利用双视角消除太阳矢量磁场观测中的180°不确定性

Using Observations of Solar Vector Magnetic Field from Dual View Points to Remove the 180° Ambiguity

随着“环日轨道器”(Solar Orbiter,SO)的在轨运行,太阳磁场观测进入了双视角遥测的时代.对利用太阳磁场的双视角观测改正矢量磁图中存在的横场(垂直于视线方向的磁场分量)180°不确定性进行了模拟,首先模拟了对解析解得到磁图的双视角观测,然后利用“日震学和磁学成像仪”(Helioseismic and Magnetic Imager,HMI)在不同时间观测到的一个老化黑子的磁图模拟了双视角观测.发现要改正一个磁图中横场方向的180°不确定性,在观测上只需要另外一个平行于视线方向的磁场即纵向磁场观测的协助.利用HMI的磁场观测模拟,估算显示30°的张角能够改正50 Gs磁场中的180°不确定性.更大的张角虽然更有利于更弱磁场的改正,但是考虑到投影效应的不利影响,30°左右的张角应该是未来空间设备进行多视角观测太阳磁场的最佳张角.

With solar orbiter being put into successful operational observation, solar magnetic observation has entered the era of remote sensing from dual view points. In this paper, we carried out a simulation of correcting the 180° ambiguity of transverse magnetic field with magnetograms from dual view points using analytical formula as well as observations made by the Helioseismic and Magnetic Imager(HMI). Magnetograms of a small mature sunspot at different times were used to simulate magnetograms from dual view points. We find that, in order to correct the 180° ambiguity of the vector magnetograms, it is sufficient to have a line-of-sight magnetogram from another view point to help to judge the direction of the transverse magnetic field. For the measuring accuracy of HMI, we estimate that a ~30° angle formed from two observational points is the smallest angle to correct the 180° ambiguity around the place with the magnetic field strength of < 50 Gs. Correction for weaker magnetic fields surely needs larger separation angle, but considering projection effect, we propose that separation angles of ~30° are the optimal angles for future space missions with the scientific aim of correcting the 180° ambiguity of vector magnetograms.