Effects of Thomson-Scattering Geometry on White-Light Imaging of an Interplanetary Shock: Synthetic Observations from Forward Magnetohydrodynamic Modelling
Effects of Thomson-Scattering Geometry on White-Light Imaging of an Interplanetary Shock: Synthetic Observations from Forward Magnetohydrodynamic Modelling
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DOI：
10.1007/s11207-012-0047-0
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发表时间：
2012-05
期刊：
影响因子：
2.8
通讯作者：
M. Xiong;J. Davies;M. Bisi;M. Owens;R. Fallows;G. Dorrian
中科院分区：
文献类型：
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作者：
M. Xiong;J. Davies;M. Bisi;M. Owens;R. Fallows;G. Dorrian
大部分内日球层的立体白光成像已被用于追踪行星际日冕物质抛射。在距离太阳较远的地方，白光的亮度取决于当地的电子密度和汤姆森散射过程的效率。为了量化汤姆森散射几何的影响，我们使用正向磁流体动力学模拟和合成白光成像研究了行星际激波。在时间延伸图中可以识别为增强亮度的倾斜条纹，行进的激波可以很容易地由位于黄道大经度范围内的观测者成像。激波锋面的不同部分构成了观测者在不同经度观测到的成像亮度模式。此外，即使对于位于固定经度的观测者，激波锋面的不同部分也会在任何给定时间对成像亮度做出贡献。观测到的每个成像像素内的亮度是沿着其相应的射线路径加权积分的结果。根据其亮度和极化程度的东西不对称，可以从光学天空图中的亮度模式推断出激波的纵向位置。因此，测量行星际偏振亮度可以显著减少从白光成像进行局部电子密度三维重建时的模糊性。
Stereoscopic white-light imaging of a large portion of the inner heliosphere has been used to track interplanetary coronal mass ejections. At large elongations from the Sun, the white-light brightness depends on both the local electron density and the efficiency of the Thomson-scattering process. To quantify the effects of the Thomson-scattering geometry, we study an interplanetary shock using forward magnetohydrodynamic simulation and synthetic white-light imaging. Identifiable as an inclined streak of enhanced brightness in a time–elongation map, the travelling shock can be readily imaged by an observer located within a wide range of longitudes in the ecliptic. Different parts of the shock front contribute to the imaged brightness pattern viewed by observers at different longitudes. Moreover, even for an observer located at a fixed longitude, a different part of the shock front will contribute to the imaged brightness at any given time. The observed brightness within each imaging pixel results from a weighted integral along its corresponding ray-path. It is possible to infer the longitudinal location of the shock from the brightness pattern in an optical sky map, based on the east–west asymmetry in its brightness and degree of polarisation. Therefore, measurement of the interplanetary polarised brightness could significantly reduce the ambiguity in performing three-dimensional reconstruction of local electron density from white-light imaging.