Simon James Walker, Karl Magnus Laundal, Jone Peter Reistad, Spencer Mark Hatch, Anders Ohma, Jesper Gjerloev
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Our investigation of these substorms shows that during substorm expansion, equivalent field-aligned currents (EFACs) derived with ground magnetometers are a poor proxy of the actual FAC. We also find that the intensification of the westward electrojet can occur without an intensification of the FACs. We present theoretical investigations that show that the observed deviation between FACs estimated with satellite measurements and ground-based EFACs are consistent with the presence of a strong local enhancement of the ionospheric conductance, similar to the substorm bulge. Such enhancements of the auroral conductance can also change the ionospheric closure of pre-existing FACs such that the ground magnetic field, and in particular the westward electrojet, changes significantly. 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引用次数: 0
摘要
利用铱卫星和北美地面磁强计的磁场测量结果,我们计算了整个电离层电流系统,并研究了亚暴电流楔。电流估计值与电离层电导无关,是基于地面磁强计的无发散(DF)电离层电流估计值和铱星的无卷曲(CF)电离层电流估计值。无发散电离层电流和无卷曲电离层电流使用球形基本电流系统(SECS)表示,该系统使用新的反演方案得出,确保电流系统的空间尺度一致。我们展示了 18 个亚风暴事件,并在 12 个事件中发现了典型的亚风暴海流楔(SCW)。我们对这些亚暴的调查表明,在亚暴扩展过程中,用地面磁强计得出的等效场对准电流(EFAC)不能很好地代表实际的场对准电流。我们还发现,西向电射流的增强可能不会导致等效场对准电流的增强。我们提出的理论研究表明,卫星测量估计的 FAC 与地面 EFAC 之间的观测偏差与电离层电导的强局部增强(类似于亚暴隆起)是一致的。极光电导的这种增强也会改变电离层对先前存在的 FAC 的闭合,从而使地面磁场,特别是西向电射流发生显著变化。这些结果表明,将西向电射流的增强归因于SCW电流闭合可能会导致对电离层和磁层状态的错误理解。
The Ionospheric Leg of the Substorm Current Wedge: Combining Iridium and Ground Magnetometers
Utilizing magnetic field measurements made by the Iridium satellites and by ground magnetometers in North America we calculate the full ionospheric current system and investigate the substorm current wedge. The current estimates are independent of ionospheric conductance, and are based on estimates of the divergence-free (DF) ionospheric current from ground magnetometers and curl-free (CF) ionospheric currents from Iridium. The DF and CF currents are represented using spherical elementary current systems (SECS), derived using a new inversion scheme that ensures the current systems' spatial scales are consistent. We present 18 substorm events and find a typical substorm current wedge (SCW) in 12 events. Our investigation of these substorms shows that during substorm expansion, equivalent field-aligned currents (EFACs) derived with ground magnetometers are a poor proxy of the actual FAC. We also find that the intensification of the westward electrojet can occur without an intensification of the FACs. We present theoretical investigations that show that the observed deviation between FACs estimated with satellite measurements and ground-based EFACs are consistent with the presence of a strong local enhancement of the ionospheric conductance, similar to the substorm bulge. Such enhancements of the auroral conductance can also change the ionospheric closure of pre-existing FACs such that the ground magnetic field, and in particular the westward electrojet, changes significantly. These results demonstrate that attributing intensification of the westward electrojet to SCW current closure can yield false understanding of the ionospheric and magnetospheric state.