Event Studies of High‐Latitude FACs With Inverse and Assimilative Analysis of AMPERE Magnetometer Data

We present examples of high‐latitude field‐aligned current (FAC) and toroidal magnetic potential patterns in both hemispheres reconstructed at a 2‐min cadence using an updated optimal interpolation (OI) method that ingests magnetic perturbation data provided by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) program. A solstice and an equinoctial event are studied to demonstrate the reconstructed patterns and to provide scientific insights into FAC response to different solar wind drivers. For the 14 June 2011 high‐speed stream event with mostly northward Bz driving, we found persistently stronger FACs in the Northern Hemisphere. Extreme interhemispheric asymmetry is associated with the interplanetary magnetic field (IMF) direction and large dipole tilt, consistent with earlier studies. FAC asymmetries seen during an isolated substorm can be attributed to dipole tilt. During relatively low geomagnetic activity, the FAC response to IMF Bx changes is identified. For the 17–18 March 2013 period, we provide global snapshots of rapid FAC changes related to an interplanetary shock passage. We further present comparisons between instantaneous and mean behaviors of FAC for the solar wind sheath passage and interplanetary coronal mass ejection southward Bz interval and northward Bz intervals. We show that (1) sheath passage results in strong FAC and high variation in the dayside polar cap region and pre‐midnight region, different from the typical R1/R2 currents during prolonged southward Bz; (2) four‐cell reverse patterns appear during northward Bz but are not stable; and (3) persistent dawn‐dusk asymmetry is seen throughout the storm, especially during an extreme substorm, likely associated with a dawnside current wedge.

我们给出了使用一种更新的最优插值（OI）方法以2分钟的时间间隔重建的两个半球的高纬度场向电流（FAC）和环型磁势模式的实例，该方法吸收了由主动磁层与行星电动力学响应实验（AMPERE）项目提供的磁扰数据。研究了一个至日事件和一个分点事件，以展示重建的模式，并为场向电流对不同太阳风驱动因素的响应提供科学见解。对于2011年6月14日主要由北向Bz驱动的高速流事件，我们发现北半球的场向电流持续更强。极端的半球间不对称与行星际磁场（IMF）方向和大的偶极倾斜有关，这与早期研究一致。在一次孤立的亚暴期间看到的场向电流不对称可归因于偶极倾斜。在地磁活动相对较低时，识别出了场向电流对IMF Bx变化的响应。对于2013年3月17 - 18日期间，我们提供了与行星际激波通过相关的场向电流快速变化的全球快照。我们进一步给出了太阳风鞘层通过以及行星际日冕物质抛射南向Bz区间和北向Bz区间中场向电流的瞬时行为和平均行为之间的比较。我们表明：（1）鞘层通过导致昼侧极盖区和子夜前区出现强场向电流和高变化，这不同于长时间南向Bz期间的典型R1/R2电流；（2）在北向Bz期间出现四单元反向模式，但不稳定；（3）在整个风暴期间，特别是在一次极端亚暴期间，看到持续的晨昏不对称，可能与晨侧电流楔有关。