标题： 日冕物质抛射变形对其与圆形截面通量绳模型的原位拟合的影响 显示英文标题

标题： Influence of the Deformation of Coronal Mass Ejections on Their In-Situ Fitting with Circular-Cross-Section Flux Rope Models

摘要： 理解日冕物质抛射（CMEs）的性质，特别是磁流体动力学（MHD）不变量，对于将CMEs从太阳到行星际空间的性质联系起来是关键的。为了研究提供航天器轨迹上CME参数一维（1-D）切片的原位测量数据中的CMEs，已经开发了各种磁通绳（MFR）模型，其中具有圆形截面的模型最为流行和广泛使用。在行星际空间传播过程中，CMEs被发现会发生变形，其中截面可能在传播方向上变平，即发展成椭圆形甚至薄饼状。我们使用二维半（2.5-D）的数值MHD模拟，利用两种具有圆形截面的线性力自由MFR模型来研究CME变形对原位拟合的影响，并重点关注轴向和环向磁通量，这些在理想MHD框架和模拟中是守恒的。我们定量比较了拟合的轴向和环向磁通量与模拟中的值。我们发现，与模拟中的值相比，这两种模型都低估了轴向磁通量，这种低估取决于CME的变形。然而，环向磁通量的拟合与变形无关。我们讨论了轴向磁通量低估的原因以及CME变形对CME原位拟合的含义。 显示英文摘要

摘要： Understanding the properties, especially the magnetohydrodynamic (MHD) invariants, of coronal mass ejections (CMEs) measured in-situ is key to bridging the CME properties from the Sun to interplanetary space. In order to investigate CMEs from the in-situ measurements that provide a one-dimensional (1-D) cut of the CME parameters over the spacecraft trajectory, various magnetic flux rope (MFR) models have been developed, among which the models with a circular cross-section are the most popular and widely used. CMEs are found to be deformed during their propagation in interplanetary space, in which the cross-section may be flattened in the direction of propagation, i.e., to develop an elliptical or even pancake-like shape. We use numerical MHD simulations in 2.5-D to investigate the influence of the CME deformation on the in-situ fitting using two linear force-free MFR models with a circular cross-section, and we focus on the axial and poloidal magnetic fluxes, which are conserved in the ideal MHD frame and simulations. We quantitatively compare the fitted axial and poloidal fluxes with those in simulations. We find that both models underestimate the axial flux compared to that in simulations, and such underestimation depends on the CME deformation. However, the fitting of the poloidal flux is independent of the deformation. We discuss the reasons for the axial flux underestimation and the implication of the CME deformation for the CME in-situ fitting.