South Pole Station, Antarctica (SPA, magnetic latitude = −74.5°, magnetic local time (MLT) = UT–3.5 h), is a unique observatory which can capture daytime auroral forms throughout austral winter season. We have studied the properties and origin of ultralow-frequency (ULF) range modulation of daytime diffuse aurora, using data acquired on June 23, 2017 by multi-instrument measurements at SPA and in situ measurements in the dayside outer magnetosphere. At 1500–1600 UT, monochromatic Pc5-range pulsations (period ∼10 min) emerged in the midday diffuse auroral region. The sequential 2-D images reveal that the auroral pulsations result from the repetitive formation of faint, diffuse auroral patches, propagating poleward at a speed of ∼1.5 km s⁻¹. Interestingly, no obviously similar magnetic pulsations were found at SPA. The results differ fundamentally from the ground optical and magnetic signatures expected for a standing field line resonance. On the other hand, the co-located riometer and VLF receiver observed clearly synchronized pulsations, suggesting that tens-of-keV electrons interact with modulated chorus waves and then are scattered down to the auroral pulsation region. During the same interval, the THEMIS-D spacecraft detected corresponding Pc5 oscillations in the dayside outer magnetosphere (9–10 R_E and ∼15 MLT). The compressional component of the magnetospheric Pc5 waves, presumably driven by an external source, exhibited a good correspondence to the daytime Pc5 auroral pulsations. The simultaneous SPA–THEMIS observations highlight the role of compressional Pc5 pulsations in the dayside outer magnetosphere in determining the periodicity of daytime high-latitude diffuse auroral pulsations.

中文翻译：

---

白天 Pc5 弥漫性极光脉动及其与外磁层 ULF 波的关联

南极洲南极站（SPA，磁纬度 = -74.5°，磁当地时间 (MLT) = UT–3.5 h）是一个独特的天文台，可以在整个南方冬季捕获白天的极光形式。我们使用 2017 年 6 月 23 日通过 SPA 的多仪器测量和白天外磁层的原位测量获得的数据，研究了日间弥散极光的超低频 (ULF) 范围调制的特性和起源。在 1500-1600 UT，正午弥散极光区出现单色 Pc5 范围的脉动（周期约 10 分钟）。连续二维图像显示，极光脉动是由重复形成的微弱的、弥散的极光斑块引起的，以~1.5 km s ^-1的速度向极地传播. 有趣的是，在SPA没有发现明显相似的磁脉动。结果与预期的常设场线共振的地面光学和磁特征有根本的不同。另一方面，共同定位的测量仪和 VLF 接收器观察到清晰的同步脉动，表明数十 keV 电子与调制的合唱波相互作用，然后向下散射到极光脉动区域。在同一时间间隔内，THEMIS-D 航天器在日侧外磁层（9-10 R _E和~15 MLT）。可能由外部源驱动的磁层 Pc5 波的压缩分量与白天的 Pc5 极光脉动表现出良好的对应关系。同时 SPA-THEMIS 观测突出了日侧外磁层中压缩 Pc5 脉动在确定白天高纬度弥漫性极光脉动周期中的作用。