A much rarer sight are so-called polar rain aurorae. They are caused by streams of electrons travelling directly from the surface of the Sun along open magnetic field lines to the polar caps. As these events are scarce and the emissions are weak, little is known about their spatial structure and dynamical characteristics. Keisuke Hosokawa and colleagues have now observed a polar rain aurora (K. Hosokawa et al. Sci. Adv. 10, eadn5276; 2024).

In December 2022, two all-sky cameras at the Kjell Henriksen Observatory in Longyearbyen, Norway, captured a smooth aurora filling the entire polar cap region; it spanned approximately 4,000 km. Typical aurorae at this latitude feature reddish emissions caused by electrons with energies below 1 keV, but the observed emissions were predominantly greenish, pointing towards higher electron energies.

更为罕见的景象是所谓的极雨极光。它们是由直接从太阳表面沿开放磁场线传播到极冠的电子流引起的。由于这些事件稀少且排放微弱，人们对它们的空间结构和动力学特征知之甚少。 Keisuke Hosokawa 及其同事现已观测到极地雨极光（K. Hosokawa 等人， Sci. Adv . 10 ，eadn5276；2024）。

2022年12月，挪威朗伊尔城谢尔·亨里克森天文台的两台全天空相机捕捉到了充满整个极冠区域的平滑极光；它横跨约4,000公里。该纬度的典型极光特征是由能量低于 1 keV 的电子引起的微红色发射，但观察到的发射主要呈绿色，指向更高的电子能量。