔所有的观测数据进行样本筛选并对数据进行预处理，其中涉及：磁场定标、横场方向修正、非正常数据剔除、数据噪音去除、活动区号匹配及耀斑记录查询。首先对光球矢量磁场满足无力场的程度进行初步分析与研究。结果表明，活动区光球矢量磁场在一定程度上还是偏离无力场条件的。从统计方面来看，约有1/3的光球活动区矢量磁场可以满足无力场的条件，有1/3明显偏离无力场条件，另外的1/3介于无力场和明显偏离无力场之间。该研究为用于磁场外推的数据样本提供了一个重要的参考依据。在选好数据样本之后我们研究了活动区磁场的空间性质与太阳耀斑爆发的关系，研究太阳耀斑爆发前后磁敏感参数的变化。研究发现69%活动区在耀斑后磁场的磁倾角增加，这意味着相对于纵场横向磁场有一定程度的增强，磁场拓扑结构发生了明显变化；74%活动区在耀斑后磁场的磁自由能有所减少，即非势程度有所减少；活动区空间磁场在耀斑爆发前后，磁自由减少和磁场倾角增加存在弱的相关性。该项研究对磁场空间性质及耀斑爆发的研究提供重要参考依据。