Medium-scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all-sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm⁻³, respectively. The electric field variations projected to the ionosphere are mainly in the east-west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere.

中文翻译：

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首次从地面和磁层卫星同时观测夜间中等尺度移动电离层扰动

中尺度行进电离层扰动 (MSTID) 是一种从高纬度到低纬度在电离层上广泛且频繁观察到的现象。夜间 MSTID 通常是由电离层中的极化电场引起的。然而，尚未确定这种极化电场向磁层的传播。在这里，我们报告了磁层中夜间 MSTID 的极化电场和相关密度变化的第一次观察。MSTID 事件是由阿拉斯加加科纳（地理纬度：62.39°N，地理经度：214.78°E，磁纬度：63.20°N）的全天气辉成像仪观测到的。2018 年 11 月 3 日，Arase 卫星在 0530-0800 UT（2030-2300 LT）内磁层中通过了 MSTID。在 630 nm 气辉图像中观察到的这个 MSTID，向西传播，水平波长约为 165 公里，南北相前沿，相速度约为 80 米/秒。电离层上的 Arase 卫星足迹在几乎垂直于 MSTID 相位前沿的方向上穿过 MSTID。Arase卫星观测到的电场和电子密度显示出与MSTID结构相关的周期性变化，幅度为~2 mV/m和~150 cm^-3，分别。投射到电离层的电场变化主要在东西方向，并且与E  ×  B漂移导致的 MSTID 增长预期的极化电场方向一致。这一观察结果表明，与电离层中 MSTID 相关的极化电场投射到磁层上，导致磁层中的等离子体密度波动。