The technique of spherical elementary current systems (SECS) is a powerful way to determine ionospheric and field-aligned currents (FAC) from magnetic field measurements made by low-Earth-orbiting satellites, possibly in combination with magnetometer arrays on the ground. The SECS method consists of two sets of basis functions for the ionospheric currents: divergence-free (DF) and curl-free (CF) components, which produce poloidal and toroidal magnetic fields, respectively. The original CF SECS are only applicable at high latitudes, as they build on the assumption that the FAC flow radially into or out of the ionosphere. The FAC at low and middle latitudes are far from radial, which renders the method inapplicable at these latitudes. In this study, we modify the original CF SECS by including FAC that flow along dipolar field lines. This allows the method to be applied at all latitudes. We name this method dipolar elementary current systems (DECS). Application of the DECS to synthetic data, as well as Swarm satellite measurements are carried out, demonstrating the good performance of this method, and its applicability to studies of ionospheric current systems at low and middle latitudes.

中文翻译：

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用于中低纬度电离层电流重建的偶极基本电流系统

球形基本电流系统 (SECS) 技术是一种从低地球轨道卫星进行的磁场测量中确定电离层和场对齐电流 (FAC) 的有效方法，可能与地面磁力计阵列相结合。SECS 方法由两组电离层电流的基函数组成：无发散 (DF) 和无卷曲 (CF) 分量，它们分别产生极向磁场和环形磁场。最初的 CF SECS 仅适用于高纬度地区，因为它们建立在 FAC 径向流入或流出电离层的假设之上。低纬度和中纬度的 FAC 远非径向，这使得该方法不适用于这些纬度。在这项研究中，我们通过包括沿偶极场线流动的 FAC 来修改原始 CF SECS。这允许该方法适用于所有纬度。我们将此方法命名为偶极基本电流系统 (DECS)。将 DECS 应用于合成数据，以及 Swarm 卫星测量，证明了该方法的良好性能，以及它在中低纬度电离层电流系统研究中的适用性。