分析电离层电流时，磁力计数据的适当坐标系是什么？
What is the appropriate coordinate system for magnetometer data when analyzing ionospheric currents?
摘要：
在本文中，我们调查的坐标表示法是最合适的分析地面磁强计数据的电离层电流，特别是向西的电射流。$\textit{AL}$和最近引入的$\textit{SML}$指数经常被用作向西电射流的监测器。这两个指数都是基于极光纬度的地面磁力计。从这些磁力计中，选择向南方向的最大扰动作为1分钟节奏下的$\textit{ AL/SML }$指数。向南的分量被定义为与地球主磁场水平部分的方向反平行，$\textbf{B}_{0, \textit{H}}$。当使用这些指数作为向西电射流的监测器时，隐含的假设是电射流垂直于$\textbf{B}_{0, \textit{H}}$流动。然而，一般来说，在考虑地球磁场的非偶极项的坐标系中，$\textbf{B}_{0, \textit{H}}$不垂直于向西方向，例如顶点和高度调整校正地磁坐标系。在本文中，我们推导出一个新的$\textit{SML}$指数，顶点坐标的基础上。我们发现，新的索引有较少的变化与经度和世界时（UT），相比传统定义的$\textit{SML}$。我们认为，当分析电离层电流使用磁强计，它是适当的组件转换为校正地磁系统。当考虑纵向或UT变化时，或者当使用来自有限区域的数据时，这是最重要的。
英文摘要：
In this paper we investigate which coordinate representation is most appropriate when analyzing ground magnetometer data in terms of ionospheric currents, in particular the westward electrojet. The $\textit{AL}$ and the recently introduced $\textit{SML}$ index are frequently used as monitors of the westward electrojet. Both indices are based on ground magnetometers at auroral latitudes. From these magnetometers, the largest perturbation in the southward direction is selected as the $\textit{ AL/SML }$ index at 1 min cadence. The southward component is defined as antiparallel to the orientation of the horizontal part of the Earths' main field, $\textbf{B}_{0, \textit{H}}$. The implicit assumption when using these indices as a monitor of the westward electrojet is that the electrojet flows perpendicular to $\textbf{B}_{0, \textit{H}}$. However, $\textbf{B}_{0, \textit{H}}$ is, in general, not perpendicular to the westward direction in coordinate systems that take nondipole terms of the Earth's magnetic field into account, such as apex and the Altitude Adjusted Corrected Geomagnetic coordinate systems. In this paper we derive a new $\textit{SML}$ index, based on apex coordinates. We find that the new index has less variation with longitude and universal time (UT), compared to the traditionally defined $\textit{SML}$. We argue that when analyzing ionospheric currents using magnetometers, it is appropriate to convert the components to a corrected geomagnetic system. This is most important when considering longitudinal or UT variations, or when data from a limited region are used.
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