Stereoscopic coronal magnetic field modeling

在立体式日冕磁场模拟项目中，我们想要研究太阳活动区的磁场。由于日冕磁场不能连续、准确地测量，为了获得日冕磁场的三维结构，人们开发了两种互补的方法：体视法和光球场外推法。这两种方法的精度都受到现有观测数据的限制，例如从不同的有利位置识别EUV图像中相应环状结构的能力、观测航天器之间的角度和光球层矢量磁图中的测量误差。因此，我们发展了一个新的模型，称为立体-非线性无力场模型(S-NLFFF)，其中从光球数据进行的NLFFF外推受到日冕观测的限制。新开发的S-NLFFFF码已经成功地用合成数据进行了测试。在我们提出的项目中，我们计划将这种新方法应用于SDO和STEREO观测，以获得前所未有的高精度的三维日冕磁场结构。在后面的步骤中，我们将推广我们的模型，只使用来自一个有利位置(SDO)的EUV图像。2010年SDO上线后，所有数据集都可以应用相应的代码。S-NLFFF的实现将分别在活动区域和全球模型的笛卡尔坐标和球坐标下进行。我们的NLFFF优化代码允许自然地通过额外的观测来约束模型，例如色球矢量磁图。这将是NLFFF方法第一次使用来自光球和色球两个不同层的矢量数据，并受到日冕观测的约束。NLFFF模型严格地仅适用于活动区日冕，而不适用于光球和色球的下部。为了对这些层进行有意义的建模，必须考虑等离子体压力梯度和重力。本课题组建立了相应的自洽磁流体模型。重建的三维磁力线投影到多波长的日冕图像上，可以用来确定沿日冕环的温度、密度和压力。然后，自洽的磁流体静力学方法在整个计算域中对这些量进行建模。

In the project 'Stereoscopic coronal magnetic field modeling', we want to study magnetic fields in solar active regions. Since continuous and accurate measurements of coronal magnetic field are not available, two complementary approaches have been developed to obtain the 3D structure of coronal magnetic fields: stereoscopy and extrapolation of photospheric field measurements.The accuracy of both methods is constrained by the available observational data, e.g., the ability to identify corresponding loop structures in EUV-images from different vantage points, the angle between the observing spacecraft and measurement errors in photospheric vector magnetograms. We therefore developed a new model, called 'Stereoscopic-NonLinear Force-Free Field model (S-NLFFF)' where NLFFF extrapolations from photospheric data are constrained by coronal observations. The newly developed S-NLFFF code was successfully tested with synthetic data.Within the proposed project we plan to apply this new approach to observations from SDO and STEREO in order to derive the 3D coronal magnetic field structure with unprecedented high accuracy. In a later step we will generalize our model to use EUV-images from one vantage point (SDO) only. The corresponding code can be applied to all datasets after the launch of SDO in 2010. The implementation of the S-NLFFF will be made in both Cartesian and spherical coordinates for active regions and global models, respectively.Our NLFFF-optimization code allows naturally to constrain the model by additional observations, e.g., chromospheric vector magnetograms. It will be the first time that a NLFFF method will use vector data from two different layers, photosphere, respectively chromosphere and be constrained from observations in the corona.NLFFF models are strictly valid only in the active region solar corona, but not in the photosphere and the lower part of the chromosphere. For a meaningful modeling of these layers, the plasma pressure gradient and the gravity force have to be taken into account. A corresponding self-consistent magneto-hydro-static model was developed by our group. The projections of the reconstructed 3D magnetic field lines onto multi-wavelength coronal images can be used to specify the temperature, density and pressure along coronal loops. The self-consistent magneto-hydro-static approach then models these quantities in the entire computational domain.