The formation of polar cap density enhancements, such as tongues‐of‐ionization (TOIs), are often attributed to enhanced dayside reconnection and convection due to solar wind changes. However, ionospheric poleward moving density enhancements can also form in the absence of changes in the solar wind. This study examines how TOI and patch events that are not triggered by solar wind changes relate to magnetospheric processes, specifically substorms. Based on total electron content and Super Dual Auroral Radar Network (SuperDARN) observations, we find substorms that occur at the same time as TOIs are associated with sudden enhancements in dayside poleward flows during the substorm expansion phase. Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) observations also show enhanced field‐aligned currents (FACs) that extend into the dayside ionosphere during this period. We suggest that the global enhancement of FACs and convection during these substorms are the drivers of these TOIs by enhancing dayside convection and transporting high‐density lower‐latitude plasma into the polar cap. However, we also find that not all substorms are coincident with polar cap density enhancements. A superposed epoch study showed that the AL index for TOIs during substorms is not particularly stronger than substorms without TOIs, but epoch studies of AMPERE observations do show events with TOIs to have a higher total FAC on both the dayside and nightside. Our results show the importance of TOI formation during substorms when solar wind drivers are absent, and the importance of considering substorms in the global current system. This work also shows the need to incorporate substorms into models of high‐latitude global convection and currents.

中文翻译：

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在亚暴期间形成的白天极地帽密度增强

极帽密度增强的形成（例如电离舌（TOIs））通常归因于日风重新连接和对流（由于太阳风的变化）而增强。但是，在太阳风没有变化的情况下，也可以形成电离层极向移动密度的增强。这项研究研究了不受太阳风变化触发的TOI和斑块事件与磁层过程（特别是亚暴）的关系。基于总电子含量和超双极光雷达网络（SuperDARN）的观测，我们发现在TOI与亚暴扩展阶段的日间极点流突然增强相关的同时发生的亚暴。主动磁层和行星电动力学响应实验（AMPERE）的观测结果还表明，在此期间，扩展的场对准电流（FAC）扩展到了日间电离层。我们建议，通过增强日间对流并将高密度低纬度等离子体输送到极地帽中，这些亚暴期间FAC和对流的全球增强是这些TOI的驱动力。但是，我们还发现并非所有的亚暴都与极地顶盖密度的增加同时发生。叠加的历时研究表明，亚暴期间TOI的AL指数并不比没有TOI的亚暴特别强，但安培观测的时代研究确实显示，TOI的事件在白天和夜晚都有较高的总FAC。我们的结果表明，在缺少太阳风驱动器的亚暴期间，TOI形成的重要性，以及在全球现有系统中考虑亚暴的重要性。这项工作还表明有必要将亚暴纳入高纬度全球对流和洋流模型中。